Long-Term Prolactin Exposure Differentially Stimulated the Transcellular and Solvent Drag-Induced Calcium Transport in the Duodenum of Ovariectomized Rats

Prolactin, having been shown to stimulate transcellular active and solvent drag-induced calcium transport in the duodenum of female rats, was postulated to improve duodenal calcium transport in estrogen-deficient rats. The aim of the present study was, therefore, to demonstrate the effects of long-term prolactin exposure produced by anterior pituitary (AP) transplantation on the duodenal calcium transport in young (9-week-old) and adult (22-week-old) ovariectomized rats. We found that ovariectomy did not alter the transcellular active duodenal calcium transport in young and adult rats fed normal calcium diet (1.0% w/w Ca) but decreased the solvent drag-induced duodenal calcium transport from 75.50 ± 10.12 to 55.75 ± 4.77 nmol·hr–1 cm–2 (P < 0.05) only in adult rats. Long-term prolactin exposure stimulated the transcellular active calcium transport in young and adult AP-grafted ovariectomized rats fed with normal calcium diet by more than 2-fold from 7.56 ± 0.79 to 16.54 ± 2.05 (P < 0.001) and 9.78 ± 0.72 to 15.99 ± 1.75 (P < 0.001) nmol·hr–1 cm–2, respectively. However, only the solvent drag-induced duodenal calcium transport in young rats was enhanced by prolactin from 95.51 ± 10.64 to 163.20 ± 18.03 nmol·hr–1 cm–2 (P < 0.001) whereas that in adult rats still showed a decreased flux from 75.50 ± 10.12 to 47.77 ± 5.42 nmol·hr–1 cm–2 (P < 0.05). Because oral calcium supplement has been widely used to improve calcium balance in estrogen-deficient animals, the effect of a high-calcium diet (2.0% w/w Ca) was also investigated. The results showed that stimulatory action of long-term prolactin on the transcellular active duodenal calcium transport in both young and adult rats was diminished after being fed a high-calcium diet. The same diet also abolished prolactin-enhanced solvent drag-induced duodenal calcium transport in young and further decreased that in adult AP-grafted ovariectomized rats. We concluded that the solvent drag-induced duodenal calcium transport in adult rats was decreased after ovariectomy. Long-term prolactin exposure stimulated the transcellular active duodenal calcium transport in both young and adult rats whereas enhancing the solvent drag-induced duodenal calcium transport only in young rats. Effects of prolactin were abolished by a high-calcium diet.

LPS-induced inflammation potentiates the IL-1β-mediated reduction of LH secretion from the anterior pituitary explants

Acting at the level of the brain, interleukin- (IL-)1 β is considered to be one of the most potent downregulators of reproduction processes during immune/inflammatory challenge. IL-1 β suppresses gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus resulting in the inhibition of the luteinizing hormone (LH) release from the anterior pituitary (AP). However, the presence of IL-1 β receptors in the AP suggests the possible direct action of this cytokine on LH secretion. The study was designed to determine the effect of IL-1 β on the LH secretion from the AP explants collected from saline and LPS-treated ewes in the follicular phase. It was found that IL-1 β suppressed (P ≤ 0.01) GnRH-stimulated LH release and LH β gene expression in AP explants in both groups. However, IL-1 β action was more potent in the explants collected from LPS-treated animals. Pituitaries from LPS-treated animals were characterized by increased (P ≤ 0.01) IL-1 type I receptor and decreased (P ≤ 0.01) GnRH receptor gene expression level compared to the saline-treated group. IL-1 β also affected the GnRH-R gene expression in explants collected from LPS-treated animals. Our results show that direct action of IL-1 β on the pituitary gonadotropes could be one of the reasons of the reproductive processes disorders accompanying an inflammatory state.

Transcriptome responses of duodenal epithelial cells to prolactin in pituitary-grafted rats

Chronic prolactin (PRL) exposure can affect several functions of duodenal epithelia, especially those associated with fluid and electrolyte transport. However, little is known regarding its molecular mechanism. To identify PRL-regulated genes, microarray analysis was performed on RNA samples from duodenal epithelial cells of anterior pituitary (AP)-grafted hyperprolactinemic rats. Herein, we identified 321 transcripts upregulated and 241 transcripts downregulated after 4 weeks of AP transplantation. Results from real-time PCR analyses of 15 selected genes were consistent with the microarray results. Gene ontology analysis demonstrated pleiotropic effects of PRL on several cellular processes, including cellular metabolic process, cell communication and cell adhesion. Interestingly, 17 upregulated transcripts and 12 downregulated transcripts are involved in the transport of ions and nutrients, e.g., Ca(2+), Na(+), K(+), Cl(-) and glucose, thus agreeing with the established action of PRL on electrolyte homeostasis. The present results provided fundamental information for further investigations on mechanism of PRL actions in the intestine.

Prolactin directly enhances bone turnover by raising osteoblast-expressed receptor activator of nuclear factor kappaB ligand/osteoprotegerin ratio

Hyperprolactinemia leads to high bone turnover as a result of enhanced bone formation and resorption. Although its osteopenic effect has long been explained as hyperprolactinemia-induced hypogonadism, identified prolactin (PRL) receptors in osteoblasts suggested a possible direct action of PRL on bone. In the present study, we found that hyperprolactinemia induced by anterior pituitary transplantation (AP), with or without ovariectomy (Ovx), had no detectable effect on bone mineral density and content measured by dual-energy X-ray absorptiometry (DXA). However, histomorphometric studies revealed increases in the osteoblast and osteoclast surfaces in the AP rats, but a decrease in the osteoblast surface in the AP+Ovx rats. The resorptive activity was predominant since bone volume and trabecular number were decreased, and the trabecular separation was increased in both groups. Estrogen supplement (E2) fully reversed the effect of estrogen depletion in the Ovx but not in the AP+Ovx rats. In contrast to the typical Ovx rats, bone formation and resorption became uncoupled in the AP+Ovx rats. Therefore, hyperprolactinemia was likely to have some estrogen-independent and/or direct actions on bone turnover. Osteoblast-expressed PRL receptor transcripts and proteins shown in the present study confirmed our hypothesis. Furthermore, we demonstrated that the osteoblast-like cells, MG-63, directly exposed to PRL exhibited lower expression of alkaline phosphatase and osteocalcin mRNA, and a decrease in alkaline phosphatase activity. The ratios of receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG) proteins were increased, indicating an increase in the osteoclastic bone resorption. The present data thus demonstrated that hyperprolactinemia could act directly on bone to stimulate bone turnover, with more influence on bone resorption than formation. PRL enhanced bone resorption in part by increasing RANKL and decreasing OPG expressions by osteoblasts.

Vascularization of rat pituitary autografts

Pituitary autotransplantation eliminates direct vascular contact between the hypothalamus and the adenohypophysis, and enables us to study the role of the hypothalamus in regulating adenohypophysial endocrine activity. The aim of this study was to investigate vascularization of the pituitary autografts. Three-month-old male Wistar rats were hypophysectomized, and their adenohypophyses were autotransplanted under the renal capsule. The animals were killed 3 weeks after autotransplantation. The grafts were removed and studied by using histology, immunohistochemistry and transmission electron microscopy. In the central portion of the grafts, organizing necrosis was apparent. The peripheral portion of the graft contained all adenohypophysial cell types, with a predominance of lactotrophs. Vascular endothelial growth factor and hypoxia-inducible factor were expressed in the graft mainly in the perinecrotic areas. Several capillaries inside the grafts were lined by continuous unfenestrated epithelium, while others were lined by fenestrated endothelium, suggesting that neovascularization is the result of two processes: ingrowths of capillaries from the renal capsule to the graft, and neoformation of capillaries from pre-existing adenohypophysial vessels. In conclusion, hypoxia seems to be an important factor in the vascularization of pituitary autografts. Mediated via hypoxia-inducible factor, hypoxia stimulates vascular endothelial growth factor secretion, which plays a crucial role in angiogenesis.

Prostate response to prolactin in sexually active male rats

BACKGROUND

The prostate is a key gland in the sexual physiology of male mammals. Its sensitivity to steroid hormones is widely known, but its response to prolactin is still poorly known. Previous studies have shown a correlation between sexual behaviour, prolactin release and prostate physiology. Thus, here we used the sexual behaviour of male rats as a model for studying this correlation. Hence, we developed experimental paradigms to determine the influence of prolactin on sexual behaviour and prostate organization of male rats.

METHODS

In addition to sexual behaviour recordings, we developed the ELISA procedure to quantify the serum level of prolactin, and the hematoxilin-eosin technique for analysis of the histological organization of the prostate. Also, different experimental manipulations were carried out; they included pituitary grafts, and haloperidol and ovine prolactin treatments. Data were analyzed with a One way ANOVA followed by post hoc Dunnet test if required.

RESULTS

Data showed that male prolactin has a basal level with two peaks at the light-dark-light transitions. Consecutive ejaculations increased serum prolactin after the first ejaculation, which reached the highest level after the second, and started to decrease after the third ejaculation. These normal levels of prolactin did not induce any change at the prostate tissue. However, treatments for constant elevations of serum prolactin decreased sexual potency and increased the weight of the gland, the alveoli area and the epithelial cell height. Treatments for transient elevation of serum prolactin did not affect the sexual behaviour of males, but triggered these significant effects mainly at the ventral prostate.

