Further studies on the regulation of the Harderian glands of golden hamsters by the thyroid gland

Summary Long-term increased or decreased circulating levels of thyroid hormones significantly modify porphyrin concentrations and morphology in the Harderian glands of male and female hamsters. Administration of T₃ reduced porphyrin concentrations in females; this treatment or decreasing thyroid hormone levels with KClO₄ suppressed the post-castration rise of porphyrins in males. Hypophysectomy led to increased porphyrins in the Harderian glands of males; this rise was suppressed in hypophysectomized males by T₃ or T₄. In females, hypophysectomy reduced porphyrins which were further reduced by daily administration of T₃ or T₄. These modifications in the normal females were identical in castrated males. Mitotic activity in the Harderian glands of females was stimulated by KClO₄ and by hypophysectomy with or without exogenous T₃. In males, castration increased mitotic activity which was suppressed by T₃ and exacerbated by KClO₄. Increased mitotic activity seemingly follows loss of tissue mass. The data show that thyroid hormones act directly on the Harderian glands rather than indirectly through modification of TSH synthesis/release. Female type glands in males are a consequence of loss of gonadal androgens by castration, or by suppression or loss of thyroid hormones by hypophysectomy or by treatment with KClO₄. However, male type glands in females are the result of androgen treatment, and/or increased levels of thyroid hormones via reduced ambient temperatures or of photic input. We conclude that regulation of the Harderian gland appears to be different in the two sexes.Abbreviations T ₃ Triiodothyronine - T ₄ Thyroxine - TSH Thyroid Stimulating Hormone - KClO ₄ Potassium Perchlorate - h hours - ml milliliter - mg milligram - g gram - male - female - castrated male - AP hypophysectomized - CON Control - ALA delta aminole-vulenic acid - HG Harderian Gland     

Interaction of harderian glands,illumination, and temperature on thyroid hormones in golden hamsters

Summary In this study, Harderianectomy (Hdx) has been shown to differentially modify circulating levels of the thyroid hormones, T₄ and T₃, in male and female golden hamsters exposed to low photic intensities or to moderately low temperatures.Specifically, low photic intensities depress circulating levels of T₄ in both control and Harderianectomized (Hdx) male and female hamsters. In addition, T₃ is decreased in both control and Hdx males but not in females, as a consequence of reduced levels of illumination. Moderately low temperatures (10°C) depress T₄ in both control and Hdx males but not in females, while T₃ is increased in both control male and female hamsters, and in Hdx males, but not Hdx females. The data suggest that the Harderian gland of males enhances the sensitivity of the TSH-thyroid axis to photic intensity and to lower temperatures, and further, that there is a considerable sexual difference in the role the Harderian glands may play in response to these two environmental factors.     

Gender differences and time course of castration-induced changes in porphyrins, indoles, and proteins in the Harderian glands of the Syrian hamster.

Sexual differences and the effects of orchidectomy were determined for porphyrin and melatonin concentrations and for the activities of the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase, which synthesize melatonin from serotonin, in the Harderian glands of the Syrian hamster. Porphyrin concentrations in intact males were about 1/400th those of intact females. Castration for 1 week increased male Harderian porphyrin concentrations 10-fold; by 3 weeks, castrated male porphyrin levels were 140 times those of control values. N-Acetyltransferase activity in intact male Harderian glands was about 4 times that of females. Castration led to a drop in N-acetyltransferase activity to female levels within 2 weeks. Hydroxyindole-O-methyltransferase activity was 7 times higher in females than in males and castration had no effect on male Harderian hydroxyindole-O-methyltransferase activity. Neither gender nor castration influenced Harderian melatonin concentrations. Soluble proteins in Harderian glands from male and female hamsters and from male hamsters castrated for 1 and 4 weeks were examined by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. The gel profiles revealed several differences among the protein distribution in male and female gland lysates. Orchidectomy led to a female protein pattern within 4 weeks.     

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.     

