Lopressor
By C. Akrabor. Saint Francis College, Brooklyn Heights, New York. 2018.
This assessment is based on the full range of preparation and administration options described in the monograph discount lopressor 12.5 mg on line fetal arrhythmia 33 weeks. Propranolol hydrochloride 1mg/mL solution in 1-mL ampoules * Propranolol hydrochloride is a non-cardioselective beta-adrenoceptor blocker. Inspect visually for particulate matter or discolor- ation prior to administration and discard if present. Monitoring Measure Frequency Rationale Heart rate Continuously * Consider withholding therapy if pulse drops to 50-- 55 bpm or lower. Respiratory function After initial dosing * May cause bronchoconstriction in susceptible or oxygen saturation individuals, e. Antidote: Stop administration and give supportive therapy as appropriate (may include atropine, bronchodilators, glucagon, dopamine -- see relevant entries). Counselling Patients may experience fatigue and cold extremities during therapy, and should report wheezing. This assessment is based on the full range of preparation and administration options described in the monograph. Protam ine sulfate (protam ine sulphate) 10mg/mL solution in 5-mL and 10-mL ampoules * Protamine sulfate is composed of a mixture of the sulfates of basic peptides prepared from the sperm or mature testes of suitable species of fish, usually Clupeidae or Salmonidae. Pre-treatment checks * Use with caution in patients with known sensitivity to fish, in vasectomised or infertile males, and inpatientswhohave receivedpreviousprotaminesulfatetherapyorprotamineinsulin dueto "risk of allergic reactions (see Counselling). Inspect visually for particulate matter or discolor- ation prior to administration and discard if present. Inspect visually for particulate matter or discolor- ation prior to administration and discard if present. Bleeding Up to 5 hours after * If insufficient protamine is given, a heparin protamine rebound occurs within 5 hours of neutralisation; administration this may be associated with clinical bleeding. Additional information Common and serious Immediate: Anaphylaxis has been reported rarely. Significant Protamine may affect fluorescence methods of estimating plasma interactions catecholamines. Action in case of Monitor coagulation tests, respiratory ventilation and symptomatic treatment. If overdose bleeding is a problem, fresh frozen plasma or fresh whole blood should be given. During vasectomy, antibodies develop against natural nucleoproteins (a component of human sperm cells) in 22--33% of patients. These antibodies have been shown to cross-react with medicinal protamines, which are extracted commercially from the testes of salmon and certain other fish. This assessment is based on the full range of preparation and administration options described in the monograph. Pre-treatment checks * Protirelin may have an effect on smooth muscle; closely monitor patients with asthma or other types of obstructive airways disease. Take a blood sample exactly 20 minutes after the injection for peak thyroid hormone assay and, if necessary, a further sample at exactly 60 minutes after injection to detect a delayed thyroid hormone response. Technical information Incompatible with Not relevant Compatible with Flush: NaCl 0. Protirelin | 723 Monitoring Measure Frequency Rationale Thyroid function Immediately before * See detail in Administration above. Protirelin also has prolactin-releasing activity and may cause breast enlargement and milk leakage in breast-feeding women. Significant * The following may "protirelin levels or effect (or "side-effects): interactions amiodarone, metoclopramide, oestrogens (in men), theophylline, thyroid hormones (overtreatment). This assessment is based on the full range of preparation and administration options described in the monograph. Pre-treatment checks * Do not give if there is known hypersensitivity to quinine, quinidine or mefloquine. A loading dose should not be given if the patient has received quinine or mefloquine during the previous 24 hours. Ifparenteral therapy is required for more than 48 hours, the maintenance dose should be reduced to 5--7mg/kg. Dose in renal impairment: adjusted according to creatinine clearance:1 * CrCl >20--50mL/minute: 5--7mg/kg every 8 hours. Inspect visually for particulate matter or discoloration prior to administration and discard if present.
