Anterior Pituitary Of Female Rats Research Articles

Spontaneous changes in LHRH release during the rat estrous cycle, as measured with repetitive push-pull perfusions of the pituitary gland in the same female rats.

In the present study, we examined the in vivo release profiles of luteinizing hormone-releasing hormone (LHRH) during the rat estrous cycle by utilizing repetitive push-pull perfusions of the anterior pituitary in the same freely behaving animal. Throughout the estrous cycle, LHRH levels were higher than those reported from previous work using a push-pull cannula placed in the mediobasal hypothalamus. A significant increase in LHRH input to the anterior pituitary was obtained in proestrus (Pro), though the magnitude of increment was different among animals. This LHRH increment in Pro was attributable to a significant increase in the amplitude of LHRH pulses. Interestingly, no changes were observed in the frequency of LHRH pulses (about 1 pulse/50 min) throughout the estrous cycle. The data demonstrate that the anterior pituitary of female rats receives an increased amount of LHRH during Pro due to changes in the amplitude of the LHRH signal without changes in the frequency.

Conversion of 17α-hydroxyprogesterone to 5α, 3α, and 20α-reduced metabolites by female rat anterior pituitary and hypothalamus

The metabolism of 17α-[ 3H]hydroxyprogesterone was examined in female rat anterior pituitary and hypothalamic tissues. After reverse isotopic dilution analysis and purification to constant specific activity, the following 5α-, 3α- and 20α-reduced products were detected in both tissues : 17α-hydroxy-5α-pregnane-3, 20-dione; 3α, 17α-dihydroxy-5α-pregnan-20-one; 17α, 20α-dihydroxy-4-pregnen-3-one and 5α-pregnane-3α, 17α, 20α-triol. While the metabolites formed were qualitatively the same, there were quantitative differences between the two tissues. The 3α, 5α-reduced metabolite, 3α, 17α-dihydroxy-5α-pregnan-20-one, was the principal product in the anterior pituitary while the 5α-reduced metabolite, 17α-hydroxy-5α-pregnane-3, 20-dione, was produced in largest amount by the hypothalamus. With both tissues, the aforementioned four products plus starting substrate accounted for nearly all of the starting radioactivity. There was no evidence for the formation of C 19 steroids (androgens) despite the presence of the 17α-hydroxy group.

Regional patterning of hormones in the female rat anterior pituitary: disproportionate changes over the estrous cycle.

The present study addressed the possibility that regional differences exist in the typical patterning of anterior pituitary hormones seen over the estrous cycle. The results show that LH in the rostral area of the pituitary, significantly higher than in other regions on diestrus, rises markedly on proestrus before falling late on that afternoon to concentrations comparable to other areas. Smaller cyclic changes were seen for lateral and caudo-central areas. The pattern of regional FSH concentrations on diestrus, while similar to LH, does not show the proestrus fall in the rostral region. Prolactin declines from a high on diestrus I to a low on late proestrus, but no regional disparities are present. TSH shows distinct regional differences and a fall in concentrations that coincides with the reported rise in serum estradiol. These findings indicate that the preovulatory surge of LH may represent a regionally disproportionate event, possibly involving inequalities in the relative amounts of gonadotropin-releasing hormone reaching various areas of the pituitary or differences in the ability of this releasing hormone to trigger LH release.

Vasoactive intestinal polypeptide and dopamine in the hypothalamus and pituitary of ageing rats with prolactinomas.

Vasoactive intestinal peptide (VIP), an dopamine have been measured in the hypothalamus and anterior pituitaries of female rats at three different ages. Rats aged 19 months had a high incidence (35%) of prolactin-secreting tumours of the pituitary and these animals had increased hypothalamic and pituitary VIP compared with three-month-old rats or rats without tumours. VIP in old animals without tumours was similar to that in young animals. The third group, with an even more advanced age of 22-28 months, had a lower incidence of PRL-secreting tumours, and pituitary and hypothalamic VIP concentrations similar to those in young animals. Dopamine was significantly increased in the pituitaries of 22-28-month-old nontumorous rats and slightly raised in 19-month-old rats. We conclude that the increased pituitary and hypothalamic VIP content of 19-month-old rats could be a factor in the development of tumours seen at this age, and the differences seen in the two groups of old rats may be related to changes in the steroid environment.