Bromocriptine prevents the castration-induced rise in porphyrin concentration in the harderian glands of the male Syrian hamster, Mesocricetus auratus

The Harderian glands in Syrian hamsters exhibit a striking sexual dimorphism. Male Harderian glands show two cell types and low levels of porphyrins and melatonin. Of the enzymes involved in the synthesis of melatonin, N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) show high and low activity levels, respectively. Female Harderian glands show but one cell type and have high porphyrin and melatonin levels, low NAT activity, and high HIOMT activity. In castrated males, the Harderian glands exhibit a female pattern of morphology, porphyrin levels, and indoleamine metabolism. In an attempt to determine whether prolactin in involved in this sexually dimorphic response of the Harderian glands, intact and castrated male and intact female hamsters were injected daily with 500 micrograms of bromocriptine, a dopamine agonist. Bromocriptine led to reduced serum prolactin levels in all groups. It had no apparent effect on the Harderian glands of intact males. In contrast, in castrated males bromocriptine prevented the postcastrational rise in porphyrin levels but had no effect on NAT or HIOMT activities. In females, bromocriptine treatment had no effect on porphyrin concentrations or HIOMT activity; it led to a statistically significant increase in NAT activity. We propose that testosterone inhibits Harderian porphyrin synthesis while dopamine or prolactin stimulates it.     

Effects of inhibition of thyroid function and of cold on melatonin synthesis and porphyrin content in the Harderian glands of male Syrian hamsters, Mesocricetus auratus

1. Indole metabolism and porphyrin content of the Harderian glands of the male Syrian hamster were measured as functions of drug-induced hypothyroidism and exposure to cold conditions. 2. Harderian gland N-acetyltransferase (NAT) activity was reduced from control levels by hypothyroidism induced by methimazole; exposure to cold had no effect on NAT activity. 3. Immunoreactive melatonin in the Harderian glands was unaffected by the state of thyroid secretion. However, immunoreactive melatonin content declined after 180 and 270 min, at 4 degrees C, suggesting that Harderian gland melatonin may be involved in thermoregulation. 4. Porphyrin content of the Harderian glands was not affected by either thyroid secretion or cold.     

Sexual dimorphism in N-acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin content in the Harderian gland of Syrian hamsters: changes following gonadectomy

The activities of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the melatonin content of the Harderian glands of intact and gonadectomized male and female Syrian hamsters were studied. NAT activity in intact male Harderian glands was twice that of the female. Prepubertal or adult castrated males exhibited a decrease in NAT activity to a level comparable to that seen in the female. Testosterone implants in the castrated males led to a recovery of the original male NAT levels. Intact male hamsters had very low levels of Harderian HIOMT activity and melatonin content in comparison with the glands of the females. Prepubertal gonadectomy but not castration of adult males raised the levels of HIOMT activity and the melatonin content to those of the females. Bilateral ovariectomy had no effect on melatonin content, NAT activity, or HIOMT activity in the female hamster Harderian gland.     

Age and food restriction alter the porphyrin concentration and mRNA levels for 5-aminolevulinate synthase in rat Harderian gland.

The effects of age and food restriction on the porphyrin concentration in Harderian glands were studied in male Fisher 344 rats. Harderian gland porphyrin concentrations increased with age; this was statistically significant in 20 month old animals compared with 3 month old animals. Food restriction (by 40%) prevented the age-associated rise in porphyrins; thus, in 20 month old food restricted rats had porphyrin concentrations similar to those found in young animals. In a second experiment, we correlated the age-associated rise in Harderian gland porphyrin concentrations with an increase in mRNA levels for 5-aminolevulinate synthase (ALV-S). Both the porphyrin concentration and ALV-S mRNA rose at 12 and 18 months of age, but decreased by 24 months of age. It is concluded that, a) porphyrin biosynthesis in the Harderian glands increases up to 20 months of age but decreases in rats that are 24 months old, and b) food restriction prevents the porphyrin rise associated with age in the Harderian gland of male Fisher 344 rats.     

