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Sebum is the excretory product of the sebaceous glands. These glands are found in the skin of all mammals except whales and porpoises. The bulk of sebum is a mixture of relatively nonpolar lipids, most of which are synthesized de novo by the gland. The lipid is excreted by a holocrine mechanism, whereby the lipid-laden cells disintegrate and pour their contents through the sebaceous duct onto the skin surface. One apparent function of sebum is to provide the skin surface and hair with a hydrophobic coating. The preen gland of birds has a similar function, but it is not a sebaceous gland.

A four-month study by serial photography of the progression of comedones in a 17-year-old white boy with untreated, moderately severe acne vulgaris showed that both open and closed comedones (blackheads and whiteheads) can become inflamed and pustular. The lesions tend to resolve in an average 13 days from the start of inflammation. Open comedones sometimes remain unchanged except for size for more than three months before becoming inflamed. Generally, the longer such lesions persist, the longer the ensuing combined periods of inflammation and pustulation. Because of their potential to become inflamed and pustular, the nontraumatic removal of comedones is suggested. [ABSTRACT FROM AUTHOR]

In most animal tissues, lipogenesis converts excessive dietary carbohydrate or protein into storage lipids and this process must obviously be under the control of homeostatic regulatory mechanisms related to dietary intake and composition. The lipids of the skin, both sebaceous and epidermal, however, are formed for a specific biological function, to maintain the integrity of the integument. Lipogenesis, on another hand, in skin regulated by the same mechanisms that operate in other tissues poses a problem.

The composition and biosynthesis of lipids in human skin have long been of considerable interest, both because of the highly unusual structures these lipids contain and because of the possible involvement of the lipids in disease processes of the skin. Despite the exceptionally complex nature of surface lipid, its composition is now known in detail. In addition, since efficient procedures are now available for analyzing the class composition of skin lipid and the individual members of these classes, the changes in composition that may occur under specialized circumstances can now be studied in large groups of subjects.

In a very short time, several significant contributions have been made in what was until recently a largely unexplored field. It appears now that the skin and probably the sebaceous glands themselves participate meaningfully in controlling their own tissue-specific stimulators and inhibitors rather than acting as passive recipients of such regulators brought to them by the circulation. This article deals mainly with those aspects of steroid metabolism that have been rather thoroughly studied in rat and mouse preputial glands. As such, it may shed some light on the mechanisms that control steroid interconversions in sebaceous glands.

Measuring the volume of a sebaceous gland is tedious and is at best only semiquantitative. More importantly the assumption that volume and sebum secretion are related is unlikely and no doubt this is why it has never been established. For example gland volume could remain the same while sebum secretion increased or decreased by a changed rate of cell turnover. For these reasons sebaceous gland activity was assess by measuring the rate of sebum secretion. A different method has been also described unlike the latter method, which measures hair lipid and not total surface lipid.

The sebaceous glands in man are aggregates of various-sized acini that empty into a duct. Glandular configuration is determined by the relative size of the glands in any given area and the number of other glands in the same area, that is by the amount of crowding they are subjected to and by the nature of the dermis in which they grow. Regardless of differences in size, shape, or position, their cellular morphology and sequence of differentiation are similar but not necessarily identical. Sebaceous differentiation is the orderly synthesis, segregation, and accumulation of lipid droplets which culminate in enlarged, misshapen cells that fragment to form sebum.

Following topical treatments of rat dorsal skin with soap solutions (under greatly exaggerated conditions compared with normal usage) to invoke a primary irritation response, keratotome sections of pure epidermis free from sebaceous glands, and dermis free from epidermis were incubated with 11C glycerol, acetate, thymidine, and glucose in order to measure skin metabolism. In the epidermis. DNA synthesis was stimulated soon after treatment, and this was rapidly followed by increased incorporation of both labelled glycerol and acetate into glycerolipids (phospholipids and triglycerides). No such changes were seen in the dermis. Of these altered lipids, the proportion of the total radioactivity incorporated into phospholipids fell drastically, but rose in triglycerides. The frequency of soap treatment was more important than its duration for the development of irritation and changes in liquid synthesis. The activity of the pentose phosphate shunt pathway, as measured by 1-14C- and 6-14C- glucose oxidation was unchanged after soap treatment, as was the synthesis of epidermal fatty acids. The altered glycerolipid metabolism was reversible if the animals were allowed to recover following mild irritation by soap. Cell fractionation and autoradiography suggested that the germinative (stratum basale) cells of the epidermis were the locus of the observed effect, and not the differentiated cells. [ABSTRACT FROM AUTHOR]

