Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PITUITARY GLAND”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
PubMed1984

Subpopulations of luteinizing hormone (LH) possessing various ratios of bioactivity to immunoreactivity in the female rat pituitary glands and their changes during the estrous cycle.

Twenty-four adult female Sprague-Dawley rats (3 from each of 8 litters), showing 4-day cycles, were used in the present study. Aqueous extracts of pools of 6 pituitary glands in each cycle date were fractionated with a column isoelectrofocusing (IEF) technique, pH range of 3.5-10. Biological and immunological LH activities were determined by an in vitro bioassay and a radioimmunoassay, respectively, in the original aqueous extracts of the pituitary glands and in the fractions separated by IEF. Pituitary content of LH was the highest in the proestrus before the preovulatory LH surge (1243.7 +/- 67.8 micrograms NIAMDD rat LH-RP-1/pituitary gland for the biological activity). In the estrus, after the LH surge, it was reduced to 688.9 +/- 51.2 micrograms/pituitary gland. The decreased pituitary content was recovered to the level in the proestrus during the metestrus and the diestrus (1047.0 +/- 53.8 and 1173.0 +/- 58.5 micrograms/pituitary gland, respectively). Rat LH in the pituitary aqueous extracts was separated into multiple subpopulations in terms of pI values by IEF; i.e. Subpopulations A (pI = 10.3), B (9.3), C (9.0), D (8.7), E (8.3), F (neutral LH), and G (acidic LH). Among them the most predominant one was Subpopulation A throughout the estrous cycle. Subpopulations A, B and C exhibited statistically significant cyclic changes as was observed in the pituitary LH content, whereas the remaining ones stayed at constant levels during the cycle. The highest ratio of biological to immunological LH activities (B/I ratio) was obtained in Subpopulation A (6.41), followed by G, C and B (5.15, 4.24 and 3.99, respectively). Depressed B/I ratios were revealed in D, E and F (2.59, 1.86 and 3.07, respectively). High alkaline LH subpopulations, i.e. A, B and C, preserving high biological potency and showing cyclic changes during the estrous cycle, seem to be the releasable types of the hormone and to be mainly discharged for the preovulatory LH surge. Although characteristic features of other types of the hormone are not known, it is possible that one of them, presumably the acidic LH, might be the newly-synthesized type of the hormone, which might attain releasability by certain molecular modifications involving a shift in the pI value.

Animals↗
PubMed1987

Possible role of dopamine and noradrenaline in the regulation of prolactin secretion from an ectopic anterior pituitary gland in female rats.

It was recently reported that anterior pituitary tissue transplanted to an ectopic site contains measurable amounts of dopamine and noradrenaline. To examine the possibility of local catecholaminergic control of prolactin secretion from ectopic pituitaries, pituitary grafted and sham-operated female rats were submitted to several pharmacological treatments modifying catecholamine synthesis. Administration of a single dose of alpha-methyl-p-tyrosine (alpha-MPT) significantly reduced dopamine content in the graft, while noradrenaline content was not modified. Similar changes in the contents of dopamine and noradrenaline after alpha-MPT administration were observed in the hypothalamus and in the in-situ pituitary in both grafted and sham-operated rats. Plasma concentrations of prolactin were increased in both grafted and sham-operated rats after administration of alpha-MPT. A single injection of L-3,4-dihydroxyphenylalanine (L-DOPA) increased dopamine content in the ectopic pituitary gland without altering the noradrenaline content, and produced similar effects in the hypothalamus and in-situ pituitary of grafted and control rats. Plasma prolactin concentrations were decreased by L-DOPA in both pituitary grafted and control rats. Administration of DL-treo-dihydroxyphenylserine (DOPS) increased noradrenaline content in the ectopic pituitary and reduced plasma prolactin concentrations in pituitary grafted rats. In contrast, injection of DOPS to control rats increased both hypothalamic noradrenaline content and plasma prolactin concentrations. These results suggest that dopamine and noradrenaline present in the ectopic pituitary tissue have a role in mediating prolactin release from pituitary transplants.

Animals↗
PubMedDate not supplied

Distribution of an enzyme which acetylates alpha-melanocyte stimulating hormone in rat brain and pituitary gland and effects of arcuate nucleus lesions.

