Daily administration of gonadotrophin-releasing hormone increases pituitary gonadotroph number and pituitary gonadotrophin content, but not serum gonadotrophin levels, in female rats on day 1 of dioestrus

1992 ◽  
Vol 132 (3) ◽  
pp. 395-NP ◽  
Author(s):  
F. Kotsuji ◽  
K. Hosokawa ◽  
T. Tominaga
Keyword(s):  
Single Cells ◽  
Chronic Administration ◽  
Serum Levels ◽  
Female Rats ◽  
Female Rat ◽  
Dependent Manner ◽  
Releasing Hormone ◽  
Rat Pituitary ◽  
Gonadotrophin Releasing Hormone ◽  
Lh Cells

ABSTRACT Gonadotrophin-releasing hormone (GnRH) has been shown to regulate the synthesis and release of gonadotrophins acutely, yet few studies have investigated the chronic effects of this agent on pituitary gonadotrophins. In the present study we determined the effect of chronic administration of GnRH on the female rat pituitary gland. Rats of 8 weeks of age were injected s.c. with various doses of GnRH daily for 30 days. After completion of the GnRH treatment, treated rats and age-matched controls were killed by decapitation at 09.00 h on the first day of dioestrus, as determined from vaginal smears. Treatment with 10 ng–10 μg GnRH/day increased pituitary contents of FSH and LH in a dose-dependent manner. The change in FSH content was much greater than that of LH content. The pituitary FSH content of rats treated with 40 μg GnRH was significantly less than that of rats treated with 10 μg GnRH. There was a marked increase in the number of cells which stained positively for FSH (266%) and LH (28%) in the anterior pituitary of rats given 10 μg GnRH, but there was no demonstrable change in the areas of single cells stained positively for FSH and LH. Serum levels of LH, FSH and oestradiol were not affected by the GnRH treatment. These data indicate that chronic administration of GnRH is capable of increasing the pituitary gonadotrophin content and numbers of FSH and/or LH-stained cells and that FSH cells are affected more than LH cells by the GnRH treatment. The increase in pituitary gonadotrophin content, however, does not necessarily produce an increase in circulating levels of gonadotrophins. Journal of Endocrinology (1992) 132, 395–400

Divergent effects of gonadotrophin-releasing hormone (GnRH) analogue and authentic GnRH on the anterior pituitary gland of rats with restricted feeding

1995 ◽  
Vol 145 (3) ◽  
pp. 501-511 ◽  
Author(s):  
K Goto ◽  
F Kotsuji ◽  
T Tominaga
Keyword(s):  
Anterior Pituitary ◽  
Serum Levels ◽  
Female Rats ◽  
Gnrh Analogue ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Loading Test ◽  
Weekly Administration ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone

Abstract The effects of gonadotrophin-releasing hormone analogue (GnRHa; buserelin) on the pituitary function and morphology of food-restricted rats were compared with those of authentic GnRH. After adult female rats had been restricted to 10 g food/day for 60 days, various doses of GnRHa (10 ng, 100 ng and 1 μg) or GnRH (10 μg) were administered either daily for 7 days or twice a week for 4 weeks from day 61 of the period of underfeeding. Underfeeding brought about a decrease in the pituitary gonadotrophin content, serum levels of gonadotrophins and oestradiol, and the number and size of both LH- and FSH-positive pituitary cells. Daily and/or twice-weekly administration of authentic GnRH to underfed rats produced an increase in pituitary and serum gonadotrophin levels and the number and size of both LH- and FSH-positive pituitary cells. The administration of GnRHa daily for 7 days increased serum gonadotrophin levels, while it produced a reduction in the pituitary gonadotrophin content and number and size of both LH- and FSH-positive pituitary cells in a dose-dependent manner. Twice-weekly administration of GnRHa also produced an elevation of serum gonadotrophin levels and reduction of pituitary gonadotrophin content, although it did not affect the numbers and areas of LH- and FSH-positive pituitary cells. A GnRH loading test performed after the GnRHa treatment showed that the GnRHa treatment performed in this study did not produce down-regulation of the GnRH receptor. Thus, it can be concluded that the gonadotrophin-synthesizing activity of GnRHa is weaker than that of authentic GnRH, or that GnRHa may preferentially exert gonadotrophin-releasing activity rather than gonadotrophin-synthesizing activity in the anterior pituitary of underfed rats. Journal of Endocrinology (1995) 145, 501–511

IN-VITRO STUDIES OF THE EFFECTS OF OESTROGEN PRETREATMENT ON THE SENSITIVITY OF THE IMMATURE FEMALE RAT PITUITARY GLAND TO STIMULATION WITH GONADOTROPHIN RELEASING HORMONE