Fixation or epidermis with osmium zinc iodide (OZI) for 24 hr at room temperature renders keratinosomes (lamellar granules of epidermis), the Golgi region, and mitochondria preferentially impregnated with heavy material while the remainder of the epidermal cell merely shows background staining. OZI fixation intensifies the heavy metal staining of the lamellae and of the envelope of keratinosomes. Extraction of epidermis with hexane prior to fixation with OZI abolishes the intensified impregnation of the lamellae and of the envelope of keratinosomes with the osmium zinc iodide stain. Because hexane theoretically extracts nonpolar lipids only and does not cause tissue disruption, it is suggested that the OZI-positive materials in keratinosomes are largely nonpolar lipids. [ABSTRACT FROM AUTHOR]

This study was directed towards the mechanisms by which solutions of some ionic surfactants increase the permeability of human skin. Ionic surfactants of three n-alkyl homologous series (R-COONa, R-OSO3Na, R-NH3CI) were selected. The low frequency, low voltage, alternating current (A.C.) conductance of isolated epidermal membranes is related to the permeability constant for water and was suitable for following effects of surfactant solutions below the critical micelle concentrations. Solutions and conditions were compared by observing differences in the induced rates of increase of A.C. conductance. A similar pattern of relative surfactant activity was shown for each series of surfactants. C8 compounds showed no effect, C10 slow but distinct increases in conductance, maximal effects occurred at C12 and C14 and less at C16. The induced changes were reversible to widely varying degrees up to a maximum of 90 percent. Members of the two anionic series were similar in effect but the alkylamine hycirochlorides produced more rapid conductance increases shortly after contact than did corresponding anionic molecules. The reversibility of the permeability changes excludes extraction of molecules as the mechanism of action for the surfactants. The absence of any similarity between the relative surfactant activities and changes in hydrophillipophil balance or detergency indicates an action against the protein rather than the lipid components of the stratum corneum. [ABSTRACT FROM AUTHOR]

Ultrastructural techniques were used to study alterations of rat-tail epidermis 24 and 72 hours after x-irradiation with 2, 4, 8, and 16 Krads. Twenty-four hours after irradiation the tissue showed changes in mitochondrial membranes. Intracellular and extracellular edema and nuclear inclusions also were observed. Seventy-two hours after irradiation cellular structure appeared even more affected. Most cells showed perinuclear lipid vacuoles, nuclear fragmentation, and severe mitochondrial changes. An attempt was made to relate these ultrastructural alterations with those induced by other sources of irradiation and other forms of injury. [ABSTRACT FROM AUTHOR]

Sebum collected from thigh, scalp, back, and face skin of adult males was examined for the presence, in either free or conjugated state, of seven androgens. Estimates of the quantities present were made by gas chromatographic analysis after separation of free from conjugated steroids, solvolysis of the conjugates, preliminary purification by thin-layer chromatography, and formation of the trimethylsilyl derivatives of the hydroxysteroids. Losses during these procedures were estimated by measuring the recovery of ³H-labeled steroids added to the sebum before treatment. Suggestive evidence was found for the presence of androstanedione, androstenedione, dihydrotestosterone, androsterone, and dehydroepiandrosterone. The amounts obtained were much lower than values that have been reported previously and were insufficient for full characterization. Testosterone and etiocholanolone were not detected. [ABSTRACT FROM AUTHOR]

Human sebaceous glands were dissected (at 25-40x magnification) under sterile conditions from scalp specimens obtained during neurosurgical procedures. Isolated glands were incubated with 14C-glucose or 14C-branched amino acids in sterile chambered Petri dishes. Lipids were extracted, separated by thin-layer chromatography (TLC), scraped from the thin-layer plate, re-extracted and weighed, and the incorporated radioactivity of each fraction was measured by liquid scintillation counting. Squalene, wax esters, triglycerides and cholesterol were identified by TLC, and their presence was confirmed by the Liebermann-Burchardt reaction. Cholesterol estes were not identified by either technique. Radioactivity was found in most lipid fractions, at least in small amounts. Specific activity was highest in the triglyceride fraction. Although free fatty acids were not visualized by TLC, radioactivity was present in the area to which free fatty acids would be expected to migrate. [ABSTRACT FROM AUTHOR]

