Some effects of X-irradiation on the activity of the thyroid and pituitary glands of Xenopus laevis (Amphibia) during metamorphosis

A histological study of irradiated thyroid and pituitary glands of metamorphosing Xenopus tadpoles was made. Both glands shrink, reaching a minimum nine hours after irradiation and recover by 24 hours. It is suggested that sudden release of hormones may explain a reported hastening of metamorphosis in irradiated tadpoles.  

Summary:

Xenopus larvae received 2500 rads of whole body X-rays.
Nine hours after irradiation both pituitary and thyroid volumes were significantly less than the controls. From 24 hours after, the volumes had returned to control levels.
The mitotic incidence in irradiated thyroids fell within five hours to one tenth of the control value and remained suppressed for at least three days.     

Beta-glucan and pectin derivatives stimulate prolactin secretion from hypophysis in vitro

Previous work has shown that various plant extracts administered to animals stimulate milk protein synthesis through the secretion of prolactin. It has also been shown that beta-glucan and pectin are the active molecules capable of stimulating prolactin release in vivo after intravenous injections. In this work, it is shown that beta-glucan and several pectin derivatives are able to stimulate prolactin secretion from hypophysis fragments incubated for 2 hr in a synthetic medium.     

Effects of different numbers of ectopic pituitary transplants on regulation of testicular LH/hCG and prolactin receptors in the hamster (Mesocricetus auratus)

Adult male hamsters were given transplants of 1/2, 1, 2, 3 or 4 pituitaries under the kidney capsule and were killed 4 weeks later. Pituitary transplants produced a significant, dose-related increase in plasma prolactin levels, no changes in plasma LH and an increase in plasma FSH. Concentration of LH/hCG receptors in the testes was significantly increased in animals with 2 or 3 transplants and concentration of testicular prolactin receptors was significantly increased in those given 2 transplants. The apparent stimulatory effects of 1/2, 1 or 4 transplants on testicular LH/hCG and prolactin binding were not statistically significant. Some of the animals were injected with 0.3 i.u. hCG/g body weight 24 h before being killed. This produced a significant reduction in the levels of prolactin receptors and an apparent reduction in the levels of LH/hCG receptors in the testes. Elevation of plasma testosterone concentrations in response to hCG was significantly greater in animals given 3 or 4 pituitary transplants than in the remaining groups. These results provide further evidence that prolactin increases the number of LH/hCG and prolactin receptors in the hamster testis and suggest that changing the number of ectopic pituitary transplants may result in biphasic effects on the testis, with 2 or 3 transplants being maximally stimulatory.     

Fasting and glucose effects on pituitary leptin expression: is leptin a local signal for nutrient status?

Leptin, a potent anorexigenic hormone, is found in the anterior pituitary (AP). The aim of this study was to determine whether and how pituitary leptin-bearing cells are regulated by nutritional status. Male rats showed 64% reductions in pituitary leptin mRNA 24 hr after fasting, accompanied by significant (30-50%) reductions in growth hormone (GH), prolactin, and luteinizing hormone (LH), and 70-80% reductions in target cells for gonadotropin-releasing hormone or growth hormone-releasing hormone. There was a 2-fold increase in corticotropes. Subsets (22%) of pituitary cells coexpressed leptin and GH, and <5% coexpressed leptin and LH, prolactin, thyroid-stimulating hormone, or adrenocorticotropic hormone. Fasting resulted in significant (55-75%) losses in cells with leptin proteins or mRNA, and GH or LH. To determine whether restoration of serum glucose could rescue leptin, LH, and GH, additional fasted rats were given 10% glucose water for 24 hr. Restoring serum glucose in fasted rats resulted in pituitary cell populations with normal levels of leptin and GH and LH cells. Similarly, LH and GH cells were restored in vitro after populations from fasted rats were treated for as little as 1 hr in 10-100 pg/ml leptin. These correlative changes in pituitary leptin, LH, and GH, coupled with leptin's rapid restoration of GH and LH in vitro, suggest that pituitary leptin may signal nutritional changes. Collectively, the findings suggest that pituitary leptin expression could be coupled to glucose sensors like glucokinase to facilitate rapid responses by the neuroendocrine system to nutritional cues.     

Prolactin and growth hormone synthesis: effects of perphenazine, alpha-methyltyrosine and estrogen in different thyroid states.