Ca2+ entry is important for excitation- contraction coupling because it gives a direct supply of activator Ca2+ to the contractile machinery lopressor 12.5mg with mastercard jnc 07 hypertension. Additional Ca2+ is provided by release from intracellular stores in the sarcoplasmic reticulum. This may lead to: (1) ectopic impulses (2) reentry Working atrial, Na current supports Ca current underlies plateau and Myocardium ventricular conduction activates contraction Cardiac Action Potential - Richard Tsien, Ph. Action potential repolarization takes place when Ca current inactivates and K current activates. Ca channels inactivate 10-100x more slowly than sodium channels, in a manner largely dependent on cytoplasmic Ca2+ and calmodulin. The K channels also turn on much more slowly than their counterparts in nerve axons. As a result, these changes tip the balance in favor of outward repolarizing current and thus terminate the plateau. Sympathetic hormone (epinephrine) interacts mainly with β- adrenergic receptors to exert coordinated effects on mechanisms controlling electrical activity and intracellular Ca2+. The power of this modulation is illustrated by electrical and mechanical recording from ventricular muscle exposed to increasing concentrations of isoproterenol (specific for β-adrenergic receptors). Note the higher (but not longer) plateau, the larger (but not more delayed) peak force, the faster relaxation. The increased Ca2+ influx through L-type channels is one important part of this response. The increase in Ca2+ channel activity is only one aspect of the multi-pronged response to adrenergic stimulation. All of this is summarized by a local artist with a nautical bent: C ardiacA ctionPotential-R ich ard Tsien,Ph. If we record his/her electrocardiogram, we find an immediate shortening of the Q-T interval, corresponding to the ventricular action potential duration, in response to the rate increase. This can also be illustrated in a table of mean Q-T intervals for different heart rates for adults and children: Heart rate Total cardiac Q-T % electrical % electrical (beats/min) interval (s) interval (s) systole diastole 40 1. This electrical adaptation is clearly useful to the proper pumping action of the heart; unless the mechanical systole is shortened, there would be no diastolic time left for ventricular filling. The frequency-duration relation may be observed at the level of isolated ventricular muscle cells. The modification of ventricular action potential duration makes sense if one recalls that the repolarization is initiated by the shutting off of inward current (Ca channel inactivation) and the turning on of outward potassium current (K channel activation). Each action potential leaves behind it some residuum of the time-dependent permeability change which decays away gradually over the next 0. For example, K channel activation decays and Ca channel inactivation is gradually reversed (channels become available again). If the next action potential is elicited prematurely, its plateau will be shorter because the various channels would already have a head-start toward the condition that set up the previous repolarization and Control Of Heart Rhythm - Richard Tsien, Ph. This explains why premature (extrasystolic) action potentials are abbreviated, as shown above. Their duration is not specifically related to heart rate as such, but rather the proximity of the extrasystolic stimulus to the previous repolarization. Long Q-T syndrome is an inherited disorder that causes sudden death from cardiac arrhythmias. Unfortunately, these treatments did not prevent arrhythmia in all patients, nor did they resolve the underlying abnormality in repolarization. Thus, multiple types of potassium channel (and a sodium channel) can give rise to multiple forms of long Q-T syndrome. This makes sense because these potassium channels show a rapid form of inactivation that limits their contribution to outward current over the voltage range where repolarization occurs, thereby sparing ion gradients during the relatively long action potential plateau. Raising the external potassium concentration opposes the inactivation, probably because these ions bind near the outer mouth of the channel where the inactivation mechanism would otherwise pinching off the channel. This is means that an individual with a mixture of functional and malfunctional K+ channel proteins will suffer from abnormal repolarization.