Alterations of the physical properties of stratum corneum induced by ether extraction were studied. In vitro changes measured included mechanical work to stretch (Instron extensometer), cross-sectional swelling, and expansion in the plane of the tissue when placed in water. Results showed that ether extraction produced a pronounced weakening of the stratum corneum as shown by the work index when measured at 5% extension. This weakening was accompanied by an increase in the cross-sectional swelling and higher expansion in the plane of the tissue. In vivo observations using scanning electron microscopy of replicas of ether-extracted skin confirmed the pronounced swelling effects seen in vitro. The results suggest that removal of lipids from the surface of the skin produces a pronounced weakening and swelling when the skin is subsequently immersed in water. This may be reflected in the appearance of cracks and upturned stratum corneum cells. [ABSTRACT FROM AUTHOR]

Morphogenesis was correlated with changes in lipid metabolism in developing skin of chick embryos. Concentrations of total lipid, neutral lipid and phospholipid fatty acids as well as sterol and sterol esters were monitored at varying time points between the 12th and 20th day of embryonic life. Chemical estimates were correlated with a shorter-term studies of in vitro incorporation of C14 acetate into skin lipids Differentiation of skin into a cornifying, stratified, squamous epithelium was associated with a shift in lipogenic patterns, specifically the enhanced production of non-polar esters of sterols and long-chain alcohols (wax esters) along with a relative decline in phospholipids. The data indicate that epidermal differentiation and cornification in chick skin may he correlated with altered lipid metabolism. [ABSTRACT FROM AUTHOR]

Anterior tibia! skin of 12-day chick embryos was grown in organ culture in the absence and presence of serum and in Vitamin A to achieve varying degrees of cornification and mucous metaplasia. Morphogenesis was correlated with ongoing lipogenesis as assessed by short term in vitro incorporation studies with C14 acetate. Shifts in the patterns of lipogenesis similar to those previously described during embryonic differentiation of chick skin suggest that organ culture provides a useful and relevant model for studies of the biochemical events in differentiation. Results further indicated that the non-specific lipogenic effects of serum on cultured skin may be distinguished horn the changes in the intrinsic lipid pathways of differentiating epidermis. [ABSTRACT FROM AUTHOR]

Composition of lipids of the forehead, nose surface, and contents of sebaceous follicles of the nose is reported for subjects whose flora is predominantly C. acnes I or C. acnes II. No differences in any of the parameters examined could be attributed to the group of C. acnes which the subjects carried. The extent of triglyceride (TG) hydrolysis was a function of the lipid extraction site with nose follicles > nose surface > forehead surface, but there was extensive subject-to-subject variation at each site. The fatty acid composition data showed that the free fatty acid (FFA) pools were higher in saturated acids and lower in unsaturated acids than were the remaining TG pools. This difference in fatty acid composition cannot be attributed to specificity of hydrolysis by C. acnes. The results are discussed in terms of the hypothesis that hydrolysis of sebum TG by microbial lipase(s) gives rise to FFA, which cause follicular irritation leading to acne. [ABSTRACT FROM AUTHOR]

Samples of normal dermis were collected from seven women and six men ranging in age from 17 to 81 years. The water content increased with age while the total lipid remained unchanged. The tissue was separated into fractions representing 'ground substance' (isotonic saline extract), cells (tryptic digest), and collagen (gelatin). Each fraction was analyzed for nitrogen, hydroxyproline, hexosamine and hexuronic acid. The amount of the saline extract changed little with age. The amount of both the trypsin and gelatin fractions decreased with age. None of the measured components could be related to the sex of the donor. The proteins of the isotonic saline extract were examined by cellulose acetate, disc and immunoelectrophoresis. Qualitatively, all fractions resembled the plasma proteins. The relative proportions of the proteins corresponded closely to those in the plasma. The hemaglobin content of the extract was less than one percent that expected if the proteins were present in whole blood. Most of the hyaluronate of the dermis was found in the ground substance. Dermatan sulfate predominated in the cellular and collagenous fractions. The age and sex of the donor could not be related to the concentration of any fraction. The residue resembled pure elastin in its appearance under the light microscope after staining with hematoxylin and eosin, Heidenhain's azan or aldehyde fuchsin; its ultrastructure after sonication; its nitrogen and hydroxyproline content; and its amino acid analysis. The amount increased three-fold between 20 and 80 years of age. [ABSTRACT FROM AUTHOR]

