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After a globiferous pedicellaria is lost from a sea urchin, a new appendage of the same kind is usually regenerated in the weeks that follow. During the latter part of regeneration, head glands and stalk glands, both of epidermal origin, develop from undifferentiated cells. Head gland cells begin morphological differentiation in the epidermis and then delaminate into the underlying dermis. In the formation of the stalk gland, by contrast, undifferentiated cells delaminate from the epidermis and then begin morphological differentiation in the dermis. During late regeneration, cells in the head and stalk glands are characterized by extensive rough endoplasmic reticulum distended with intracisternal material; moreover, the Golgi complex is closely associated with some of the large cytoplasmic vacuoles. The accumulating secretions of the two glands differ both in fine structure and in site of storage. Head gland secretions are stored intracellularly in the cytoplasmic vacuoles, while stalk gland secretions leave the gland cells in an apocrine fashion and are stored in an extracellular lumen. After regeneration, the mature cells of the head glands and stalk glands contain relatively little distended endoplasmic reticulum, although a Golgi complex is still present. Presumably, mature gland cells, in comparison to regenerating gland cells, produce relatively little secretion; instead, the glandular products elaborated during regeneration are probably stored in the mature glands with little augmentation or turnover.

The sites and hormonal control of lipogenesis in hamster ear sebaceous glands are reported. Sebaceous lipogenesis was determined in ear biopsies by incubation with glucose and tracer concentrations of 14C-acetate in buffer. The 14C-labeled lipids were saponified, extracted, and determined by liquid scintillation counting. Histologically, the ears contained many sebaceous glands. The glands of male animals were much larger and more heavily lipid-stained than glands from females. Lipogenesis was almost entirely confined to the sebaceous glands in the dermal stroma. Lipogenesis was considerably higher in ear biopsies from male hamsters than from female, castrate male, or hypophysectomized male hamsters. In contrast to published data using hypophysectomized rats, where dihydrotestosterone potently and testosterone only weakly increased sebum secretion, both testosterone and dihydrotestosterone potently increased lipogenesis in the ears of hypophysectomized male hamsters. Dihydrotestosterone was somewhat more potent than testosterone in the hamster. Hypophyseal hormones do not appear to be essential for androgen stimulated lipogenesis in the hamster. In female hamsters, 5 alpha-androstane-3 alpha, 17 beta-diol, testosterone, dihydrotestosterone, 4-androstene-3,17-dione, and 5 alpha-androstane-3,17-dione produced dose-dependent increases in lipogenesis. From this and other studies, it is suggested that androgens other than dihydrotestosterone could be physiologically important in man and animals in stimulating lipogenesis in sebaceous glands.

Subcutaneous injection of epidermal growth factor (EGF) into the pinna of adult female and castrated male Syrian hamsters resulted in an increase in the number of cells per sebaceous gland unit. The effect of EGF on the sebaceous cell number was localized to the treated ear and accompanied by epidermal hyperplasia. The injection of testosterone into the ear also produced an increase in the cell number. When testosterone and EGF were injected together, the two hormones exerted an additive effect on the sebaceous glands of female hamsters. This is the first demonstration of a sebotrophic action of this polypeptide hormone.

It is argued that the close endocrine control of human sebaceous glands and the likely effects of acne on selection indicate that both gland and disease have persisted because they are biologically useful. Two possibilities are proposed: sebum may provide precursor substrates for metabolism and synthesis by the epidermis of compounds of both local and systemic importance; and the adjuvent properties of corynebacteria which colonise the active sebaceous glands of acne may facilitate certain general immunological membrane.

