Rathke's pouch grafts in adult brain sites

Donor tissue containing Rathke's pouch (RP) with its associated mesenchyme and neural lobe was isolated from 15-day fetal rats and stereotaxically transplanted either to hypothalamic hypophysiotropic sites or to cerebral cortex of adult females for 30 days. Hosts either were intact or had been hypophysectomized 2-4 weeks prior to transplantation of Rathke's pouch. Grafts in the hypothalamus of either intact or hypophysectomized hosts were pleomorphic and large, often as wide as 1-2 mm, and occasionally larger. Grafts in the cortex of either intact or hypophysectomized hosts were nodular and occasionally projected upward in association with the meninges (cortex/meninges grafts). Certain features were characteristic of the grafts in all experimental groups, i.e., development of histotypic pars distalis with cell cords and fenestrated capillaries. In all experimental groups gonadotrophs and somatotrophs, when present, were localized at the graft margin adjacent to the connective-tissue interface; mammotrophs, when present, were distributed throughout the graft. Features specific to each experimental group also were apparent. Grafts in the hypothalamus of both intact and hypophysectomized hosts typically were encapsulated by a labyrinthine meshwork of cell processes, whereas cortex/meninges grafts directly abutted dense connective tissue or neural tissue. In hypothalamic grafts in intact hosts, moderately differentiated mammotrophs, gonadotrophs, and somatotrophs could be identified by their cytological features and immunopositivity for prolactin, luteinizing hormone, and growth hormone, respectively. In hypothalamic grafts in hypophysectomized hosts, mammotrophs were absent, and gonadotrophs and somatotrophs were poorly granulated and not abundant. Grafts in the cortex of intact hosts contained numerous, well-differentiated mammotrophs, gonadotrophs, and somatotrophs. Many of the mammotrophs in these grafts were hypertrophied, and profiles of exocytosis were common. In grafts in the cortex of hypophysectomized hosts, mammotrophs were either absent or very few, whereas gonadotrophs and somatotrophs were numerous. Gonadotrophs in these grafts were dramatically hypertrophied, although exocytosis was rare. The results indicate that development of histotypic pars distalis may occur in hypophysiotropic and non-hypophysiotropic brain sites and that the hormonal state of the host as well as implantation site modulate cytodifferentiation of specific pars distalis cell types.     

The origin of yolk in the oocytes of Nereis virens (Annelida,Polychaeta)

Summary Comparative studies have been made of development of the adenohypophysis using the Rathke's pouch (RP)-derived model system. Rathke's pouch with associated mesenchyme and ventral hypothalamus, was microsurgically isolated from 15-day fetal rats and placed in mild trypsin solution. Three variations of donor tissue were isolated and transplanted beneath the kidney capsule of adult hosts: A) pure pouch epithelium; B) pouch epithelium plus mesenchyme; and C) pouch epithelium with mesenchyme and ventral hypothalamus. After 30 days the grafts were isolated and processed for light and electron microscopy. Cell types were characterized by immunostaining as well as by morphological criteria. In group A well differentiated mammotrophs dominated the grafts, many of which were hypertrophied with widely dilated endoplasmic reticulum and Golgi saccules. Mammotrophs, frequently with mitotic figures, were distributed evenly throughout the grafts. Somatotrophs and gonadotrophs were neither abundant nor well differentiated in group A, but were both abundant and more extensively differentiated in groups B and C. Both somatotrophs and gonadotrophs were typically localized at margins of the graft adjacent to connective tissue spaces. Well differentiated mammotrophs were present in groups B and C although there were fewer hypertrophied mammotrophs than in group A; and immunoreaction to prolactin was weaker than in group A.Tumor-like features found in all three groups included some loss of tissue integrity and large, vascular lakes unlined by endothelium.These findings suggest that differentiation of mammotrophs may be inhibited in part by mesenchyme associated with Rathke's pouch, since in the absence thereof these cells become hyperplastic. Conversely, differentiation of somatotrophs and gonadotrophs appears more dependent on these mesenchymal elements for normal development.     

