Pituitary galaninergic system activity in female rats: the regulatory role of gonadal steroids

The well-recognized sensitivity of the galanin gene in the anterior pituitary gland to estrogen suggests that estrogen receptor activity may influence the galaninergic system through modulation of galanin receptor (GALR) gene expression. Here, we evaluated the following: (i) the effects of estrogen on GALR mRNA expression; (ii) the estrogen receptor subtype that is specifically involved in this activity; and (iii) the effects of progesterone in the absence or presence of estrogen on galanin concentration in anterior pituitary gland. In the first experiment, ovariectomized 4-month-old rats were pre-treated subcutaneously with 17β-estradiol (3 x 20 μg), the ESR1 (ERα) agonist propyl pyrazole triol (PPT) (3 x 5 mg), and the ESR2 (ERβ) agonist diarylpropionitrile (DPN) (3 x 0.5 mg). In the second experiment, 4-month-old ovariectomized females received daily subcutaneous injections of 17β-estradiol (3 x 20 μg), progesterone (2 x 5 mg), or combined estradiol (3 x 20 μg) and progesterone (2 x 5 mg). Anterior pituitaries were excised the day after the final 17β-estradiol injection (experiment I) and 1 hour after receiving the second progesterone dose. Relative GALR1, GALR2, and GALR3 mRNA expression was evaluated using quantitative real-time PCR, and pituitary galanin concentration was determined using a specific radioimmunoassay. The results revealed that estrogen predominantly induced a 5-fold increase in GALR3 gene transcription. To a lesser extent, 17β-estradiol also increased GALR1 mRNA expression, but had no effect on GALR2 mRNA levels. The estrogen-induced increase in GALR3 gene expression occurred exclusively through ESR1 activation. The increase in GALR1 gene expression occurred through activation of both estrogen receptor subtypes, but the ESR2 subtype was predominantly involved. Furthermore, the results revealed that progesterone regulates the activity of the pituitary galaninergic system by facilitating estradiol-induced galanin synthesis in the female rat anterior pituitary gland.

The effect of valproate (VPA) treatment on inositol phosphates (IPs) accumulation in non-stimulated and GnRH-treated female rat anterior pituitary cells in vitro

OBJECTIVE

Mechanism(s) responsible for VPA-induced effects on reproductive axis activity are not fully recognized. Previously we reported that VPA suppressed only GnRH-stimulated but not the basal LH release from rat anterior pituitary (AP) cells in vitro. Since the inhibitory effect of VPA was exerted only in GnRH-activated cells, potential VPA impact on GnRH-R-coupled IP3/PKC signaling could not be excluded. In this study the effect of VPA on IPs synthesis in non-stimulated and GnRH-treated rat AP cells was examined.

MATERIAL AND METHODS

In the first experiment 5 × 105 cells/ml were incubated for 3h with VPA (10 nM-10 μM), PMA (100 nM), GnRH (100 nM), PMA (100 nM) + VPA (10 nM-10 μM), GnRH (100 nM) + VPA (10 nM-10 μM). In the second experiment cells were preincubated for 24h with 1μCi myo-[23 H]-inositol, then for 30 min with 10 mM LiCl and finally for 3hr with GnRH (100 nM) VPA (1 μM, 10 μM), GnRH (100 nM) + VPA (1 μM, 10 μM). LH concentration was measured by RIA and intracellular IPs accumulation by ion-exchange chromatography analysis.

RESULTS

VPA diminished GnRH-stimulated LH release without affecting PMA-induced LH release at any dose tested. Moreover, VPA-induced increase of IPs accumulation occurred in both non-stimulated and GnRH-treated cells and intensity of cellular response was similar in both groups.

CONCLUSION

VPA affects IP3/PKC pathway activity through its up-regulatory effect on IPs synthesis in AP cells. VPA-induced inhibition of GnRH-stimulated LH release from gonadotrope cells appears to be the result of still unrecognized cellular mechanism.

The evaluation of estradiol and leptin action on the activity of the somatotropic and gonadotropic axes in peripubertal female rats

OBJECTIVE

Available data suggest that estrogens and leptin play a role in the control of the pubertal process. In humans and some mammal species the increase of the activity of gonadotropic axis accompanies the decrease in the rate of growth at puberty. The effect of 17β-estradiol and/or leptin administration on the somatotropic and gonadotropic axes was studied using prepubertal female rats as an animal model.

