Effects of prepubertal manipulation with androgens on the development of sexual differences in the harderian glands of Syrian hamsters.

The onset of sexual differences in the metabolism of porphyrins and melatonin in the Harderian glands of Syrian hamsters was studied. Three weeks after birth, the porphyrin concentrations were already higher in glands of females than in those of males. Castration of 22-day-old male hamsters led to an increase in Harderian porphyrin concentrations, although the levels of intact females were not reached. The administration of testosterone to 22-day-old female hamsters resulted in a marked decrease in porphyrin concentrations. Study of the development of sexual differences in the enzymes involved in melatonin synthesis, N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) indicated that not all the sexual differences observed in these glands begin at the same time. Thus, while differences in NAT activity were detected after the age of 3 weeks, male-female differences in HIOMT activity were only observed after 7 weeks. Castration of prepubertal male hamsters lowered NAT but not HIOMT activities. The administration of testosterone to prepubertal female hamsters led to male activity levels in both enzymes. Although circulating androgens seem to have a crucial role in maintaining sexual differences, other hormones including those from the pituitary and thyroid glands are probably also important for generating these sexual differences.

Hypophysectomy prevents the castration-induced increase in porphyrin concentrations in the harderian glands of the male golden hamster: a possible role for prolactin.

The Harderian glands of golden hamsters contain high concentrations of porphyrin pigments, with female hamsters having considerably higher porphyrin concentrations than males. Castration of male hamsters leads to a rapid increase in porphyrin concentrations; testosterone treatment of females has the opposite effect, suggesting a central role for androgens in inhibiting the realization of high porphyrin concentrations by this organ. Previous studies in our laboratories have shown, however, that administration of a dopamine agonist to castrated hamsters prevents the normal increase in Harderian porphyrins from occurring. This suggests that prolactin is necessary for low androgen levels to lead to maximal increases in Harderian porphyrin concentrations. The present study tested the hypothesis that prolactin is involved in the control of Harderian porphyrin levels in the golden hamster. Although hypophysectomy of male hamsters reduced serum testosterone to levels in castrated hamsters, the resultant increase in Harderian porphyrin concentrations was much less than that seen after a similar period of castration. Furthermore, combining the two procedures (castration and hypophysectomy) also led to a blunted increase in Harderian porphyrin, suggesting that a pituitary hormone is necessary for low testosterone levels to lead to increased porphyrins. Evidence that this pituitary hormone is prolactin comes from the observations that eliminating all pituitary hormones except prolactin, by severing the connection of the pituitary with the hypothalamus or transplanting the pituitary to a distant site (beneath the kidney capsule) led to greatly augmented Harderian porphyrin levels, in intact or castrated male hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

N-acetyltransferase activity in the Harderian glands of the Syrian hamster, Mesocricetus auratus, is regulated by androgens and by hormones of the pituitary-thyroid axis.

This study tested the hypothesis that activity of the enzyme N-acetyltransferase (NAT) in the Harderian gland of the Syrian hamster is regulated both by androgens and by hormones of the pituitary-thyroid axis. To test the effects of castration and hypothyroidism, intact or castrated male hamsters were given either tap water or methimazole in their drinking water for 3 weeks. Methimazole suppresses iodination of thyroglobulin, thereby decreasing circulating levels of thyroid hormones and increasing TSH levels. Hypothyroidism or castration caused elevated or depressed Harderian gland NAT activities respectively, compared with euthyroid controls. When castration and hypothyroidism were combined, the animals exhibited high NAT activity compared with castrated euthyroid males. To test the effects of castration and hyperthyroidism, male hamsters were given daily injections of thyroxine (T4) or diluent and were either castrated or left intact for 4 weeks. Intact animals given T4 had depressed Harderian NAT activity; serum thyroid hormone levels were elevated and TSH levels were depressed compared with those of intact controls. Castrated animals had depressed NAT activity below that of intact controls; serum thyroid hormone levels were normal but TSH levels were depressed. Castrated animals given T4 injections had NAT activity similar to that of euthyroid castrated hamsters; thyroid hormone levels were elevated but TSH levels were similar to those seen in euthyroid castrated hamsters. In another experiment, both T4 and tri-iodothyronine (T3) were equally effective in decreasing NAT activity in intact males. To determine the effects of the removal of pituitary influences, male hamsters were hypophysectomized. NAT activity in the Harderian glands of these animals was reduced compared with intact controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Manipulation of toxicity and tissue distribution of tubercidin in mice by nitrobenzylthioinosine 5'-monophosphate.