Administration of gonadal steroids to neonatal rats affects beta-endorphin levels in the adult

Administration of gonadal steroids to neonatal rats has a profound effect on the function of the neuroendocrine system in the adult animal. Considering that gonadal steroids modulate hypothalamic and pituitary levels of beta-endorphin (BE) in adult male and female rats, the effects of neonatal gonadal steroid treatment on BE levels in the adult animal were investigated. Neonatal male rats were administered testosterone and neonatal female rats were treated with estrogen. Matched control littermates received vehicle. All animals were sacrificed at 90 days of age. Neonatal gonadal steroid treatment did not affect the level of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP) of male rats but did result in a significant increase in IR-BE in the AP of female rats. Neonatal administration of gonadal steroids produced a significant decrease in IR-BE in the neurointermediate lobe of the pituitary (NIL) of both male and female rats, with the magnitude of the decrease being greater in the NIL of the female rats. IR-BE levels in the hypothalamus of male or female rats were not altered by the treatments. Column chromatography indicated that the increase in IR-BE in the AP represented a proportional increase in BE and beta-lipotropin, while the reduction in IR-BE in the NIL of the treated rats represented a reduction in BE. These findings suggest that gonadal steroids may influence the development of the neurotransmitter systems which regulate BE levels in the adult pituitary, the development of the biosynthetic mechanisms of the adult pituitary, or both.

Leukotrienes stimulate gonadotropin release in vitro.

Monolayer cell cultures of female rat anterior pituitaries were used to investigate the effect of leukotrienes (LT) LTA4, LTB4, LTC4, LTD4, LTE4 and other lipoxygenase metabolites of arachidonic acid (5-HETE, 5-HPETE, and 15-HETE) in vitro. 3H-arachidonic acid was rapidly incorporated into pituicytes and its release was enhanced by gonadotropin releasing hormone (GnRH) in superfused pituitary cells. Leukotrienes were found to be very potent stimulators of the release of luteinizing hormone (LH) when added as pulses to superfused pituicytes. At equimolar concentrations, LTA4, LTB4, LTC4 and LTE4 were found to be more potent than the physiological stimulus GnRH. LTD4 did not affect gonadotropin secretion. Other lipoxygenase metabolites of arachidonic acid, such as 5-HETE, 5-HPETE and 15-HETE were less effective on the exocytosis of LH. These results suggest that leukotrienes are potential mediators of GnRH action on gonadotropin secretion and are possible sites of regulation of pituitary function.

Differential isoform distribution between stored and secreted prolactin.

PRL exists within the mammotroph population in a number of different molecular forms. Three of these forms are best described as isoforms, as they have the same mol wt (24K) but differ in their net molecular charges. In this study we have examined the relative proportions of newly synthesized isoforms found in stored (intracellular) vs. secreted (extracellular) PRL. Dissociated cells from female rat anterior pituitaries were cultured for 48 h and then incubated in [35S]methionine (6 h; 37 C). Intracellular and medium proteins were then extracted and resolved by one- and two-dimensional polyacrylamide gel electrophoresis, followed by silver staining or autoradiography. Control experiments, in which biosynthetically labeled PRL was re-extracted, ensured that the isolation conditions did not in themselves promote isoform interconversion. The relative proportions of the PRL isoforms were determined by densitometric scanning of developed autoradiograms. In the cell extracts, the relative proportions were 13.6 +/- 2.1% isoform 1 (least negatively charged), 71.5 +/- 3.26% isoform 2, and 14.7 +/- 1.9% isoform 3 (most negatively charged). In the medium, the relative proportions were 60 +/- 2.89% isoform 1, 20 +/- 1.75% isoform 2, and 11 +/- 1.14% isoform 3. When the labeling was performed in the presence of 0.5 mM cysteamine (an agent we show to distinguish between newly synthesized and older stored hormone and, hence, between the previously described functional subpopulations of mammotrophs), the same ratios of newly synthesized isoforms were secreted from the cells. We conclude that secretion of the different isoforms is more complex than simple proportional release of each form, and based on the cysteamine results, this nonproportional release cannot be attributed to release of one isoform per functional subpopulation of mammotrophs.