CONCLUSION

The prostate is a sexual gland that responds to prolactin. Mating-induced prolactin release is required during sexual encounters to activate the epithelial cells in the gland. Here we saw a precise mechanism controlling the release of prolactin during ejaculations that avoid the detrimental effects produced by constant levels. However, we showed that minor elevations of prolactin which do not affect the sexual behaviour of males, produced significant changes at the prostate epithelium that could account for triggering the development of hyperplasia or cancer. Thus, it is suggested that minute elevations of serum prolactin in healthy subjects are at the etiology of prostate abnormal growth.

Folliculostellate cells determine the susceptibility of lactotropes to estradiol's mitogenic action

Estradiol is known to increase lactotropic cell proliferation, but estradiol susceptibility varies among human populations and among various strains of rats. We had reported that folliculostellate (FS) cells regulate estradiol's mitogenic action on lactotropes; therefore, we studied their role in determining the susceptibility to estradiol in a high estradiol-responsive rat strain, Fischer 344 (F344), and in a low-responsive strain, Sprague Dawley (SD). Determination of total S-100-positive FS cells in the pituitary revealed that F344 rats have significantly more FS cells than do SD rats. Estradiol treatment did not change the number of FS cells in both F344 and SD rats. When cotransplanted with F344 pituitaries under the kidney capsule or cocultured with F344-derived lactotropes in vitro, FS cells derived from F344 rats increased estradiol's mitogenic action. They also increased estradiol's mitogenic action on SD-derived lactotropes in primary cultures. However, SD-derived FS cells failed to increase estrogen's action on F344- or SD-derived lactotropes. The levels of basic fibroblast growth factor production and secretion by TGF-beta 3 and estradiol were much higher in F344-derived FS cells than in SD-derived FS cells. However, the lactotropes' growth response to basic fibroblast growth factor was similar in both strains. These data suggest that cell-cell interaction between FS cells and lactotropes regulates estradiol's mitogenic action on lactotropes and also determines lactotrope susceptibility to the steroid.

Increase in the number of integrinbeta1-immunoreactive monocyte-lineage cells in experimentally-induced adenomyosis in mice

Uterine adenomyosis is a disease in which hyperplastic endometrial stroma and glands invade the myometrium. We have previously demonstrated that hyperprolactinemia leads to the development of adenomyosis in mice. In the present study, a subtracted cDNA library was made by suppression subtractive hybridization to find specific genes that are abundantly expressed in the adenomyotic but not normal tissue in mice. A cDNA fragment of integrinbeta1 (ibeta1) was found in the library, and the expression of the gene product was increased in the adenomyotic uteri at mRNA and protein levels. Intense ibeta1-immunoreactivity was localized on a group of cells dispersing throughout the endometrial stroma. The number of ibeta1-immunoreactive (ibeta1-ir) cells was significantly greater in the uteri of mice with adenomyosis than normal mice. The majority of the ibeta1-ir cells expressed CD14-ir signal, a marker for monocyte-lineage cells, whereas an increase in the number of CD14-ir cells was also evident in the adenomyotic uteri, especially in the ectopic endometrial tissue. Thus, the adenomyotic stromal tissue contained numerous monocyte-lineage cells with higher expression levels of ibeta1, one of their products. The relationship between the increased number of monocyte-lineage cells and the hyperplastic proliferation of endometrial tissues was discussed with a view to understanding the progressive mechanism of adenomyosis.

Priming effects of novel nonsteroidal progesterone receptor modulators CP8816 and CP8863 on the development of adenomyosis in the mouse uterus

The possibility of therapeutic application of novel nonsteroidal progesterone receptor modulators CP8816 and CP8863 for preventing the development of uterine adenomyosis was investigated in mice. First priming effects of CP8816 on 17beta-estradiol (E2)-induced cell division in uterine tissues were examined. As a result, pretreatment with CP8816 or progesterone significantly suppressed the elevation of the mitotic activity in the luminal epithelial cells of mice treated with E2 later. Priming with CP8816 had little effect on the stromal cells, but progesterone priming caused an increase of stromal mitotic activity in mice treated with E2 later. To evaluate the inhibitory effect of these compounds on the development of adenomyosis induced experimentally by pituitary grafting, 7-week-old female mice were isografted with a single anterior pituitary in the uterus and divided into four groups. Two groups of mice were given daily subcutaneous injections of 1 mg of CP8816 or the vehicle alone for 6 weeks from the day after the grafting. Remaining two groups of mice were given oral administration of 1 mg of CP8863 or the vehicle only for 5 weeks starting one week after the grafting. The incidence of adenomyosis was significantly lower in the groups of mice treated with CP8816 and CP8863 than in the respective control groups. The mechanism by which CP compounds inhibited the development of adenomyosis might be related to their priming effects, i.e., their inhibitory effect on epithelial cell division and lack of effect on stromal cell division after subsequent exposure to E2.

Are folliculo-stellate cells in the anterior pituitary gland supportive cells or organ-specific stem cells?

Folliculo-stellate cells (FS-cells) in the anterior pituitary gland are star-shaped cells and form tiny follicles. FS-cells are positive for S-100 protein and produce many cytokines or growth factors, such as interleukin-6 (IL-6), leukemia inhibitory factor (LIF), basic fibroblastic growth factor (bFGF) and vascular endothelial cell growth factor (VEGF). Therefore, it is generally accepted that FS-cells regulate endocrine cells through these growth factors. FS-cells also exhibit a phagocytotic activity and are known to work as scavenger cells. In addition to these functions, FS-cells are considered to have some unknown functions. In order to reveal the biological significance of FS-cells in the anterior pituitary gland, we performed a morphological study and obtained some new findings. First, we were interested in the colloid formation in the senescent porcine pituitary gland. We analyzed the colloids and found that clusterin is a major protein in them. We also found that the accumulation of clusterin in the colloids is related to the phagocytotic activity of FS-cells. In our next study, we found that FS-cells have the potential to differentiate into striated muscle cells. From FS-cells show multi-potent cell character and other cytological evidence, we propose that FS-cells are candidate of organ-specific stem cells in the anterior pituitary gland.

Stimulatory effects of hyperprolactinemia on aldosterone secretion in ovariectomized rats

BACKGROUND

To evaluate the effects of hyperprolactinemia on aldosterone secretion and its mechanisms of action in ovariectomized (OVX) rats.

METHODS

Hyperprolactinemia was induced by the transplantation of rat anterior pituitary (AP) glands under the kidney capsule for 6 weeks in female rats. Control rats underwent cerebral cortex (CX) transplantation. Four weeks after transplantation, the rats were OVX 2 weeks before decapitation. After decapitation, the trunk blood was collected, and the adrenal glands of CX- and AP-grafted rats were prepared as zona glomerulosa (ZG) cells for in vitro study.

RESULTS

Plasma prolactin and aldosterone in the rats were increased by AP gland transplantation. In the in vitro study, the basal aldosterone secretion by the adrenal ZG cells was higher in AP-grafted rats than in CX-grafted rats. The AP-grafted group showed increased responsiveness to angiotensin II (10(-8) M), KCl (8 x 10(-3) M), or 8-bromo-adenosine 3',5'-cyclic monophosphate (8-br-cAMP; 10(-4) M, a membrane-permeable analogue of cAMP) with regard to aldosterone secretion as compared with the CX-grafted group. N-(2-[p-Bromocinnamylamine]ethyl)-5-isoquinolinesulfonamide (H89; 10(-6), 10(-5) M, a protein kinase A inhibitor) or tetrandrine (10(-5) M, a blocker for both L-type and T-type Ca2+ channels) induced a greater suppression of aldosterone secretion in the AP-grafted group than in the CX-grafted group. No significant differences between the CX- and AP-grafted groups were observed, however, with regard to the adrenocorticotropichormone (10(-9) M)-, forskolin (10(-5) M, an adenylyl cyclase activator)-, or nifedipine (10(-5) M, an L-type Ca2+ channel blocker)-induced responsiveness of aldosterone secretion. In addition, there was no difference in the expression of desmolase (i.e., cytochrome P450 side-chain cleavage enzyme) in ZG cells between AP- and CX-grafted rats. The conversions of 25-OH-cholesterol into pregnenolone in the presence of trilostane (an inhibitor of 3beta-hydroxysteroid dehydrogenase) and corticosterone into aldosterone, as well as the expression of the steroidogenic acute regulatory protein in ZG cells, were greater in AP-grafted rats than in CX-grafted rats.

CONCLUSIONS

These results suggest that hyperprolactinemia increases basal, angiotensin II- and KCl-stimulated aldosterone secretion by ZG cells in OVX rats through activation of T-type Ca2+ channels, the post-cAMP and protein kinase A pathway, cytochrome P450 side-chain cleavage enzyme, and aldosterone synthase, as well as by causing increased expression of steroidogenic acute regulatory protein in ZG cells.