Pre-treatment checks * Do not use in acute respiratory depression purchase 25mg lopressor with visa arterial nosebleed, where there is a risk of paralytic ileus, in "intracranial pressure and in head injury, in comatose patients, in heart failure secondary to chronic lung disease and phaeochromocytoma. Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Inspect visually for particulate matter or discolor- ation prior to administration and discard if present. Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Monitoring Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Measure Frequency Rationale Pain At regular intervals * To ensure therapeutic response. Monitor for side- * Can cause side-effects such as itching and nausea effects and toxicity and vomiting and constipation, which may need treating. Papaveretum | 643 Additional information Common and serious Common: Nausea and vomiting (particularly initially), constipation, dry mouth, undesirable effects urticaria, pruritus, biliary spasm, " or #pulse, hallucinations, euphoria, drowsiness. Counselling If the patient is pregnant or breast feeding she should inform her doctor. May cause drowsiness and dizziness that may affect the ability to perform skilled tasks; if affected do not drive or operate machinery. This assessment is based on the full range of preparation and administration options described in the monograph. Pre-treatment checks * Do not use in acute respiratory depression, where there is a risk of paralytic ileus, in "intracranial pressure and in head injury, in comatose patients, in heart failure secondary to chronic lung disease and phaeochromocytoma. Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Papaveretum with hyoscine hydrobromide | 645 Subcutaneous injection Preparation and administration 1. Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Technical information Incompatible with Not relevant Compatible with Not relevant pH 2. Monitoring Close monitoring of respiratory rate and consciousness is recommended for 30 minutes in patients receiving an initial dose, especially elderly patients or those of low bodyweight. Measure Frequency Rationale Pain At regular intervals * To ensure therapeutic response. Monitor for side- * Can cause side-effects such as itching and nausea effects and toxicity and vomiting and constipation, which may need treating. Additional information Common and serious Common: Nausea and vomiting (particularly initially), constipation, dry mouth, undesirable effects urticaria, pruritus, biliary spasm, " or #pulse, hallucinations, euphoria, drowsiness, blurred vision, difficulty with micturition. Action in case of Symptoms to watch for (papaveretum): "Sedation, respiratory depression. Counselling If the patient is pregnant or breast feeding she should inform her doctor. May cause drowsiness and dizziness that may affect the ability to perform skilled tasks; if affected do not drive or operate machinery. This assessment is based on the full range of preparation and administration options described in the monograph. Paracetam ol (acetam inophen) 10mg/mL solution in 50-mL and 100-mL vials * Paracetamol has analgesic and antipyretic activity and some anti-inflammatory activity. Dose in renal impairment: adjusted according to CrCl: * CrCl < 30mL/minute: normal adult dose but increase dose interval to a minimum of 6 hours. Dose in hepatic impairment: in adults with hepatocellular insufficiency, chronic alcoholism, chronic malnutrition (low reserves of hepatic glutathione) or dehydration, the maximum daily dose must not exceed 3g. Inspect visually for particulate matter or discoloration prior to administration and discard if present. Technical information Incompatible with No information Compatible with Flush: NaCl 0.
Comparative effects of ciprofloxacin and lomefloxacin on the oxidative metabolism of theophylline generic lopressor 50mg without a prescription blood pressure medication harmful. Allelic variants of human cytochrome P450 2C9-baculovirus-mediated expression, purification, structural characteriza- tion, substrate stereoselectivity, and prochiral selectivity of the wild-type and 13591 mutant forms. Comparative studies on the catalytic roles of cytochrome P450 2C9 and its Cys- and Leu-variants in the oxidation of warfarin, flurbiprofen, and diclofenac by human liver microsomes. Formation of (R)-8-hydroxywarfarin in human liver - microsomes - a new metabolic marker for the (S)-mephenytoin hydroxylase, P4502C19. Ketoconazole and sulfaphenazole as the respective selective inhibitors of P4503A and 2C9. Inhibition of the human cytochrome-P450-dependent metabolism of warfarin by fluconazole - in vitro studies. Relationship between phenytoin and