Median S-phase lengths of pinna epidermis and sebaceous glands, and of epithelia from the oesophagus and under surface of the tongue of Albino Swiss S mice were estimated by the percentage labelled mitoses method (PLM). The 18.4 and 18,8 hr for the median length of S-phase for pinna epidermis and sebaceous glands respectively made it possible for these two tissues to be used experimentally for testing tissue specificity in chalone assay experiments. The 10.0 and 11.5 hr for oesophagus ang tongue epithelium respectively made experimental design for chalone assay difficult when pinna epidermis was the target tissue. The results of the Labelling Index measured each hour throughout a 24-hr period showed no distinct single peaked diurnal rhythm for pinna epidermis and sebaceous glands. Instead a circadian rhythm with several small peaks occurred which would be expected if an S-phase of approximately 18 hr was imposed on the diurnal rhythm. This indicates that there may be very little change in the rate of DNA synthesis. The results are given for the assay in vivo of purified epidermal G1 and G2 chalones, and the 72--81% ethanol precipitate of pig skin from which they could be isolated. These experiments were performed over a time period which took into account the diurnal rhythm of activity of the mice as well as the S-phase lengths. Extrapolating the results with time of action of the chalone shows that the G1 chalone acts at the point of entry into DNA synthesis and that the S-phase length was approximately 17 hr for both the pinna epidermis and sebaceous glands. This may be a more correct value since the PLM method overestimates the median S-phase length as it is known that in pinna skin the [3H]TdR is available to the tissues for 2 hr and true flash labelling does not take place. The previous reports that epidermal G1 chalone acts some hours prior to entry into S-phase resulted from experiments on back skin where the S-phase is shorter and there is a pronounced diurnal rhythm which could mask the chalone effect. The epidermal G2 chalone had no effect on DNA synthesis even at different times in the circadian rhythm. Thus the circadian rhythms and S-phase lengths of the test tissues need to be considered when experiments are performed with chalones. Ideally, the target tissues selected for cell line specificity tests should have the same cell kinetics for the easier and more accurate assessment and interpretation of results. When the tissues have markedly different cell kinetics, experimental procedures and results need to be evaluated accordingly. The point of action of G1 chalone can only be assessed if the effect is measured over the peak of incorporation of [3H]TdR into DNA. The results of the effects of skin extracts are analysed in relation to changes in the availability of [3H]TdR for the incorporation into DNA and to the possibility of there being two distinct populations of proliferating cells.

1. Preputial gland function in male Microtus montanus is androgen-dependent, both in terms of preputial weights and in the production of a series of lipids which are present in M. montanus and absent from Microtus pennsylvanicus. 2. Production of these species-typical lipids is decreased but not eliminated in castrates, as well as in adrenalectomized castrates treated with corticosterone. Therefore, in the total absence of androgens, a low level of these lipids is still produced. 3. 5 alpha-dihydrotestosterone and 17 beta-estradiol enanthate have limited effects on maintenance of preputial weight, suggesting that testosterone itself is the active steroid in the preputial gland of this species.

Sprague-Dawley rats were castrated either within 24 h of birth or at 4 weeks of age. Control animals were sham operated. Intact female rats were also included for comparison. Sebum production was assessed at 80 days of age by measuring the amount of skin-surface lipids that could be extracted with acetone and which had been produced during 2 days. The removal of the testes at birth reduced the activity of the sebaceous glands to level more nearly approaching that seen in the female rats whereas castration at 4 weeks of age only partially decreased the rate of sebum secretion so that it was intermediate between the male and female rats. The weights of the pituitary gland, thyroid and adrenal glands increased after castration but there were no differences between rats castrated at birth and those castrated at 4 weeks of age except in the weight of the thyroid gland. It would appear that the role of the testes in the control of the activity of the sebaceous glands is a sequential event which has already started at birth.

The sebaceous glands of man show age-related differences in their activity as determined by quantitative and qualitative examination of sebum. Sebaceous secretion is low in children and begins to increase in mid- to late childhood under the influence of androgens. This rise continues until the late teens, after which no further significant change takes place until late in life. In elderly men, sebum levels remain essentially unchanged from those of younger adults until the age of 80. In women, sebaceous secretion decreases gradually after menopause and shows no significant change after the 7th decade. The most likely explanation for the decrease in sebaceous gland secretion with age in both men and women is a concomitant decrease in the endogenous production of androgens. Although surface lipid levels fall with age, paradoxically the sebaceous glands become larger, rather than smaller, as a result of decreased cellular turnover. Nonetheless, as the higher surface lipid levels after administration of fluoxymesterone (a synthetic testosterone derivative) indicate, the glands have the capacity to respond to androgens.

