Effect of chronic exposure to a gonadotrophin-releasing hormone agonist on in vitro responsiveness of ovine pituitary cells to inhibin, activin and oestradiol

1994 ◽  
Vol 140 (3) ◽  
pp. 483-493 ◽  
Author(s):  
S Muttukrishna ◽  
P G Knight
Keyword(s):  
Gnrh Agonist ◽  
Inhibitory Effect ◽  
Pituitary Cells ◽  
Cell Content ◽  
Releasing Hormone ◽  
Basal Release ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

Abstract To investigate the extent to which the direct actions of inhibin, activin and oestradiol on pituitary output of FSH and LH are dependent on the presence of functional gonadotrophin-releasing hormone (GnRH) receptors, we have compared the effects of these agents on cultured ovine pituitary cells derived from control and GnRH agonist-suppressed ewes. Chronic treatment with GnRH agonist reduced plasma LH and FSH levels (P<0·01) and abolished GnRH-induced release of LH and FSH both in vivo and in vitro. As expected, basal LH release and LH cell content in vitro were drastically reduced in GnRH agonist-suppressed cells (P<0·001). However, basal FSH release and FSH cell content were approximately twofold higher than in control cells (P<0·001). Irrespective of whether the cells had been desensitized to GnRH, inhibin and oestradiol were both found to suppress basal FSH release and FSH cell content in a dose-dependent fashion (P<0·001). Although inhibin had no effect on basal release of LH from control cells, it markedly enhanced GnRH-induced release (P<0·001). In contrast, inhibin increased (P<0·001) basal LH release from GnRH agonist-suppressed cells (which were unresponsive to the GnRH challenge). Inhibin had no overall effect on total LH content/well for either control or GnRH agonist-suppressed cells. Treatment with oestradiol, on the other hand, reduced total LH content/well, an effect which was more pronounced with GnRH agonist-suppressed cells (−44%; P<0·001) than with control cells (−14%, P<0·01). Whereas in control cells activin had no significant effect on any aspect of FSH production examined, in GnRH agonist-treated cells activin enhanced basal FSH release, residual cell content and total FSH content/well (P<0·001). Altering GnRH receptor status also modified the LH response to activin. With control cells activin increased basal release (P<0·001), decreased GnRH-induced release (P<0·001) and increased total LH content/well (P<0·001). With GnRH agonist-treated cells, however, activin had a uniform inhibitory effect on each aspect of LH production examined (P<0·001 in each case). It was concluded that desensitization of ovine gonadotrophs to GnRH by chronic agonist treatment results in a paradoxical enhancement of FSH output in vitro but has little effect on the responsiveness of the cells (in terms of gonadotrophin release and content) to either inhibin or oestradiol. In contrast, GnRH agonist treatment leads to qualitative changes in cellular reponsiveness to activin. Journal of Endocrinology (1994) 140, 483–493

Effects of crude and highly purified bovine inhibin (Mr 32 000 form) on gonadotrophin production by ovine pituitary cells in vitro: inhibin enhances gonadotrophin-releasing hormone-induced release of LH

1990 ◽  
Vol 127 (1) ◽  
pp. 149-159 ◽  
Author(s):  
S. Muttukrishna ◽  
P. G. Knight
Keyword(s):  
Primary Cultures ◽  
Suppressive Effect ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Α Subunit ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Primary cultures of ovine pituitary cells (from adult ewes) were used to investigate the actions of steroid-free bovine follicular fluid (bFF) and highly-purified Mr 32 000 bovine inhibin on basal and gonadotrophin-releasing hormone (GnRH)-induced release of FSH and LH. Residual cellular contents of each hormone were also determined allowing total gonadotrophin content/well to be calculated. As in rats, both crude and highly purified inhibin preparations promoted a dose (P < 0·001)- and time (P < 0·001)-dependent suppression of basal and GnRH-induced release of FSH as well as an inhibition of FSH synthesis, reflected by a fall in total FSH content/well. However, while neither inhibin preparation affected basal release of LH or total LH content/well, GnRH-induced LH release was significantly (P< 0·001) increased by the presence of either bFF (+ 75%) or highly-purified inhibin (+ 64%) in a dose- and time-dependent manner. This unexpected action of bFF on GnRH-induced LH release was abolished in the presence of 5 μl specific anti-inhibin serum, confirming that the response was indeed mediated by inhibin. Furthermore, neither oestradiol-17β (1 pmol/l–10 nmol/l) nor monomeric α-subunit of bovine inhibin (2·5–40 ng/ml) significantly affected basal or GnRH-induced release of LH. These in-vitro findings for the ewe lend support to a number of recent in-vivo observations and indicate that, in addition to its well-documented suppressive effect on the synthesis and secretion of FSH, inhibin may actually facilitate LH release in this species, in marked contrast to its action in the rat. Journal of Endocrinology (1990) 127, 149–159