Immunocytochemical analysis of somatotrophs and mammotrophs in the pars distalis of postnatal dwarf (dw) mutant mice

Summary The postnatal differentiation of somatotrophs and mammotrophs in the pars distalis of normal and dwarf (dw/dw) mice was analyzed by means of immunocytochemistry at the electron-microscopic level. Thin sections of Araldite-embedded pituitaries from postnatal mice ranging in age from 2 days to 3–4 months were exposed to antigrowth hormone serum (anti-GH) or to anti-prolactin serum (anti-PRL) and were processed immunocytochemically by means of the colloidal-gold technique. In the normal adult pars distalis, somatotrophs reacted strongly with antiGH, and mammotrophs showed a positive anti-PRL reaction. In the dwarf adult, the granulated cells were unreactive with either anti-GH or anti-PRL. However, at 6 days postnatally, some cells in the dwarf pars distalis showed a positive reaction with anti-GH, though the reaction was not as strong as in the 6-day normal pars distalis. The 6-day dwarf was only faintly reactive with anti-PRL, and by 14 days the dwarf was unreactive with anti-GH as well as anti-PRL, in contrast to the strong positive reactivity to these two antisera in the normal 14-day pars distalis.Supported by USPHS grant HD12308     

Fine structure of somatotrophs and mammotrophs in the pituitary pars distalis of the little (lit) mutant mouse

The cellular pathology and postnatal differentiation of somatotrophs and mammotrophs in the pars distalis of little (lit/lit) and normal (+/+; lit/+) mice were studied by means of electron microscopy. The results indicate that in little the pituitary at birth contains recognizable somatotrophs and mammotrophs; however, between 14 and 24 days of age a contrast between little and normal becomes conspicuous with respect to the somatotrophs. Little somatotrophs are less heavily populated with granules, have granules of smaller size, and show less developed organelles than do normal somatotrophs at comparable stages. Beyond 24 days the little somatotrophs become more difficult to locate, and those that do occur show a minimal increase in complexity from that present at 14 days. In contrast, the mammotrophs in little are similar in appearance to normal mammotrophs and show increasing complexity as development proceeds, often sending forth cellular processes between neighboring cells, as do normal mammotrophs.     

Postnatal development of somatotrophs and mammotrophs in the pars distalis of the C57BL mouse

Summary The pars distalis of the pituitary gland of the C57BL mouse was studied by means of electron microscopy during postnatal stages of males ranging in age from newborn through 24 days, with particular emphasis on the somatotrophs and mammotrophs. During this period, growth curves were plotted in order to correlate postnatal growth patterns with the state of differentiation of the somatotrophs in the pars distalis. In the newborn, the somatotrophs show well developed organelles, including rough endoplasmic reticulum and Golgi complexes. These cells are not as densely packed with granules as the adult somatotrophs; however, from days 5 through 24, they show a progressive accumulation of granules. Although mammotrophs are scarce in the newborn, they are readily distinguishable in the pars distalis at 5 days. Male mice in small litters show a progressive increase in body weight between birth and 11–12 days, at which time the rate slackens until 18–19 days when the rate again increases. Growth curves for mice from large litters are similar to those from smaller litters, except that the transitory decrease in rate is more prominent.Supported by NIH grant no. HD12308 from the National Institute of Child Health and Human Development, USPHSThe authors wish to thank Pratima Ganguly for technical assistance     

Topographical distribution of the gonadotrophs,mammotrophs, somatotrophs and thyrotrophs in the pituitary gland of the baboon (Papio cynocephalus)

The identification and regionalization of four pituitary parenchymal cell types, gonadotrophs, mammotrophs, somatotrophs and thyrotrophs, were studied in the baboon (Papio cynocephalus) hypophysis using immunocytochemistry. The gonadotrophs were homogeneously distributed throughout the entire pars distalis. Both mammotrophs and somatotrophs predominate at the superior and inferior poles of the organ. The medial and anteromedial regions are populated by mammotrophs and thyrotrophs, while the lateral and posterior portions of the pars distalis contain large numbers of somatotrophs.     