The i.v. administration of tubercidin, an analog of adenosine, in a single dose of 45 mg/kg caused death in about 90% of B10D2F1 mice so treated. Serum and urine analysis, as well as histological examination of tissues, related the lethality of tubercidin to hepatic injury, which was markedly reduced when mice were treated with the inhibitor of nucleoside transport, nitrobenzylthioinosine 5'-monophosphate (NBMPR-P), at i.p. doses higher than 10 mg/kg 30 min prior to tubercidin injection. With high NBMPR-P doses (100 mg/kg, i.p.) followed by tubercidin injection (45 mg/kg, i.v.), kidney damage and high mortality occurred. The tissue distribution of 3H following (( G-3H]tubercidin administration paralleled hepatic or renal injury: NBMPR-P treatment decreased the content of tubercidin-derived 3H in liver and increased that in kidney. Furthermore, the half-life of the decline in tubercidin levels in serum during the first minute after[3H]tubercidin administration was longer in NBMPR-P-treated mice (26 sec) than in untreated mice (10 sec), with the result that 3H levels in serum were more than ten times higher in the former than in the latter at an early stage during the distribution of tubercidin. Within 15 min after i.p. administration, the tissue distribution of (( 3H]tubercidin was complete. The i.p. administration of tubercidin caused ascites and the appearance of amylase in the peritoneal fluid evidently because of peritonitis and pancreatic injury. Administration of NBMPR-P by the i.p. route, but not by the i.v. route, prevented these injuries and shifted the LD50 of i.p. injected tubercidin (5 mg/kg) to markedly higher values (a 4-fold increase with NBMPR-P at 100 mg/kg). The protection of mice by NBMPR-P against lethal injuries caused by i.p. injected tubercidin was consistent with the inhibition by NBMPR-P of tubercidin accumulation in mesentery and pancreas. The tissue specificity of the NBMPR-P influence on the tissue distribution of tubercidin may reflect differences in NBMPR-P pharmacokinetics and/or in properties of the nucleoside permeation mechanism among various tissues.

Androgenic control of 1-alkyl-2,3-diacylglycerol in the harderian gland of the golden hamster, Mesocricetus auratus.

Harderian glands of golden hamsters produce a copious lipid secretion, most of which is in the form of 1-alkyl-2,3-diacylglycerol (ADG). Sexual differences are seen in the composition of golden hamster ADG and in the morphology of secretory lipid droplet. ADGs from females contained abundant iso- and anteiso-branched chain alkyl groups and fatty acids [Seyama, Y., Otsuka, H., Ohashi, K., Vivien-Roels, B., and Pevet, P. (1995) J. Biochem. 117, 661-670]. Female hamsters were either untreated or given subcutaneous testosterone pellets. Treatment of females with testosterone led to the disappearance of such branched chain alkyl groups and fatty acids. Intact males had ADGs with entirely saturated straight chain alkyl groups and fatty acids. Castration led to the appearance of iso- and anteiso-branched chain alkyl groups and fatty acids. These observations suggested that the production of branched chain fatty acids in the Harderian gland of golden hamster is inhibited by testosterone at the step of isovaleryl-CoA dehydrogenase and 2-methyl branched-chain acyl-CoA dehydrogenase

Indole and porphyrin content of the Syrian hamster harderian glands during the proestrous and estrous phases of the estrous cycle.

Porphyrin and indole metabolism was studied in the Harderian glands of Syrian hamsters during the proestrous and estrous stages of the estrous cycle. Porphyrins remained unaltered during these stages, but levels of different indoles (5-hydroxytryptophan, 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, and 5-hydroxyindole acetic acid) exhibited pronounced changes during the dark:light period in both proestrous and estrous. There was a strong parallelism between 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine and 5-hydroxyindole acetic acid levels. Hydroxytryptophan rhythms appeared slightly shifted from those of the other indoles. Immunoreactive melatonin present in the Harderian glands did not show a significant day-night change during the stages studied.

The Harderian gland: perspectives.