The kinetic mechanism of the anterior pituitary progesterone 5α-reductase

An analysis of the kinetic mechanism of the microsomal NADPH-linked progesterone 5α-reductase obtained from female rat anterior pituitaries was performed. Initial velocity, product inhibition and dead-end inhibition studies indicate that the kinetic mechanism for the progesterone 5α-reductase is equilibrium ordered sequential. Analysis of the initial velocity data resulted in intersecting double reciprocal plots suggesting a sequential mechanism [apparent K m(progesterone) = 88.2 ± 8.2 nM; apparent K ia(NADPH) = 7.7 ± 1.1 μM]. Furthermore, the plot of 1/v vs 1/progesterone intersected on the ordinale which is indicative of an equilibrium ordered mechanism. Additional support for ordered substrate binding was provided by the product inhibition studies with NADPH versus NADP and progesterone versus NADP. NADP is a competitive inhibitor versus NADPH (apparent K is = 7.8 ± 1.0 μM) and a noncompetitive inhibitor versus progesterone (apparent K is = 9.85 ± 2.1 μM and apparent K ii = 63.2 ± 12.5 μM). These inhibition patterns suggest that NADPH binds prior to progesterone. In sum, these kinetic studies indicate that NADPH binds to the microsomal enzyme in rapid equilibrium and preferentially precedes the binding of progesterone.

Pituitary progesterone 5α-reductase: Solubilization and partial characterization

The microsomal progesterone 5α-reductase activity from female rat anterior pituitary has been solubilized and partially characterized with regard to some of its kinetic and physical properties. The solubilization of progesterone 5α-reductase has been achieved through the use of either an n-octyl glucoside (OG)-KC1- or a digitonin-KCl-extraction. The total yield and specific activity of solubilized enzyme activity is greater using the OG-KC1 method. Kinetic analyses of microsomal and OG-KCl-solubilized progesterone 5α-reductase have indicated that both of these preparations exhibit a similar apparent K m for progesterone (microsomal K m = 117 ± 12 nM; solubilized K m = 123 ± 11 nM), suggesting that the solubilization procedure does not appreciably alter the kinetic behavior of this enzyme activity. The OG-KCl-extracted progesterone 5α-reductase activity also appears quite stable, since essentially no enzyme activity is lost following dialysis at 4°C for 22 h. In addition, the activity of the solubilized-dialyzed enzyme preparation can be slightly stimulated via the addition of phospholipids. Studies on the properties of the microsomal enzyme activity have indicated that this preparation is unaffected by metal chelators (EDTA or EGTA) but can be completely inhibited by the powerful sulfhydryl blocking agent p-chloromercuribenzoic acid. An evaluation of the possible role of flavins (as a hydride carrier between NADPH and the steroid) has shown that progesterone 5α-reduction is inhibited by high levels of flavins and flavin analogs.

Combined effects of vasoactive intestinal peptide and dopamine on adenylate cyclase in prolactin-secreting cells

VIP stimulates adenylate cyclase activity of male and female rat anterior pituitaries and human prolactinomas, while dopamine inhibits the enzyme activity of female rat pituitaries and prolactinomas. A dopamine inhibited cyclase can be detected also in male rats provided the enzyme activity is increased by VIP. The analysis of the dose-response curves for one agent (VIP or dopamine) in the absence or in the presence of the other indicates that the two agents exhibit a different pattern of interaction in the different systems. In fact, in female rat pituitaries and in human prolactinomas, the curves for dopamine±VIP and for VIP±dopamine were parallel, indicating that the two agents exherted their effects independently from one another. On the contrary, in male rat pituitaries, the curves were definitively non parallel, that is, the inhibitory effect of dopamine was greatly amplified by VIP. In no case was the apparent affinity (EC 50) of one agent modified by the presence of the other. It is concluded that two different modes of interaction between stimulatory and inhibitory neurohormones might exist at the level of adenylate cyclase from anterior pituitary cells.

Properties of rat anterior pituitary vasopressin receptors: relation to adenylate cyclase and the effect of corticotropin-releasing factor.