The effects of bromocriptine and prolactin on porphyrin biosynthesis in the Harderian gland of the male hamster,Mesocritecus auratus

Porphyrin biosynthesis was examined in the Harderian gland of the male golden hamster by fluorometric assays of gland porphyrin content and by measuring the activity of a rate-limiting enzyme for haem biosynthesis, 5-aminolaevulinic acid synthase. Both porphyrin content and enzyme activity are low in normal male glands but were greatly raised in males castrated for 6 weeks. However, porphyrin synthesis remained at basal levels in castrates given the dopamine agonist bromocriptine; this suppression could be reversed by simultaneous prolactin administration, and castrated males receiving prolactin alone exhibited very high enzyme activity and porphyrin content. Bromocriptine also prevents the morphological feminisation of the Harderian gland which would normally occur after castration; again, the simultaneous administration of prolactin permits feminisation to occur. The results support the hypothesis that, while androgens have an inhibitory effect on porphyrin synthesis within this model, other factors, including prolactin, are permissive.Abbreviations ALA 5-aminolaevulinic acid - ALA-s 5-aminolaevulinate synthase - GH growth hormone     

High-performance liquid chromatographic analyses of porphyrins in hamster Harderian glands

Porphyrin content and 5-aminolaevulinate synthase activity of the Harderian gland were measured in intact and gonadectomized male and female hamsters; porphyrin profiles were analysed by high-pressure liquid chromatography. The total porphyrin content of the two female groups was similar, but enzyme activity in females ovariectomised for 20 weeks significantly decreased. Intact males have low porphyrin content and enzyme activity, while in castrates (6 weeks) both increased to female levels. Protoporphyrin IX formed 93% of total porphyrins in intact females, compared with 70% of total porphyrins in intact males. The remainder in both sexes was chiefly penta- and hexacarboxylic porphyrins and coproporphyrin and (in females) Harderoporphyrin. Gonadectomy in either sex resulted in protoporphyrin levels intermediate between male and female values.     

Sexual differences and effects of castration on secretory mode and intracellular calcium ion dynamics of golden hamster Harderian gland

The aim of the present work was to study the sexual differences in secretory mechanisms and intracellular calcium ion dynamics in the Harderian gland of the golden hamster. In both sexes the Harderian gland consisted of small and large lobes. In the intact control male glands the secretory portions of both lobes showed wide lumina that contained secretory material and cytoplasmic fragments, suggestive of the occurrence of exocytosis and apocrine secretion. After perfusion with HEPES-buffered Ringer's solution containing 10 microM carbamylcholine (CCh), the glandular cells showed features of enhanced secretion and a rise in intracellular calcium concentration ([Ca2+]i). In the intact control female gland the lumina of most secretory portions in the large lobe contained porphyrin accretions, and exocytosis was the sole secretory mechanism. Stimulation of the large lobe with 10 microM CCh did not raise [Ca2+]i or cause enhanced secretion. The small lobe in females resembled the male gland in secretory functions, and CCh administration caused enhanced secretion and a rise in [Ca2+]i. Castration in males abolished apocrine secretion; exocytosis became the sole secretory mechanism, and stimulation of the glandular cells with CCh did not cause enhanced secretion or induce a rise in [Ca2+]i. To the contrary, in females, castration restored apocrine secretion and CCh administration caused enhanced secretion and a rise in [Ca2+]i. Castration did not affect the secretory mechanisms and the effect of CCh on the glandular cells in the small lobes of both male and female glands. The present study points to the possibility that sex hormones may control the functioning or expression of muscarinic receptors in the Harderian gland of the golden hamster.     