Uptake and retention of sex steroids by the baboon pituitary gland--evidence of sexual dimorphism with respect to dihydrotestosterone

The localization and identification of the target cells for estradiol (E2) and dihydrotestosterone (DHT) were studied in the pituitary gland of male and female baboons (Papio cynocephalus) using autoradiography and autoradiography combined with immunocytochemistry. The largest number of cells which sequestered 3H-E2 were located in the pars distalis of both the males and females. Immunocytochemistry revealed that these target cells were predominantly gonadotrophs and mammotrophs, albeit a few somatotrophs and thyrotrophs were also labeled. A distinct sexual dimorphism was not observed with respect to the uptake and retention of the tritiated estrogen but was clearly evident in those animals given 3H-DHT. Significantly more cells in all three lobes of the male baboon, the partes distalis, intermedia and nervosa, concentrated the radiolabeled androgen as compared to that found in the females. Regardless of sex, however, the gonadotrophs were the major cell type in the pars distalis which was labeled. A small population of mammotrophs, somatotrophs and thyrotrophs also retained 3H-DHT. In both males and females, the pars nervosa was the portion of the hypophysis most sensitive to 3H-DHT. These findings indicate that all three lobes of the hypophysis of the male and female baboon contain target cells for E2 and DHT and that the propensity for DHT uptake is greater in males than in females.     

Neuroembryogenesis of ventral hypothalamus transplanted to kidney capsule

Summary Parts of the floor of the hypothalamus were microsurgically isolated from 12-day rat embryos and transplanted beneath the kidney capsule (KC) of adult hosts. The grafts became vascularized with extensive areas of neural tissue developing from 17 days through 33 days. Host animals were either hypophysectomized or intact, and no significant morphological differences could be detected in the transplants.Neural tissue developed with a high degree of organization, with neurons and glial cells, and an abundance of dendritic and axonal processes clustered among glial processes. Glial processes with junctional attachments formed a complete layer at the basal lamina of the neural tissue which prevented nerve endings from making direct contact with the basal lamina. Small clusters of synaptic vesicles were common in nerve endings and in addition some endings contained synaptic vesicles and 600–900Å diameter dense-core granules. Junctional complexes ranged from well-formed synapses of the adult type to areas of membrane contact having minimal specialization. Synapses appeared increased in number, and to assume more mature features, with longer growth periods.The results indicate that the morphologically undifferentiated floor of the hypothalamus of the 12-day rat embryo can undergo morphological differentiation along lines similar to normal development even in an ectopic site such as the KC.Supported in part by Grant No. R01-CA-21426 from the National Cancer Institute, DHEW; California Division ACS Special Grant No. 851; NIH Grant No. RO1-HD-08126; and a Cancer Research Training Fellowship to D.G. under NIH Grant No. Ca 05297 at the University of Southern CaliforniaThe authors gratefully acknowledge the technical assistance of Sheila Odnert, Vivian Charca, Alicia Thompson and Linda Melsek     

Estrogen-induced transformation of somatotrophs into mammotrophs in the rat

Summary In the normal male rat pituitary tritiated thymidine labeled mainly STH cells (somatotrophs), no labeled prolactin cell was found. Following estradiol treatment for 21 days tritiated thymidine labeled mainly prolactin cells (mammotrophs). To determine the origin of these mammotrophs tritiated thymidine was given before the estradiol treatment started, thus labeling many somatotrophs. After 21 days of estradiol, out of 42 labeled cells, 14 were mammotrophs and 13 were somatotrophs; these results suggest that there might be a true transformation of somatotrophs into mammotrophs under the influence of estradiol or that there exist two types of somatotrophs: 1) a committed somatotroph which is not transformed by estrogen treatment, and 2) an uncommitted mammosomatotroph, which under normal conditions bears the features of a somatotroph, but which transforms into a mammotroph under the influence of estradiol.This work was supported by grants MA-552 and MT-2701 from the Medical Research Council of Canada. The authors wish to thank Dr. G. M. Brown, Clarke Institute of Psychiatry, University of Toronto, for the radioimmunoassays of growth hormone and prolactin. Reagents for both radioimmunoassays were kindly provided by the National Institute of Arthritis and Metabolic Diseases, through the Rat Pituitary Hormone Distribution Program. — We are also thankful to Dr. L. Endrenyi, Department of Pharmacology, University of Toronto, for the statistical analysis of our data.Fellow of the Medical Research Council of Canada.     