Crude plasma membrane fractions were prepared from female Wistar rat anterior pituitaries. These fractions contained a single population of specific 3H-labeled [8-lysine]vasopressin [( 3H]vasopressin) binding sites with a dissociation of constant (Kd) of 8 +/- 2 X 10(-9) M and maximal binding capacity of 244 +/- 45 fmol/mg of protein. The Kd values for a series of vasopressin structural analogues with selective vasopressor or antidiuretic activities were determined together with the corresponding corticotropin-releasing activities (isolated perfused pituitary cells were used). A good correspondence was found between the two sets of values, suggesting that the detected vasopressin binding sites are the receptors involved in vasopressin-induced corticotropin release. The order of potency of these analogues for the binding to hypophysial receptors was similar to that found for the binding to the receptors involved in the vasopressor response. Corticotropin-releasing factor and angiotensin did not affect vasopressin binding to pituitary membranes. Median eminence extracts inhibited [3H]vasopressin binding with an efficiency very close to that expected from their vasopressin content. Corticotropin-releasing factor activated, and angiotensin inhibited, the adenylate cyclase activity of pituitary membranes. Under the same experimental conditions, vasopressin did not influence adenylate cyclase activity nor did it affect the corticotropin-releasing factor-induced activation. These data support the view that vasopressin is one component of the multifactorial regulation of corticotropin release and that it acts through a cAMP-independent pathway. The potentiation by vasopressin of corticotropin-releasing factor-induced cAMP accumulation in intact cells very likely proceeds through indirect mechanisms, which are not expressed in broken cell preparations.

A developmental study of adenohypophyseal dopaminergic receptors and of haloperidol-induced prolactin release in rats

The ontogenesis of adenohypophyseal dopamine receptors, assessed by haloperidol-displaceable [ 3H]didydroergocryptine (DHE) binding of 1-, 12-, 20-, 28-day-old female rats was studied in correlation with the prolactin releasing effect of haloperidol (1 mg/kg), a dopaminergic antagonist. A specific dopaminergic receptor could be quantified at the time of birth (B max = 2.5 ± 0.5 fmol/mg; K d = 1.5 ± 0.2 μM), anterior pituitary receptor density (fmol bound/mg) increased non-significantly henceforth and a slight ontogenic increase of K d values was also observed. Haloperidol failed to increase prolactin in newborn female rats; at 4 days, a significant increase was evidenced, and from then onwards the response rose markedly with age. As sex differences in the dopaminergic modulation of prolactin release have been documented, the hyperprolactinemic effect of haloperidol in correlation with [ 3H]DHE binding in anterior pituitary of 28-day-old female and male rats was studied. Though the prolactinemic increment achieved by haloperidol was significantly higher in female than in male rats, [ 3H]DHE binding was not statistically different between sexes. These data indicate: (a) a specific binding site for [ 3H]DHE in anterior pituitary of female rats is present from the first postnatal days. From then onwards, a gradual but slight increment in both, B max and K d for the dopaminergic agonist is observed until puberty; (b) at 28 days, no clear difference in B max and K d is present in [ 3H]DHE binding between male and female rats; (c) by contrast, haloperidol shows a prolactin releasing effect that increases markedly with age in the female. At 28 postnatal days, serum prolactin levels attained after haloperidol in the female were significantly higher than those achieved in the male. Thus, differences of magnitude in the coupled response may sometimes not be accounted for by differences in number, or affinity, of receptor sites.

A high affinity inhibitor of pituitary progesterone 5 alpha-reductase.

The capacity of the 5 alpha-dihydroprogesterone analog, 4-aza-4-methyl-5 alpha-pregnane-3,20-dione (AMPD), to inhibit progesterone 5 alpha-reductase and both 5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase activities (NADPH- and NADH-linked) from the female rat anterior pituitary has been investigated. Dose response studies demonstrate that AMPD is a powerful inhibitor of pituitary progesterone 5 alpha-reduction but is ineffective at inhibiting either of the 3 alpha-hydroxysteroid oxidoreductase activities, even at concentrations up to 10 microM. A kinetic analysis of the interaction of AMPD with progesterone 5 alpha-reductase indicates that it is a competitive inhibitor vs. progesterone [Kislope = 7.2 +/- 0.6 nM; apparent Michaelis-Menten constant (Km) (progesterone) = 193 +/- 18 nM] and an uncompetitive inhibitor vs. NADPH (Kiintercept = 17.9 +/- 1.4 nM). These inhibition patterns are consistent with the view that NADPH binding precedes that of either AMPD or progesterone. Furthermore, AMPD does not appear to be an irreversible inhibitor since preincubation of the enzyme (at 37 C) with AMPD and NADPH, for periods of time up to 60 min, does not lead to a time-dependent loss of activity. The inhibition can also be readily removed by dilution, even after a 60-min preincubation with the inhibitor and NADPH. It is postulated that the selective and potent inhibition of the 5 alpha-reduction of progesterone by AMPD may be due to the steroid functioning as a transition state analog. This inhibitor should prove useful in studying the properties of progesterone 5 alpha-reductase and the function of anterior pituitary progestin metabolism.