The mucous gland of the red-spotted newt, Notophthalamus viridescens viridescens, Rafinesque was examined by histochemical and ultrastructural techniques and its cytological responses to various hormonal conditions were studied. Its secretory epithelial cells produce and release in merocrine fashion a neutral, unsulphated mucosubstance. The secretory epithelium is bounded peripherally by a thin, but apparent non-functional, myoepithelium. The duct of this mucous gland consists of a single keratinized tubular cell that extends from the neck region of the gland to the surface of the epidermis. Mucous secretion is absent or greatly reduced on the skins of newts maintained under laboratory conditions for a few weeks but reappears after injection of ovine prolactin. Mucous glands in laboratory conditioned animals show a 4-fold increase in volume brought about by the engorgement of their epithelial cells with secretory granules. Ovine prolactin reduces the volume of the glands to unconditioned levels with a corresponding reduction in granular content, suggesting that prolactin functions in the release of the granules. This view is reinforced by the findings that autotransplantation of the pituitary gland prevents the conditioning effect and that glandular volume increases in autotransplanted animals given ergocornine. Granular accumulation begins also in hypophysectomized newts but ceases after a week, indicating the need for some hypophyseal factor in the synthesis as well as the release of the granules. Ovine prolactin restores mucous glands of hypophysectomized newts to the unconditioned state. Contrary to earlier findings, ovine prolactin induces a reduction in the volume of the mucous gland in thyroidectomized newts.

alpha 2u-Globulin, the principal urinary protein of the male rat, has extensive sequence homology with many lipid binding proteins. The highest concentration of alpha 2u-globulin is found in the preputial gland, a holocrine secretory organ with pheromonal function. Meibomian and perianal glands are two other modified sebaceous glands with holocrine secretory cycles and pleiomorphic peroxisomes capable of synthesizing pheromonal lipids. Immunocytochemical examination shows the presence of alpha 2u-globulin in the acinar cells of all three of these modified sebaceous glands. Whereas in the preputial gland all of the acinar cells exhibit immunoreactivity, in the meibomian and perianal glands only selective cells contain alpha 2u-globulin. In the case of the preputial gland, in addition to the acinar cells some stratified epithelial cells also were immunoreactive. In the perianal and meibomian glands, keratinocytes lining nearby hair shafts and select cells of accessory oil glands stained for alpha 2u-globulin. In situ hybridization with a cloned cRNA probe confirmed the immunocytochemical data. Presence of the alpha 2u-globulin mRNA in these glands was also established by Northern blot analysis. Immunoelectron microscopic examination of preputial alpha 2u-globulin showed the presence of this protein in secretory granules of various maturational stages. Immunolabeled alpha 2u was also found in attached vesicles containing protein and lipid inclusions. The lytic cells were not only loaded with alpha 2u-globulin but also contained sharp-edged, irregularly shaped electron-dense granules which stained heavily for this protein. Specific localization of alpha 2u-globulin and its mRNA in three pheromone-producing sebaceous glands and its structural homology with known lipid binding proteins indicate a pheromone carrier role of alpha 2u-globulin.

Several factors affecting the stimulus-induced vacuolation in cat tracheal submucosal glands described in a companion paper [Am. J. Physiol. 241 (Cell Physiol. 10): C18-C24, 1981] were examined. Stimulation with predominantly alpha-adrenergic, beta-adrenergic, and cholinergic agonists at various concentrations and in the presence of appropriate blockers showed that alpha-adrenergic or cholinergic stimulation is more effective in inducing vacuolation than beta-adrenergic stimulation. In addition, Ca- or HCO3- deficient incubation medium or low incubation temperature either blocked or significantly decreased the vacuolation response. Stimulation in the presence of the Na-K-ATPase inhibitor ouabain prevented vacuolation. The known roles of these factors in fluid transport are consistent with the possibility that stimulus-induced vacuolation possibly arises in response to disturbances in cytoplasmic fluid, which are induced in the secretory cell when the fluid component of secretion is intensely stimulated. A model is presented that possibly relates the observed responses to intracellular event and suggests the possibility of ion pumps in the apical membrane.

The effect of alpha-MSH on sebum secretion and preputial gland weight was examined in intact, castrated and hypophysectomized male rats and in hypophysectomized rats receiving treatment with either testosterone propionate (TP) or progesterone. After treatment with alpha-MSH for 2 weeks, increases in sebum secretion occurred in intact, castrated and hypophysectomized rats, but larger responses were found in the hypophysectomized rats that had received treatment with either TP or progesterone, suggesting that alpha-MSH acts synergistically with TP and progesterone to stimulate sebum secretion. Alpha-Melanocyte-stimulating hormone also increased preputial gland weight in intact rats, but there was no response after castration and only a small response after hypophysectomy. However, when the hypophysectomized rats received simultaneous treatment with either TP or progesterone, alpha-MSH increased preputial gland weight. It is suggested that alpha-MSH acts directly on the sebaceous glands to stimulate lipogenesis and, together with steroid hormones, may have an important role in controlling sebaceous glandd function in the rat and other hairy mammals. With the evolution of hair, certain of the MSH peptides may have lost their significance as pigmentary hormones and have developed a sebotrophic function. For this reason, it might be more appropriate to refer to these peptides as the 'sebotrophins'.