1977 ◽  
Vol 74 (1) ◽  
pp. 11-21 ◽  
Author(s):  
M. WILKINSON ◽  
D. DE ZIEGLER ◽  
DANIELLE CASSARD ◽  
K. B. RUF
Keyword(s):  
Pituitary Gland ◽  
Brain Lesion ◽  
Culture Technique ◽  
Female Rats ◽  
Female Rat ◽  
Immature Female ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
Unilateral Brain Lesion

The effects of oestrogen priming on the sensitivity of the anterior pituitary gland to stimulation with gonadotrophin releasing hormone (GnRH) was investigated in immature female rats using a new organ culture technique. Hemipituitary glands obtained from animals primed with a single dose of oestradiol benzoate (OB; 20 μg/100 g body weight) released significantly more LH when pulsed with GnRH (4 nmol/l) than did control hemipituitary glands. This potentiating effect was detectable as early as 5 days after birth. After a second stimulation, LH secretion remained high. These results were compared with those obtained from animals treated to induce increased levels of endogenous oestrogen on day 26 of life. Thus, hemipituitary glands were obtained from animals given two injections of OB, an injection of pregnant mare serum gonadotrophin (PMSG) or a unilateral brain lesion placed in the basal hypothalamus. Pituitary tissue was stimulated as before with a pulse of GnRH. Two injections of OB enhanced the sensitivity to stimulation. Conversely, both PMSG and lesion treatment severely reduced the sensitivity to GnRH, although PMSG-treated and lesioned animals have been used as models for the study of ovulation.

ANTERIOR PITUITARY SENSITIVITY IN IMMATURE FEMALE RATS STIMULATED WITH GONADOTROPHIN RELEASING HORMONE IN VIVO: EFFECT OF PRIMING WITH OESTROGEN, PREGNANT MARE SERUM GONADOTROPHIN OR BRAIN LESION

1977 ◽  
Vol 74 (1) ◽  
pp. 99-109 ◽  
Author(s):  
D. DE ZIEGLER ◽  
M. WILKINSON ◽  
DANIELLE CASSARD ◽  
K. B. RUF
Keyword(s):  
Brain Lesion ◽  
Treated Group ◽  
Female Rats ◽  
Similar Degree ◽  
Female Rat ◽  
Immature Female ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
Pregnant Mare Serum Gonadotrophin

An investigation of pituitary sensitivity, assessed in terms of increments in plasma LH and FSH concentrations, to stimulation with one or two injections of gonadotrophin releasing hormone (GnRH) was carried out on 26-day-old immature female rats which had received one of the following priming treatments: 10 μg oestradiol benzoate (OB) as a single injection on day 23 or day 25, or on both days; 10 i.u. pregnant mare serum gonadotrophin (PMSG) on day 24; an electrochemical brain lesion placed in the mediobasal hypothalamus on day 23; control animals received either vehicle alone or a sham lesion. Pituitary sensitivity assessed at 10.00 h on day 26, after one or two injections of GnRH (100 ng/100 g body weight, s.c.), was enhanced to a similar degree in the three groups treated with OB in terms of LH (P < 0-01). The FSH response also increased after OB treatment but was not statistically significant. In contrast, 48 h after the injection of PMSG (i.e. when the rats were in a 'pro-oestrous-like' condition) pituitary sensitivity in terms of both LH and FSH dropped sharply (P < 0·001). In lesioned animals, pituitary sensitivity to one injection of GnRH was unchanged. A second GnRH injection administered after a 60 min interval induced a slightly larger LH response in control animals. In contrast, the ratio of the second response to the first increased in animals treated with PMSG, despite the state of overall decrease in sensitivity, being 4·5:1 in PMSG-treated rats versus 1·4:1 in controls. In a second set of experiments, we investigated the variation of pituitary sensitivity in conjunction with an experimentally induced gonadotrophin surge. In animals treated with OB on day 23 and with 1 mg progesterone at 12·00 h on day 26, pituitary sensitivity was increased at both 14.00 and 17.00 h as compared with that in the day 23 OB-treated group at 10.00 h. The PMSG-treated animals maintained their state of decreased responsiveness at 14.00 h, but exhibited increased pituitary sensitivity at the time of the gonadotrophin surge (17.00 h). These results show that OB increases pituitary sensitivity to GnRH in 26-day-old female rats and that the induction of a gonadotrophin surge further increases this sensitivity. In contrast, PMSG-treated rats displayed a state of decreased responsiveness 48 and 52 h, but not 55 h, after the injection. Pituitary sensitivity on the second day after PMSG treatment thus clearly differs from that observed during pro-oestrus in the adult cyclic female rat.