This study describes the distribution of an alpha-melanocyte stimulating hormone (alpha-MSH) acetyltransferase (MAT) in rat brain and pituitary gland. Highest activities of MAT were found in the neurointermediate lobe of the pituitary gland with the anterior lobe containing slightly less. Within the brain, lowest MAT activities were measured in the hypothalamus, the region which contained the highest concentrations of alpha-MSH. Relatively high enzyme activities of MAT were measured in the hippocampus, cortex and cerebellum--regions with very low alpha-MSH concentrations. The fact that MAT activity levels did not parallel alpha-MSH concentrations indicates that MAT was not solely localized to alpha-MSH synthesizing neurons or endocrine cells. Furthermore, arcuate nucleus lesions which depleted brain alpha-MSH failed to deplete MAT activity. Although MAT was not solely localized to alpha-MSH synthesizing cells, it may have functional significance for alpha-MSH acetylation due to compartmentalization with alpha-MSH in alpha-MSH synthesizing endocrine cells and neurons. Alternatively a second regionally specific MAT may exist.

Acetylation↗
PubMed1989

Ovariectomy permits progesterone to increase the binding of [3H]spiperone to the anterior pituitary gland in estrogen-primed rats.

The binding of the dopamine (DA) D2 antagonist spiperone to DA receptors in the anterior pituitary gland was evaluated in intact and ovariectomized (OVX) estrogen-primed rats in which circulating levels of progesterone (P) were varied. Nembutal (PB; 35 mg/kg, ip) was administered at 1130 h to intact proestrous animals to prevent the LH-stimulated release of ovarian P. Two hours later some of these intact rats were QVX to remove the endogenous ovarian steroids. Both intact and OVX rats were given exogenous P. All rats were killed on the following morning, and adenohypophysial binding of [3H]spiperone was evaluated at a saturating concentration. The binding in intact PB-blocked rats that received P was only 52% of that in PB-blocked rats that were OVX and received P. The binding of [3H]spiperone in PB-treated rats that were OVX and given P did not differ statistically from that in normal estrous rats. A parallel experiment was conducted on other rats that had been OVX 7 days before the sc implantation (on day 0) of Silastic capsules containing estradiol (E2). Two days later (day 2), some of these rats were injected with Nembutal at 1130 h. Two hours later, the E2 capsules of some rats were removed to simulate ovariectomy; Silastic capsules containing P were implanted into both E2-bearing and non-E2-bearing rats. All rats were killed the following morning (day 3), and the density of adenohypophysial DA receptors was assessed. Binding densities were greatest in rats bearing both E2 and P capsules and in rats from which E2 capsules were removed and replaced with P capsules. We conclude that treatment of OVX rats with the sequential combination of E2 and P increases the density of DA receptors in the anterior pituitary gland. However, in intact rats an additional ovarian product prevents the P-induced increase in the density of adenohypophysial DA receptors.

Animals↗
PubMed1993

Expression of neuroendocrine secretory protein 7B2 mRNA in the mouse and rat pituitary gland.

The secretory polypeptide 7B2 is produced in different endocrine and neuroendocrine cells, where it is presumed to play a role in the hormone secretion mechanism. In this study, we examined a pattern of 7B2 mRNA expression in the mouse and rat pituitary gland. When [35S]-labeled antisense cRNA probes were used for in situ hybridization, 7B2 mRNA transcripts were detected within virtually all endocrine cells of the anterior lobe (gonadotrophs, thyrotrophs, corticotrophs, somatotrophs and lactotrophs) and of the intermediate lobe (melanotrophs). The posterior lobe was negative. By immunocytochemistry, 7B2 accumulation was observed within melanotrophs in the intermediate lobe and within gonadotrophs and thyrotrophs in the anterior lobe. The question of 7B2 production in other pituitary cells, such as corticotrophs, somatotrophs and lactotrophs, was studied under culture conditions. The corticotroph AtT-20 and somatrotroph GH3 cell lines both expressed 7B2 mRNA and contained 7B2 protein detectable by radioimmunoassay. However, this protein could not be visualized by immunocytochemistry. Thus, it is possible that 7B2 is produced in all hormone-synthesizing cells of the pituitary gland, being stored only within some of them and rapidly exported after synthesis from others.

Animals↗
PubMed1990

The influence of adrenal hormone status on neuroendocrine peptides in the rat anterior pituitary gland.