The effects of bromocriptine and prolactin on porphyrin biosynthesis and morphology in the female hamster Harderian gland

Porphyrin biosynthesis was examined in the Harderian gland of the female golden hamster by fluorometric assays of gland porphyrin content and by measuring the activity of a rate-limiting enzyme for haem biosynthesis, -aminolaevulinic acid synthase. Both porphyrin content and enzyme activity are high in normal female glands. Enzyme activity was lowered in females ovariectomised for 6 weeks, and both enzyme activity and porphyrin content were greatly lowered in ovariectomised females given the dopamine agonist bromocriptine; this suppression could be prevented by simultaneous prolactin administration. Bromocriptine (but not ovariectomy alone) also masculinised the morphology of the Harderian gland, resulting in the appearance of type II cells and polytubular complexes; again, the simultaneous administration of prolactin prevented masculinisation. The results support the hypothesis that while androgens have an inhibitory effect on porphyrin synthesis within this model, prolactin may have a major facilitatory role.Abbreviations ALA -aminolaevulinic acid - ALA-s -aminolaevulinate synthase     

Harderian gland: regulation of sexual "type" by gonads and pineal gland

The sexual dimorphism of the Harderian glands of golden hamsters is regulated by a complex interaction of the gonads and pineal gland. Ovariectomy was shown to prevent the conversion to male-type gland which normally follows blinding. Testosterone administration in combination with blinding and ovariectomy promoted the male type. Ovariectomy after 8 wk of blinding was ineffective in reversing the effects of blinding on the Harderian glands, but ovariectomy and pinealectomy caused complete reconversion to the female type. To our knowledge, this is the first report to demonstrate an influence of the ovaries on the Harderian gland of the hamster. In males, administration of testosterone for 7 days after 8 wk of castration was shown to have little effect on the conversion to the female type which normally attends castration, whereas testosterone injection followed by a period of blinding completely reversed the effects of castration on the Harderian gland. These studies, along with previously published reports, strongly suggest that the male-type Harderian gland is expressed whenever significant androgen levels are present, or when the glands are exposed to androgen priming during or just prior to a period of blinding-induced pineal activation. The probable role of ovarian androgens in mediating conversion to the male-type gland is discussed.     

Effects of human chorionic gonadotropin and progesterone administration on porphyrin biosynthesis and histology of the Harderian glands in male and female Syrian hamsters.

We investigated the influence of hCG and progesterone on the control of porphyrin biosynthesis and histology in the Syrian hamster Harderian glands. Castration of male hamsters caused a marked elevation in porphyrin biosynthesis as revealed by the concentrations of porphyrins and the mRNA levels of the porphyrin pathway rate-limiting enzyme, 5-aminolevulinate synthase (ALV-S). Injection of hCG into castrated male hamsters also resulted in a significant increase in both porphyrin concentrations and levels of ALV-S mRNA compared with those in saline-injected castrated hamsters. Type II cells, which are filled with large lipid vacuoles and are characteristic of male phenotype, disappeared after castration, but administration of hCG partially prevented this change. On the other hand, neither administration of hCG nor progesterone implants could increase the very high porphyrin concentrations and ALV-S mRNA levels characteristic of female Syrian hamsters. As in the case of castrated male hamsters, injections of 20 IU hCG to female Syrian hamsters increased the relative number of Type II cells per square millimeter, whereas progesterone administration did not modify the relative number of Type II cells. These results indicate that hCG can modify Harderian gland morphology in both male and female hamsters and can exert a positive control in the expression of ALV-S gene in castrated male hamsters.     

Sex dimorphism in the thyroid gland. IV. Cytologic aspects of sex dimorphism in the rat thyroid gland

This study was designed to explain whether the sex-dependent differences in the structure of the thyroid gland of adult male and female rats depend on quantitative or qualitative changes in the thyroid follicular cells. Absolute thyroid gland weight was similar in male and female rats, but its relative weight was markedly higher in females however. Volume fractions of epithelium and stroma were higher and that of colloid lower in male than in female rats and the epithelium/colloid ratio was higher in the males. Also absolute the volumes (in mm3) of epithelium and stroma were higher in the males; the thyroid gland of females contained more colloid. The average volume of a thyroid follicular cell, estimated by stereology, was higher in males than in females, although the thyroid gland contained similar numbers of follicular cells in both sexes. Also, thyroid glands from both male and female rats contained a similar DNA quantity. Results of the present study show that the sex dimorphism in the rat thyroid depends upon a difference in the mean volume of thyroid follicular cells, with males having larger cells than females. However, in both sexes the thyroid gland contains a similar quantity of these cells.     