Immunocytochemical and ultrastructural correlates of the pineal inhibition of prolactin cell activity in blind-anosmic female rats

Summary The effects of the pineal gland on the light microscopic-immunocytochemical and ultrastructural appearance of pituitary mammotrophs were studied in female rats eight weeks after prepubertal blinding and olfactory bulbectomy.Blinding and anosmia resulted in a marked decrease in the size of the pars distalis concomitant with a reduction in the apparent number and size of PRL cells as compared with intact animals. Ultrastructurally, these cells appeared much less active than those of intact rats. The small and angular-shaped mammotrophs of blind-anosmic rats characteristically exhibited scant arrays of rough endoplasmic reticulum, small Golgi complexes with few immature secretory granules, few mature secretory granules and rare exocytosis patterns.Pinealectomy tended to reverse the effects of blinding and anosmia on pars distalis size and PRL cell size, apparent number and ultrastructure. In fact, the mammotrophs of blind-anosmic-pinealectomized rats were quite similar in ultrastructural appearance to those of intact rats.From these data we conclude that the pineal causes mammotroph hypotrophy and hypoplasia in blind-anosmic female rats.Supported by USPHS Biomedical Research Support Grant # RR 05675. The authors thank Dr. Bruce A. Richardson for his kind help with the immunocytochemistry     

Glycoconjugate localization with lectin and PA-TCH-SP cytochemistry in rat hypophysis

Glycoconjugates were localized by light microscopy with lectin-peroxidase conjugates and by electron microscopy with the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) sequence in immunocytochemically or morphologically identified cell types in rat pituitary. Lectin histochemistry demonstrated sialic acid and glycoconjugates with N-glycosidically linked oligosaccharides in gonadotrophs, thyrotrophs, and corticotrophs. Galactose penultimate to sialic acid was observed mostly in gonadotrophs. The terminal galactose-N-acetylgalactosamine disaccharide was detected in a few gonadotrophs and in a moderate number of mammotrophs. Fucose was localized in only corticotrophs with two fucose-binding lectins and in thyrotrophs with another. Several different monosaccharides were seen in glycoconjugates in melanotrophs and in Herring bodies. Melanotrophs displayed heterogeneous staining with fucose-binding lectins. A small number of nonsecretory cells were also visualized in the pars distalis by virtue of their glycogen content. PA-TCH-SP staining revealed complex carbohydrates in secretory granules and some Golgi cisternae in all types of hormone-producing cells in the pars distalis except for the somatotrophs. Melanotrophs of pars intermedia exhibited stained secretory granules and irregular dense bodies containing a stained meshwork. Corticotrophs of the pars distalis lacked the latter bodies, although they form the same glycoprotein precursor hormone as melanotrophs. Lectin conjugates and the PA-TCH-SP sequence stained some groups of secretion granules in Herring bodies, possibly representing vasopressin-containing granules as well as other cell types in the pars nervosa.     

Early Development of Mouse Anterior Pituitary: Role of Mesenchyme

Epithelial-mesenchymal interaction in the early development of the anterior pituitary gland was examined by chronological observations on fetal pituitary epithelium grafted in vivo with and without its own mesenchyme. At 8.5 days of gestation, the RATHKE'S pouch began to evaginate toward the diencephalon. The mesenchymal tissue around the pouch was at first very sparsely scattered, but then condensed, on day 10 becoming visible under a dissecting microscope. When RATHKE'S pouch epithelia from 10- and 12-day fetuses were transplanted alone under the kidney capsule, they proliferated slightly to form cysts, the cells of which differentiated into ACTH-producing cells, but not into prolactin-producing cells. Pituitary morphogenesis did not occur. When these epithelia were recombined with homotypic mesenchyme and transplanted, the epithelia proliferated remarkably on one side of the wall of the pouch, resulting in formation of a pars distalis that contained both ACTH-producing cells and prolactin-producing cells. Heterotypic mesenchyme, such as lung, dermis and mammary gland mesenchyme, could induce 12-day epithelium, but not 10-day epithelium to develop into pars distalis. Thus, fetal pituitary epithelium has the capacity of autodifferentiation into ACTH-producing cells, not into prolactin-producing cells, and requires mesenchymal support for development of the pars distalis.     