Neuropeptide Y (NPY), neurotensin (NT), substance P (SP) and vasoactive intestinal peptide (VIP) are four structurally unrelated neuroendocrine peptides which affect anterior pituitary function. All four peptides appear to be locally synthesized in the anterior pituitary gland and have been shown to be regulated by thyroid and/or sex hormone status. We show here that NT, SP and VIP but not NPY are influenced by adrenal hormone status in the male rat pituitary gland. Adrenalectomy increased the content of VIP (35.4 +/- 4.0 (S.E.M.) vs control 11.9 +/- 1.1 pmol/g wet weight) but decreased that of SP (18.8 +/- 2.3 vs control 36.7 +/- 3.5 pmol/g wet weight). Adrenalectomy combined with castration decreased the content of SP (14.6 +/- 3.5 vs control 36.7 +/- 3.9 pmol/g wet weight) but had no effect on VIP content. Treatment with dexamethasone produced significant decreases in NT, SP and VIP contents (17.8 +/- 2.3 vs control 32.6 +/- 3.4 pmol/g wet weight, 5.5 +/- 0.9 vs control 36.7 +/- 3.9 pmol/g wet weight and 4.2 +/- 0.6 vs control 11.9 +/- 1.1 pmol/g wet weight respectively). The changes in pituitary peptide contents occurred in parallel with changes in mRNA levels, suggesting that alterations in glucocorticoid hormone status can alter the synthesis of these peptides. These results, together with the known effects of these neuroendocrine peptides suggest possible functions for locally produced SP and VIP in regulating the secretion of adrenocorticotrophin and/or other pro-opiomelanocortin-derived peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex Hormones↗
PubMed1993

In vitro control of prolactin (PRL) and growth hormone secretion of neonatal rat pituitary glands: effects of ovine PRL, salmon calcitonin, endothelin-3, angiotensin II, bromocryptine and somatostatin.

Bromocryptine potently decreased prolactin (PRL) secretion of pituitary glands of 2-day-old rats in vitro (up to 85% inhibition; ED50 between 0.1 and 1.0 nM) without altering the bioactivity to immunoreactivity (B/I) ratio. Bromocryptine tended to suppress growth hormone (GH) secretion although the effect did not reach statistical significance. Angiotensin-II (A-II; 1-1000 nM) stimulated PRL secretion in a dose-dependent manner without affecting secretion of GH. The B/I ratio of PRL secreted in response to A-II was increased. Somatostatin (SRIF) had no effect on PRL secretion but inhibited GH secretion in a dose-dependent manner; significant inhibition (50%) was observed at 100 nM. A 6-h exposure to ovine PRL (oPRL) in concentrations equipotent with 1.2-120 ng/ml rat PRL (rPRL) in the Nb2 bioassay had no effect on immunoreactive rPRL secretion. Salmon calcitonin (sCT) and endothelin-3 (ET-3; 0.1-100 nM) failed to inhibit secretion of PRL or GH. PRL secretion was slightly stimulated by sCT with no apparent dose-response relationship. The present findings suggest that neonatal pituitary glands do not display autoregulation of PRL secretion, and sCT and ET-3 (either endogenous or milk-derived) may not function as PRL inhibiting factors in 2-day-old pups. Thus, the receptors of PRL, sCT and ET-3 on lactotropes, or their functional coupling with inhibition of basal PRL secretion, occur at a later stage of development. The specificity of the PRL releasing factor (PRF) activity of A-II at this age is unique for established PRFs and might reflect a physiological function of PRL in osmoregulation. The increased B/I ratio of PRL secreted in response to A-II may be due to the release of specific PRL variants, and might be a sign of functional heterogeneity among lactotropes. The differential sensitivity of PRL and GH to the applied secretagogues suggests that the intracellular regulation of PRL and GH are compartmentalized in the mammosomatotrope cell.

Angiotensin II↗
PubMed1993

The distribution of neuropeptide Y and dynorphin immunoreactivity in the brain and pituitary gland of the platyfish, Xiphophorus maculatus, from birth to sexual maturity.

Immunoreactive neuropeptide Y and dynorphin have been localized in the brain and pituitary gland of the platyfish, Xiphophorus maculatus, at different ages and stages of development from birth to sexual maturity. Immunoreactive neuropeptide Y was found in perikarya and tracts of the nucleus olfactoretinalis, telencephalon, ventral tegmentum and in the neurohypophysis and in the three regions of the adenohypophysis. Immunoreactive dynorphin was found in nerve tracts in the olfactory bulb and in cells of the pars intermedia and the rostral pars distalis of the pituitary gland.