Human skin specimens, previously incubated with 14C-cholesterol, were irradiated with a mercury arc lamp for 2, 10, 20 and 60 minutes. Total lipids were extracted and preliminary separation of the lipid classes obtained by thin-layer chromatography. Cholesterol-derived photoproducts were observed as polar materials remaining at the origin of the chromatogram. The occurrence of these products was further verified by silicic acid column chromatography. Among those photoproducts tentatively identified by co-chromatography with reference oxidation compounds of cholesterol were cholestan-3β, 5α, 6β-triol, 7α and β-hydroxycholesterol, 7-ketocholesterol and cholesterol α-oxide. Quantitation and relative concentrations of the photoproducts were based upon 14C-radioactivity measurements. Formation of these products was approximately proportional to exposure time. Further identification of two of these products, 7-ketocholesterol and cholesterol α-oxide, was obtained by gas-liquid chromatography-radiotracer analysis. The latter, cholesterol α-oxide, has been reported to possess carcinogenic properties when administered to experimental animals. [ABSTRACT FROM AUTHOR]

The importance of lipid dependent yeasts in the hydrolysis of triglycerides in human skin was investigated by selective antibiotic therapy and monitoring of the lipid composition and the microbial flora in healthy volunteers. The yeast density was reduced with topical amphotericin treatment. In the presence of high populations of Corynebacterium acnes, lipid composition was unchanged. When C. acnes was also inhibited by systemic demethylchlortetracycline, triglyceride hydrolysis was reduced to very low levels. The aerobic cocci were not implicated in lipid hydrolysis. [ABSTRACT FROM AUTHOR]

Epidermal slices can produce ATP by both glycolytic and respiratory reactions. Via glycolysis, ATP is produced at a maximal rate of about 0.1 μmole/hr/mg of fresh tissue when slices are incubated in the presence of glucose at concentrations equivalent to normal blood levels. Most of the glucose is converted to lactate, and only a small percentage of the glucose metabolites are oxidized. Respiration generates the majority of the energy for the epidermis, producing ATP at a rate of 0.5 μmole/hr/mg of tissue. The main respiratory reactions of the epidermis in vitro are β-oxidation of lipids and the Krebs cycle. Slices of human epidermis in culture show a relatively constant rate of respiration for several hours in the absence of added substrate, and endogenous components are the main substrates of respiration even in the presence of added nutrients. Cellular phospholipids are probably the major endogenous nutrients for this oxidation. The constant rate of epidermal respiration, the limited oxidation of glucose metabolites, and the Pasteur effect indicate that epidermal energy metabolism is subject to a strong and complex control by biochemical factors. These factors are more prominently expressed in the intact epidermis than in homogenates or extracts. Data are cited which suggest that nucleotide cofactors, particularly ATP, play an important part in energy control by modifying key enzymes of the energy pathways. In light of these data and current concepts of biochemical regulation, an hypothesis is presented in which nucleotides and other intermediates synchronize the rates of glycolysis and respiration, markedly limiting the oxidation of pyruvate by the Krebs cycle. They also may contribute to the accumulation of glycogen, which is observed in wounds and psoriatic epithelium. [ABSTRACT FROM AUTHOR]

Aerobic bacteria were excluded as a major source of lipases when it was found, in a previous study, that their virtual eradication by topical neomycin did not lower the free fatty acids (FFA) in scalp lipids. We now report the reciprocal experiment in which an oral tetracycline was used to suppress the anaerobic organisms. Nine healthy adults received 600 mgm of demethylchlortetracycline (DMCT) daily for 6 weeks. During this time we followed the composition of scalp lipid by thin layer chromatography and the densities of C. acnes, aerobes and yeasts on scalp and forehead. Six subjects had high initial levels of C. acnes. In these the FFA fell from 43% to 23% with a more than 99% reduction in the density of C. acnes. In three who initially had insignificant quantities of C. acnes the FFA were at the start only 25% and did not decline with treatment. The density of the aerobic population was not affected by DMCT owing to development of resistance. Yeasts were also unaffected. The finding that the FFA were proportional to the level of C. acnes suggests that these organisms are the chief source of lipolytic enzymes. The FFA levels began to decline earlier than the density of C. acnes. This might be explained either by enzyme inhibition or by bacteriostatic effect. [ABSTRACT FROM AUTHOR]