MATERIAL AND METHODS

Prepubertal female rats received estradiol/saline, estradiol/leptin, oil/leptin or oil/saline (vehicles) respectively. The changes of growth rate, and serum 17β-estradiol, leptin, GH, IGF-I and gonadotropins levels as well as LHRH and estrogen receptor (ER) concentrations in the medial basal hypothalamus (MBH) and the pituitary were determined. All hormones concentrations were measured by radioimmunoassay and ER by radioligand methods .

RESULTS

In estradiol and/or leptin treated animals noticeable reduction of rate of growth was found. The decrease of growth in response to estradiol treatment accompanied the increase GH level and the decrease of IGF-I concentration in the circulation. Both hormones operating together activated reproductive axis, what was manifested by a significant increase of LHRH abundant in the hypothalamus as well as elevated LH and FSH levels in the circulation. In these rats a significant decrease of the estrogen receptor concentrations in the pituitary was observed.

CONCLUSION

The role of estradiol and leptin in the control of growth and reproduction seems to overlap only partially. Estradiol plays a significant role in the activation of the reproductive axis, and leptin takes part as a permissive factor in pubertal process.

Valproate inhibits GnRH-induced gonadotropin release from anterior pituitary cells of male rat in vitro

OBJECTIVE

Valproate (VPA) a potent antiepileptic drug has been claimed to induce reproductive disturbances in men. Long-term VPA treatment can affect sperm morphology and induce testicular atrophy in non-epileptic rats. It has been reported that VPA reduced testosterone secretion stimulated by hCG in isolated rat Leydig cells. These results suggest direct effect of VPA on testes in rats. However centrally mediated effects at hypothalamo-pituitary level can therefore not be excluded. This study focused on the dose and time-dependent effects of VPA on basal and GnRH-induced LH and FSH release from the primary anterior pituitary cells culture of male rats.

MATERIAL AND METHODS

The dose-dependent effect of 10 nM-100 mM of VPA on basal LH release from anterior pituitary cells after 3h of incubation was examined. To determine the time-dependent effects on LH, FSH, TSH and PRL release short (3 h) and long-term (24 h) incubations in the presence of 10 nM, 100 nM and 1 μM of VPA were maintained.To assess whether VPA can affect GnRH-induced LH and FSH release, cells were incubated for 3 h with 10 nM, 100 nM and 1 μM of VPA in the presence of GnRH. The concentration of rLH, rFSH, rPRL and rTSH in incubation medium was determined by RIA method.

RESULTS

VPA did not affect the basal LH, FSH, PRL and TSH release from the primary anterior pituitary cells culture of male rats. VPA in concentration 1µM significantly suppressed GnRH-induced LH secretion. However VPA at all tested doses diminished GnRH-induced FSH release.

CONCLUSIONS

VPA may diminish gonadotropin release in vitro but this effect can only be achieved after GnRH-dependent specific receptor activation. Both gonadotropins differ in their pattern of response for increasing doses of VPA.

The role of neuropeptides in the disturbed control of appetite and hormone secretion in eating disorders

OBJECTIVE

It has been reported that neuropeptides may play a role in the control of appetite and in the mechanism of hormone release. Neuropeptides such as beta-endorphin, neuropeptide Y (NPY), galanin and leptin may affect hormones release, on the other hand the hormonal status may modulate neuropeptide activity.

METHODS

The material consisted of 90 obese women, 30 women with Anorexia Nervosa, and 30 healthy, lean women of control group. Plasma beta-endorphin, NPY, leptin, somatostatin and serum pituitary and gonadal hormones concentrations were measured with RIA methods.

RESULTS

We observed the highest plasma NPY levels in obese hypertensive and diabetic patients. After carbohydrate administration (OGTT) a marked increase of insulin, beta-endorphin and NPY was found. The blunted response of GH to GH-RH may be connected with increased somatostatin activity and hyperinsulinemia. The abnormal response of LH to opioid blockade may be a result of disturbed opioid and NPY activities in obese patients. However in patients with anorexia nervosa, plasma leptin and NPY concentrations were low. The disturbances in beta-endorphin release are also observed.