This is the three-hundred and second anniversary of the first description of Harderian glands by Johann Jakob Harder. Despite more than three centuries of study, many features of these glands, including their definition and function, are not yet established to everyone's satisfaction. Some topics of Harderian biology will be reviewed. Morphology, ontogeny: Mammalian Harderian glands secrete largely by exocytosis, which is unusual in a lipid-secreting exocrine gland. Polytubular complexes are features of male hamster glands; their significance is unknown. Porphyrins: High levels of porphyrin in rodent Harderian glands have made this an attractive organ for research on the control of porphyrin synthesis. Attempts to use it as a model of human porphyria, however, have been disappointing. We do not know the function of Harderian porphyrin. The golden (hamster) age: Syrian (golden) hamster Harderian glands show marked sexual differences, including porphyrin levels. This has made them a very useful experimental animal for endocrine studies. The pineal connection: Rodent Harderian glands contain melatonin. Pinealologists often also study Harderian glands, and Harderianologists also often study the pineal. This relationship has contributed valuable insights to our knowledge of both systems. Lipids: Rodent Harderian glands are about 20% lipid by wet weight, and the main secretory product is lipid. The main lipid in many animals is 1-alkyl-2, 3-diacylglycerol. Harderian gland lipid is extensively studied for insights into lipid biochemistry; less has been done on understanding the function of lipids in the physiology of the glands. Behavior: Lipids may function as vehicles for pheromone secretion. In addition, the possible use of Harderian secretion during cold temperatures by gerbils has been noted. Immunology: Bird Harderian glands are probably lymphoid organs. This does not seem to be true of mammals, though the female Syrian hamster shows large numbers of mast cells. Harderian glands of amphibians and reptiles: Research on nonmammalian Harderian glands has been limited, though important insights continue to emerge from these studies.

Sexual dimorphism in the harderian gland of the Syrian hamster is controlled and maintained by hormones, despite seasonal fluctuations in hormone levels: functional implications.

The Harderian gland of the Syrian hamster (Mesocricetus auratus) is unusual amongst rodents in the degree of dimorphism present. Other types of hamsters have Harderian glands which are apparently identical in male and female animals. Laboratory populations of Syrian hamsters are derived from very limited genetic stock, which makes one concerned lest they not be representative of wild populations; however, until wild stocks of M. auratus become available, we should assume that insights derived from studies of dimorphism in Syrian hamsters represent important considerations for the life of these animals. Two dimorphic features are the histology and the porphyrin content of the Harderian glands. About 95% of the lipid droplets in female glands are small (type 1), whereas only about 65% of those in males in type 1, with the other 35% being type 2 (large droplets). Five weeks of castration of males led to an increase in type 1 droplets to 90%. On the other hand, 2 weeks treatment of females with testosterone led to a reduction in type 1 droplets to about 82%. Short day photoperiods led to a large increase in type 2 droplets in both males and females (to 52% in males, 35% in females after 8 weeks). These results suggest that the lipid contained in type 2 droplets is important to hamsters of both sexes during the winter. Porphyrin concentrations are 100-1,000 times higher in females than males, and this is largely controlled by testosterone as orchidectomy leads to increased male levels and testosterone treatment leads to reduced female levels. However, a number of treatments which also lead to reduced testosterone levels do not lead to increased porphyrins and may, in fact, prevent the rise which would normally follow orchidectomy. One of these antiporphyrinogenic treatments is exposure to short day photoperiods. Thus, the sexual differences in porphyrin, levels in Syrian hamsters are maintained, despite seasonal fluctuations in hormone levels. This suggests that this dimorphism is important for the function of the gland.

In vivo effects in mice produced by a 3'-branched homologue of alpha-2'-deoxythioguanosine.

Studies with a 3'-branched chain homolog (alpha-3'-BCTGdR) of 2'-deoxythioguanosine (alpha-TGdR) showed that it did not prolong the survival of mice bearing the Mecca lymphosarcoma. Host toxicity was quite profound and resembled that seen with 6-thioguanine (6-TG). Evidence was obtained that this nucleoside derivative was not appreciably converted to 6-TG in the mouse. Mice treated with toxic doses of 6-TG or alpha-3'-BCTGdR were found to have very similar pathological changes. The granulocytes were eliminated from the peripheral blood, bone marrow was acellular, and some more limited damage was seen in the intestinal crypts. Experiments with radiosulfur-labeled drugs demonstrated that alpha-3'-BCTGdR was incorporated into the DNA of mouse bone marrow, predominantly in the chain-terminating position, with the result that shorter chains of DNA accumulated. The new homolog, unlike alpha-TGdR, was phosphorylated in bone marrow as well as in tumor, and incorporated well into the DNA both of bone marrow and of the neoplastic cells. In devising other homologs attention must be given to the specificity of the kinases, i.e., to whether phosphorylation is superior in tumor cells or in the growing normal cells.