Effect of hyperprolactinemia induced by pituitary grafts or castration on porphyrin content of the mouse Harderian gland

The histology and porphyrin concentrations of Harderian glands and plasma prolactin levels were examined in B6C3F1 mice castrated or isografted with pituitaries in combination with the administration of bromocriptine (2-bromo-á-ergocryptine), a potent suppressor of prolactin. Four pituitaries were transplanted underneath the bilateral kidney capsules of each mouse. Furthermore, we investigated Harderian porphyrins and plasma testosterone levels in mice that were castrated or treated with neuroleptic butyrophenone (timiperone), a potent accelerator of prolactin, and treated concurrently with bromocriptine. Light microscopically, pituitary grafts increased the concretion of porphyrin pigments within the Harderian gland lumina. Pituitary grafts or castration increased both Harderian porphyrin concentrations and plasma prolactin levels compared with the intact control mice. In pituitary-grafted or castrated mice, bromocriptine distinctly prevented the rise in both porphyrins and prolactin levels. Administration of butyrophenone did not result in any marked change in testosterone levels, although Harderian gland porphyrins were significantly increased. The present results indicate that in mice prolactin stimulates the porphyrin production of the Harderian gland and has an important role in the regulation of Harderian gland porphyrins.

Prolactin and cyclosporine modulate adenosine transporters and adenosine A1 receptors in the rat brain

The existence of adenosine A1 receptors and adenosine transporters in the central nervous system has been well demonstrated, although their possible modulation by hormones and/or exogenous drugs is poorly understood. To further analyze these modulatory mechanisms, the effects of prolactin and cyclosporine (CyA) on adenosine A1 receptors and transporters were analyzed in the central nervous system. For this purpose the number and affinity of adenosine A1 receptors were measured using the specific antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and the transporters with the high affinity ligand nitrobenzylthioinosine (NBTI). This procedure was carried out in hyperprolactinemic and control male rats treated with CyA or its vehicle for 8 days. As expected, pituitary grafting increased plasma prolactin levels (p<0.01). CyA treatment reduced but did not normalize (p<0.05) this parameter in hyperprolactinemic rats and did not modify circulating prolactin in control animals. Both hyperprolactinemia and CyA treatment reduced the number of adenosine transporters by 70% and by 40% the number of A1 receptors. The Kd for transporters was also reduced in all experimental groups. Hyperprolactinemia increased the affinity of A1 receptors (p<0.01) and CyA treatment did not further modify this parameter. These data demonstrated that prolactin and CyA influence adenosine transporters and A1 receptors at the central nervous system and suggest the existence of an interaction between prolactin and CyA may be operating to modulate these processes.

Paradoxical effect of imipramine in hyperprolactinemic female rats exposed to the forced swimming test

This study was designed to investigate the effect of hyperprolactinemia, with high or low estrogen levels, on the response to imipramine in the forced swimming test. Three groups of female rats were studied: (1) ovariectomized controls, with low serum prolactin (PRL) and estrogen levels, (2) ovariectomized, estrogen-treated rats, with high PRL and high estrogen levels, and (3) pituitary-grafted rats, with high PRL and low estrogen levels. The hyperprolactinemic groups did not show significant behavioral changes in the forced swimming test preceded by saline injection. Imipramine decreased the immobility time by 37.5% in ovariectomized controls but not in the pituitary-grafted group, and there was an increment of 48.4% in immobility time following imipramine administration in the estrogen-treated group (p<0.05). This paradoxical response to imipramine was significantly correlated with serum PRL (r = 0.59, p<0.01) but not with estradiol levels. These findings suggest that, at least in female rats submitted to the forced swimming model, PRL may induce reversed behavioral effects in response to imipramine, independently of circulating estrogen levels.

Direct effects of prolactin on corticosterone release by zona fasciculata-reticularis cells from male rats

The role of prolactin (PRL) in the male is not fully defined. The aim of this study was to investigate the function and mechanism of PRL on the production of corticosterone by zona fasciculata-reticularis (ZFR) cells in vitro. The ZFR cells were obtained from male rats under normal, hyperprolactinemic, or hypoprolactinemic situation. PRL stimulated the corticosterone release in a dose-dependent pattern in the ZFR cells from normal male rats. The cellular adenosine 3'-5'-cyclic monophosphate (cAMP) concentration positively correlated with PRL concentration in the presence of forskolin or 3-isobutyl-1-methylxanthine (IBMX). PRL enhanced the stimulatory effects of cAMP mimetic reagents, i.e., forskolin, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP), and IBMX on the release of corticosterone. The adenylate cyclase inhibitor (SQ22536) inhibited the corticosterone release in spite of presence of PRL. Nifedipine (L-type calcium channel blocker) did not inhibit corticosterone release. The hyperprolactinemic condition was actualized by transplantation of donor rat anterior pituitary glands (APs) under kidney capsule. By comparison with the cerebral cortex (CX)-grafted group, AP-graft resulted in an increased release of corticosterone, 3beta-hydroxysteriod dehydrogenase (HSD) activity and cAMP production by ZFR cells. Acute hypoprolactinemic status was induced by bromocriptine for 2 days. The results showed the productions of corticosterone were lower in hypoprolactinemic group than in control group, which were persistent along with different ACTH concentrations. These results suggest that PRL increase the release of corticosterone by ZFR cells via cAMP cascades and 3beta-HSD activity.

Effects of hyperprolactinemia on calcitonin secretion in male rats

The role of prolactin (PRL) in calcitonin (CT) release by the thyroid C cell in male rats was studied. Anterior pituitary (AP)-grafted male rats were characterized by hyperprolactinemia. Brain cortex (CX)-grafted male rats were used as control animals. AP- and CX-grafted rats were infused intravenously with CaCl2 and bled from the jugular catheter at 0, 30, 60, and 120 minutes following the CaCl2 challenge. Rat thyroid gland was incubated with or without 3-isobutyl-1-methylxanthine (IBMX) at 37 degrees C for 30 minutes. Thyroid C cells were incubated in culture medium at 37 degrees C for 60 minutes. Cyclic adenosine 3',5'-monophosphate (cAMP) in rat thyroid tissues following incubation with IBMX was extracted by 65% ethanol. AP-grafted rats had higher plasma levels of PRL and CT compared with CX-grafted rats. Both the release of CT and accumulation of cAMP in thyroid glands were higher in AP-grafted versus CX-grafted rats. Direct administration of ovine PRL (oPRL) on the thyroid glands did not increase CT secretion in vitro. Thyroid C cells of AP-grafted rats secreted more CT compared with CX-grafted rat cells. These results suggest that hyperprolactinemia increases the release of CT by thyroid C cells in rats through a cAMP-dependent pathway caused by an indirect effect of PRL.

Age-related differences in the secretion of calcitonin in female rats

The mechanism that causes hypercalcitonemia in female rats and is associated with aging was investigated. Young (3 mo), adult (8 mo), middle-aged (12 mo), and old (21 mo) rats were infused with CaCl2 and were bled from a jugular catheter after a CaCl2 challenge. To mimic some of the hormonal changes caused by aging, the anterior pituitary (AP)-grafted ovariectomized rats with hyperprolactinemic syndrome were used to mimic the physiological status of aging. The rat thyroid gland was incubated with or without ovine prolactin (oPRL; 40 or 80 ng/ml) at 37 degreesC for 30 min. Old rats possessed the lowest levels of plasma estradiol and progesterone yet had the highest levels of plasma prolactin and calcitonin (CT) compared with young, adult, and middle-aged rats. The basal release of thyroid CT in vitro in thyroid glands gradually increased with age. Compared with cortex (CX)-grafted rats, the AP-grafted rats possessed higher levels of plasma PRL, basal and CaCl2-induced levels of plasma CT, and the release of thyroid CT in thyroid glands. After stimulation with oPRL, the in vitro release of thyroid CT increased in both CX- and AP-grafted rats. These results suggest that the hypersecretion of CT in old rats is due at least in part to hyperprolactinemia.

Animal model of uterine adenomyosis: induction of the lesion in rats by ectopic pituitary isografting

Adenomyosis is a benign pathologic disorder of the uterine endometrial tissues whereby endometrial components, such as glands and stroma, invade the myometrium. Transplantation of a single anterior pituitary gland into the uterine lumen induced adenomyosis in six of eight Wistar rats 12 months after the grafting. Adenomyotic changes were not observed in six sham-operated control rats. Electron microscopic observations indicated that cells of the inner layer of the myometrium were reduced in size and irregularly shaped in the areas bearing adenomyotic changes. In pituitary-grafted rats, healthy corpora lutea remained in the ovaries, whereas control rats had degenerating ovaries. These findings are consistent with the results of pituitary-grafted mice reported previously and support our assertion that a hormonal milieu induced by pituitary grafting is favorable for development of uterine adenomyosis.