Flurothyl-induced convulsions delay the onset of sexual maturation in the female rat

1982 ◽  
Vol 95 (1) ◽  
pp. 37-41 ◽  
Author(s):  
M. Wilkinson ◽  
R. Bhanot ◽  
J. A. Pincock ◽  
L. Donald
Keyword(s):  
Sexual Maturation ◽  
Serum Levels ◽  
Female Rats ◽  
Female Rat ◽  
Basal Serum ◽  
Age Related ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Related Increase

We have investigated whether sexual maturation in female rats is affected by repeated flurothyl-induced convulsions. This treatment had no effect on the normal age-related increase in body weight though puberty (vaginal opening) was significantly delayed when compared with non-convulsed control rats. In an attempt to probe the mechanism of this delaying effect we observed that (1) anterior pituitary response to gonadotrophin releasing hormone in vitro was normal in terms of LH release but FSH secretion was impaired and (2) progesterone injection in oestrogen-primed convulsed rats failed to generate an ovulatory-type surge of LH or FSH. Basal serum levels and basal in-vitro secretion of LH and FSH were normal. We conclude that repeated convulsions adversely affect the hypothalamo-pituitary-gonadotrophin system of immature female rats.

Effects of the daily administration of gonadotrophin-releasing hormone on the anterior pituitary gland of rats with restricted feeding

1992 ◽  
Vol 134 (2) ◽  
pp. 177-NP ◽  
Author(s):  
F. Kotsuji ◽  
K. Hosokawa ◽  
T. Tominaga
Keyword(s):  
Weight Loss ◽  
Weight Reduction ◽  
Anterior Pituitary ◽  
Serum Levels ◽  
Female Rats ◽  
Daily Administration ◽  
Pituitary Cells ◽  
Restricted Feeding ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone

ABSTRACT To investigate the influence of weight reduction on pituitary function and its modulation by gonadotrophin-releasing hormone (GnRH), female rats were restricted to 10 g food/day for 60 days. GnRH (5 μg) or saline (0·2 ml) were administered daily between days 31 and 60 of the period of underfeeding. Underfeeding brought about a decrease in the pituitary gonadotrophin content, serum levels of gonadotrophins and oestradiol, and the number and size of both LH- and FSH-positive pituitary cells. The administration of GnRH to underfed rats produced an increase in the pituitary and serum gonadotrophin levels and the number and size of both LH- and FSH-positive pituitary cells. These observations suggest that underfeeding and/or weight loss diminish the number and activity of the pituitary gonadotrophs, and that daily administration of GnRH both increases the number of gonadotrophs and augments their activity. Journal of Endocrinology (1992) 134, 177–182

Short-term effects of oestradiol and 4-hydroxyoestradiol on gonadotrophin-releasing hormone induced luteinizing hormone secretion by rat pituitary cells in culture

1986 ◽  
Vol 111 (3) ◽  
pp. 312-320 ◽  
Author(s):  
G. Emons ◽  
O. Ortmann ◽  
U. Fingscheidt ◽  
P. Ball ◽  
R. Knuppen
Keyword(s):  
Hormone Secretion ◽  
Female Rats ◽  
Pituitary Cells ◽  
Luteinizing Hormone Secretion ◽  
Releasing Hormone ◽  
Rat Pituitary ◽  
The Media ◽  
Gonadotrophin Releasing Hormone ◽  
Rat Pituitary Cells ◽  
Sensitizing Effect

Abstract. Dispersed pituitary cells from adult female rats were preincubated for different time periods (0– 12 h) in the absence or presence of 10−9 moestradiol (E2) or 4-hydroxyoestradiol (4-OHE2). Then the media were changed and the cells incubated for 4 h with either vehicle, or E2, or 4-OHE2 and additionally with different concentrations (10−11– 10−7 m) of gonadotrophin-releasing hormone (GnRH). Treatment of pituitary cells with E2 for 4 h (i.e. no preincubation with E2) significantly decreased the LH-response to GnRH at concentrations ≥ 10−10 m of the decapeptide. During a transition time of approximately 10 h (i.e. in cultures preincubated with E2 or vehicle for 2, 4, 6 or 8 h and then coincubated with E2 or vehicle and GnRH for 4 h) no differences between E2-and vehicle-treated cultures were observed. After 14 and 16 h of E2-treatment (i.e. 10 or 12 h preincubation and 4 h coincubation with GnRH) the LH-responses to GnRH in these cultures were significantly higher than in the respective controls. A nearly identical reaction pattern was observed when 4-OHE2 was used instead of E2. In a second series of experiments dispersed rat pituitary cells were suspended in a carrier gel and continuously perifused with medium, using small chromatography columns. When these cells were exposed for 4 min to 10−9 m GnRH at 60 or 48 min intervals, they reacted with reproducible pulsatile LH-discharges during at least 6 subsequent stimuli with the decapeptide. When E2 (10−9 m) was added to the perifusion medium, the LH-responses to GnRH were significantly reduced, starting 36 min after the onset of E2-treatment. These data indicate: 1) In the rat, the negative oestrogen effect is at least in part directly mediated at the pituitary level. 2) The sensitizing effect of oestrogens on rat gonadotrophs to GnRH is significant already after 14 to 16 h. 3) E2 and the catecholoestrogen 4-OHE2 have the same effects in this system. 4) The negative E2-effect on GnRH-induced LH-release is significant after only 36 min, a finding bringing up the question of a non-genomic mechanism.