The effects of thyroid hormones on prolactin (PRL) and growth hormone (GH) synthesis by the rat anterior pituitary gland were assessed in vitro. A marked reduction (84-87%) in the rate of H3-leucine incorporation into GH was evident 2-4 weeks after thyroidectomy, while incorporation into PRL was 52-71% less than that measured in glands from intact rats. A single injection of T4 (200 mug/kg) administered to thyroidectomized (THX) rats 48 hr before sacrifice significantly increased incorporation into both pituitary hormones, although the stimulation of GH synthesis was much more dramatic. Perphenazine, alpha-methyltyrosine and estrogen enhanced the rate of PRL synthesis in intact rats. Thyroid ablation did not affect the response to perphenazine, but significantly increased the response to alpha-methyltyrosine and estrogen. On the other hand, administration of T4 to THX rats receiving perphenazine, alpha-methyltyrosine or estrogen diminished the stimulatory influence of these treatments on PRL synthesis. Perphenazine, alpha-methyltyrosine and estrogen had no effect on the rate of GH synthesis in THX rats, nor did they alter the ability of T4 to restore GH synthesis in these animals. These results indicate that GH synthesis in the rat is dependent upon thyroid hormones and support the concept that these hormones exert their stimulatory effect directly on pituitary somatotrophs. Pituitary lactotrophs, however, appear to retain much of their capacity to synthesize PRL under conditions of thyroid deficiency. The changes in pituitary PRL levels and synthesis rate induced by thyroid ablation might reflect differences in the number rather than the activity of these cells.     

Pituitary luteinizing hormone level in the male house musk shrew, Suncus murinus L., following castration and testosterone treatment

The effect of castration and replacement therapy with testosterone propionate (TP) on the pituitary LH concentration and contents in the house musk shrew was investigated by using an in vitro bioassay for LH, the Rat Interstitial Cell Testosterone assay. The concentration and contents of LH increased slightly 10 days after castration, but decreased progressively thereafter to about a half of the pre-operation level by 90 days after the operation. The replacement with TP (100 micrograms/day) for 7 days significantly depressed LH contents when it was begun 10 days after castration, while the same treatment started immediately after or 30 days after the operation did not significantly affect the pituitary LH level. The feedback mechanism between the gonad and the pituitary may be slightly different in the shrew from that in other mammals. TP replacement, started immediately after castration, completely inhibited the decrease in the weight of male accessory sex organs in castrated shrews. In castrated animals when more than 10 days had elapsed after the operation, however, the decreased weight of the organs could not be fully restored by the TP replacement for 7 days.     

Effect of prolonged incubation of male rat whole pituitary or pituitary-hypothalamus complex with testosterone on release of gonadotrophin and prolactin in vitro.

Investigations were undertaken to study the effect of in vitro addition of testosterone (0.3 mM) on the release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) by pituitary-hypothalamus complex (PHC) or the whole pituitary (PI) incubated for 72 hr, with incubation media changed every 24 hr. PHC or PI were from adult intact or castrated (7 days post castration) rats. The tissues incubated with or without testosterone were further exposed to 0.1 nM luteinizing hormone-releasing hormone (LHRH) for 4 hr. Incubation media and the pituitary were analyzed for PRL and gonadotrophin content. While PHC from normal and castrated rats released increasing amounts of LH with diminishing amounts of FSH and PRL at different periods of incubation, PI showed a decrease in the amounts of gonadotrophin and PRL released. Co-incubation of PHC or PI of intact or castrated rats with testosterone stimulated the release of LH and FSH during the first or second-24 hr incubation but inhibited the release of PRL in all the three incubations of 24 hr each. The extent of PRL inhibition increased with increasing incubation period. Testosterone had no effect on LHRH induced release of PRL but inhibited LHRH induced release of LH and FSH by pituitaries from constructs of normal rats. Testosterone reduced intrapituitary contents of PRL and FSH of intact and castrated rats. The data are interpreted to suggest that hypothalamus is essential for the maintenance of functional pituitary in vitro and that intrinsic differences exist in mechanisms regulating the secretion of LH, FSH and PRL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantification of prolactin messenger ribonucleic acid, pituitary content and plasma levels of prolactin, and detection of immunoreactive isoforms of prolactin in pituitaries from turkey embryos during ontogeny.

The content of prolactin mRNA as well as total prolactin content and type of isoforms of prolactin were measured in single pituitary glands from turkey embryos and poults. Levels of mRNA and pituitary content of prolactin remained low until 5 days before hatching, while plasma concentrations remained low until 2 days before hatching. Levels of prolactin mRNA then increased until the day of hatch, stayed stable during the 3 first days of age, and significantly increased until 2 wk of age. Similar changes were observed in pituitary content and plasma levels of prolactin. Two immunoreactive bands of apparent molecular masses of 24 and 27 kDa, corresponding to the nonglycosylated and glycosylated form of prolactin, respectively, were visualized on Western blots. In pituitary glands from embryos at 22 days of incubation, 31.5% of the protein was glycosylated, whereas in embryos at 27 days of incubation and poults at 1 and 7 days of age, 48.6%, 48.0%, and 56. 0% of prolactin was glycosylated, respectively. The results indicate that the increases in the synthesis and the release of prolactin occur mainly around and after the time of hatching in the turkey embryo. Higher percentages of glycosylated isoforms were associated with increasing levels of total prolactin in the pituitary gland. Thus, the synthesis of prolactin and its post-translational modifications may be important factors involved in the physiologic changes occurring around the time of hatching.     