Pineal lysosomal enzymes in the Syrian hamster: circadian rhythm and effects of castration or short photoperiod treatment.

A circadian rhythm in acid phosphatase and hexosaminidase was found in adult male hamsters exposed to a long photoperiod (14:10 h light/dark [LD]; lights on 06.00 h) and killed at 08.00, 14.00, 20.00, 02.00, 04.00, 05.50 and 0.615 h. Hexosaminidase and beta-glucuronidase activity at 02.00, 04.00 and 05.50 h (values pooled for these times before lights on) were significantly elevated compared to enzyme activity at 06.15 and 08.00 h (pooled values after lights on), suggesting a fall in activity associated with lights on. Hypogonadism was induced in female Syrian hamsters by exposure to a short photoperiod (10:14 h LD) until a majority of them were vaginally acyclic. Pineal lysosomal enzyme activities (acid phosphatase, beta-glucuronidase, hexosaminidase, alpha-arabinosidase and beta-galactosidase) were significantly elevated in short photoperiod-exposed animals compared to animals in 14:10 LD, when measured near the middle of the light phase. In the third experiment, castrated animals were used to determine if lowered androgen levels might also affect pineal lysosomal enzyme activity. The results indicated that light phase beta-glucuronidase, hexosaminidase and beta-glucosidase activities were lower in castrated males compared to their intact controls. In summary, these results demonstrate that (1) lysosomal enzyme activity is present in the Syrian hamster pineal, (2) changes can be observed which suggest involvement of this activity in pineal function and, (3) a circadian rhythm in enzyme activity is present with peak activity occurring during the night. In the short photoperiod and castration experiments, the changes in lysosomal enzyme activity could reflect either a hormonal manipulation or a change in circadian regulation of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo administration of isoproterenol or forskolin during the light phase induces increases in the melatonin content of the Syrian hamster pineal gland without a rise in N-acetyltransferase activity.

In vivo melatonin production was stimulated during the daytime in pineal glands of female Syrian hamsters following the administration of several injections of either isoproterenol, a beta-receptor agonist, or forskolin, an adenylate cyclase stimulator. The large increase in melatonin following either isoproterenol or forskolin administration was not accompanied by significant changes in N-acetyltransferase (NAT) activity. The results suggest that the Syrian hamster pineal gland, as in other species, responds by producing melatonin during the light phase if the stimulus is adjusted to its particular and specific regulatory mechanisms, i.e., if beta-adrenergic stimulation is continued for 4-8 h. The lack of a commensurate increase in NAT activity raises the question of the need of maximal enzymatic activity for a significant rise in melatonin production in the Syrian hamster pineal gland.

Pineal lysosomal enzyme circadian rhythms in male hamsters exposed to natural decreasing photoperiod and temperature conditions.

Circadian rhythms in acid phosphatase (ACP), hexosaminidase (HEX) and beta-glucuronidase (RON) activity were studied in the pineal glands of adult male Syrian hamsters exposed to control (20 +/- 2 degrees C and 14:10 LD) conditions or to naturally decreasing autumn photoperiod and temperature conditions (outside) for 8 weeks. Testes and testosterone levels (p less than 0.001 in both instances) were severely depressed in animals exposed to natural environmental conditions illustrating that the treatment period was of sufficient length to produce pineal-mediated gonadal atrophy. Significant rhythms were found in all enzymes in the pineal glands of control and outside animals with the exception of HEX activity in the control animals. Significant acrophase differences in outside vs. control animals were noted in ACP (7.9 hr earlier, p less than 0.001) and RON (9.8 hr later, p less than 0.001). A significant drop in RON and HEX activity (p less than 0.01 in both instances) was noted in association with the acute lights exposure in the morning to which control animals were exposed. The around-the-clock mean value of each enzyme was significantly lower in outside vs. control hamsters. These results demonstrate that environmental changes which provoke the pineal-mediated depression in gonadal activity also alter the activity of and shift the circadian rhythmicity of lysosomal enzymes in the pineal itself.

Melatonin levels in idiopathic scoliosis. Diurnal and nocturnal serum melatonin levels in girls with adolescent idiopathic scoliosis.