CONCLUSIONS

The neuroendocrine disturbances in obesity and in anorexia nervosa are opposite. The feedback mechanism between leptin and NPY is disturbed in both in obesity and in anorexia nervosa. An abnormal activity of neuropeptides may lead to disturbed control of appetite and hormonal dysregulation in eating disorders.

The relationship between neuropeptides and hormones in starvation

OBJECTIVES

Some hormonal disturbances were demonstrated in starvation. Leptin, NPY and galanin play an important role in the control of appetite and in the mechanism of hormone release.

METHODS

In order to evaluate the effect of starvation on the relationship between leptin, neuropeptide Y (NPY) galanin and pituitary and gonadal hormones release, plasma leptin, NPY and galanin as well as serum LH, FSH, prolactin (PRL), estradiol, progesterone levels in non-starved female rats (in diestrus) and after 72 hrs of starvation were measured with RIA methods. Effects of leptin, NPY and galanin administration on pituitary and gonadal hormones were investigated in vivo and in vitro experiments.

RESULTS

Plasma leptin, NPY and galanin as well as serum estradiol and progesterone concentrations were significantly lower in starved rats as compared with non-starved rats. However serum prolactin level was significantly higher in starved rats. Opposite effects after leptin and NPY administration on hormone release in vivo and in vitro experiments were observed in non-starved rats. However, in starved rats we did not find changes in pituitary and gonadal hormones release after leptin, NPY and galanin injection or the hormonal response was blunted.

CONCLUSIONS

1) The disturbances in neuropeptides activity and in hormones release were observed in starvation. 2) Leptin, NPY and galanin have direct and indirect effects on pituitary and gonadal hormones release. 3) In starvation the hormonal response to leptin, NPY and galanin is impaired.

Plasma leptin, neuropeptide Y (NPY) and galanin concentrations in bulimia nervosa and in anorexia nervosa

OBJECTIVES

It has been reported that leptin and neuropeptide Y (NPY) play a role in the control of appetite and in the regulation of hormonal secretion.

METHODS

Plasma leptin, neuropeptide Y (NPY) and galanin concentrations were estimated in 13 women with bulimia nervosa (BN) 19 women with anorexia nervosa (AN) and in 19 healthy women of the control group (CG).

RESULTS

Plasma leptin concentration in BN was significantly higher than that in AN and it was lower as compared with the control group, despite the same BMI (body mass index) in both the groups. Plasma leptin level in AN was significantly lower as compared with the controls. Plasma galanin concentrations in AN and BN did not differ significantly from the control group. Plasma NPY concentration in AN was lower than that in the control group. However, plasma NPY level in BN was significantly higher as compared with AN and with the control group (CG). The observed increase of NPY in BN was independent of BMI because BMI in bulimia nervosa was normal.

CONCLUSIONS

The data may suggest that other factors than body weight changes may be involved in the modulation of leptin and NPY release in BN. The pathological behaviour of patients with bulimia nervosa may result from disturbed NPY release which is the strongest orexigenic factor.

New analogs of somatostatin: inhibiting effectively GH, glucagon and insulin levels

The in vivo effects of three new analogs of somatostatin (ASS-51, ASS-52 and ASS-53 analogs) on GH, insulin and glucagon were studied in WKY rats. The solid phase method was used for the synthesis of ASS. Octreotide and ASS were given iv. in a dose of 0.05 &mgr;g/kg per animal in a time-dependent manner. ASS-52 and ASS-53 were longer acting and more potent somatostatin analogs when compared to octreotide in producing the inhibition of GH. ASS-51 was found to be the most potent and selective inhibitor of insulin and glucagon release. Our results show that the increased inhibitory effect and the higher selectivity of the new somatostatin analogs may result from the differences in their chemical structure. ASS-52 is most active in inhibiting GH release. The mechanism by which ASS-52 inhibits preferentially GH release may involve the opioid system and the activation of GABA-ergic receptors. In studies in vitro ASS-52 inhibited GH release from pituitary cells" culture.