In-vivo inhibition of the preovulatory LH surge by substance P and in-vitro modulation of gonadotrophin-releasing hormone-induced LH release by substance P, oestradiol and progesterone in the female rat

1991 ◽  
Vol 130 (2) ◽  
pp. 169-175 ◽  
Author(s):  
T. Battmann ◽  
S. Mélik Parsadaniantz ◽  
B. Jeanjean ◽  
B. Kerdelhué
Keyword(s):  
Substance P ◽  
Inhibitory Effect ◽  
Female Rat ◽  
Neuroendocrine Control ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

ABSTRACT The effects of substance P (SP) on the preovulatory surge of LH and on the inhibitory and stimulatory effects of oestradiol-17β and progesterone on gonadotrophin-releasing hormone (GnRH)-induced LH release were investigated in vivo and in vitro in the rat. A single s.c. injection of 100 μg SP at 12.00 h on the day of pro-oestrus significantly decreased the preovulatory surge of LH. In vitro, the inhibitory effect of oestradiol-17β on GnRH-induced LH release was not modified by treatment with SP. The stimulatory effect of progesterone on GnRH-induced LH release was reduced by treatment with SP. It is concluded that SP may play a modulatory role in the neuroendocrine control of the preovulatory LH surge. Journal of Endocrinology (1991) 130, 169–175

Stimulatory effect of thyrotrophin-releasing hormone (TRH) on the release of luteinizing hormone (LH) from rat anterior pituitary cells in vitro

1983 ◽  
Vol 61 (2) ◽  
pp. 186-189 ◽  
Author(s):  
Noboru Fujihara ◽  
Masataka Shiino
Keyword(s):  
Luteinizing Hormone ◽  
Anterior Pituitary ◽  
Pituitary Cells ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Anterior Pituitary Cells ◽  
Lh Release ◽  
Lh Rh

The effect of thyrotrophin-releasing hormone (TRH, 10−7 M) on luteinizing hormone (LH) release from rat anterior pituitary cells was examined using organ and primary cell culture. The addition of TRH to the culture medium resulted in a slightly enhanced release of LH from the cultured pituitary tissues. However, the amount of LH release stimulated by TRH was not greater than that produced by luteinizing hormone – releasing hormone (LH–RH, 10−7 M). Actinomycin D (2 × 10−5 M) and cycloheximide (10−4 M) had an inhibitory effect on the action of TRH on LH release. The inability of TRH to elicit gonadotrophin release from the anterior pituitary glands in vivo may partly be due to physiological inhibition of its action by other hypothalamic factor(s).

The effect of gonadotrophin surge-inhibiting factor on the self-priming action of gonadotrophin-releasing hormone in female rats in vitro

1992 ◽  
Vol 134 (3) ◽  
pp. 427-436 ◽  
Author(s):  
D. W. Koppenaal ◽  
A. M. I. Tijssen ◽  
J. de Koning
Keyword(s):  
Protein Synthesis ◽  
Priming Effect ◽  
The Self ◽  
Pituitary Cells ◽  
Inhibiting Factor ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Functional Antagonism