Treatment of long-term anestrous sows with estradiol benzoate and GnRH: response of serum LH and occurrence of estrus

Seventeen primiparous sows, anestrous for 41 +/- 4 days after weaning, received i.m. injections of 500 mug estradiol benzoate (EB) or corn oil. At 48 hr after treatment, LH averaged 12.1 +/- 2.6 ng/ml in EB-treated sows and 0.7 +/- 0.1 ng/ml in corn oil-treated sows. At 55 hr after EB or corn oil, each sow was given 50 mug gonadotropin releasing hormone (GnRH). Average LH 1 hr after GnRH was 5.7 +/- 1.1 and 5.1 +/- 0.9 ng/ml in EB- and corn oil-treated sows, respectively. All EB-treated sows exhibited estrus 2.3 +/- 0.2 days after treatment and were mated. None of the corn oil-treated sows exhibited estrus and all were slaughtered two weeks after treatment. Examination of reproductive tracts revealed that the ovaries of corn oil-treated sows were small and did not contain corpora lutea. In mated sows, progesterone concentrations in blood two weeks after mating indicated luteal function in eight of the nine animals. Positive pregnancy diagnoses were made in all eight animals; however, only three sows farrowed, with litter sizes of four, five and seven, respectively. Results of the present experiment indicate that the hypothalamus and anterior pituitary of long-term anestrous sows are capable of responding to endocrine stimuli (i.e. estradiol and GnRH). Moreover, estradiol induced estrus and ovulation, but subsequent farrowing rate was only 33 percent and size of litters was small.     

Immunocytochemistry of somatotrophs,gonadotrophs, prolactin and adrenocorticotropin cells in larval sea bream (Sparus auratus) pituitaries

Summary The chronological appearance of endocrine cells in the pituitary of sea-bream (Sparus auratus) larvae was studied using antisera against salmon prolactin, trout growth hormone, salmon gonadotropin and N-terminal human adrenocorticotropin. The larval pituitary (1–12 days after hatching) was oval in shape and was composed of a dense mass of cells with few neurohypophysial fibres. By 60 days after hatching it began to resemble the adult and was divisible into a distinct rostral pars distalis containing prolactin and adrenocorticotropin cells; a proximal pars distalis containing somatotrophs and gonadotrophs and a pars intermedia. Cells immunoreactive with antisera against growth hormone were observed immediately after hatching (2 days post-fertilization). Weakly staining prolactin cells were observed 2 days later in the region corresponding to the rostral pars distalis. Cells immunoreactive with anti-gonadotropin and anti-adrenocorticotropin sera were observed in the pituitary 6 and 8 days after hatching, respectively. All the cell-types studied were immunoreactive from the time they were first identified until the final samples 90 days after hatching.     

Effects of growth hormone-releasing hormone on somatotrophs in anterior pituitary gland allografts in hypophysectomized,orchidectomized hamsters

Summary We investigated the influences of growth hormone-releasing hormone (GHRH) on the percentage, size, and shape of somatotrophs in ectopic anterior pituitary tissue. Entire pituitary glands removed from 7-week-old male hamsters were placed beneath the renal capsules of 12-week-old hamsters that had been hypophysectomized and castrated 3 weeks previously. Beginning 6 days after each host had received a single allograft, each was injected subcutaneously twice daily with 4 g GHRH in 100 l of vehicle or 100 l of vehicle for 16 days. Six hosts in each group were killed by decapitation on day 17, 16 h after the last injection. Nine normal male hamsters were also decapitated and their pituitary glands were removed. Sections of anterior pituitary tissue were stained for GH and with hematoxylin. The percentage of anterior pituitary cells that stained for growth hormone was similar in the 3 groups. In contrast, somatotrophs in grafts had a smaller mean cross-sectional area than those observed in glands in situ. This effect was reversed by GHRH. Analysis of the shape of somatotrophs in both groups of grafts disclosed that they were less circular in cross-section than those in glands in situ. The results suggest that GHRH may not play a role in maintaining the percentage of somatotrophs among anterior pituitary cells, but that it does play a role in maintaining their size.     