The main indices of mitotic cell division in rat sebaceous glands (external auditory meatus and tarsales gl.) were studied autoradiographically using H3-thymidine and with colchicine method. The duration of mitotic cycle and its separate phases, the number of cells involved in the proliferative pool, as well as the turnover of terminals of the epithelium in both the glands were stated to be nearly identical. The duration of the mitotic cycle was: T -- 28.1 hour; tG1 -- 18.64; tS -- 6.3; tG2 -- 1.80; tM -- 1.34 hours. The proliferative pool (Pc) -- 31.45%, turnover of the basal layer cells -- 89.25 hours. These indices for the stratified epithelium of excretory ducts were respectively; T -- 33.0 hours; tG1 -- 21.74; --8.06; tG2 -- 1.6; tM -- 1.6; Pc -- 26.8% and the turnover for the cells of the basal layer -- 123 hours. Thus, the sebaceous glands are to be regarded as organs where a rapid renovation of epithelia cells occurs.

The prosomal glands of Tetranychus urticae (Acari, Tetranychidae) were examined light and electron microscopically. Five paired and one unpaired gland are found both in females and males. The silk spinning apparatus consists of paired silk glands which extend laterally on both sides of he esophagus into the pedipalps. There, they enter the terminal silk gland bag which opens into a silk bristle at the apex of hte pedipalps. The salivary secretions are formed in three paired glands which have an interconnecting duct, the podocephalic canal. The dorsal podocephalic glands may produce a serous secretion, the anterior podocephalic glands a mucous secretion, and the coxal organ may add a liquid, ion-rich secretion. These secretions pass the podocephalic canal and reach the mouth at the apex of the gnathosome. The function of the paired tracheal organs and the unpaired tracheal gland is still unclear. The tracheal gland may produce a secretion which facilitates the movement of the fused chelicerae and the stylets.

Sexually experienced male rats were used to test the attractiveness of body odors of female rats. The attractiveness of these odors varied with the estrous cycle. Odors from female rats in proestrus were the most attractive to male rats and those from female rats during the darkness hours of diestrus the least attractive. The preputial glands appeared to be the source of these odors for the male rats showed no preference for the odors of proestrous female rats that had been preputialectomized. Administration of 1 microgram estrdiol benzoate (EB) for 5 days increased the attractiveness of body odors of ovariectomized rats. A higher dose of EB (5 microgram) had the same effect when administered for 1 or 5 days although the increase that occurred after 3 days was not significant. A single dose of progesterone (P) (500 microgram) on the other hand, decreased the attractiveness of ovariectomized female odors although no change was seen after 3 days of treatment. A single injection of P also decreased the attractiveness of odors of ovariectomized females that had received EB for 3 days. However, P failed to decrease the attractiveness of odors in ovariectomized females after preputialectomy. We conclude that the preputial glands are an important source of sex attractant odors in the female rat and that the changes in the release of these odors that occur throughout the estrous cycle and pregnancy are controlled by ovarian steroids. While estrogen acts to stimulate the production and release of these odors P appears to inhibit their release.

Mongolian gerbil pups are attracted to maternal and parental nest odors. They approach these odors in preference to the odors of either virgin females or clean bedding. The pups do not distinguish between maternal or parental odors and odors of unfamiliar lactating females. Thus lactating female gerbils produce a maternal pheromone similar to that of rats and other rodents. Attraction to the pheromone develops by two weeks of age and persists for at least three weeks. The primary source of the pheromone is the mother's enlarged ventral scent gland. Removing this gland eliminates maternal attractiveness. Development of attraction to maternal scent gland odors depends on prior exposure to them. Pups raised by mothers lacking scent glands do not approach lactating females that have sent glands. The father's presence during development alters the responses of gerbil pups to odors of other males. Pups raised by both parents avoid odors of other pairs with young, whereas pups raised by their mothers only do not. Pups are not attracted to their father's odors.