Effect of melatonin on serum cholesterol and phospholipid levels, and on prolactin, thyroid-stimulating hormone and thyroid hormone levels, in hyperprolactinemic rats

The effects of melatonin treatment and pituitary transplants on serum total and free cholesterol levels, cholesterol esterification index, phospholipid levels and prolactin, thyroid-stimulating hormone (TSH), thyroxine (T4) and triiodothyronine (T3) levels were examined in rats. Male rats were grafted an anterior pituitary under the kidney capsule or were sham-operated on day 30th of life. Thirty days later, the rats received 4 daily s.c. injections of melatonin (25, 50 or 100 microg/rat) or vehicle, 2 h before lights off, and were killed 15 h after the last injection, and after a 24-hour fasting period. In pituitary-grafted rats, a decrease in serum free cholesterol with unmodified total cholesterol levels, and thus an augmented cholesterol esterification index, occurred. Pituitary-grafted rats showed also an increase in serum phospholipids. In control, but not in pituitary-grafted rats, melatonin injection decreased free cholesterol without modifying total cholesterol levels. Melatonin treatment (50 microg/day or greater) normalized the augmented serum phospholipid levels found in pituitary-grafted rats and increased serum phospholipids in control rats. Melatonin injection also reduced the high serum prolactin and T3 levels found in pituitary-grafted rats, and decreased T4 concentration in control rats. Neither melatonin nor pituitary grafts modified serum TSH concentration. The results demonstrate that melatonin counteracts in part lipid disturbances of hyperprolactinemic rats and lowers free plasma cholesterol and augmented serum phospholipids in control rats.

Sleep in rats rendered chronically hyperprolactinemic with anterior pituitary grafts

A hyperprolactinemic rat model [rats bearing anterior pituitary grafts under the capsule of the kidney (AP-grafted rats)] was used to study sleep-wake activity and cortical brain temperature (T(crt)). Fisher 344 male rats (n = 24) were implanted with anterior pituitaries from rat pups; the control rats (n = 12) were sham-operated. Sleep-wake activity and T(crt) were recorded for 2 days between weeks 3 and 7 after surgery. The hyperprolactinemic state of the rats was confirmed by plasma prolactin (PRL) assays on week 7 and by determination of PRL mRNA levels in the anterior pituitary of the AP-grafted rats. Neither growth hormone plasma concentration nor pituitary mRNA levels were affected by the pituitary grafts. Duration of non-rapid eye movement sleep (NREMS) was slightly enhanced in the AP-grafted rats. A large increase in rapid eye movement sleep (REMS) during the 12-h light period was the major effect of the implantation of the extra pituitaries. Both the duration and the frequency of the REMS episodes increased and persisted for weeks 4-7 post-implantation. The nocturnal states of vigilance, T(crt), and intensity of NREMS (EEG slow wave activity) were not altered. The results clearly indicate that the enhancements in REMS persist during hyperprolactinemia, and support the hypothesis that PRL possesses REMS-promoting activity.

Regulation of anterior pituitary galanin and vasoactive intestinal peptide by oestrogen and prolactin status

The neuropeptides vasoactive intestinal peptide (VIP) and galanin are synthesized in the anterior pituitary, galanin in the lactotroph and VIP probably in another cell type, and both stimulate prolactin secretion. Oestrogen regulates anterior pituitary VIP and galanin, galanin expression reflecting physiological variation in oestrogen status, whilst VIP is induced by pharmacological concentrations of oestrogen. Implanting anterior pituitaries under the renal capsule to induce hyperprolactinaemia we studied the regulation of anterior pituitary VIP and galanin synthesis and storage by prolactin and its interaction with oestrogen status. Five groups of animals were studied: control, hypophysectomized implanted, implanted, hyperoestrogenized (oestradiol-17 beta; 250 micrograms/day) and hyperoestrogenized implanted. Spontaneously cycling animals were followed through two cycles prior to implanting and were maintained for at least 1 week and then killed once they were in dioestrus. Circulating prolactin levels were significantly elevated in implanted animals but not in hypophysectomized implanted animals compared with controls. There was a more marked increase in prolactin levels in hyperoestrogenized animals and hyperoestrogenized implanted animals, with no significant difference between these two groups. Native anterior pituitary galanin and VIP content was suppressed in implanted animals, and markedly increased in hyperoestrogenized animals. Pituitary implantation only marginally reduced the effect of hyperoestrogenization on galanin content but abolished the effect of hyperoestrogenization on VIP content. Implant peptide content was suppressed to less than 10% of native anterior pituitary content. Galanin was not detected in implants from hypophysectomized-implanted animals but implant VIP content was unaffected by hypophysectomy. VIP content was increased in implants from hyperoestrogenized implanted animals but implant galanin content was unaffected by hyperoestrogenization. Peptide mRNA levels changed in parallel with peptide content except that the implant galanin mRNA levels were increased by hyperoestrogenization. Thus it appears that prolactin negatively regulates anterior pituitary galanin and VIP gene expression and content, probably due to a direct effect on the anterior pituitary and by altered secretion of hypothalamic factors. Oestrogen is a potent stimulus to expression of both peptide genes. Its positive effect on anterior pituitary peptide gene expression and content is greatly diminished by the effect of implant-induced hyperprolactinaemia, suggesting that circulating prolactin levels may be controlled by a negative feedback effect of prolactin on galanin and VIP. A similar effect of hyperoestrogenization is observed in the implants, except that galanin content remains at a low level, suggesting that the combination of hyperoestrogenization and the absence of dopamine may lead to uncontrolled release of high levels of galanin.

Age-dependent effect of pituitary transplants on immune responses in rat spleen: modulatory effect of cyclosporine

Male rats were grafted an anterior pituitary within breast muscles on day 5 or under the kidney capsule on day 30 or 60 of life. On the 70th day of life (rats operated on the 5th or 30th day) or on the 100th day of life (rats operated on the 60th day), rats were injected subcutaneously with Freund's complete adjuvant, being killed 2 days later. Rats that had received a pituitary graft on the 30th day showed a greater degree of hyper-prolactinemia than rats grafted on the 5th or 60th day. Analyzed as main factors in a factorial analysis of variance (ANOVA), pituitary transplants augmented splenic natural killer (NK) activity and lipopolysaccharide (LPS)- and concanavalin A (Con A)-induced cell proliferation, and decreased splenic cell number. As indicated by significant interactions between treatment and age of transplantation in a factorial ANOVA, splenic NK activity augmented in rats grafted on the 30th day of life, while LPS and Con A splenic cell proliferation augmented in rats grafted neonatally. Spleen cellularity decreased after pituitary transplants in 30- and 60-day-old rats. In a second study, the effect of cyclosporine on spleen immune responses was tested by administering cyclosporine (5 mg/kg) or vehicle to rats grafted as in experiment 1 for 5 days before sacrifice. Cyclosporine decreased splenic NK activity and LPS- and Con A-induced cell proliferation regardless of the presence of a pituitary graft. In rats grafted on the 30th day of life, cyclosporine reversed the effect of pituitary grafts on splenic NK activity, and ectopic pituitary augmenting NK activity in vehicle-treated rats while decreasing it in cyclosporine-injected rats. Cyclosporine reversed the inhibitory effect of pituitary transplants on spleen cell number. The high circulating prolactin levels found in rats with pituitary grafts were decreased by cyclosporine administration. The results are compatible with age-dependent promoting and inhibitory effects of hyperprolactinemia on the immune responses of the spleen, which were antagonized by cyclosporine immunosuppression.

Possible interactions of cyclosporine and hyperprolactinemia modulating the episodic secretion of prolactin

The interrelationship between the effects of prolactin and cyclosporine (CsA) appears to be very complex and until now poorly understood. The aim of the present work was to analyze whether chronic treatment with CsA could modify the episodic secretion of prolactin in male rats and whether the presence of an ectopic pituitary could counteract the effects of the drug on the pulsatile secretion pattern of this hormone. At 30 days of age, male rats were implanted with one anterior pituitary under the kidney capsule or where sham-operated. Both pituitary-grafted and sham-operated rats were injected sc for 30 days with the vehicle or CsA (5 mg/kg/day), beginning on the day of surgery. Pituitary grafting and/or CsA administration changed the pulsatile secretion pattern of prolactin. In pituitary-grafted male rats, mean serum prolactin levels, absolute pulse amplitude, and half-life of the hormone increased, while the pulse frequency decreased, compared with the values found in sham-operated rats. CsA administration to sham-operated rats increased the relative amplitude of prolactin peaks and diminished the half-life of the hormone, compared with rats of the same group treated with vehicle. However, CsA treatment in pituitary grafted rats led to lower mean serum prolactin levels and absolute amplitude, while the frequency, duration, and relative amplitude of prolactin pulses were not modified. Plasma prolactin levels did not change in control animals, whereas a reduction in circulating values of the hormone was found in pituitary grafted animals. These data suggest that CsA modifies the pulsatile secretory pattern of prolactin in pituitary-grafted male rats. The different effects observed in the control and pituitary-grafted animals might be due to a direct effect of the drug on the ectopic lactotrophs that are submitted to local regulatory influences different from those of the in situ pituitary which are submitted to the regulatory influence of the hypothalamus.