Testosterone, luteinizing hormone, follicle stimulating hormone, and prolactin response to unilateral castration in prepubertal Holstein bulls

Hemicastration of Holstein bulls at 3 months of age resulted in increased (P<0.005) testicular weitht and testis sperm cell content at 330 days after treatment, but did not alter sperm cell concentration in the remaining hypertrophied testis. Radioimmuroassay of blood hormones at 1, 6, 12, and 24 weeks after treatment revealed that unilateral castration did not alter (P>0.1) basal levels or GnRH response profiles of either LH or testosterone compared to intact bulls. Hemicastration caused FSH to be elevated (P<0.01) compared to intact bulls at all sampling periods in both unstimulated and GnRH stimulated bulls. Prolactin varied with season and was greater (P<0.001) in hemicastrated bulls than in intact bulls at 1 and 6 weeks after treatment. Results indicate that unilateral castration at 3 months of age caused testicular hypertrophy of both steroidogenic and gametogenic function and this phenomena may be triggered by increased FSH or prolactin secretion, or both. Further, results indicate different testicular regulation mechanisms exist for pituitary LH and FSH release in bulls.     

Effects of an organophosphate pesticide, quinalphos, on the hypothalamo-pituitary-gonadal axis in adult male rats

The effects of chronic sub-lethal doses (7-14 mg kg-1 a day for 15 days) of quinalphos were evaluated in adult male rats for changes in testicular morphology, circulatory concentrations of hormones (LH, FSH, prolactin and testosterone), activities of acetylcholinesterase (AChE) and angiotensin converting enzyme (ACE) as well as metabolism of biogenic amines (dopamine, noradrenaline and 5-hydroxytryptamine (5-HT)) in the hypothalamus and pituitary. Hormones were assayed by radioimmunoassay or chemiluminescent immunoassay (testosterone). The enzymes were estimated after spectrophotometry and the biogenic amines by HPLC-electrochemistry. Sub-lethal chronic administration of quinalphos resulted in: decreased testicular mass and AChE activity in central as well as peripheral organs; increased serum LH, FSH, prolactin and testosterone concentrations; decreased pituitary or increased testicular ACE activity; severe disruption of spermatogenesis with increasing doses of pesticide; and no significant effects on dopamine, noradrenaline or 5-HT concentrations in the hypothalamus or pituitary. Administration of oestradiol (50 micrograms per rat a day) during pesticide treatment resulted in: a significant decrease in the mass of the testis and accessory sex organs; decreases in serum LH, FSH, testosterone concentrations; an increase in prolactin concentration; and a decrease in dopamine or an increase in noradrenaline and 5-HT in the hypothalamus or pituitary. Oestradiol had a marked effect: in pesticide-treated animals, the pesticide effects were significantly reversed. This indicates that in pesticide toxicity, the hypothalamo-pituitary-gonadal axis is operational. Since many of the observed pesticide effects could be inhibited by oestradiol, it is suggested that the pesticide acts directly on the gonadotrophins. In conclusion, quinalphos decreases fertility in adult male rats by affecting the pituitary gonadotrophins.     

Role of the hypophysis in thyroid regeneration after partial thyroidectomy.

The role of the hypophysis in thyroid regeneration was investigated by measuring the mitotic activity of the thyroid remnant in hemithyroidectomized rats as well as the blood levels of thyroid hormone at various time-intervals after hemithyroidectomy. Mitotic activity underwent a significant increase to reach a peak (a 5- to 8- fold increase) 2 days after hemithyroidectomy. The thyroid hormone level in blood was lower than in controls. Histologically, the thyroid gland showed signs of an elevated rate of functional activity, as indicated by losses of colloid and cell hypertrophy. In a second approach, the mitotic activity of the thyroid remnant was estimated in hypophysectomized and in thyroxine treated rats. Both hypophysectomy and thyroxine injection prevented occurrence of the mitotic peak at 2 days. The regeneration of the thyroid after hemithyroidectomy, as it occurred in the present work, may be explained by a release of thyroid stimulating hormone from the pituitary, brought about by the low level of circulating thyroid hormone, itself resulting from a loss of thyroid tissue.     