STUDY DESIGN: Matched pairs of adolescent girls were used to compare serum melatonin levels in adolescent patients and control subjects with idiopathic scoliosis during the day and in the middle of the night. OBJECTIVES: To compare serum melatonin levels in patients with adolescent idiopathic scoliosis and matched control subjects during the day and in the middle of the night. SUMMARY OF BACKGROUND DATA: Recent studies using the chick as the animal model have suggested that the pineal gland and its main product, melatonin, might be involved in the cause of scoliosis. There have been no studies of melatonin levels in patients with adolescent idiopathic scoliosis. METHODS: Blood was collected from seven adolescent girls with idiopathic scoliosis and a group of seven age-matched control subjects. Two samples were collected, one in the middle of the day and one in the middle of the night, to examine the diurnal variation of melatonin production. Serum melatonin levels were measured using a radioimmunoassay technique. RESULTS: No significant differences were found in serum melatonin levels between experimental and control groups either during the day, when melatonin levels were low, or during the night, when melatonin levels were high. CONCLUSIONS: Whereas pinealectomy in young chickens leads to reduced melatonin levels and the development of scoliosis, the results of this study suggest that melatonin levels in mature patients who already have severe scoliosis do not differ from healthy subjects. Whether melatonin levels differ in humans between healthy subjects and patients with scoliosis at the time of onset of the disease remains to be seen.

Studies on the effects of the pineal hormone melatonin on an androgen-insensitive rat prostatic adenocarcinoma, the Dunning R 3327 HIF tumor.

The effects of the pineal indole melatonin on a transplantable androgen-insensitive fast-growing rat prostatic adenocarcinoma, the Dunning R 3327 HIF tumor, were examined. Afternoon injections of melatonin given to intact male rats enhanced tumor growth, while leading to a reduction in the weights of gonads and dorsal and ventral prostates. In anosmic hosts, this treatment had no effect on tumor growth or reproductive organ size. In castrated anosmic hosts, melatonin injections led to reductions in the growth of tumors, when compared with those in castrated hosts. Continuously available melatonin, in beeswax pellets, had no effect on growth of these tumors. These results are discussed in relation to the anticancer effects of melatonin and the effects of tumors on endogenous melatonin rhythms.

Light-microscopic stereology for the study of the ventral and dorsal prostates of the syrian hamster: Strategy, techniques, and applications.

A stereological approach to studying the architecture of the ventral and dorsal prostates of the Syrian hamster is described. In this approach, the prostate is considered to consist of acinar and interacinar compartments. The acinar compartment is divided into luminal, epithelial, lamina proprial, and muscular stromal compartments. Volume fractions of acini and interacinar tissue are calculated with reference to the volume of the gland; those of the acinar components are calculated with reference to the acinar volume. Volume fractions are determined from point counts. The surface fraction of the secretory epithelium is determined from intercept counts, with reference to the volume of the epithelium. By assuming that the acini are cylindrical, the acinar length fraction is calculated with reference to the volume of the gland. Absolute values for the volumes of different components, epithelial surface area, and acinar length can be determined from the weight of the gland, its specific gravity, and the volume fraction of that component, or epithelial surface fraction, or acinar length fraction, respectively. Finally, from these values and assuming a cylindrical shape for acini, characteristics of the typical acinus, including its radius, the thicknesses of its epithelium, lamina propria, and muscular stroma, and the amount of mucosal folding can be calculated from simple geometrical formulae. This approach is illustrated from a consideration of the ventral and dorsal prostates of 20-week-old Syrian hamsters.

Composition, secretion, and fate of the glands in the miracidium and sporocyst of Fasciola hepatica L.

The anterior end of the miracidium of Fasciola hepatica contains a large flask-shaped apical gland and four unicellular lateral glands, all of which have ducts which pass to the tip of the apical papilla. These glands appear to be involved in penetration of the larva into the snail host. The apical gland secretes as the miracidium proves the epidermis of the host before attachment. It seems likely that its secretion is a chemical which lyses the epidermal cells. The lateral glands are PAS-positive and may contain a neutral mucopolysaccharide. They also secrete as the miracidium probes the snail and a layer of PAS-positive material may be seen at the leading edge of the apical papilla as the larva penetrates into the host. Both the apical gland and the lateral glands may be visible in the sporocyst for several days after penetration.

Architecture of the dorsal and ventral lobes of the prostate of the Syrian hamster, Mesocricetus auratus, after regrowth from short day-induced regression.