ABSTRACT The present study was designed to explore further the functional antagonism between gonadotrophin-releasing hormone (GnRH) and the ovarian factor, gonadotrophin surge-inhibiting factor (GnSIF). In all experiments, pituitary tissue was exposed to various amounts of GnSIF, after which the self-priming action of GnRH was studied. GnSIF was increased in vivo by FSH treatment and increased in vitro by adding various amounts of follicular fluid (FF) to cultured pituitary cells. Treatment with 3 or 10 IU FSH suppressed the initial LH response and delayed the maximally primed LH response to GnRH. Treatment with FSH was only effective in intact rats on days 1 and 2 of dioestrus. There was no difference in the rate of maximal LH release irrespective of treatment with either FSH or saline. Since FSH treatment was ineffective in long-term ovariectomized rats, it was concluded that the initial suppressive effect of FSH on LH release was mediated by GnSIF. Cycloheximide prevented the self-priming action of GnRH by inhibiting GnRH-induced protein synthesis. The initial protein synthesis-independent GnRH-stimulated LH release, which was already suppressed by FSH treatment, remained suppressed in the presence of cycloheximide. Pretreatment with GnRH in vivo increased the protein synthesis-independent GnRH-induced LH release during subsequent incubation of the glands. This increase did not occur after FSH treatment. Pituitary cells, cultured for 20 h in medium only, failed to elicit the self-priming effect of GnRH. Preincubation with FF maintained the self-priming effect. This was independent of the concomitant presence of various amounts of oestradiol. Preincubation with bovine FF suppressed the initial GnRH-stimulated LH release dose-dependently. Porcine FF, human FF and testicular extract suppressed the release of LH in a similar way. It was concluded that GnSIF suppresses the initial LH response to continuous GnRH stimulation. Increased levels of GnSIF caused by FSH treatment also delayed the primed LH release. The mechanism of functional antagonism between GnSIF and GnRH could give rise to the occurrence of the phenomenon of GnRH self-priming. Journal of Endocrinology (1992) 134, 427–436

Effects of 31 kDa bovine inhibin on FSH and LH in rat pituitary cells in vitro: antagonism of gonadotrophin-releasing hormone agonists

1988 ◽  
Vol 119 (2) ◽  
pp. 233-241 ◽  
Author(s):  
P. G. Farnworth ◽  
D. M. Robertson ◽  
D. M. de Kretser ◽  
H. G. Burger
Keyword(s):  
Pituitary Cells ◽  
Sprague Dawley ◽  
Releasing Hormone ◽  
Pretreatment Period ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Constitutive Synthesis ◽  
Rat Pituitary Cells ◽  
Median Effective Concentration

ABSTRACT The effects of 31 kDa bovine inhibin on the release of FSH and LH stimulated by gonadotrophin-releasing hormone (GnRH) or its agonist analogue buserelin have been studied using 5-day-old cultures of pituitary cells prepared from adult male Sprague–Dawley rats. Exposure of cultures to increasing concentrations of inhibin for 3 days before and during a 4-h stimulation with GnRH resulted in the progressive suppression of both basal and stimulated gonadotrophin release. At the highest inhibin concentrations FSH release was abolished (inhibin median inhibitory concentration (IC50) = 0·15 U/ml) whereas LH release was suppressed by 75% (IC50 = 0·93 U/ml). To correct for the reduced size of the FSH pool resulting from inhibin pretreatment, the amount of FSH or LH released by an agonist was expressed as a proportion of the total hormone available for release in each case. Following this adjustment, concentrations of inhibin producing maximal effects increased the GnRH median effective concentration for FSH release 4·1-fold and that for LH release 2·2-fold, with inhibin IC50 values of 0·45 and 0·32 U/ml respectively. Inhibin also suppressed the maximum proportion of both FSH and LH that excess GnRH released in 4 h by 36%, with IC50 values of 0·53 and 0·76 U/ml respectively. These effects were not changed by reduction of the inhibin pretreatment period from 3 days to 1 day or by exclusion of inhibin during the stimulation period. After a 3-day pretreatment, inhibin inhibited gonadotrophin release by buserelin less effectively than that by GnRH, but the pattern of antagonism was the same. The results show that purified bovine inhibin antagonizes the release of both FSH and LH stimulated by either GnRH or buserelin in vitro by reducing the apparent potency of GnRH agonists and by decreasing the proportion of total available gonadotrophin that can be released by an excess of GnRH agonist. Higher concentrations of inhibin are required for these common actions against stimulated release of FSH and LH than for the inhibition of FSH tonic synthesis/basal release, indicating one or more secondary sites of inhibin action in addition to its primary selective action to suppress the constitutive synthesis of FSH. J. Endocr. (1988) 119, 233–241