The Harderian gland of the Mexican volcano mouse Neotomodon alstoni alstoni (Merriam 1898): a morphological and biochemical approach

The Harderian glands of rodents are large intraorbital exocrine glands with histologic organization that varies among mammalian species. Here we describe some ultrastructural and biochemical features of the Harderian gland in the Mexican volcano mouse Neotomodon alstoni alstoni, a species of restricted habitat. The Harderian glands from male and female adult mice were dissected, processed and embedded in Epon 812 for light and electron microscopy studies. Porphyrin and total lipids were biochemically determined. The macroscopic appearance of the Harderian gland is similar in the male and female. The gland is a bilobulate structure, situated in the orbit towards the posterior side of the eyeball, of whitish color and is surrounded by a connective tissue capsule. The male gland is slightly heavier (127 mg) than that of the female (113 mg). The Harderian gland shows a tubulo-alveolar organization and is composed exclusively of one type of secretory cells. No branched duct system within the gland was found. Adrenergic nerves endings and mast cell were observed in the interstices of the alveoli. Male and female glands produce similar levels of porphyrins. Triglyceride levels were significantly higher (P < 0.05) in the female compared to the male. Abundance of lipids could induce corneal lubrication of the Harderian gland which may confer a protective and adaptative function to the volcano mouse in its natural habitat during the dry and cold seasons.     

Sex differences in secretion pattern of neonatal rat Harderian gland under various environmental lighting conditions

1. Secretion pattern of Harderian gland of neonatal rats maintained under (a) diurnal lighting conditions; (b) continuous light or (c) continuous darkness was studied at light microscopy level. 2. All animals were placed in especially designed cages at 13:00 hr on day 1 and studied on day 7 at 13:00 and 23:00 hr, respectively. 3. Acini with intraluminal secretion were counted in glands from each animal and the results were separately grouped for male and female animals. 4. A diurnal rhythm in secretion pattern of rat Harderian gland in neonatal period was demonstrated. 5. A statistically significant difference was observed in the gland secretion pattern between males and females at both, 13:00 and 23:00 hr when the animals were kept under diurnal lighting conditions. 6. Under continuous light or continuous darkness, the diurnal rhythm in secretion pattern was lost and no significant differences were seen when data from males were compared to those from female neonates. 7. Results are discussed in terms of the possible function of Harderian gland as element of an extraretinal photoreceptor system involved in the regulation of pineal function in neonatal rats.     

Androgenic control of immunoreactive somatostatin in the Harderian gland of the Syrian hamster

Harderian glands of Syrian hamsters contained measurable levels of immunoreactive somatostatin. After an extraction procedure, serial dilutions of tissue were assayed and showed parallelism in the displacement curve with dilutions of purified somatostatin standard in the radioimmunoassay. Somatostatin concentrations were higher in female hamsters (10.0 +/- 2.1 ng/mg protein) than in males (2.6 +/- 0.4 ng/mg protein). Castrated males had somatostatin values in the range of females (12.4 +/- 2.3 ng/mg protein) at 1 month after gonadectomy. Testosterone implants prevented the rise of Harderian gland somatostatin in castrated males. Gonadectomized males had lower somatostatin content in the gland than did control males (1.0 +/- 0.2 ng/mg protein) at 2 months after castration. Somatostatin values in females were unaffected by gonadectomy, but there were variations during the oestrous cycle, with a nadir detected at dioestrus-1 and maximal values coincident with the day of the ovulation.