Animals↗
PubMed1994

Neurotrophins and their receptors in the rat pituitary gland: regulation of BDNF and trkB mRNA levels by adrenal hormones.

We studied the expression of messenger ribonucleic acids (mRNAs) for neurotrophins and neurotrophin receptors in the rat pituitary gland and examined the influence of adrenal hormones on their mRNA levels, using in situ hybridization and Northern blot analysis. The only neurotrophin present at detectable levels in the pituitary was brain-derived neurotrophic factor (BDNF), which was observed in the anterior and intermediate lobes. Several transcripts of the putative receptor for BDNF, trkB, were present in the anterior and posterior lobes of the pituitary. A low amount of trkC mRNA was found in both the anterior and the intermediate lobe. Dexamethasone treatment decreased both BDNF and trkB mRNA levels in the anterior lobe of the pituitary. Adrenalectomy had no effect on trkB expression, but it decreased BDNF mRNA levels in comparison to the control animals. This effect could not be reversed by dexamethasone substitution, suggesting that BDNF, mRNA levels may be regulated not only by glucocorticoids but also by other adrenal hormones. These results demonstrate that BDNF, trkB and trkC are expressed in the pituitary gland and that glucocorticoids and possibly other adrenal hormones may modulate pituitary functions by regulating the expression of neurotrophic factors and their receptors. Whether BDNF acts as a secreted hormone, a trophic factor, or has autocrine/paracrine functions within the pituitary through its receptor, trkB, remains to be studied.

Animals↗
PubMed1987

Melanin concentrating hormone inhibits the release of alpha MSH from teleost pituitary glands.

A radioimmunoassay was developed for salmonid melanin concentrating hormone (MCH) and used to measure immunoreactive (ir)MCH in the hypothalamus and pituitary of trout (Salmo gairdneri) and eels, (Anguilla anguilla) maintained under different regimes of background color. In trout, 95% of the total irMCH was located in the pituitary gland. The amount of MCH in both pituitary and hypothalamus was increased when white-adapted trout were transferred to a black background. In eels, a similar change of background led to an accumulation of MCH in the pituitary but not in the hypothalamus. The results suggest that MCH is released from the neurohypophysis in association with physiological color change. Neurointermediate lobes of trout and eels released both ir alpha MSH and irMCH when they were cultured in vitro. The release of alpha MSH was significantly enhanced when endogenous MCH was immunoabsorbed by MCH antiserum added to the culture medium. The results indicate that MCH can induce pallor in fish not only by its peripheral effect on the melanophores but also by an inhibitory action on the release of alpha MSH from the pituitary.

Anguilla↗
PubMed1980

Nuclear uptake and retention of androgen by the pituitary gland of the hamster and the rat.

Castrated adult male hamsters and castrated adult female rats were injected with either 0.2 microgram (hamsters) or 0.5 microgram (rats) of 3H-dihydrotestosterone (107 Ci/mmole)/100 grams body weight and killed 1 1/2 h later. The pituitary glands were removed and processed for both autoradiography and immunocytochemistry (hamster) or only autoradiography (rats). Localization of the androgen was found in 10-15% of the cells of the pars distalis in both species. Only cells that stained for luteinizing hormone (LH) in the hamster's pars distalis concentrated the androgen. Also cells in both the pars intermedia and pars nervosa (1-5%) concentrated the androgen in both species. Although the number of cells that concentrated the androgen in the pars intermedia and pars nervosa was small, this finding may be related to recent physiologic data that suggest that the gonadal steroids may play a role in regulating water retention and natriuresis.

Animals↗
PubMed1982

A procedure for the purification of somatotrophs isolated from rat anterior pituitary glands using Percoll density gradients.