Effects of cyclosporine on circulating levels of prolactin, LH, FSH, TSH and GH in chronic hyperprolactinemic male rats

The effects of cyclosporine (CyA) on pituitary hormone secretion in animals with previously high plasma prolactin levels have been studied. Hyperprolactinemia was either induced in 30 day old male rats by the transplantation of one anterior pituitary gland from a litter mate donor or they were sham-operated to be used as controls. Both pituitary-grafted and sham-operated animals were injected s.c. with the vehicle or CyA (5 mg/kg weight per day) for 10 days, beginning 30 days after surgery. As expected, pituitary grafting markedly increased plasma prolactin levels as compared with the values found in control animals. Hyperprolactinemia was associated with reduced plasma LH and GH levels, increased plasma TSH levels and with no changes in circulating FSH levels. CyA administration to control animals increased plasma prolactin and TSH levels, decreased plasma levels of LH and did not modify circulating values of FSH and GH. Furthermore, CyA administration to pituitary-grafted animals decreased plasma prolactin and TSH levels, whereas plasma concentrations of GH and gonadotropins did not change. These data suggest that CyA differentially affect the release of pituitary hormones and that there is an interrelationship between previously high plasma prolactin levels and CyA to modulate pituitary hormone secretion.

Cell proliferation and apoptosis during mammary carcinogenesis in pituitary isografted mice

In the present study, pituitary isografted animals serve as a model for evaluating the changes in differentiation, cell proliferation and programmed cell death (apoptosis) in mammary epithelial cells during carcinogenesis. The percentage of bromodeoxyuridine (BrdU)-labeled ductal and alveolar cells was significantly higher in pituitary isografted animals than in non-isografted control animals. BrdU-labeled cells increased in lobular hyperplastic nodules, keratinized nodules and mammary carcinomas; similar changes were observed with apoptotic cells, which were rare in mammary glands of adult non-isografted animals (one to three apoptotic cells per 2000 mammary epithelial cells), but their number increased in hyperplastic lesions and mammary carcinomas. Among hyperplastic nodular lesions, variants with high, moderate and low proliferative activity and/or apoptotic cell death were identified, which suggests that they may have different growth potentials and different propensities for malignant transformation. After removing pituitary isografts, apoptosis occurs in hyperplastic lesions but not in mammary carcinomas-implying that malignant tumors are hormone-independent. The dynamics of the changes in apoptotic cell death among various hyperplastic lesions after removal of pituitary isografts suggests that these lesions are composed of heterogeneous cell populations, as far as the initiation of apoptosis is concerned. Our data indicate that apoptosis can be used together with cell proliferation as a potential marker in characterizing the growth potential and phenotypic diversity of hyperplastic, premalignant and malignant mammary gland lesions.

Adenohypophysial allografts releasing prolactin decrease prolactin mRNA concentration in the host hamster's adenohypophysis in situ

The inhibitory effects of pituitary allografts on the prolactin (PRL)-secretory system are presumed to be consequences of the unabated release of PRL by the allografts. In the present studies we used pituitary allografts in the Golden Syrian hamster to address the following questions: (a) Do allografts of adult adenohypophysial tissue which elevate serum PRL levels decrease the concentration of PRL mRNA in the host's adenohypophysis? (b) Is this effect shared by allografts of neonatal hypophysial tissue or neonatal muscle tissue which do not elevate serum PRL levels? (c) Do any of these types of allograft alter growth hormone mRNA in the host's adenohypophysis? Prolactin mRNA concentration, but not growth hormone mRNA concentration, was decreased in the adenohypophyses in situ in the hosts bearing adult adenohypophysial allografts in which serum PRL levels were elevated. In contrast, serum PRL in hosts with neonatal hypophysial or muscle allografts were not elevated and PRL mRNA levels in the adenohypophysis in situ were not decreased when compared to the levels measured in hamsters with sham transplants. Prolactin mRNA levels in hosts with neonatal muscle allografts were not different from levels in hosts with neonatal hypophysial allografts but were increased when compared to the levels measured in hamsters with sham transplants. There were no differences in PRL concentration in the adenohypophyses in situ between any of the groups. Also, PRL concentrations in neonatal hypophysial allografts were similar to those in adult adenohypophysial allografts. To our knowledge these observations are the first demonstrating that short-loop feed-back of PRL includes a decrease in PRL mRNA concentration. The observations also support the working hypothesis that PRL and not another pituitary factor exerts the negative feedback.

N-Ethyl-N-nitrosourea induces mammary cancers in the pituitary-isografted mouse which are histologically and genotypically distinct from those induced by N-methyl-N-nitrosourea

N-Ethyl-N-nitrosourea (ENU) and N-methyl-N-nitrosourea (MNU) are alkylating agents which respectively ethylate or methylate nucleophilic centers in the cell such as DNA. In vitro studies with naked DNA and bacterial mutagenesis assays suggest that these two compounds induce different spectra of genetic lesions. In addition, the ethyl-DNA adducts induced by ENU persist longer than the methyl-DNA adducts induced by MNU. Since MNU is a known mammary carcinogen in the pituitary-isografted mouse, these data suggest that ENU may be an even more potent carcinogen than MNU. The purpose of this study was to determine whether ENU was a mammary carcinogen in the pituitary-isografted mouse and if so, to compare the genotype and phenotype of ENU-induced mammary tumors with those induced by MNU. Fifteen adult female virgin BALB/c mice were isografted with two pituitaries and subsequently treated with a single intravenous injection of ENU (50 micrograms/g body weight). Mammary adenocarcinomas arose in all of the survivors (n=12) with a median latency of 27 weeks and a mean frequency of 1.4 cancers per mouse. When tumor DNA was analyzed for mutations in the 12th and 61st codons of c-Ki-ras or c-Ha-ras protooncogenes, only wild type sequences were found. This is in contrast to MNU which causes a G to A transition mutation in the 12th codon of the c-Ha-ras proto-oncogene in about one of five mammary cancers induced in pituitary-isografted mice. Furthermore, the ENU-induced tumors were solid viable papillary adenocarcinomas, whereas MNU induced tumors are highly necrotic adenocarcinomas with squamous metaplasia. These results demonstrate that, in the pituitary-isografted mouse, ENU is as potent a mammary carcinogen as MNU and suggest that oncogenes other than c-Ki-ras or c-Ha-ras may be involved in ENU-induced mammary cancers.

Changes in percentages of adenohypophysial gonadotrophs associated with the sex-specific, selective increase in serum follicle-stimulating hormone concentration in the juvenile female hamster

In normal hamsters, we investigated whether the sex-specific, selective increase in serum FSH concentration in the juvenile female was associated with sex-specific changes in the percentages of adenohypophysial gonadotrophs. Serum LH concentrations did not rise between Day 4 and Day 19 in either sex and did not differ significantly between the sexes on Days 4, 7, 12, 14, and 19 after birth. Serum FSH concentrations were about 2-fold higher on Days 7, 12, and 14 than on Days 4 or 19 in males. In females, serum FSH rose markedly between Days 4 and 7, declined slightly by Day 12, rose to peak levels by Day 14, and declined slightly by Day 19 to levels not different from those seen on Day 7. Body weights rose between Days 4 and 19 and were similar in both sexes. There were no sex differences in pituitary gland weights, which rose between Days 4 and 12 and did not increase significantly further by Day 19. On Day 0, the percentages of immunoreactive LH and FSH cells were about 6 and 1%, respectively, in both sexes. These percentages increased progressively between Days 0 and 7 and between Days 7 and 14. On Day 7, but not on Day 14, the percentages of LH and FSH cells were greater in females than in males. There were more LH than FSH cells in males on Days 0, 7 and 14, and in females on Day 0 but not on Day 7 or 14. Matching of 10 FSH cells per gland with LH cells in serial sections of each of 30 glands showed FSH immunoreactivity to occur only in cells staining for LH. In hypophysectomized-gonadectomized adult hamster hosts with allografts of neonatal pituitary glands beneath the renal capsule, we investigated whether these sex-specific changes in the percentage of cells might be predetermined by the time of birth or dependent on sex differences in the internal environment existing in the postnatal hamster. Groups consisted of male donors-male hosts, male donors-female hosts, female donors-female hosts, and female donors-male hosts. The percentages of LH cells in allografts in all four groups increased from Days 0 to 7 and from Days 7 to 14. Percentages of LH cells on Day 14 in all four groups were not different from those in age-matched male or female adenohypophyses in situ. In contrast, the mean percentages of FSH cells were low (about 1-3%) on Days 0, 7, and 14 in all four groups. In other males hosts, administration of a low dose of LHRH for 7 days did not alter the percentage of LH cells in male allografts but increased the percentage of FSH cells to approach that observed in age-matched male adenohypophyses in situ. Administration of a larger dose of LHRH for 7 days to other male hosts with male allografts increased the percentages of LH and FSH cells to percentages not different from those in age-matched female adenohypophyses in situ. Matching of 10 FSH cells/allograft with LH cells in serial sections of each of 58 allografts showed FSH immunoreactivity to occur only in cells staining for LH. The results of experiments conducted on normal hamsters demonstrate that more marked increases in the percentages of adenohypophysial LH cells and FSH cells occur in females than in males in association with the onset of the selective increase in serum FSH levels in females. The results of experiments employing allografts suggest that the greater increase in LH and FSH cells in females is due to sex differences in the internal environment existing in the postnatal hamster, which can be accounted for by differences in LHRH secretion, rather than to inherent differences between female and male adenohypophyses at the time of birth. We conclude that the greater increases in gonadotrophs observed in female hamster pups on Day 7 after birth and the accompanying sex-specific, selective elevation in serum FSH concentration are probably due to sex differences in LHRH secretion during the juvenile period.