Prolongation and cessation of estrous cycles in aging C57BL/6J mice are differentially regulated events

The relative contributions of ovarian failure and hypothalamic-pituitary dysfunction to the prolongation and cessation of estrous cycles were assessed by measuring the ability of acutely ovariectomized (OVX) middle-aged (12 mo) mice to cycle after receiving grafts (under the renal capsule) of ovaries from young (2 mo) mice. The potentially disruptive effect of the acyclic state on the cycling response to grafted, young ovaries was avoided restricting grafting to middle-aged hosts that were still cycling. The effect of chronic exposure to ovarian secretions before the cessation of cyclicity on age-related hypothalamic-pituitary dysfunction was also assessed. The cycling ability of long-term OVX middle-aged mice (i.e., OVX at 3 mo) bearing grafts of young ovaries was compared to that of age-matched acutely OVX controls. Grafted young ovaries extended the cycling lifespan of acutely OVX middle-aged hosts by 60%. The length of this extended cycling lifespan, however, was only 80% of that achieved by young hosts bearing grafts of young ovaries. Young ovaries in middle-aged mice markedly lowered the incidence of long cycles (greater than 5 days), shifting the modal cycle length to 5 days. However, young ovaries in middle-aged mice failed to increase the incidence of 4-day cycles, the modal cycle of young controls. Middle-aged ovaries grafted into young hosts lengthened their cycles and shortened their cycling lifespan to middle-aged values. Long-term ovariectomy failed to increase the cycling lifespan of middle-aged hosts bearing grafts of young ovaries beyond that achieved in acutely OVX mice. Long-term ovariectomy did shorten the modal cycle length of middle-aged mice to 4 days, although the duration of 4-day cycling was only one-third (2 mo) that of young controls. These results indicate that the relative contributions of ovarian and neuroendocrine factors to three major events of reproductive aging vary with each event. Whereas the hypothalamic-pituitary unit appears to play an important role in the initial shift from 4- to 5-day cycles, the aging ovary plays the major role in the subsequent shift to longer cycles and in the ultimate cessation of cyclicity. Although chronic exposure to ovarian secretions during the period of cyclicity does not play a major role in the cessation of cyclicity, it appears to contribute to the hypothalamic-pituitary changes responsible for the initial shift from 4- to 5-day cycles.     

The pituitary of non-pregnant and pregnant viscachas (Lagostomus maximus maximus): a comparative study by immunohistochemistry and morphometric analysis

The neuroendocrine hypothalamic-pituitary axis undergoes morphological and biochemical changes throughout gestation. In viscacha, pregnancy lasts approximately 154 days, and three stages can be described: early, mid- and late pregnancy. The aim of this work was to study the pituitary LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, corticotrophs and thyrotrophs of non-pregnant and pregnant adult viscachas by immunohistochemistry and morphometric analysis. Immunopositive percentage area (%IA), cell percentage in the pars distalis (%PDC), number of cells per reference area (n°cell/RA), and major cellular (MCD) and nuclear (ND) diameters were analyzed. The different cell populations showed a well-defined morphology, immunolabeling patterns and regionalization in the pars distalis (PD). In the early pregnancy of animals the morphometric analysis demonstrated that %IA, %PDC and n°cell/RA increased in the FSH-gonadotrophs and decreased in the somatotrophs in relation to non-pregnant animals. In mid-pregnancy, there was an increase in %IA, %PDC, and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, and thyrotrophs. The MCD of LH-gonadotrophs and FSH-gonadotrophs increased. In late pregnancy, the %IA, %PDC and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs and corticotrophs decreased whereas the values of the thyrotrophs remained constant. The MCD of LH-gonadotrophs, FSH-gonadotrophs and corticotrophs decreased. No significant changes were observed in the ND of the studied cell types. In conclusion, this work provides evidence for histological and morphometric changes in the different cell types of the pituitary PD in viscachas during pregnancy, probably according to the requirements of this physiological stage.     

Hypophysial portal vascular infusion of TRH in the rat: an ultrasturctural and radioimmunoassay study.