tolbutamide hydroxylations in human liver microsomes. Extent of urinary excretion of p-hydroxyphenytoin in healthy subjects given phenytoin. Kinetics of carboxytolbutamide excretion following tolbutamide and carboxytolbutamide administration. Validation of the tolbutamide metabolic ratio for population screening with the use of sulfaphenazole to produce model phenotypic poor metabolizers. The effects of selective serotonin reuptake inhibitors and their metabolites on S-mephenytoin 4 -hydroxylase activity0 in human liver-microsomes. The role of (S)-mephenytoin 4 -hydroxylase0 in imipramine metabolism by human liver microsomes: a two-enzyme analysis of N-demethylation and 2-hydroxylation. Identification of human liver cyto- chrome-P450 isoforms mediating omeprazole metabolism. A methodological investigation on the estimation of the (S)-mephenytoin hydroxylation phenotype using the urinary S/R ratio. The mephenytoin oxidation polymorphism is partially responsible for the N-demethylation of imipramine. The N-demethylation of imipramine correlates with the oxidation of (5)-mephenytoin (S/R ratio). The hydroxylation of omeprazole correlates with S-mephenytoin metabolism: a population study. Hydroxylation polymorphism of debrisoquine and mephenytoin in European populations. Metoprolol oxidation polymorphism in a Korean population: comparison with native Japanese and Chinese populations. Inhibition of desipramine hydroxylation in vitro by serotonin-reuptake inhibitor antidepressants, and by qui- nidine and ketoconazole—a model system to predict drug-interactions in vivo. The oxidative metabolism of metoprolol in human liver microsomes-inhibition by the selective serotonin reup- take inhibitors. Serotonin selective reuptake inhibitor drug- interactions and the cytochrome-P450 system. Pharmacokinetic drug-interaction potential of selective serotonin reup- take inhibitors. Effect of antidepressant drugs on cytochrome-P-450 isoenzymes and its clinical relevance-differential profile. Drug interactions of clinical significance with selective serotonin reuptake inhibitors. Metabolism of the newer antidepressants-an overview of the pharmaco- logical and pharmacokinetic implications. Protease inhibitors as inhibitors of human cytochromes P450-high-risk associated with ritonavir. A correlation between the response to debrisoquine and the amount of unchanged drug excreted in the urine. Dextromethorphan O-demethylation in liver microsomes as a prototype reaction to monitor cytochrome P-450 dbl activity. Polymorphic dextromethorphan metabolism: co-segregation of oxidative O-demethylation with debrisoquine hydroxylation. Use of quinidine inhibition to define the role of the sparteine/debrisoquine cytochrome P450 in metoprolol oxidation by human liver microsomes.
It gently stimulates the functional action of the organs order 50mg lopressor pulse pressure map, promotes normal secretion and relieves irritation. It is without doubt, our best remedy with which to restore the secretion in post Ellingwood’s American Materia Medica, Therapeutics and Pharmacognosy - Page 54 scarlatinal or post diphtheritic nephritis. In conjunction with a persistent application of heat, it will be found useful in post puerperal nephritis, of an acute character, and probably in other cases, where sudden suppression has resulted from profound sepsis. Where we find colic with loose, slimy stools, it points to intestinal disorders, while convulsive movements are reflex symptoms, consequent upon the intestinal disease. Santonine influences these conditions by stimulating the great sympathetic and giving tone to the functions of digestion and nutrition. It has been employed with advantage in nervous failure of sight, nervous vomiting and nervous diarrhea; but it is doubtful whether it has ever improved the sight in amaurosis or cataract, as has been claimed. Santonine causes yellow vision and yellow urine, Where worms are demonstrated to exist in the bowels, it is a common practice to give santonine with a cathartic of podophyllin, or follow it with castor oil. The agent is toxic, as stated, and should not be given in material doses for the special purpose of destroying worms, when the child is constipated or suffering from fever. He gives it alone when he needs to restore the menses, and says he needs nothing with it. For young girls with their early menstruation and in cases of painful menstruation, he uses an infusion of the fresh root and expects to get satisfactory results. He takes one ounce of the root and lets it steep slowly for one hour in a pint of water and sweetens it. He takes from five to ten drops of the fluid extract to a cupful of hot sweetened water and gives this every