Effects of in vivo gonadal hormone environment on in vitro hGRF-40-stimulated GH release

1985 ◽  
Vol 249 (3) ◽  
pp. E276-E280 ◽  
Author(s):  
W. S. Evans ◽  
R. J. Krieg ◽  
E. R. Limber ◽  
D. L. Kaiser ◽  
M. O. Thorner
Keyword(s):  
Female Rats ◽  
Male Rats ◽  
Gonadal Hormone ◽  
Base Line ◽  
Pituitary Cells ◽  
Intact Male ◽  
Castrate Male ◽  
Basal Release

The effects of gender and the gonadal hormone environment on basal and stimulated growth hormone (GH) release by dispersed and continuously perifused rat anterior pituitary cells were examined. Cells from intact male and diestrus day 2 female rats and from castrate male rats either untreated or treated with testosterone (T) or 17 beta-estradiol (E2) were used. Basal GH release (ng/min per 10(7) cells; mean +/- SE) by cells from diestrus day 2 female rats was less than by cells from castrate rats treated with T (4.3 +/- 0.6 vs. 11.4 +/- 2.7, respectively; P less than 0.025). No other differences in basal release were detected. Concentration-response relationships were documented between human GH-releasing factor 40 (hGRF-40; 0.03-100 nM given as 2.5-min pulses every 27.5 min) and GH release. Mean (+/- SE) overall GH release (ng/min per 10(7) cells) above base line was greater by cells from intact male rats (496 +/- 92) than by cells from castrate (203 +/- 37.3; P less than 0.0001), castrate and T-treated (348 +/- 52.8; P = 0.008), or castrate and E2-treated (58.1 +/- 6.8; P less than 0.001) male rats or by diestrus day 2 rats (68.6 +/- 9.5; P = 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Varying the patterns and concentrations of gonadotrophin-releasing hormone stimulation does not alter the ratio of LH and FSH released from perifused sheep pituitary cells

1986 ◽  
Vol 109 (2) ◽  
pp. 155-161 ◽  
Author(s):  
J. E. A. McIntosh ◽  
R. P. McIntosh
Keyword(s):  
Dose Response ◽  
Dose Interval ◽  
Follicular Phase ◽  
Pituitary Cells ◽  
Ovulatory Cycle ◽  
Short Term ◽  
Releasing Hormone ◽  
Dissociated Cells ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Our aim was to determine whether release of LH and FSH can be controlled differentially by the characteristics of applied signals of stimulatory gonadotrophin-releasing hormone (GnRH) alone, free of the effects of steroid feedback or other influences from the whole animal. The outputs of both gonadotrophins were significantly correlated (r≈0·90; P<0·0005) when samples of freshly dispersed sheep pituitary cells were perifused in columns for 7 h with medium containing a range of concentrations of GnRH in various patterns of pulses. Hormone released in response to the second, third and fourth pulses from every column was analysed in detail. Dose–response relationships for both LH and FSH were very similar when cells were stimulated with 5–8500 pmol GnRH/1 in 5-min pulses every hour. When GnRH was delivered in pulses at a maximally stimulating level, the outputs of both hormones increased similarly with increasing inter-pulse intervals. Efficiency of stimulation (release of gonadotrophin/unit stimulatory GnRH) decreased (was desensitized) with increasing pulse duration in the same way for both hormones. Thus, varying the dose, interval and duration of GnRH pulses did not alter the proportions of LH and FSH released in the short-term from freshly dissociated cells. However, the same cell preparations released more LH relative to FSH when treated with maximally stimulating levels of GnRH for 3 h in the presence of 10% serum from a sheep in the follicular phase of its ovulatory cycle compared with charcoal-treated serum. Because there was no gonadotrophin synthesis under the conditions used in vitro these results suggest that changes in the LH/FSH ratio seen in whole animals are more likely to result from differential clearance from the circulation, ovarian feedback at the pituitary, differential synthesis in intact tissue or another hormone influencing FSH secretion, rather than from differences in the mechanism of acute release controlled by GnRH. J. Endocr. (1986) 109, 155–161