The response of the sebaceous gland to total caloric deprivation was studied in 18 obese patients undergoing fasts for periods of four to eight weeks. Sebum production was measured in 11 of the patients and was found to decrease in each individual, with an average reduction of 40%. Diminished secretion usually occurred by the fourth week but was sometimes seen as early as one or two weeks. The composition of the sebum, analyzed in 14 patients, was also altered, and this could be detected as early as five days after the onset of fast. The qualitative changes in surface lipid consisted of a reduction in the amount of triglyceride fatty acids, wax esters, cholesterol and cholesterol esters but with no significant alteration in the amount of squalene. [ABSTRACT FROM AUTHOR]

Lipids were extracted from slices taken horizontally through the epidermis of the cow snout. The phospholipid, triglyceride, cholesterol, fatty acid and glucose content of each slice was determined. The pattern of the changes in lipid composition in the epidermis is discussed and related to the process of keratinization. [ABSTRACT FROM AUTHOR]

The aerobic microflora of the scalp, predominantly cocci, was virtually eliminated by the daily application of 1% aqueous neomycin for one month. This was done to test whether these organisms are an important source of the lipases which liberate fatty acids from the sebaceous triglycerides. This treatment had no effect on the proportion of free fatty acids in the surface lipids as determined by thin layer chromatography. The follicle-residing anaerobic C. acnes, was not attacked by neomycin and the yeast-like fungus P. ovale increased somewhat. The percentage of free fatty acids in any individual's sebum before and after treatment was positively correlated with the density of C. acnes. The latter organism is probably mainly responsible for lipolysis of triglycerides. [ABSTRACT FROM AUTHOR]

The diffusion of tritiated water through hairless mouse skin and human abdominal autopsy skin was determined in vitro prior and subsequent to the application of organic solvents to the epidermal side of the skin. The classes of extracted lipids were separated by thin-layer chromatography. The amounts and types of lipids extracted were correlated with changes in tritiated water diffusion. Seven classes of lipids were identified from hairless mouse skin extracted with acetone, diethyl ether and chloroform, but only minimal amounts of four classes of lipids were identified from skin extracted with dimethylsulfoxide. All of the solvents increased the rate of diffusion of tritiated water, but there was no correlation between the type or amount of lipid extracted and the degree of alteration of the water barrier function. Results obtained with human abdominal autopsy skin were similar in that dimethylsulfoxide removed a minimal amount of lipid, but markedly increased the diffusion rate of tritiated water. [ABSTRACT FROM AUTHOR]

Xanthomas, in themselves, are usually harmless. However, they frequently occur in patients with atherosclerosis and abnormal lipoprotein metabolism. Therefore, studies dealing with xanthomas in experimental animals and humans, in whom hyperlipoproteinemia is present, may lead to useful information about the manner in which lipids accumulate in the foam cells of xanthonms and, more important, how the pathologic processes in the skin might mirror events occurring in the foam cells of atherosclerotic plaques. This article will review some of the current concepts of the biochemical and morphologic abnormalitites occurring in xanthomas as derived from studies of these cutaneous lesions in humans and experimental animals. This will include a discussion of the metabolism of certain lipoprotiens of importance in xanthomatosis as well as a consideration of the new hyperlipoprotein syndromes described by Fredrickson et al. (1) as they relate to various forms of xanthomas. Where possible, an attempt is made to correlate the pathologic and biochemical alterations observed in xanthomas with these occurring in atheromas. [ABSTRACT FROM AUTHOR]

TLC† analysis of comedo lipids from the face, neck, chest and back of acne patients of both sexes, ages 12 to 26 years, (some 65 specimens) gave the same gross composition except for hydrocarbons more saturated than squalene and lipids more polar than free cholesterol. Quantitative data (chromatography plus GLC of isolated fractions) on both comedo and surface lipids from each of 3 acne patients revealed the following. Free fatty acids plus triglycerides comprised ∼63% of both comedo and skin surface lipids. However, for the comedo, 90% of this sum was free fatty acids compared with only 25% for surface lipid. This implies that triglycerides in comedo lipids are nearly completely hydrolyzed but only 25% hydrolyzed in surface lipids. GLC patterns of the free fatty acids were almost identical for both surface and comedo lipids in all 3 subjects except for slightly more unsaturated acids in surface lipids. For comedo and surface lipids respectively, wax esters were 14% and 24%, sterol esters 4% and 2%, free cholesterol 12% and 2%, and squalene 8% and 9%. Absence of free alcohols and constancy of GLC composition of the entire wax ester fraction indicated it was not hydrolyzed in either surface or comedo lipids. GLC composition of the entire sterol ester fraction from comedones indicated that the fatty acids were derived from epidermis and sebum. [ABSTRACT FROM AUTHOR]