half hour or every one or two hours as the patient needs. Ellingwood’s American Materia Medica, Therapeutics and Pharmacognosy - Page 55 The stimulant properties of this agent are of a local character, acting directly upon the mucous lining of the intestinal tract, and overcoming flatulence. It is also a stimulant to the secretory function of the skin, acting as a mild but efficient diaphoretic. In inflammatory conditions it should be avoided, but after the inflammation has abated, it will mildly stimulate the function of digestion and food appropriation. Other of our writers believe that it has a more important place than that given by most of our authors. Therapy—In acute nasal catarrh, where the discharge has not appeared, or has been suppressed, with the usual symptoms of headache and general oppression, muscular aching and general discomfort, it is given with good results. Inflammation of the conjunctiva, from taking cold, where there is profuse and constant lachrymation, will be relieved by it. In painful or longstanding spasmodic affections of the pulmonary region, as in whooping cough or bronchitis, it will be advantageous and, at the same time, it influences the digestive apparatus, correcting nausea, cholera and diarrhea, which may be present. Newton considered its most important influence to be exercised upon the generative apparatus. It is a stimulant to the muscular structure of the womb and to the ovaries, and is abortive and an active parturient, and may be given to good advantage in recent cases of amenorrhea from cold. During labor, when the pains are excessive, and when there is extreme erythism, a few drops of the tincture may be put in half a glass of water and a teaspoonful administered every five or ten minutes. In metrorrhagia and in menorrhagia, where the flow is steady but not free, where there are cutting pains in the abdomen and groin, extending down the thighs, with aching in the back, the patient nervous and irritable, this remedy will restore the flow to its normal proportions, will relieve the nerve tension and subdue pain. Violent pain in the small of the back on the approach of the menstrual epoch, which seems to interfere with the breathing, is said to be a diagnostic indication for this Ellingwood’s American Materia Medica, Therapeutics and Pharmacognosy - Page 56 remedy. Where there is melancholy and nervous disturbance in the early part of pregnancy, so that miscarriage seems to be threatened, a teaspoonful of asarum every two or three hours will sometimes restore the patient to normal condition. Swamp milkweed affects the heart and arteries like digitalis, and is a speedy and certain diuretic. Specific Symptomatology—Asclepias Incarnata strengthens the heart and is given in small doses, instead of digitalis, as a diuretic in dropsy. It often promptly relieves the general distress from extreme infiltration of the tissues especially the dyspnea. Therapy—It may be given in coughs and colds, rheumatism from cold, painful stitches in the chest with threatened inflammation of the lungs and pleura, asthma, chronic gastric catarrh, diarrhea, dysentery, dropsy, worms, erysipelatous diseases. It improves digestion, and is a good remedy in chronic catarrh of the stomach, and in catarrhal inflammation of the respiratory organs. It is both emetic and cathartic and may be used with advantage in the early stages of dysentery and diarrhea. In rheumatic and catarrhal inflammations it should be given to produce slight nausea.
Further lopressor 25mg discount hypertension nursing intervention, the speed at whichone cell is depolarized (represented by the slopeofphase 0) determines how quickly the next cell is stimulated to depolarize, and thus determines the speed at which Mechanismsofcardiac tachyarrhythmias 7 the electrical impulse is propagated. Ifsomething causes the slopeof phase 0 to change, the conduction velocity also changes; the faster the depolarization of the cardiaccells, the faster an electrical impulse moves across the heart. Similarly, onceacell is depolarized, it cannot be depolarized again until the ionic fluxes that occur during depolarization are reversed. Repolarizationcorrespondstophases 1 through3,and therefore accounts for almost the entire duration of the actionpo- tential. Because the cell is refractory to depolarizationuntil after it isrepolarized, the time from the end of phase 0 to late in phase 3 is called the refractory period of the cell. The duration of the actionpo- tential thus determines the refractory period; ifone does something to change the duration of the actionpotential, one also changes the refractory period. Repolarization beginsrapidly (phase 1), but the pro- cess isalmost