Chronic effect of hyperprolactinemia on blood glucose and lipid levels in mice

We studied the chronic effects of hyperprolactinemia, induced by ectopic pituitary grafting, on blood glucose and lipid levels in adult male mice. For one year after pituitary grafting, we measured the blood levels of prolactin, growth hormone (GH), insulin, glucose and free fatty acid (FFA) at various intervals. The graft caused consistent hyperprolactinemia without changes in the serum GH levels. Hypoglycemia developed at 1 and 3 months after grafting but was not accompanied by any changes of the serum insulin levels. Thereafter, the blood glucose and serum insulin levels began to increase in the pituitary-grafted (PG) mice, and at 12 months after the operation, both levels became significantly higher in PG mice than controls. The serum FFA levels and the weight of epididymal fat bodies were significantly lower in PG mice than controls from 3-12 months after the grafting. Thus, hyperprolactinemia leads to persistent hypolipidemia and biphasic changes in the blood glucose level.

Changes in mediobasal hypothalamic dopamine and indoleamine metabolism after superior cervical ganglionectomy of rats

Eight days after bilateral superior cervical ganglionectomy (Gx) of rats, norepinephrine content of medial basal hypothalamus (MBH) decreased significantly by 44-50%. To obtain information on other possible neurochemical sequela of Gx in MBH, we examined the metabolism of dopamine and serotonin in MBH of Gx rats by employing a high pressure liquid chromatography procedure. Eight days after Gx, MBH dopamine levels augmented significantly. Assessment of dopamine metabolism by measuring dihydroxyphenylacetic acid (DOPAC)/dopamine and homovanillic acid (HVA)/dopamine indexes indicated a significant decrease of MBH DOPAC/dopamine ratio after Gx. MBH serotonin levels increased, and 5-hydroxyindoleacetic acid (5-HIAA)/serotonin index decreased significantly in Gx rats. To examine the interaction Gx-induced changes on MBH dopamine and serotonin with the modified hormonal milieu produced by an ectopic pituitary transplant, adult male rats bearing an ectopic pituitary within the pectoral muscles from day 5 of life were submitted to Gx on day 60 of life and were studied 8 days later. MBH dopamine content increased significantly after pituitary grafting, an effect counteracted by a subsequent Gx, while Gx alone augmented MBH dopamine levels. DOPAC and HVA contents augmented in pituitary-grafted animals, an effect counteracted by Gx. Gx increased MBH serotonin content in control but not in pituitary-grafted rats. After pituitary grafting a decrease in MBH 5-HIAA levels was found, an effect reversed by Gx. Pituitary transplants brought about a significant increase of MBH DOPAC/dopamine index, and a significant decrease in 5-HIAA/serotonin index, both effects being counteracted by Gx. Gx of control rats resulted in a significant decrease of MBH 5-HIAA/serotonin index. Analyzed as a main effect in a factorial analysis of variance, Gx decreased MBH DOPAC/dopamine and HVA/dopamine indexes significantly. Plasma prolactin increased in pituitary-grafted rats, an effect further increased by a subsequent Gx. In pituitary-grafted, Gx rats plasma GH levels augmented significantly. The data suggest that superior cervical ganglion removal affects differentially dopamine and indoleamine metabolism in MBH of control and pituitary-grafted rats.

Changes in citrate concentration in the mouse uterus with experimentally-induced adenomyosis

Components of the uterine fluid in mice with experimentally-induced adenomyosis and in controls were examined by proton nuclear magnetic resonance spectroscopy. One of the components was markedly different in mice with adenomyosis. As this component was estimated to be citrate by comparison with authentic samples (standard spectrum), its levels in uterine fluid, uterine tissue and blood were determined by enzymatic analysis. The fluid obtained from the uterus with adenomyosis showed significantly lower concentration of citrate than that from normal uterus. However, the uterine tissue concentration was significantly higher in the experimental mice with adenomyosis. There was no difference in the blood citrate level between the experimental and the control groups. Since adenomyosis was induced by chronic hyperprolactinemia, the change of citrate level in the uterus with this lesion might imply some effects of prolactin (PRL) on metabolism and/or secretion of citrate. However, in normal mice, no significant change was demonstrated in uterine citrate concentration after short-term experimental modulation of the circulating PRL level. Thus, it is unlikely that PRL can regulate directly citrate metabolism in the uterus, indicating some other cause for changes in citrate level accompanying the development of adenomyosis.

Effects of cyclosporine on ovarian function in sham-operated and pituitary-grafted young female rats

Effects of cyclosporine (CyA) on ovarian function and the possible role of prolactin in mediating these effects were examined in young female rats. The animals were sham-operated or rendered hyperprolactinemic by transplanting pituitary glands under the renal capsule. Cyclosporine prevented the increase in plasma prolactin levels in grafted rats. However, in sham-operated animals plasma prolactin levels were increased after 8 days of CyA treatment. Plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were reduced 8 days after pituitary grafting and increased by CyA at both Day 2 and Day 8 of treatment. The content of LHRH in the hypothalamus was not affected on Day 2 but was reduced on Day 8 after grafting on CyA therapy. Plasma estradiol levels were increased by CyA in sham-operated rats on Day 2 and 8 of treatment, and in pituitary-grafted rats on Day 8 of therapy. In sham-operated rats, ovarian estradiol content was reduced after 2 and after 8 days of CyA administration. In pituitary-grafted rats, the ovarian estradiol content was suppressed after 8 days, and CyA treatment prevented this effect. Ovarian estradiol release in vitro under basal conditions was greater in ovaries derived from 38-day-old than in those from 32-day-old animals. The ovarian estradiol response to human chorionic gonadotropin (hCG) in vitro was increased 2 days after pituitary transplantation. Administration of CyA for 8 days increased basal and hCG-stimulated estradiol release in both sham-operated and pituitary-grafted animals. The present findings suggest that CyA can alter ovarian function by acting directly at the gonadal level. However, a hypothalamic-hypophyseal site of action cannot be ruled out.

Induction from posterior hypothalamus is essential for the development of the pituitary proopiomelacortin (POMC) cells of the toad (Bufo japonicus)

The role of the posterior hypothalamus in the development of the epithelial hypophysis was studied in Bufo embryos. In animals from which the central part of the neural plate (NP) had been surgically removed at the open neurula stage, the infundibulum did not develop, and the epithelial hypophysis was formed away from the normal site without morphological connection with the brain. Immunoreactive MSH cells and ACTH cells, i.e., the pituitary POMC cells, were not detected in any of the surgically treated animals, while other types of secretory cells (PRL, GH, TSH and GTH cells) were invariably present. In view of the fact that POMC cells originate in the anterior neural ridge, and not in the neural plate, the embryonic brain seems to exert an inductive influence upon the primordial pituitary POMC cells. Since these cells differentiate in a tail graft, isolated from the brain at a later stage (tail-bud stage), the inductive stimuli must be conveyed from/via the posterior hypothalamus to the pituitary anlage between the open neurula and the tail-bud stages.

Opioids and the pulsatile prolactin secretory pattern: effects of hyperprolactinemia

It is well known that opioids regulate prolactin secretion through unknown mechanisms. The present study describes the effects of morphine and naloxone administration on pulsatile prolactin secretion in adult sham-operated and pituitary-grafted female rats. Animals were rendered hyperprolactinemic by transplanting 2 pituitary glands beneath the kidney capsule. Naloxone (2 mg/kg/h), morphine (50 mg/kg/h)+naloxone or saline (0.5 ml/h) were administered i.v. through a jugular cannula and bled at 7-min intervals for a period of 3 h. Pituitary grafting increased mean serum prolactin levels, the absolute amplitude and the duration of the pulses, but decreased their frequency. Naloxone, in sham-operated rats, reduced mean serum prolactin levels, the absolute amplitude and the frequency of the pulses. However, morphine+naloxone administration increased mean serum prolactin levels and the absolute amplitudes of prolactin pulses in pituitary-grafted rats. Naloxone administration did not decrease previously increased mean serum levels of prolactin in pituitary-grafted rats. These results suggest that opioids synchronize the pulsatile pattern of prolactin and that these effects are blunted in pituitary-grafted animals.