Using fused-silica capillary gas chromatography, we investigated sebum samples from 55 healthy individuals to discover the effects of aging on the sebaceous gland activity and on the fatty acid composition of wax exters. The sebaceous gland activity, which was expressed by the ratio of wax esters/[cholesterol + cholesterol esters] (WE/[C + CE]), showed a distinct change from infancy through maturity to senescence; the curve of the ratio made a peak in our subjects's 20s. Using the fatty acid analyses, we found an interesting relationship between C16:1 straight and C16:1 iso-branched chains, each of which occupied a large proportion in the fatty acids of wax esters; the former increased in proportion from infancy toward the 20s, with a correlation with aging (r = 0.788, p less than 0.01), and decreased thereafter until our subject's 50s (r = -0.611, p less than 0.01). In contrast, the proportion of the latter followed an entirely reversed course with advancing age. The percentages of C16:1 straight chain components were correlated positively with the WE/[C + CE] ratio (r = 0.642, p less than 0.01), while there was found to be a negative correlation between the proportion of C16:1 iso-branched chain components and the WE/[C + CE] ratio (r = -0.556, p less than 0.01). The results suggest that more active sebaceous glands in lipid production excrete lipids with a higher proportion of C16:1 straight chain fatty acid and a lower proportion of C16:1 iso-branched chain fatty acid. As well as the sebaceous gland activity, the fatty acid composition in sebum wax esters is affected by advancing age in Japanese.

Earlier experiments demonstrated that the injection of alpha-melanocyte stimulating hormone into one mouse of a male pair results, 15 minutes later, in the release of an olfactory cue which increases the aggressive behavior of its partner. Because the preputial gland, whose activity is dependent upon testosterone and alpha-MSH, produces an odor which stimulates aggressive behavior, its relationship with the MSH response was investigated. Preputialectomy failed to prevent the release of the odor by an MSH-treated subordinate mouse of a pair, although preputialectomy of one mouse of a naive pair resulted in it later displaying higher levels of aggression than its intact partner, which then became subordinate. Swabs taken from the perineal region of alpha-MSH-injected subordinates, contained more aggression-promoting factor than swabs taken from saline injected subordinates. It is concluded that the short-term effects of alpha-MSH upon aggression are probably via a product of glandular or urinary origin other than the preputial gland and that the latter is more involved in long-term aggression-promoting cues.

This review describes the various types of sebaceous glands, their locations, and where possible their different functions. All sebaceous glands are similar in structure and secrete sebum by a holocrine process. However, the nature of this secretion and the regulation of the secretory process seem to differ among the various types of glands. Methods for measuring sebum secretion and assessing sebaceous gland activity are also described. The area of major interest during the last 20 years has undoubtedly been the mechanisms that control sebaceous gland function. Most studies have focused on the endocrine control and in particular on the role of androgens and pituitary hormones, although evidence suggests that nonendocrine factors may also be important. However, many questions remain and during the next few years attention will certainly be given to the role of retinoids and their mode of action in the treatment of acne.

Childhood (3 to 9 years) is a calm period of constant growth throughout which social contacts are discovered and intelligence and discretion take place. Consequently, most diseases are infectious. Microrelief was found twice shallower and skin (epidermis + dermis) twice thinner than in adults. Intervals between furrows were reduced parallel to total body surface, thus ruling out the possible existence of special shelters favouring bacterial growth. Sweating is lower, as are skin surface lipid levels, in contrast to the post-natal period, inducing dryness of skin. Although total skin stiffness in vivo was found to be identical to young adult skin, skin chapping is much more frequent. Since detergents as well as extended hot baths may reduce the stratum corneum water binding capacity, they should be used with discretion. Hence, skin care in this period of age should be based upon different criteria than in adults.

In this study we report on isoproterenol-induced changes in short-circuit current (SCC) that are located in the glands of the frog skin. Following complete inhibition of the SCC with amiloride (10(-4) M), the addition of isoproterenol (9.0 X 10(-7) M) to the serosal side of the skin elicits a significant increase in SCC from 0.6 +/- 0.1 to 3.9 +/- 0.5 microA/cm2 (p less than 0.001). The conductance is doubled, and both effects are blocked completely with the beta-blocking agent propranolol. In the split-skin preparation, in which no glands are present, there is no current response to isoproterenol following amiloride. This indicates that the amiloride-insensitive isoproterenol-stimulated SCC resides in the glands. In the intact skin, removal of sodium (choline replacement) from the serosal (but not the mucosal) medium abolishes this current change. The postisoproterenol current change in amiloride-inhibited skins is also dependent on the presence of chloride in the serosal bath. Preincubation of the amiloride-inhibited skin with ouabain (10(-4) M) for 10 min prior to the addition of isoproterenol reduces the isoproterenol response by 50%. These results indicate that there is a sodium- and chloride-dependent ouabain-sensitive secretory mechanism in the skin glands of the frog that is responsible for the development of the isoproterenol-stimulated SCC observed in the presence of amiloride.