The hypophysial portal vessels and anterior pituitary gland of adult male Wistar rats were exposed surgically. A hypophysial portal vessel was cannulated and infused for one minute with saline or thyrotrophin (TRH). Anterior pituitary glands were collected at 1,5,15,30 or 60 minutes after cessation of infusion, for light and electron microscopic examination. Before and immediately after cannulation of a portal vessel, a 1-ml sample of blood was collected at 1,5,15,30, or 60 minutes, from the femoral vein for radioimmunoassay (RIA) of growth hormone. Thyrotrophs from anterior pituitary glands of rats infused with TRH displayed emiocytic activity at all time-periods studied. Rough endoplasmic reticular (RER) cisternae were dilated at 15 minutes following infusion and remained dilated at 30 and 60 minutes. TRH was observed to stimulate emiocytic activity in most pituitary cell-types. Extensive dilations of RER cisternae were also observed in mammotrophs and gonadotrophs, but were not observed in somatotrophs or adrenocorticotrophs. The demonstration that thyrotrophs, mammotrophs, somatotrophs, and gonadotrophs respond to TRH suggests that some common features may be shared by these cells. Preliminary analysis of the RIA data show that TRH was potent in elevating radioimmunoassayable growth hormone levels. Significant increases (p less than 0.02) in plasma GH levels were present at the earlier time periods studied (1,5, and 15 minutes) following the infusion of TRH, but no at 30 or 60 minutes. These findings provide additional support for the non-specific action of TRH upon hte various adenohypophysial cell types, and demonstrate that TRH stimulates these cells by a direct action on the adenohypophysis.     

Estrogen-induced tumors: changes in the vasculature in two strains of rat

The influence of estrogen on the vasculature of the pars distalis has been studied in two strains of rat that differ in estrogen responsiveness. (Fischer 344 rats are highly estrogen-responsive in comparison to Sprague-Dawley rats.) Ovariectomized adults were implanted with silastic capsules containing 17 beta-estradiol benzoate. Control and experimental animals were sacrificed 10 and 20 days after implantation of the silastic capsules. Pituitary weights and plasma prolactin were elevated dramatically in estrogen-treated Fischer rats in comparison to more moderate increases in Sprague-Dawley rats. Although both strains exhibited the hypertrophy of mammotrophs expected after estrogen stimulation, the vasculature in Fischer rats were dramatically altered from normal. The pars distalis of the 20-day, estrogen-treated Fischer rats contained well-formed arteries. In addition, capillaries frequently were disrupted, contributing to the formation of hemorrhagic lakes unlined by an endothelium. Even in intact capillaries, basal laminae delimiting the pericapillary spaces often were disrupted or absent. Perivascular connective tissue cells were prominent within the perivascular spaces and often contained numerous, large lysosomal dense bodies as well as clusters of small dumbbell-shaped bodies. These granule clusters also were apparent adjacent to the perivascular space within parenchymal cells, most frequently within follicular cells. The vasculature of Sprague-Dawley rats maintained a more normal appearance after estrogen treatment, although perivascular connective tissue cells did appear activated and basal laminae delimiting the pericapillary spaces were disrupted occasionally. However, no capillaries were disrupted, nor were any hemorrhagic lakes evident, and no arteries were present.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of estradiol on aldosterone secretion in ovariectomized rats

The effects and action mechanisms of estradiol on aldosterone secretion in female rats were studied. Replacement of estradiol benzoate (EB) increased the levels of plasma estradiol and aldosterone in ovariectomized (Ovx) rats. The aldosterone release from zona glomerulosa (ZG) cells was higher in EB-treated rats than in oil-treated animals. EB treatment potentiated the responses of aldosterone release to adrenocorticotropic hormone (ACTH), forskolin (FSK), and 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP). Administration of EB in vivo did not alter cAMP production in response to ACTH or FSK. Although angiotensin II (Ang II) increased aldosterone secretion by rat ZG cells, the stimulatory effect of Ang II on the release of aldosterone was not altered by EB treatment. The conversions of [3H]-deoxycorticosterone to [3H]-corticosterone and [3H]-corticosterone to [3H]-aldosterone in EB-treated groups were greater than those in the oil-treated group. These results suggest that estradiol increases aldosterone secretion in part through the mechanisms involving the activation of the post-cAMP pathway, 11beta-hydroxylase and aldosterone synthase activity.