Modifications of mesolimbic and nigrostriatal dopaminergic activities after intracerebroventricular administration of prolactin

In the present study we examined the effects of intracerebroventricular (i.c.v.) injections of prolactin (PRL) on the presynaptic activity and post-synaptic sensitivity of mesolimbic and nigrostriatal dopaminergic neurons. In addition, the effects of PRL on in vitro release of dopamine (DA) from perifused striatal fragments were examined. Tyrosine hydroxylase (TH) activity and D2 receptor density in the striatum decreased after i.c.v. PRL administration; this was accompanied by an increase in D2 receptor affinity. These effects occurred after i.c.v. administration of PRL to normoprolactinemic rats, although normally they did not appear after administration to animals with pituitary grafting-induced hyperprolactinemia. Thus, in these animals, i.c.v. PRL failed to decrease TH activity and D1 and D2 receptor densities to a significant extent. In the case of D2 receptors, this was probably due to the fact that pituitary grafting-induced hyperprolactinemia itself was able to reduce the density of this receptor. No changes were observed in DA or L-3, 4-dihydroxyphenylacetic acid (DOPAC) contents after i.c.v. administration of PRL to both normo-and hyperprolactinemic animals. Basal and K(+)-evoked DA release in vitro from perifused striatal fragments of normoprolactinemic rats were not affected by the addition of PRL, whereas this hormone enhanced K(+)-evoked DA release when added to perifused striatal fragments from hyperprolactinemic animals. In the limbic forebrain, i.c.v. administration of PRL to normoprolactinemic animals produced a decrease in DA and DOPAC contents and D1 receptor density. Interestingly, none of these effects appeared when PRL was injected to hyperprolactinemic animals. In summary, our results suggest a possible inhibitory role of PRL on the activity of both the nigrostriatal and mesolimbic dopaminergic neuronal systems. These inhibitory effects were reflected in the decreases elicited in a set of neurochemical parameters, indicating either presynaptic activity or postsynaptic sensitivity, after i.c.v.-administered PRL. This observation supports the hypothesis of a possible neuromodulatory role for an extrapituitary PRL on the activity of these neurons, although the fact that most of these effects did not appear when i.c.v. administration was performed in hyperprolactinemic rats also suggests that they are influenced by peripheral PRL levels.

Prolactin modulates the incidence of diabetes in male and female NOD mice

The nonobese diabetic (NOD) mouse develops diabetes spontaneously due to autoimmune destruction of the pancreatic islets with a higher incidence in the female than the male. Prolactin (PRL), a hormone whose role has been previously focused on reproduction and lactation has been demonstrated to influence immune responses. In this study, we investigated the effect of hypoprolactinemia and hyperprolactinemia on the incidence of diabetes in male and female NOD mice. Our hypoprolactinemia model was induced from the time of weaning (21 days of age) to 112 days of age by daily injections of 200 micrograms of bromocriptine (CB-154). A hyperprolactinemic model was induced by a syngeneic anterior pituitary transplant (APT) to the kidney capsule at 35 days of age and maintained until 112 days of age. Additional experimental groups were also investigated. A group of males received pituitary transplants combined with daily subcutaneous injections of CB-154. A group of females treated with CB-154 was also given daily subcutaneous injections of 30 micrograms of oPRL. An ovariectomized (OVX-Control) group of females was also established to serve as a second control for the OVX-APT group. Bromocriptine administration did not significantly decrease plasma PRL levels compared to controls (CTRL) while APT animals had plasma PRL levels that were significantly higher (P < 0.01) than those of CTRL and CB-154 animals. These differences were observed in animals of both sexes. Bromocriptine treatment of APT groups significantly lowered plasma PRL levels from their respective controls. Plasma PRL from the OVX-Control group was markedly lower than the intact female control. The incidence of diabetes was significantly lower in female mice receiving CB-154 injections compared to the intact female CTRL group at 84, 98 and 112 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammary tumour induction by pituitary grafting in male mice: an animal model for male breast cancer

Isologous anterior pituitary grafting, 4 each, to 3-4-month-old SHN and SLN male mice resulted in an appearance of mammary tumours from 8 months of age and the incidence at 12 months reached 53.8% in each strain. All tumours were diagnosed as type B adenocarcinomas. In association with the results, normal mammary gland growth and mouse mammary tumour virus (MMTV)-gp52 antigen levels in the submaxillary glands were stimulated by the treatment in these strains. The effect of pituitary grafting was much less in GR/A male mice in which no mammary tumours appeared.

Gonadotropin secretion, synthesis, and gene expression in two types of bovine growth hormone transgenic mice

Expression of the mouse metallothionein-I (MT) promoter/bovine growth hormone (bGH) or the phosphoenolpyruvate carboxykinase (Pepck) promoter/bGH fusion genes in male transgenic mice is associated with alternations in adenohypophyseal function and fertility. To determine the effects of these gene constructs on gonadotropin synthesis and secretion, we have examined basal and GnRH-stimulated LH and FSH release in vitro using static incubations and perifusions of the pituitary; we have also examined pituitary content of LH, FSH, LH beta mRNA, and FSH beta mRNA in MT/bGH and Pepck/bGH transgenic mice as well as in normal mice. In addition, we have measured LH and FSH release from normal pituitaries transplanted under the kidney capsules of Pepck/bGH transgenic or normal mice. We found that in Pepck/bGH transgenic mice, pituitary contents of FSH and FSH beta mRNA were reduced, while FSH release in vitro in pituitary incubations and perifusions was increased. Steady-state levels of LH beta mRNA as well as LH responses to GnRH in perifusions were reduced; LH release in incubations and pituitary LH content were not changed; and basal LH secretion in perifusions was increased. In MT/bGH transgenic mice, in which peripheral bGH levels are much lower than in Pepck/bGH mice, similar trends were observed, but most of the apparent differences between transgenic and normal animals were not statistically significant. When normal pituitaries were transplanted under the kidney capsules of Pepck/bGH transgenic mice, the expected decrease in LH and FSH secretion was attenuated and the response to GnRH stimulation was lost.(ABSTRACT TRUNCATED AT 250 WORDS)

Incidence of c-Ki-ras activation in N-methyl-N-nitrosourea-induced mammary carcinomas in pituitary-isografted mice

We found previously that mouse mammary epithelial cells cultured in the presence of the mammogenic hormones progesterone and prolactin and treated with the carcinogen N-methyl-N-nitrosourea produced a high frequency of hyperplastic alveolar nodules and carcinomas with squamous metaplasia upon transplantation to syngeneic mice. The majority of these mammary transformants had an activated c-Ki-ras proto-oncogene with a specific point mutation in codon 12 (G35 to A35). To determine whether these in vitro findings parallel mammary carcinogenesis in vivo, virgin female mice were pituitary isografted to increase their circulating levels of progesterone and prolactin. The pituitary isograft results in an increase in proliferation, leading to lobulo-alveolar development and differentiation of the mammary epithelial cells. Five weeks after pituitary isografting, the mice were treated with a single injection of N-methyl-N-nitrosourea (50 micrograms/g body weight). Greater than 90% of the N-methyl-N-nitrosourea-treated mice developed mammary carcinomas between 3 and 7 months after treatment. The majority (75%) of the carcinomas had histopathology identical to that of tumors induced in vitro in the presence of progesterone and prolactin. A number of the mammary cancers (17%) induced in pituitary-isografted mice also had the identical point mutation in the c-Ki-ras proto-oncogene found in the in vitro studies. These results suggest that the hormonal milieu around the time of carcinogen exposure affects not only the incidence and phenotype of the mammary transformants but also the molecular events associated with mammary carcinogenesis.

Hypogonadism does not mediate urinary calcium loss in pituitary-grafted rats

Rats rendered chronically hyperprolactinemic by implantation of extra anterior pituitary glands (AP) under the kidney capsule have excess urinary calcium excretion. Although serum testosterone levels are normal in male AP-grafted rats, more subtle androgen deficiency might contribute to the increased calcium loss. Female AP-grafted rats lose the normal estrous cycle, which might also alter calcium homeostasis. The urinary calcium and calcium/sodium excretion ratio in gonadectomized AP-grafted rats of both sexes were compared with that of otherwise intact AP-grafted rats and muscle-grafted control rats. AP-grafted rats had increased urinary calcium excretion and calcium/sodium excretion ratio, regardless of gonadal status. Treatment of castrated male AP-grafted animals with testosterone or dihydrotestosterone did not have a significant effect on urinary calcium loss, nor did estrogen replacement of ovariectomized female AP-grafted rats. These studies indicate that the hypercalciuria of the AP-grafted rat is not mediated via an anti-gonadal effect of the prolactin-secreting pituitary graft.

Evidence for prolactin feedback actions on hypothalamic oxytocin, vasoactive intestinal peptide and dopamine secretion

Ovariectomized rats, when transplanted with 4 anterior pituitaries (APs) to the kidney capsule for 2-3 weeks, had elevated plasma prolactin (PRL) levels (3.8-fold) and showed decreased in situ AP weights (0.62-fold) and PRL concentrations (0.63-fold). The concentrations of dopamine (DA) and oxytocin (OT) in pituitary portal plasma of hyperprolactinemic rats were increased 1.7- and 1.9-fold, respectively. However, the levels of vasoactive intestinal peptide (VIP) in pituitary portal plasma of these rats were decreased 0.31-fold. The secretion of DA, dihydroxyphenylalanine (DOPA) and OT from fetal hypothalamic cells in primary culture was increased, whereas VIP secretion from these cells was reduced in a dose-dependent fashion following PRL treatment. These data are the first in vivo and in vitro demonstration of a stimulatory action of PRL on OT release and an inhibitory action of PRL on VIP release. Furthermore, these data suggest that a subtle imbalance between the secretion of the PRL-inhibiting factor (DA) and the PRL-releasing factors (VIP and OT) during elevated systemic levels of PRL is responsible for decreased lactotrophic function.