Dopamine internalization by and intracellular distribution within prolactin cells and somatotrophs of the rat anterior pituitary as determined by quantitative electron microscopic autoradiography.

The internalization and intracellular distribution of [3H]dopamine in PRL cells and somatotrophs of the female rat anterior pituitary were investigated. Dissociated pituitary cells were incubated with [3H]dopamine for 5 min and subsequently chased in medium lacking radioactive dopamine for various time periods up to 3 h. The localization of [3H]dopamine was monitored by high resolution quantitative electron microscopic autoradiography. Results obtained by grain density analysis revealed that dopamine is internalized by these cells and sequestered in a multiplicity of intracellular membranous organelles. These included the lysosomes and those organelles involved in the secretory pathway, chief among which were the Golgi cisternae and the immature (type I and II) and mature (type III and IV) secretory granules. The highest grain density values throughout the entire chase period were recorded for the lysosomal compartment. This is consistent with the finding that approximately 70% of the internalized dopamine was lost from the PRL cells within the time frame of the chase period, most likely due to its metabolism or release. Although the overall grain density of the nucleus was low at all chase periods, analysis of the grain density distribution of the various nuclear profiles of the post-pulse time point revealed that nuclear labeling was not uniform, suggesting that dopamine is taken up by the nucleus and localized in discrete areas of this compartment. The internalization event itself was found to be a receptor-dependent one since the simultaneous incubation of pituitary cells with [3H] dopamine and physiological concentrations (10-5 M and 10-7 M) of its unlabeled analog resulted in a 50–60% decrease in the uptake of [3H]dopamine by PRL cells, as indicated by grain density analysis. Somatotrophs showed a similar pattern of dopamine internalization and sequestration with the exception that labeling of the Golgi cisternae could not be established with certainty by the analytical methods employed. The data obtained provide a firm morphological basis for the intracellular distribution of dopamine in the two numerically most frequent (PRL cells and somatotrophs) cell types of the rat anterior pituitary gland.

Progesterone, 5α-dihydroprogesterone and R5020 binding in female rat anterior pituitary

Progestin binding, which may represent receptor binding, was examined in female rat anterior pituitary cytosol. Specific progesterone, 5α-dihydroprogesterone (5α-DHP) and R5020 binding, as well as cortico-steroid binding globulin (CBG)-like complexes, were assayed in cytosol from five animal models: estradiol benzoate primed-ovariectomized-adrenalectomized (EB-OVX-ADX), ovariectomized-adrenalecto-mized (OVX-ADX), estradiol benzoate primed-ovariectomized (EB-OVX), ovariectomized (OVX) and intact rats. With all three progestins, estrogen priming consistently and significantly enhanced specific binding levels, and cytosol from EB-OVX-ADX rats had the greatest amount of binding. In contrast, presumptive CBG-like levels increased with adrenalectomy but not with EB treatment. Specific progesterone and 5α-DHP complexes dissociated more rapidly during Sephadex LH-20 elution than specific R5020 and CBG-like binding complexes. Maximal values for progesterone and 5α-DHP binding were rapidly attained at 4°C and the binding was decreased in the presence of protease, but not DNase or RNase. 5α-DHP binding had an apparent K d of 0.9 to 2 × 10 −9 M and the number of binding sites increased with EB treatment in the OVX-ADX rat. The 5α-DHP binding exhibited greater specificity for progestins (particularly progesterone and R5020) than for androgens, glucocorticoids or estradiol.

Estrogen interaction with the anterior pituitary of female rats differential cytosol binding, nuclear translocation and stimulation of RNA synthesis by 17β-estradiol and tamoxifen