Effect of basal and pulsatile LH release on FSH-stimulated follicle growth in ewes chronically treated with gonadotrophin-releasing hormone agonist

1991 ◽  
Vol 128 (3) ◽  
pp. 449-456 ◽  
Author(s):  
H. M. Picton ◽  
A. S. McNeilly
Keyword(s):  
Gnrh Agonist ◽  
Follicular Development ◽  
Follicle Growth ◽  
Releasing Hormone ◽  
Normal Number ◽  
Stage Of Development ◽  
Normal Diameter ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Follicular Response

ABSTRACT Ewes chronically treated with gonadotrophin-releasing hormone (GnRH) agonist were used to investigate the importance of the peripheral concentration of LH in FSH-stimulated follicular development. Twenty-four Welsh Mountain ewes were treated with two agonist implants containing 3·3 mg buserelin. During week 6 of treatment all the ewes were given a 72-h continuous infusion of ovine FSH alone (3 μg/h) or FSH with large (7·5 μg)- or small (2·5 μg) amplitude pulses of ovine LH delivered at 4-hourly intervals. The importance of baseline LH throughout the FSH infusion was evaluated in six animals which were treated with a specific antiserum against bovine LH (LH-AS) 15–20 h before the start of FSH treatment. In the absence of LH-AS, infusion of FSH alone or with large or small pulses of LH stimulated the development of a normal number of small follicles (≤ 2·5 mm in diameter) and large follicles (> 2·5 mm in diameter). These follicles had normal diameter and steroid secretion compared with control ewes on day 8 of the luteal phase. In contrast, the animals pretreated with LH-AS developed no follicles > 2·0 mm in diameter but the number of small follicles per ewe was significantly (P < 0·05) increased. These results support the hypothesis that FSH in the absence of pulsatile LH release stimulates preovulatory follicular development in ewes treated with GnRH agonist. The follicular response to LH pulses of different amplitude is dependent on both the stage of development of the follicle and the peripheral concentration of FSH. The endogenous basal level of LH present throughout the FSH infusion is essential for FSH to induce follicle growth beyond > 2·5 mm in diameter. Journal of Endocrinology (1991) 128, 449–456

Dichotomic action of glucocorticoids on growth hormone secretion

1987 ◽  
Vol 116 (2) ◽  
pp. 165-171 ◽  
Author(s):  
Koji Nakagawa ◽  
Tatsuya Ishizuka ◽  
Takao Obara ◽  
Miyao Matsubara ◽  
Kazumasa Akikawa
Keyword(s):  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Inhibitory Effect ◽  
Female Rats ◽  
Pituitary Cells ◽  
Gh Secretion ◽  
Normal Rat ◽  
Rat Pituitary Cells

Abstract. The mechanism of apparently discrepant actions of glucocorticoids (GC) on GH secretion, in vivo suppression and in vitro potentiation, was studied in rats. Dexamethasone (Dex), at the concentration of 50 nmol/l, Potentiated basal and GHRH-stimulated GH release from monolayer culture of normal rat pituitary cells in 48 h. On the other hand, in vivo administration of Dex, 165 μg daily for 3 days, consistently suppressed serum GH levels in female rats. In these rats, the hypothalamic content of immunoreactive (IR) SRIH was significantly increased, whereas that of IR-GHRH was significantly decreased in comparison with the untreated rats. Bioassayable GH-releasing activity was also lower in Dex-treated rats. These findings indicate that the suppressing effect of GC on GH release in vivo is, at least partially, due to the increase in hypothalamic SRIH release and probably also to the decrease in GHRH release, and these effects surpass the potentiating effect of GC on GH release at the pituitary level, resulting in a net inhibitory effect in vivo.

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