We have used fractionation on density gradients of Percoll to separate the cell types in the rat anterior pituitary gland and to produce a purified preparation of somatotrophs. The method differs from those described previously which used, for example, albumin or Ficoll gradients, in being more rapid and avoiding low temperatures, and therefore gives cells with improved viability. Anterior pituitary glands from male rats were dispersed with trypsin to produce 1.5 x 10 (6) -2.0 x 10 (6) cells/gland. These were fractionated on hyperbolic density gradients of Percoll. Two bands of cells containing somatotrophs were detected, one of which (band A; density 1.075-1.082 g/cm3) contained approximately 90% somatotrophs, whereas the other (band B; density 1.055-1.068 g/cm3) contained about 70% somatotrophs mixed with other cells, especially lactotrophs. Cells in band A appeared more responsive to secretagogues than those in band B; growth hormone secretion was stimulated markedly by cyclic AMP derivatives and prostaglandin E2, and inhibited by somatostatin. Such purified somatotrophs are well suited to biochemical studies on the mechanism of the control of growth hormone secretion.

Adrenocorticotropic Hormone↗
PubMed1992

Characterization of an ovine glucocorticoid receptor cDNA and developmental changes in its mRNA levels in the fetal sheep hypothalamus, pituitary gland and adrenal.

Fetal sheep tissues possess glucocorticoid receptors (GR), and these change in number during the last two-thirds of gestation. There is, however, no information about developmental changes in tissue GR mRNA levels which might account for alterations in fetal GR content. We have therefore cloned and sequenced a 942 bp GR cDNA from a sheep liver cDNA library, and used it to study the relative abundance of GR mRNA in fetal and neonatal sheep tissues. Analysis of the cDNA revealed a partial sequence of the ovine GR which displayed over 80% identity with residues 143-453 in human GR and 163-472 in rat GR. Furthermore, the first zinc finger motif in these receptors was perfectly conserved among species. The relative abundance of GR mRNA was studied in hypothalami, anterior pituitary glands and adrenals in fetuses at days 60-70, 100-110, 125-130 and at term (approximately 145 days), and in newborn lambs. Total RNA extracts (20 micrograms) were analysed by Northern blot analysis. A single 5.6 kb transcript was detected in all three fetal tissues, and its relative abundance did not change significantly throughout gestation. However, in newborn lambs, levels of GR mRNA increased significantly in the hypothalamus and pituitary gland but decreased to undetectable levels in the adrenal. These tissue-specific changes in the relative abundance of GR mRNA did not correlate with alterations in GR content in fetal tissues, which suggests that the latter may reflect alterations in GR mRNA translation, subsequent modifications and/or GR turnover. In addition, the pattern of developmental changes in GR mRNA content of the adrenal differs from that of the hypothalamus and pituitary gland in neonatal lambs, and indicates that tissue-specific factors may influence GR gene expression in neonatal sheep.

Adrenal Glands↗
PubMed2007

Expression of androgen receptor and its co-localization with estrogen receptor-alpha in the developing pituitary gland of sheep fetus.

No information is known concerning the expression of androgen receptor (AR) and its co-localization with estrogen receptor alpha (ERalpha) in the developing pituitary of sheep fetus. In the present study, we detected AR expression and its co-localization with ERalpha in the anterior pituitary of sheep fetus from day 60 of gestation to the postnatal by dual immunochemistry. The results showed that both AR immunoreactivity (AR-ir) and ERalpha immunoreactivity (ERalpha-ir) were predominantly localized in the nuclei of LH positive gonadotropes. The cell counting results showed that the percentage of the anterior pituitary cells expressing AR fluctuated from 13.51 +/- 0.92 to 17.05 +/- 1.83% during the examined stages, but there were no significant differences between sexes and among ages examined (P > 0.05). However, the proportion of AR-ir cells containing LH markedly increased from day 60 of gestation to the neonatal (P < 0.05). The percentage of AR-ir cells expressing ERalpha-ir significantly increased from day 60 of gestation to the neonatal, respectively (P < 0.05), but no significant differences were seen between genders at each stage examined. These results indicate that both AR and ERalpha are mainly expressed in the gonadotropes of anterior pituitary gland of sheep fetuses, whereas the functions and interaction of AR and ERalpha expressions in the developing pituitary gland are required to be elucidated further.

Animals↗
PubMed1996

Immunocytochemical distribution of catecholamine-synthesizing neurons in the hypothalamus and pituitary gland of pigs: tyrosine hydroxylase and dopamine-beta-hydroxylase.