The structures of the dorsal and ventral lobes of the prostate of 4 groups of Syrian hamsters were studied by a stereological approach. Groups studied were young hamsters (kept in long-day photoperiods for 4 weeks) in their first breeding season, older hamsters (kept in short-day photoperiods for 24 weeks so that their prostates had regressed and regrown) in their second breeding season, and two groups of older hamsters in an extended first breeding season (either because they were kept in long days for 24 weeks or because they were pinealectomized before being put into short-day photoperiods for 24 weeks). There were very few differences between groups, but generally dorsal prostates of older hamsters in their second breeding season closely resembled those of young hamsters in their first breeding season. More differences were noted between either of these two groups and older hamsters in an extended first breeding season than between these two groups. The differences noted generally involved increases in the amount of smooth muscle in the walls of secretory tubules in the dorsal prostates of hamsters in an extended first breeding season. This may be associated with the fact that these glands had not regressed and regrown. Ventral prostates were very similar in all 4 groups, which may reflect the fact that they normally regress very little in short days.

Fine structure of the ventral and dorsal lobes of the prostate in the young adult Syrian hamster, Mesocricetus auratus.

The normal ventral and dorsal prostatic lobes of the young adult Syrian hamster were examined at the light and electron microscopic levels. Each lobe is composed of branched tubular secretory units separated from each other by loose interacinar connective tissue and draining into the urethra. The lumen of each acinus is lined by a simple epithelium composed of columnar secretory cells with occasional small basal cells. The epithelial layer, with the thin underlying lamina propria, forms a mucosa that is often highly folded. The whole acinus is bounded by a thick muscular stroma. In each of the ventral lobes, there are three main ducts, each one formed of tubular branched tributary secretory units. The walls of the secretory acini are moderately folded. Microvilli dominate the lumenal surface of the secretory epithelial cells. The Golgi complex is very extensive and shows dilated cisternae and secretory vesicles and vacuoles of various sizes. Membrane-bounded secretory granules populate the Golgi and apical areas and are released into the acinar lumen by exocytosis. The rough endoplasmic reticulum is dispersed throughout the cytoplasm, except in the region of the Golgi apparatus. In each of the dorsal lobes, there are several main tubular ducts that open into the urethra. Both proximal (ductal) and distal portions of the glandular tree are secretory in nature. Microvilli and cytoplasmic bulges and blebs dominate the lumenal surface of the secretory cells. The cells are also characterized by highly dilated cisternae of rough endoplasmic reticulum. The secretory cells show heterogeneity in the degree of dilation and distribution of rough endoplasmic reticulum, and this heterogeneity may reflect location in the glandular tree.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the photoperiod in modulating the androgenic control of 1-alkyl-2,3-diacylglycerol composition in the harderian gland of the golden hamster, Mesocricetus auratus.

The golden hamster Harderian gland produces a lipid secretion consisting mainly of 1-alkyl-2,3-diacylglycerol. We investigated the composition of alkyl and acyl groups in male and female hamster Harderian alkyldiacylglycerol, in animals kept in long and short photoperiods. Female hamsters in long days have alkyl groups with long saturated straight chains (C18:0 and C20:0) and methyl-branched chains (even and odd chain length iso-branched and odd chain length anteiso-branched chains). Acyl groups in females in long days are mostly long straight chains (C16:0) and methyl-branched chains. In females, short photoperiods led to reductions in the proportions of methyl-branched chains and changes in the proportions of straight chain alkyl and acyl groups; these changes were prevented by pinealectomy. Male hamsters with intact gonads, maintained in long days, had no methyl-branched chain alkyl or acyl groups; saturated straight chains were generally shorter than those of females and the odd chain length saturated C15:0 acyl group was common. Short photoperiods did not significantly alter the composition of male alkyldiacylglycerol. Castrated male hamsters in long days showed a distinctively female phenotype, with long straight chains and methyl-branched alkyl and acyl groups. Castrated males in short days showed a mixture of male and female characteristics: shorter straight chain alkyl and acyl groups, a total absence of methyl-branched alkyl groups, and the presence of methyl-branched acyl groups. These results and those of other studies suggest that testosterone controls the enzymes isovaleryl acyl-CoA dehydrogenase and 2-methyl branched-chain acyl-CoA dehydrogenase; in the absence of these enzymes, the primers for the synthesis of methyl-branched chain fatty acids are produced. Our results indicate that this control is modulated by short photoperiods (perhaps due to reduced prolactin levels). It is also suggested that characteristics of male-type alkyldiacylglycerol are better adapted to conditions of autumn and winter than are those of female-type alkyldiacylglycerol.