Lysosomal enzymes in the rat harderian gland are altered by either bromocriptine treatment or hypophysectomy and hormone replacement therapy

Four groups of adult male hypophysectomized rats were injected subcutaneously twice daily between 0800-0900 hr and 1600-1700 hr with either saline diluent, 150 micrograms sheep prolactin and/or growth hormone (GH); intact rats received either saline or 150 micrograms bromocriptine twice daily. After 4 days of treatment, lysosomal enzyme assays revealed significant elevations in both acid phosphatase and alpha-mannosidase enzyme activities in the Harderian glands of saline-injected hypophysectomized rats compared to those in intact controls. beta-Glucuronidase levels were depressed and hexosaminidase activity unaffected by hypophysectomy treatment alone compared to intact controls. Lysosomal enzyme activities in hypophysectomized animals treated with prolactin were not different from the hypophysectomized control animals. However, treatment with GH alone or in combination with prolactin had a significant inhibitory effect on beta-glucuronidase, hexosaminidase, and alpha-mannosidase enzyme activities in the Harderian gland of hypophysectomized animals. Bromocriptine treatment in intact rats only elevated acid phosphatase activity. In summary, the patterns of responses did not reveal a role for prolactin in the control of Harderian gland lysosomal enzyme activities by the pituitary. However, some of the influence on this target system may be exerted by growth hormone.     

Short-term effects of vasoligation upon plasma follicle-stimulating hormone, luteinizing hormone, and prolactin in the adult rat: further evidence for a direct neural connection between the testes and the central nervous system

The purpose of these experiments was to determine whether bilateral vasoligation of adult male rats had any short-term effects upon plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Adult male rats (250-300 g) were either bilaterally vasoligated or sham vasoligated, and blood samples were obtained by cardiac puncture preoperatively and at 24 h and 7 days following surgery. Plasma levels of both FSH and LH were significantly (P less than 0.01) decreased at 24 h following vasoligation compared to preoperative levels and those of sham-operated controls. However, the response was differential since, at 7 days following vasoligation, plasma FSH was still significantly decreased while LH was returning to control levels. Conversely, plasma prolactin levels were significantly (P less than 0.01) increased at 24 h compared to preoperative values and those in sham-operated controls, and at 7 days prolactin had returned to preoperative control levels. Sham vasoligation did not significantly change plasma levels of FSH, LH, or prolactin at any of the time intervals investigated. These results provide further evidence that suggests that there may be a direct connection between the testis and central nervous system that may be involved in the short-term regulation of gonadotropin and prolactin secretion.     

Pineal and pituitary involvement in the photoperiodic regulation of body weight, coat color and testicular size of the Djungarian hamster, Phodopus sungorus

Hypophysectomy of 40-day-old male hamsters kept under long photoperiods resulted in a change in coat color from the brownish summer coat to the whitish winter coat, within 5 wk of the surgery, cessation of growth, and, most frequently, an additional loss in body weight. The testes of the hypophysectomized animals were involuted within 14 days after surgery. Continuous substitution of prolactin by implantation of two anterior pituitaries under the kidney capsule was able to reverse partly or totally the inhibitory effects of hypophysectomy on coat color and body weight, although there was no influence on testicular volume. The same effects could be achieved by daily s.c. injections of prolactin (100 micrograms ovine-PRL/day) into hypophysectomized hamsters, whereas the injection of adrenocorticopropic hormone (5 IU porcine-ACTH/day) or melanocyte-stimulating hormone (35 micrograms synthetic alpha-MSH/day) was ineffective. Additional pinealectomy influenced neither the inhibitory effects of hypophysectomy on coat pigmentation and body weight nor the stimulatory effects of prolactin substitution in hypophysectomized animals. Thus, the study provides evidence that the effects of the pineal gland on annual changes in body weight and coat color are mediated via the pituitary.     

Vinblastine-induced microtubular paracrystals in prolactin cells of anterior pituitary gland of lactating rats.

Vinblastine sulfate in physiological saline was injected directly into the pituitary glands of lactating rats. Injections were made through the ear canal using a syringe equipped with a 24-gauge needle. The animals were killed at 2, 4, or 6 hours after the injections. When the anterior pituitary glands were examined by electron microscopy, many microtubular paracrystalline deposits were seen in the prolactin and growth hormone cells. The usual cytoplasmic microtubules and microfilaments were not seen in the cytoplasm of these cells. Granular extrusion (exocytosis) was markedly depressed, and an accumulation of secretory granules was definitely observed in the prolactin cells after the administration of vinblastine.     