Human skin surface debris collected from ether extracts of the scalp catalysed the hydrolysis of triolein, tristearin and methyl stearate, but not cholesteryl stearate or cetyl palmitate, when suspended in ether or hexane solutions of these lipids. The activity was slowly destroyed by heating at 120° C, but was not inhibited by addition of tetracycline. [ABSTRACT FROM AUTHOR]

Quantitative thin-layer chromatography was employed for determining the amount and composition of skin surface lipid from the forehead, cheek, chest, back, side, arm, and leg of adult male subjects. These data served as a basis for determining the relative contribution of epidermal and sebaceous lipids to the extractable surface lipid. The results indicate that lipid produced by the epidermis is an insignificant fraction of the total extractable surface lipid on areas rich in sebaceous glands, but can affect surface lipid composition on the limbs and on the trunk away from the midline. The amount of epidermal lipid recovered from the skin surface averaged between 5 and 10 μ per sq cm, compared with average recoveries of 150 to 300 μ of sebum per sq cm from the forehead. [ABSTRACT FROM AUTHOR]

Epidermal cells were obtained from human skin epidermis by trypsinization and exposed to acetate-1-C14 while maintained in a variety of culture media. Maximum amounts of radioactivity were incorporated into all lipids when a complete medium was used. Acetate-C14 proved to be a more effective precursor than glucose-C14. Saponifiable lipids were converted to their methyl esters, which were resolved according to unsaturation, using silver TLC, and then by GLC. A portion of each ester was condensed and its radioactivity assayed by scintillation counting. Another portion was degraded to find the per cent of activity in the carboxyl carbon. Long-chain acids, with 20 carbons or more, were found to be heavily labelled, with high specific activities, with the exception of 20:4. The distribution of radioactivity did not alter greatly with time. The specific activities of long-chain acids increased several fold with time. Data on carboxyl carbon activity suggested the operation of a de novo synthesis of saturated acids to C16 and a stepwise elongation of C16 by C2 units. [ABSTRACT FROM AUTHOR]

Skin surface lipids from the foreheads of 51 subjects between the ages of five days and fifteen years were analyzed by quantitative thin-layer chromatography. The cholesterol concentrations were low at birth, at maximum levels at six years of age, and low again, almost to adult levels, at nine years. Conversely, average concentrations of wax esters were high at birth, low between the ages of three and six years, and rising towards adult levels by nine years. There was no significant change in the combined concentrations of triglycerides plus free fatty acids during development. Concentrations of squalene were highly variable, in contrast to the constant proportions previously reported for adults. [ABSTRACT FROM AUTHOR]

The present study was designed to compare inhibition of DNA synthesis in human epidermis by lipid-soluble analogues of methotrexate and by other inhibitors of dihydrofolate reductase to find a potentially useful topical agent for the therapy of psoriasis. Skin samples were preincubated for 30 min with 10 -6 M concentrations of a series of 11 compounds. The inhibition of DNA synthesis by these compounds was assayed by measuring the incorporation of deoxyuridine-3H into extracted DNA following a 2-hr incubation. A ratio of inhibitory activity expressed as the % inhibition by 10-6 M drug to the % inhibition by 10-6 M methotrexate was calculated for each compound. Maximum inhibitory activity was obtained with the dimethyl and diethyl esters of methotrexate and the same esters of dichloromethotrexate, with mean ratios of 1.34, 1.34, and 1.35, 1.42, respectively. Further increases in alkyl chain length resulted in a decrease in inhibitory activity. Dichloromethotrexate yielded a 1.23 ratio, aminopterin a 1.32 ratio, while the pyrimethamine ratio was 0.11 and that of trimethoprim was 0. It is not known yet whether these results reflect differences in cell penetration due to lipid solubility characteristic's and/or differences in binding of drug by dihydrofolate reductase. [ABSTRACT FROM AUTHOR]