A search for specific proteins involved in newt limb regeneration, using monoclonal antibodies against forelimb blastemas, led to the detection of an antigen in the regenerate epithelium. Fluorescent-antibody-labeled cells first appeared just prior to blastema outgrowth. From bud through early digit stages this antibody reacted with nearly all of the regenerate epithelial cells. Other tissues also reacted, including nerve, blood vessels, and gastrointestinal tract. The behavior of the reactive cells in the regenerate epithelium, and their close association with immediately adjacent skin glands, raises several new possibilities for the origin of the regenerate epithelium.

Proper understanding of the cause, nature, and treatment of diseases affecting the skin requires an intimate knowledge of the anatomy and physiology of normal as well as pathologic skin. This article thus lays the groundwork for the discussions of specific pathologic conditions that follow in this issue.

A new approach studying the characteristics of the stratum corneum is presented: the electrophoretic mobility of corneocytes by laser Doppler spectroscopy. The detergent scrub technique was used for harvesting corneocytes from three body regions (forehead, palm, and sole) of normal persons (n = 20) under casual conditions and after thorough defattening of the skin with 70% isopropyl alcohol or petrol. Similarly, cells from the forehead, shoulder, and palm were obtained from 22 acne patients treated with isotretinoin (13-cis retinoic acid) 0.5-0.7 mg/kg body weight (b.wt.)/day for 12-16 weeks, and in patients receiving arotinoid (Ro 15-0778) 192 mg (n = 5) or 500 mg (n = 5) per kg/b.wt./day for 6 weeks (forehead and shoulder). In another experiment, cell suspensions with a pH ranging from 5.0-7.3 were evaluated. Measurements were performed by dynamic laser light scattering. This laser application allows exact electrophoretic mobility measurements in a short time (3 min). When cells pass the laser beam, the scattered light is frequency-shifted due to the optical Doppler effect. These frequency shifts are analyzed by the heterodyne light beating technique. The analog signal of the photodetector is converted into a power spectrum by Fourier analysis. This power spectrum represents the spectrum of electrophoretic cell mobility distribution. Results showed different electrophoretic mobility values for corneocytes dependent on the topographic region: forehead 1.18 +/- 0.16, palm 1.10 +/- 0.14, and sole 0.83 +/- 0.10 (means +/- SEM) micron cm/Vs. Defattening with isopropyl alcohol decreased the mobility values to 0.90 +/- 0.09 (p less than or equal to 0.01), 0.95 +/- 0.10, and 0.77 +/- 0.10 micron cm/Vs respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of estriol (Sigma Chemical Co., U.S.A.) in the female young-adult pigeons at a dose of 50 micrograms/bird/day for 7 consecutive days caused atrophy of the uropygial gland, associated with increased cytopycnosis and drastic cell loss within the holocrine alveoli and reduction in the content of the glandular lipids. Probable mode of action of this steroid upon the uropygial gland has been suggested in the light of the recent data on its anti-estradiol property manifested in rat uterus.

The photoperiod (i.e., the daylight fraction of the 24-h day and its seasonal changes) influences the annual cycle of many mammalian species. Especially the Syrian hamster (Mesocricetus auratus), which is an appropriate animal model to investigate the sebaceous gland activity, shows a strong photoperiodism controlling the sexual development as well as the function of androgen-controlled organs such as sebaceous glands. Short photoperiods with accompanying long dark periods lead to a sexual regression while long photoperiods stimulate the recrudescence. In light-physiologic studies Syrian hamsters were exposed to different light schedules. The daily light exposure was increased from 8 to 12, 13, 14, and 16 h. Sebaceous gland areas, weight of testes and accessory glands, tubular areas, and plasma levels of testosterone were determined. Syrian hamsters are sexually stimulated at a daily light exposure of 14 h. Below this light threshold the sexual regression begins. At a light schedule of 8 h the testes shrink, plasma testosterone levels and sebaceous gland areas show a significant reduction ("photoperiodic castration"). Therefore, in experiments of androgen-controlled organs of the Syrian hamster a minimum daily light period of 14 or 16 h is necessary for a sufficient testicular function and therefore for an effective stimulation of the sebaceous gland activity. Control animals of the same age and the same light schedule should be required to avoid pitfalls of photoperiodic effects.