Immunostaining of growth hormone and prolactin in paraffin-embedded and stored or previously stained materials.

In attempts to evaluate immunocytochemically autopsy and biopsy material previously obtained and processed for conventional histologic staining, we had to resort to immunostaining of tissues embedded years ago or even sections already stained with hematoxylin-eosin or aldehyde thionin-PAS-orange G. Hypophysial growth hormone and prolactin proved remarkably resistant to such prior treatment with regard to their antigenic properties, and could be readily immunostained in tissue embedded in paraffin 3-4 years earlier, and after destaining of sections prepared up to 7 years earlier. The results of such "retrospective" immunocytochemical evaluation of autopsy and biopsy materail is illustrated with the staining of "pregnancy cells" for prolactin in the hypophysis of a woman postpartum, the immunostaining for prolactin in the cells of adenomas associated with marked hyperprolactinemia, the staining for growth hormone in adenomas removed from children with gigantism, and the immunostaining for prolactin, growth hormone or both in several adenomas that were discovered at autopsy and not associated with a known clinical history of endocrine aberrations.     

III. DECREASE OF LABELED DNA IN CELLS OF THE ADRENAL MEDULLA AFTER INTERMITTENT EXPOSURE TO COLD

Italico rats were injected with thymidine-³H 6 hr after the end of 300 hr of intermittent cold treatment. This plan of experiment ensured replacement in the adrenal medulla of lost DNA which is specifically sensitive to cold treatment and has a labeling index sufficiently high for statistical evaluation. The labeling index in the adrenal medulla decreases to one-half of the initial value within 10 days in animals subjected to further intermittent cold treatment and within 32 days in animals kept at room temperature. The very low mitotic index and the absence of doubling of the labeling index show that the observed labeling cannot be ascribed to pre-mitotic DNA synthesis. The concept of metabolic DNA adequately explains the findings.     

The identification of the thyrotropic cells in the adenohypophysis of the cichlid fish Cichlasoma biocellatum and the role of these cells and of the thyroid in osmoregulation

Summary In order to identify the thyrotropic cells in the pituitary gland of Cichlasoma biocellatum, adult animals were treated with thyroxine. Periodic acid Schiff (PAS)- and aldehyde fuchsin (AF)-positive, and Alcian blue (AB)-negative basophils in the meso-adenohypophysis as well as the thyroid were strongly inactivated by such treatment. Since other cell types in the adenohypophysis were not affected, it is concluded that the PAS-positive and AB-negative basophils in the meso-adenohypophysis are the thyrotrops. In normal animals the thyrotrops and the thyroid are very active. Propylthiouracil did not cause a further activation of TSH cells. Keeping the animals in 25% sea-water caused a strong inactivation of the prolactin cells, the thyrotrops and the thyroid. In deionized water the prolactin cells were stimulated, but the thyroid was less active than in controls. Injections of ovine prolactin did not enhance the activity of the thyroid in salt water animals. It is suggested that in Cichlasoma biocellatum prolactin does not have a direct stimulatory effect on the thyroid.Thanks are due to Prof. Dr. P. G. W. J. van Oordt for his continual interest and valuable suggestions, and to Dr. L. Boomgaart for correcting the english. We are indebted also to Messrs. H. van Kooten and E. van der Vlist for making the photographs. The National Institutes of Health, Bethesda, Maryland (U.S.A.) kindly presented the ovine prolactin.     

The activity of some intracellular oxidative enzymes in the thyroid follicular epithelium of Xenopus laevis Daud. in experimental long-term hypokinesia.

Histoenzymological methods were applied to examine the activities of previously little studied intracellular oxidative enzymes in the cells of the thyroid follicular epithelium of Xenopus laevis Daud. specimens kept in aquarium. Succinate, lactate, alpha-glycerophosphate, glucose-6-phosphate and reduced NAD and NADP dehydrogenases and cytochrome oxidase were studied. In comparison with other chordate species a very strong activity was revealed particularly by lactate dehydrogenase. The data obtained suggest that the metabolism in thyroid cells of the motionless Xenopus is based on glycolysis mainly.     

Thyrotropin releasing hormone: direct evidence for stimulation of prolactin production by pituitary cells in culture

Addition of thyrotropin releasing hormone (TRH) to the medium of 2 clonal strains of functional rat pituitary cells stimulated the production of prolactin and inhibited growth hormone production. There was no effect on cell growth. Stimulation of prolactin production by TRH was detected within 4 hr, it reached a maximum level (2–5 times control) at 24–48 hr and persisted for at least 20 days in the continued presence of TRH. Stimulation was observed with a concentration of TRH as low as 0.10 ng/ml.