immediately interrupted by a plateauphase (phase 2), which is uniquetocardiaccells (e. Phase 2is mediated by “slow” calcium channels, which allowpositively chargedcalcium ionstoenter the cell slowly and thustointerruptrepolarization and prolong the duration of the ac- tionpotential. The most important ionic shift that occurs during repolarization is the outward flow of positively chargedpotassium ions, which has the effectofreturning the actionpotential towardits baseline, neg- atively polarized state. At least six different potassium “currents” have beenidentified; they operate at differenttimes during the ac- tionpotential and are modulated by differentfactors (including volt- age, calcium ions, muscarinic receptors, acetylcholine, and adeno- sinetriphosphate) under different circumstances. Dumping sodium and calcium ions into a cardiaccell to depo- larize itand thendraining potassium ionsout of the cell to repo- larize it may return the transmembrane voltage to baseline levels, but these actions do not return the cell chemistry to the baseline state. Various poorly characterizedmechanisms are called on to rec- tify remaining chemical imbalances (the most importantofwhich is the sodium–potassium pump). Although depolarization seems 8 Chapter 1 fairly straightforward,any attempttofully understand repolariza- tion quickly leadsone into a maze of seemingly conflicting channels, gates, receptors, and pumps whichonly a basic electrophysiologist could love. Fortunately, the essential features of repolarization are relatively simple: (1) repolarization returns the cardiac actionpotential to the resting transmembrane potential; (2)this process takes time; (3) this time, roughly corresponding to the width of the actionpotential, is the refractory period of cardiac tissue; (4) depolarizationmainly dependson sodium channels, and repolarizationmainly dependson potassium channels. The resting phase For most cardiaccells, the resting phase (the period of time between twoactionpotentials, corresponding to phase 4) isquiescent; there is no net movementofionsacross the cell membrane. For some cells and in some circumstances, however, the so-called resting phase is not quiescent. Instead, there is leakageofionsback and forth across the cell membrane during phase 4insuchaway as to cause a gradual increase in transmembrane potential (Figure 1. When the transmembrane potential reaches the threshold volt- age, the appropriate channels are engaged and the cell is depolarized (since, as noted, the channels mediating depolarization are voltage dependent). Depolarization, in turn,stimulates nearby cells to depo- larize, and the resultantspontaneously generated electrical impulse is thenpropagated across the heart. This phase 4 activity, which leads to spontaneous depolarization, is called automaticity. In some cardiaccells, leakageofionsacross the cell membrane during phase 4causes a gradual, positively directedchange in the transmembrane voltage. When the transmembrane voltagebecomes sufficiently positive, the appropriate channels are automatically activated to generate another actionpotential. Mechanismsofcardiac tachyarrhythmias 9 Automaticity is the mechanism by which the normal heart rhythm is generated. Localized variations Twolocalizeddifferences in the heart’s electrical system are impor- tant in understanding cardiac arrhythmias:differences in the action potential and differences in autonomic innervation. Localized differences in the action potential The cardiac actionpotential does not have the same shape in every cardiaccell. Actionpotentials generatedindifferent areas of the heart have different shapes because dif- ferent electrophysiologic properties (i. Localized differences in autonomic innervation Ingeneral, an increase in sympathetic tone causes enhanced auto- maticity (pacemaker cells fire more rapidly), increasedconduction velocity (electrical impulses spreadmore rapidly), and decreased re- fractory periods(cells are ready for repeateddepolarizations more quickly). Parasympathetic tone has the opposite effect(depressed automaticity, decreasedconduction velocity, and increased refrac- tory periods). In the remainder of the heart’s electrical system, althoughsympathetic innervationis reasonably abundant, parasym- pathetic innervationissparse. Inmost of the heart, the depolarizationphase of a cell is essentially instantaneous(occurring in 1–3 ms), and occurs sequentially from cell to cell. Changes in the spread of the electrical impulse, such as those that occur in bundle branch block or a transmural myocardial infarction, can be readily discerned. Incontrast, the repolarizationportion of the actionpotential (phases 1–3) has significant duration.