scholarly journals Direct Stimulatory Effects of Oxytocin in Female Rat Gonadotrophs and Somatotrophs In Vitro: Comparison With Lactotrophs

Endocrinology ◽  
2014 ◽  
Vol 156 (2) ◽  
pp. 600-612 ◽  
Author(s):  
Arturo E. Gonzalez-Iglesias ◽  
Patrick A. Fletcher ◽  
José A. Arias-Cristancho ◽  
Ruth Cristancho-Gordo ◽  
Cleyde V. Helena ◽  
...  
Keyword(s):  
Receptor Antagonist ◽  
Cell Types ◽  
Pituitary Hormones ◽  
Prolactin Secretion ◽  
Female Rats ◽  
Pituitary Cells ◽  
Female Rat ◽  
Dependent Manner ◽  
Rat Pituitary Cells

The peptide oxytocin (OT) is secreted by hypothalamic neurons and exerts numerous actions related to reproduction. OT stimulation of prolactin secretion in female rats is important during the estrous cycle, pregnancy, and lactation. Here we report that OT also stimulates transients of intracellular Ca2+ concentration in somatotrophs and gonadotrophs as well as the release of GH and LH in a dose-dependent manner with EC50 values that closely correspond to the ligand affinity of the OT receptor (OTR). Remarkably, the hormone-releasing effect of OT in these two cell types is 2 orders of magnitude more sensitive than that in lactotrophs. The specific OTR agonist [Thr4,Gly7]-oxytocin acutely stimulated the release of LH, GH, and prolactin from female rat pituitary cells in primary culture and increased intracellular Ca2+ concentration in gonadotrophs, somatotrophs, and lactotrophs. In these three cell types, the effects on hormone release and intracellular Ca2+ of both OT and [Thr4,Gly7]oxytocin were abolished by the specific OT receptor antagonist desGly-NH2-d(CH2)5[D-Tyr2,Thr4]OVT but not by the highly selective vasopressin V1a receptor antagonist, d(CH2)5[Tyr(Me)2,Dab5]AVP. Furthermore, 10 nM arginine vasopressin stimulated LH and GH release comparably with a dose of OT that was at least 10 times lower. Finally, the presence of the OTR-like immunoreactivity could be observed in all three cell types. Taken together, these results show that OT directly stimulates gonadotrophs, somatotrophs, and lactotrophs through OT receptors and suggest that OT signaling may serve to coordinate the release of different pituitary hormones during specific physiological conditions.

Induction of growth hormone (GH) mRNA by pulsatile GH-releasing hormone in rats is pattern specific

2000 ◽  
Vol 278 (5) ◽  
pp. E885-E891 ◽  
Author(s):  
Russell J. Borski ◽  
Wellington Tsai ◽  
Roberta Demott-Friberg ◽  
Ariel L. Barkan
Keyword(s):  
Growth Hormone ◽  
Weight Gain ◽  
Body Weight Gain ◽  
Somatic Growth ◽  
Pulse Amplitude ◽  
Female Rats ◽  
Mrna Levels ◽  
Female Rat ◽  
Constant Frequency ◽  
Releasing Hormone

Growth hormone-releasing hormone (GHRH) is a main inducer of growth hormone (GH) pulses in most species studied to date. There is no information regarding the pattern of GHRH secretion as a regulator of GH gene expression. We investigated the roles of the parameters of exogenous GHRH administration (frequency, amplitude, and total amount) upon induction of pituitary GH mRNA, GH content, and somatic growth in the female rat. Continuous GHRH infusions were ineffective in altering GH mRNA levels, GH stores, or weight gain. Changing GHRH pulse amplitude between 4, 8, and 16 μg/kg at a constant frequency (Q3.0 h) was only moderately effective in augmenting GH mRNA levels, whereas the 8 μg/kg and 16 μg/kg dosages stimulated weight gain by as much as 60%. When given at a 1.5-h frequency, GHRH doubled the amount of GH mRNA, elevated pituitary GH stores, and stimulated body weight gain. In the rat model, pulsatile but not continuous GHRH administration is effective in inducing pituitary GH mRNA and GH content as well as somatic growth. These studies suggest that the greater growth rate, pituitary mRNA levels, and GH stores seen in male compared with female rats are likely mediated, in part, by the endogenous episodic GHRH secretory pattern present in males.

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