The interaction of tamoxifen ( trans-1-( p- β-dimethylaminoethoxyphenyl)-1,2-diphenylbut-1-ene) with the cytosol estrogen receptor of the anterior pituitary of female rats was studied. No differences were recorded between incubations of cytosol samples with 17β-[ 3H]estradiol performed in the presence or absence of unlabeled 17β-estradiol and tamoxifen, respectively, thus suggesting that these interactions were at common receptor sites and excluding possible cooperative interactions. Competition experiments and Scatchard plot analysis of saturation experiments add further evidence for common receptor sites. A dissociation constant for tamoxifen of K d = 2 nM was recorded. Tamoxifen was found to be bound to a moiety sedimenting in the 4–5 S region, on a 6–24% linear sucrose density gradient at low salt concentrations, whereas 17β-estradiol sedimented in the 8–9 S area. These data suggest possible conformational changes of the receptor in the presence of tamoxifen. Furthermore, nuclear estrogen receptor levels remained elevated for at least 80 h after the application of tamoxifen alone or in a combination with 17β-estradiol, and a concomitant inhibition of cytosol receptor replenishment was noted. Tamoxifen and 17β-estradiol, respectively, were found to stimulate progesterone receptor levels when applied through 5 days. Tamoxifen plus 17β-estradiol administration elevated progesterone receptor contents above those found for each of the two compounds alone. On the other hand, tamoxifen enhanced the 17β-estradiol-induced prolactin serum levels, but did not stimulate prolactin serum levels by itself. These data combine to suggest that tamoxifen interacts with common estrogen receptor sites at the rat anterior pituitary.

Activity alterations of metabolic enzymes in the anterior pituitary of female rats during acute and chronic starvation, as well as after refeeding.

The activity of glycolysis and hexose monophosphate shunt decreases while the activity of some oxydative enzymes and acid phosphatase increases in the anterior pituitary of adult female rats during starvation. The alterations depend on the severity of starvation. The polypeptide hormone production also decreases. A close relationship exists between the metabolic activity of the gland and its endocrine function.

Conversion of testosterone into 5α-reduced metabolites in the anterior pituitary and in the brain of maturing rats

The anterior pituitary of normal female rats shows a considerable 5α-reductase activity. Such an activity is higher in the very first days of life and decreases from birth until the 28th day of age. The anterior pituitary of normal male rats also shows 5α-reductase activity, but this is smaller than that of the anterior pituitary of female animals. Significant differences between activities present in the two sexes can be observed from birth until the 21st day of age. A slight difference in the 5α-reductase activity of the hypothalami of maturing male and female animals has also been observed. As previously stated, the 5α-reductase activity of the anterior pituitary of female rats is much higher than that of male animals on day 14 of life. Castration performed on neonatal male rats brings about an increase in the 5α-reductase activity of their anterior pituitaries evaluated on day 14 of age. The levels of the enzyme become very similar to those found in the anterior pituitary of normal females of the same age. Conversely, the neonatal administration of testosterone propionate to female rats induces a decrease of the 5α-reductase activity of their pituitaries measured on day 14 of life. Such an activity becomes very similar to that of normal males of the same age. Analogous variations, although of a smaller magnitude, have been observed at hypothalamic level following neonatal castration in male animals or following neonatal administration of testosterone to female animals.

404. Control of estrogen receptors in male and female rat anterior pituitary and hypothalamus

We have previously shown that male and female rats possess similar levels of seemingly identical pituitary and hypo-hypothalamic cytoplasmic 17beta-estradiol (E2) receptors. The present study was designed to examine potential physiological modulators of receptor populations. Cytosol receptor binding was studied following injection of E2 (10 mcg) 17alpha-estradiol (25 mcg) or dimethylstilbestrol (50 mcg). All compounds depleted cytoplasmic receptor within 1 hour followed by greater than 50% cycloheximide-sensitive replenishment in 10 hours. No significant differences in response were observed between males and females. CI-628 (50 mcg) depleted male and female pituitary receptor but did not induce resynthesis. Hypothalamic depletion by CI-628 was more pronounced in the male (although neither sex showed total depletion in this tissue following CI-628). The influence of androgenic compounds on E2-receptor complex formation was also studied. Dihydrotestosterone (DHT) but not testosterone inhibited the rate of association between E2 and the cytosol receptor of either tissue. The inhibition was dose-dependent and did not appear to involve competition for binding sites. Thus male and female receptor systems in these tissues respond similarly to the compounds employed. Modulation of E2 binding by androgens may however be of importance in ultimate control of gonadotropin secretion.(FULL TEXT)

Release and synthesis of luteinizing hormone and follicle-stimulating hormone in pituitary cultures in response to hypothalamic preparations.

SummaryAddition of microgram amounts of highly purified porcine LH-RH twice daily for 3 days to female rat anterior pituitaries in vitro significantly increased the quantities of LH and FSH released. Total LH and FSH contents in stimulated tissue and medium exceeded those of controls as measured by radioimmunoassays for LH and FSH and by bioassay for FSH.