Effects of neuropeptide Y (NPY), galanin and vasoactive intestinal peptide (VIP) on pituitary hormone release and on ovarian steroidogenesis

Ovarian folliculogenesis is regulated by the gonadotrophins, but in recent years other peptides have been found to serve as local regulators of ovarian function. The aim of this study is to evaluate the effects of NPY, galanin and VIP on pituitary and gonadal hormone release. Effects of NPY, galanin and VIP on progesterone, estradiol production by cultured rat granulosa and effects of these peptides on pituitary hormone release by cultured pituitary cells were examined according to methods previously described. Maximal effects of NPY, galanin and VIP on pituitary hormone release and on gonadal steroids were observed after administration of 10 nM of these peptides during 60 mins incubation. VIP and NPY, but not galanin, stimulated PRL release from cultured pituitary cells. VIP increased also LH release whenever NPY and galanin did not change LH release from pituitary cells. Galanin, but not NPY and VIP, leads to an increase of GH production. VIP, NPY and galanin did not change TSH and FSH release. NPY, galanin and VIP markedly stimulated progesterone release from cultured granulosa cells. NPY, galanin and VIP did not change estradiol and testosterone release. Conclusions. Direct effects of NPY, galanin and VIP on pituitary hormone release may indicate their role in the mechanism of pituitary hormone release. A marked increase of progesterone from cultured granulosa cells after VIP, NPY and galanin suggests that these peptides may be involved in the local ovarian steroidogenesis.

Effects of growth hormone (GH) and growth hormone releasing hormone (GHRH) on progesterone and estradiol release from cultured rat granulosa cells

OBJECTIVES: It has been reported that GHRH-GH-IGF-1 system plays an important role in the regulation of ovarian follicular development and maturation. METHODS: In order to evaluate the direct effects of growth hormone releasing hormone (GHRH) and growth hormone (GH) on steroidogenesis, the effects of GHRH and GH on progesterone and estradiol release from cultured rat granulosa cells were examined. The progesterone and estradiol in supernatants were measured with RIA methods. RESULTS: Our results demonstrated that the addition of GH to the culture medium produced a marked stimulation of progesterone and estradiol. The stimulating effects were observed after administration of GH in all concentrations: 1, 10, 100 nM during 60 and 120 mins of incubation. During 240 mins of incubation the minimal stimulation of progesterone and estradiol was found. However, GHRH administered in 1, 10 and 100 nM did not change progesterone and estradiol release from cultured granulosa cells. CONCLUSION: Growth hormone (GH) but not GHRH has direct stimulating effects on progesterone release from cultured rat granulosa cells.

Disturbed release of gastrointestinal peptides in anorexia nervosa and in obesity

AIM

It is commonly accepted that some neuropeptides play an important role in the control of appetite and hormonal secretion. Several gastrointestinal peptides may affect on central control of appetite via vagal and spinal nerves. The aim of this study was to evaluate the release of gastrointestinal peptides in anorexia nervosa and in obesity, because in these diseases the disturbances in the control of appetite and hormonal secretion were found. Material consisted of 30 women with anorexia nervosa aged 16-29 years (mean 22 years) and 23 women with obesity aged 19-33 years (mean 29 years) and 25 lean women of control group.

METHODS

In women with anorexia nervosa as compared with control group we observed a significant increase of plasma vasoactive intestinal peptide (VIP) levels (p < 0.01) and a significant decrease of leptin (p < 0.001), beta-endorphin (p < 0.01), gastrin (p < 0.05), cholecystokinin (CCK; p < 0.05) and somatostatin (S-S; p < 0.01). In obese women we found a significant increase of neuropeptide Y (NPY; p < 0.001), leptin (p < 0.01), galanin (p < 0.001), beta-endorphin (p < 0.001), gastrin (p < 0.01), CCK (p < 0.001) and S-S (p < 0.01) and a significant decrease of VIP concentrations (p < 0.001) as compared with control group.

CONCLUSION

Our results indicate that the release of gastrointestinal peptides is disturbed in obesity and in anorexia nervosa. These findings suggests that dysfunction of brain-gut axis may be also an important factor in the abnormal control of appetite axcept of hypothalamic dysfunction.