This study describes the distribution of catecholaminergic neurons in the hypothalamus and the pituitary gland of the domestic pig, Sus scrofa, an animal that is widely used as an experimental model of human physiology in addition to its worldwide agricultural importance. Hypothalamic catecholamine neurons were identified by immunocytochemical staining for the presence of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase. Tyrosine hydroxylase-immunoreactive perikarya were observed in the periventricular region throughout the extent of the third ventricle, the anterior and retrochiasmatic divisions of the supraoptic nucleus, the suprachiasmatic nucleus, the ventral and dorsolateral regions of the paraventricular nucleus and adjacent dorsal hypothalamus, the ventrolateral arcuate nucleus, and the posterior hypothalamus. Perikarya ranged from parvicellular (10-15 microns) to magnocellular (25-50 microns) and were of multiple shapes (rounded, fusiform, triangular, or multipolar) and generally had two to five processes with branched arborization. No dopamine-beta-hydroxylase immunoreactive perikarya were observed within the hypothalamus or in the adjacent basal forebrain structures. Both tyrosine hydroxylase- and dopamine-beta-hydroxylase-immunoreactive fibers and punctate varicosities were observed throughout areas containing tyrosine hydroxylase perikarya, but dopamine-beta-hydroxylase immunoreactivity was very sparse within the median eminence. Within the pituitary gland, only tyrosine hydroxylase fibers, and not dopamine-beta-hydroxylase immunoreactive fibers, were located throughout the neurohypophyseal tract and within the posterior pituitary in both pars intermedia and pars nervosa regions. Generally, the location and patterns of both catecholamine-synthesizing enzymes were similar to those reported for other mammalian species except for the absence of the A15 dorsal group and the very sparse dopamine-beta-hydroxylase immunoreactive fibers and varicosities in the median eminence in the pig. These findings provide an initial framework for elucidating behavioral and neuroendocrine species differences with regard to catecholamine neurotransmitters.

Animals↗
PubMed1981

Relative concentrations of prolactin, gonadotropin and thyrotropin in the pituitary gland and blood serum during different phases of annual reproductive cycle in the freshwater catfish, Clarias batrachus.

Variations in prolactin content of the pituitary gland and blood serum were studied throughout a year in relation to the concentration of gonadotrophin and thyrotrophin hormones during the different phases of annual reproductive cycle in Clarias batrachus. Prolactin content showed a cyclic variation. Increasing trend in its potency kept pace with the rising concentration of gonadotrophin and thyrotrophin both in the pituitary gland and blood. Upward movement in the above hormones started with the onset of gonadal development from the preparatory phase, reached their peaks during spawning period and then began to subside with the approach of postspawning phase.

Animals↗
PubMed2001

Endothelin-like immunoreactivity in lactotrophs, gonadotrophs, and somatotrophs of rat anterior pituitary gland are affected differentially by ovarian steroid hormones.

It has been previously found that all hormone-producing phenotypes of the anterior lobe of the pituitary gland are capable of producing endothelin (ET)-like substances. The aim of this study was to determine whether the expression of ET-1-like peptides in lactotrophs, gonadotrophs, and somatotrophs is influenced by different in vivo ovarian hormonal conditions. Anterior lobes of the pituitary gland were harvested from ovariectomized and ovarian steroid-replaced adult female rats 10-12 d after surgery. Quantitative immunocytochemistry was performed on enzymatically dispersed pituitary cells. The presence of ET-1-like immunoreactivity in prolactin-, luteinizing hormone-, or growth hormone-producing cells was demonstrated by double-label immunocytochemistry. The incidence of ET-1 immunopositive pituitary cells was unaffected by progesterone treatment alone. Estradiol replacement caused a modest decrease in the number of lactotrophs and somatotrophs expressing ET-1 but increased the incidence of ET-1 immunopositive cells among gonadotrophs. Combined treatment with estradiol and progesterone robustly increased the incidence of ET-1 immunopositive lactotrophs and gonadotrophs but had no effect on somatotrophs. These data reveal that the synthesis of ET-1-like peptides in lactotrophs and gonadotrophs (and, to a lesser extent, in somatotrophs) is sensitive to ovarian steroids. Furthermore, these findings predict that ovarian steroids modulate ET-1 biosynthesis during the estrous cycle, suggesting a possible mechanism by which the ovarian steroid milieu may regulate the responsiveness of lactotrophs and gonadotrophs to their hypothalamic secretagogues.

Animals↗