Regulation of GH and TSH release from hyperplastic and ectopic pituitaries: effects of dopamine in vitro

This study was undertaken to examine the consequences of prolonged removal of the pituitary from hypothalamic control and of estrogen-induced pituitary tumors on the susceptibility of GH and TSH release to regulatory influences of dopamine (DA). Adult male Fischer 344 rats were treated with transplants of female anterior pituitaries under the renal capsule or with Silastic capsules containing diethylstilbestrol (DES). Capsules with DES remained in place until the animals were killed (DES-IN) or were removed 7 weeks prior to sacrificing the rats (DES-OUT). Both pituitary grafts and DES caused the expected elevation in plasma prolactin and suppression of plasma GH and TSH levels. Basal GH release in vitro was not affected by exposure to DES in vivo but was reduced by transplantation of the pituitary to an ectopic site. Treatment with DA in vitro suppressed GH release from the in situ pituitaries of control, DES treated and grafted rats but increased GH release from the ectopic pituitaries. Basal release of TSH in vitro was reduced in the pituitaries of DES-IN and DES-OUT animals but was not affected by the presence of pituitary transplants. No detectable TSH was released from the ectopic pituitaries in the absence of DA. DA decreased TSH release from the pituitaries of control, DES-OUT and DES-IN rats but not from the in situ pituitaries of grafted rats. In contrast, DA produced an increase in TSH release from ectopic pituitaries. These results demonstrate that somatotrophs and thyrotrophs removed from the hypothalamic influences on subjected to direct and indirect effects of DES exhibit abnormal responses to DA. We suspect that prolonged absence of normal pituitary control leads to the development of regulatory mechanism of pituitary hormone release which are different from those operating under physiological conditions.

Survival of adenohypophyseal homologous transplants in the rat striatum associated with prolactin-like immunoreactivity in the surrounding neuropil of the striatum

By means of Cresyl violet stainings and immunocytochemical studies on prolactin-, luteinizing hormone (LH)-, and adrenocorticotropin (ACTH)-like immunoreactivities evidence has been obtained that homologous adenohypophyseal transplants survive for many weeks in the rat neostriatum. Gland cells maintain their endocrine properties and appear to secrete prolactin but not ACTH and LH into the surrounding neuropil of the rat neostriatum, since it contains a strong diffuse prolactin-like immunoreactivity. The diffuse zone of prolactin-like immunoreactivity disappears following inhibition of prolactin secretion by the dopamine agonist bromocriptine. The results support the existence of volume transmission in brain and offer a model for its analysis.

Effect of passive immunization against substance P in rats with hyperprolactinemia

Substance P, an undecapeptide isolated from gut and brain tissues, was reported to stimulate prolactin release. It was suggested that substance P may play a role in the control of prolactin secretion. In this investigation we studied the effects of the blockade of endogenous substance P by the administration of a specific anti-substance P serum on serum prolactin levels in rats in the evening of proestrus, in lactating rats after suckling, and in male rats with hyperprolactinemia induced by grafting 2 anterior pituitary glands under the kidney capsule. The injection of the anti-substance P serum was followed by a significant decrease of the prolactin surge induced by 30 min suckling in lactating rats, when the antiserum was administered 24 hr but not 5.30 hr earlier. Anti-substance P serum also induced a significant decrease in serum prolactin levels in pituitary grafted rats, but induced no change in the proestrous surge of prolactin and LH. These results show that substance P may be involved in the release of prolactin induced by suckling and that this peptide may have an intrapituitary role in the process of prolactin release. On the other hand, substance P does not seem to play a significant role in the proestrous peak of prolactin and LH.

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

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 micrograms GHRH in 100 microliter of vehicle or 100 microliter 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.

Estrogen inhibits luteinizing hormone (LH), but not follicle-stimulating hormone secretion in hypophysectomized pituitary-grafted rats receiving pulsatile LH-releasing hormone infusions

The differential feedback actions of estrogen (E2) on gonadotropin secretion were studied by means of an in vivo isolated pituitary paradigm. Adult female rats were hypophysectomized (hypox) and the next day received single anterior pituitary transplants (graft) under the kidney capsule. At the same time rats underwent bilateral ovariectomy. On the third day each animal was fitted with a catheter system which allowed for intermittent infusions of LHRH (250 ng/5 min.h) and chronic blood sampling. Rats received LHRH infusions for 7 days. On the sixth day of LHRH infusions blood samples were collected for 4 h 5, 15, 25, 35, 45 min after each hourly LHRH pulse. After 1 h of sampling, animals received sc injections of 2 micrograms estradiol benzoate (EB; n = 5) or oil vehicle (n = 5). Plasma LH, FSH, E2, and PRL levels in samples from all groups were determined by RIA. In hypox/graft rats LH release, but not FSH release, was pulsatile in response to the hourly LHRH infusions. Injection of EB in the hypox/graft rats significantly (P less than 0.05) suppressed LH release within 3 h by 57%, while FSH was unaffected. PRL levels were elevated by approximately 10-fold in the hypox/graft animals compared to those in pituitary-intact rats. These levels, however, were not changed as a function of steroid treatment and, therefore, could not account for the effects of EB on LH secretion. On the basis of these observations we conclude that 1) a major inhibitory effect of an acute injection of EB on LH secretion is exerted by a direct action on pituitary gonadotropes, and 2) E2 can differentially affect the release of LH and FSH by an intrapituitary mechanism. It is hoped that development of this model will allow for further investigation of the cellular mechanisms that mediate feedback actions of E2 on pituitary gonadotropes exposed to intermittent LHRH stimulation.

Hypothyroidism increases substance P concentrations in the heterotopic anterior pituitary

The regulatory effects of thyroid hormone on adenohypophysial substance P (SP) were studied in heterotopically implanted anterior pituitaries. Three or four anterior pituitaries from 21-day-old rat pups were implanted under the renal capsule in 175- to 200-g adult rats. The donor and recipient animals were sex matched. One week after implantation, animals were thyroidectomized or sham operated. A separate group of animals received daily T4 treatment (1.5 g/100 g, ip). After 2 weeks, the native and heterotopic pituitaries were assayed for SP, TSH, PRL, and LH. Thyroidectomy resulted in a 3- to 10-fold increase in the SP concentration in both the heterotopic and native pituitaries compared to euthyroid values. T4 treatment suppressed the SP levels in the heterotopic pituitaries of the thyroidectomized rats. In contrast to the reduction of TSH concentrations in native pituitaries in thyroidectomized animals vs. controls, TSH concentrations in the heterotopic pituitaries of thyroidectomized rats were approximately 10 times greater than those in euthyroid animals. PRL concentrations were unaffected by hypothyroidism in native and heterotopic pituitaries. Thyroidectomy resulted in a decrease in LH concentrations in the native anterior pituitary, without affecting LH concentrations in the implanted pituitary. These findings indicate that a direct link from the hypothalamus to the anterior pituitary is not required for the pituitary SP response to hypothyroidism.

Growth hormone is secreted by ectopic pituitary grafts and stimulates maternal behavior in rats

The onset of maternal behavior at parturition in rats is hormonally regulated. Recently, we reported that treatment of behaviorally inexperienced, hypophysectomized (hypox), ovariectomized (ovx) rats with a sequential steroid treatment of progesterone (P) and estradiol (E2), and either ectopic anterior pituitary grafts or prolactin (PRL), stimulated maternal responsiveness toward foster young. That growth hormone (GH) has a number of PRL-like activities led us to ask whether the actions of PRL on maternal behavior were specific to PRL or might be shared by other PRL-like protein hormone, i.e., GH. In Experiment 1 we quantified plasma concentrations of GH and PRL by RIA in groups of hypox female rats that were ovariectomized and treated with a combination of ectopic pituitary grafts (Days 1-23) and Silastic capsules filled with P (Days 1-11) and E2 (Days 11-23). Blood samples were collected from Days 1 to 23 of treatment. Both plasma PRL and GH levels increased after grafting, initially rising 10- to 60-fold by Day 4 and gradually declining throughout the remainder of the 23-day sampling period. Throughout the 3-week period after grafting plasma GH levels were as high or higher than those of PRL. In Experiment 2 the behavioral effects of exogenously administered ovine (o)-GH were measured in groups of hypox, ovx rats that were treated with P and E2 as in Experiment 1. Experimental rats were injected twice daily with 0.25 mg oGH beginning on Day 1. Testing for maternal behavior toward foster young was conducted daily from Day 12 to Day 22. In steroid-treated rats, GH treatment stimulated a more rapid onset of maternal behavior (latencies of 3 vs greater than 10 days for vehicle-injected controls). These data indicate that GH, like PRL, is secreted by ectopic pituitary grafts and is capable of stimulating maternal behavior.