Both linoleic acid (C18:2 ∆9 buy lopressor 12.5 mg lowest price blood pressure jumps up and down, 12) and the ∆5, 8 isomer of linoleic acid have been identified (28). The ∆9, 12 isomer is derived from the diet (29); whereas, the ∆5, 8 isomer is synthesized in the gland. Interestingly, the proportion of the ∆5, 8 isomer relative to ∆9, 12 is in- creased in acne patients (28). In the triglyceride fraction, the saturated and mo- Figure 2 Representative structures of the major lipid classes of human sebum. Most of the monounsaturated fatty acids are derived from C16:1 ∆6, or to a much lesser extent 18:1 ∆9, by extension or removal of 2-carbon units, and a small percentage of the monounsaturated fatty chains have iso or anteiso methyl branches (22,25). The chain lengths of the monounsaturates are almost entirely within the range of 14 through 18 carbons with C16:1 ∆6 (called sapienic acid) being the most abundant. Saturated Species The saturated fatty acids are almost entirely in the range of 12 through 18 carbons in length with palmitic acid (C16:0) being the most abundant (22,25). Generally, the straight-chain species predominate, but the proportions of methyl branched species can be highly variable (31). There are also a wide variety of other mono and multi methyl branched saturated chains (32), but for a given individual the pattern of methyl branching appears to be constant (31). Sebum 51 Also, identical twins appear to have identical sebaceous fatty acid compositions, including the pattern of methyl branching, while nonidentical twins, although generally having similar branching patterns, sometimes differ as much as nontwin groups (33). All of this supports the contention that sebum composition is largely under genetic control. Other Species All terrestrial mammals produce sebum, and in all cases the lipid mixture is a viscous liquid consisting of several types of nonpolar lipids (34,35). Among the most widely distributed seba- ceous lipids are sterols and sterol esters. Sebum from the cow also contains triesters that contain 1,2-diols with an α-hydroxyacid esterified to one of the hydroxyls and a normal fatty acid ester-linked to the other (36). The lactones constitute from about 50 to 70% of the total sebum mass and are formed by cyclization of 30- through 36-carbon ω-hydroxyacids. In general, the degree of unsaturation and methyl branching of the giant ring lactones from the different species of the equidae are in accord with the taxo- nomic relationships among these species (38). Equus caballus, the domestic horse, produces lactones that predominantly contain one double bond and a methyl branch on the penultimate carbon. The lactones of the donkey, Equus asinus, are made from 30-, 32-, and 34-carbon straight-chained ω-hydroxyacids. The lactones of the mule, Equus caballus/Equus asinus, are monounsaturated and 50% of the chains have the methyl branch while the other 50% are straight (38). First, it is a water repellent on the fur, which is clearly advantageous for aquatic mammals and for mammals living in moist environments. Second, 7-dehydrocholesterol secreted from the sebaceous glands onto the skin surface is photochemically converted to previta- min D, which is then converted to vitamin D in a temperature-dependent, nonen- 52 Wertz and Michniak zymatic reaction (39). When the animal licks its fur during grooming, the vitamin D is recovered by means of a salivary vitamin D binding protein (40). In humans, a function for sebum is less well established, and it is possible that sebum produc- tion is a functionless vestige of our ancestors. One clue in this regard comes from the species known to produce squalene as a component of their sebum. In addition to human sebum, squalene is found in the sebum of the otter, beaver, kinkajou, and mole, Scalopus aquaticus (41,42). The otter and beaver are aquatic; the kink- ajoo lives in the canopies of tropical rain forests; and Scalopus aquaticus lives in moist–wet soil. Could it be that our ancestors spent a great deal of their time in water along coasts or rivers and benefited from the waterproofing afforded by a coating of squalene? Sebum no doubt contributes a degree of lubrication to the skin surface, and it has sometimes been suggested that dry skin results from insufficient sebum production. First, as has been pointed out, prepubertal children produce almost no sebum but most do not suffer dry skin or other skin problems (43). Second, in one study in which the sebum secretion rate was measured and subjects were surveyed about the condition of their skin, no correlation could be found between the occurrence of xerosis and sebum production (44).
