Effect of pre-treatment of long-term ovariectomized rats with anti-LRH on the response of the pituitary gland in vitro to the analogue of LRH D-ser-(tBu)6-des-gly10-ethylamide-LRH (Buserelin®)

1983 ◽  
Vol 104 (3) ◽  
pp. 272-278 ◽  
Author(s):  
G. P. van Rees ◽  
J. A. M. J. van Dieten ◽  
J. de Koning ◽  
A. F. P. M. de Goey
Keyword(s):  
Pituitary Gland ◽  
Ovariectomized Rats ◽  
Rabbit Serum ◽  
Normal Rabbit Serum ◽  
Basal Release ◽  
Pituitary Glands ◽  
Lh Release ◽  
Pre Treatment

Abstract. Ovariectomized rats were injected iv with an antiserum against LRH or normal rabbit serum. AntiLRH caused a decrease of plasma LH and FSH. After 24 or 48 h, the rats were decapitated and the pituitary glands incubated in the presence of an analogue of LRH which reacts minimally with anti-LRH (Buserelin). Pretreatment with anti-LRH caused an increased response of pituitary LH release to Buserelin. Similar results were obtained with regard to FSH. In this case, however, basal release of FSH was lowered by pre-treatment with antiLRH. Pituitary LH and FSH contents were not affected by anti-LRH, but synthesis of LH and FSH in vitro was smaller than in control glands obtained from rats pretreated with normal rabbit serum.

Release of LH in vitro from anterior pituitary glands of ovariectomized rats by LRH or elevated potassium concentration after pre-treatment with oestradiol benzoate in vivo

1982 ◽  
Vol 99 (2) ◽  
pp. 206-210 ◽  
Author(s):  
A. M. I. Tijssen ◽  
J. de Koning ◽  
G. P. van Rees
Keyword(s):  
Ovariectomized Rats ◽  
Bicarbonate Buffer ◽  
High K ◽  
Oestradiol Benzoate ◽  
Negative Effect ◽  
Pituitary Glands ◽  
Lh Release ◽  
Pre Treatment ◽  
Positive Effect

Abstract. Pituitary glands from ovariectomized rats which had been pre-treated with oestradiol benzoate (OeB) or solvent oil were incubated in Krebs-Ringer bicarbonate buffer with glucose containing either LRH (1000 ng/ml) or a high K+ concentration (50 mM). OeB (7 μg sc) or oil was injected at 2.5 or 6.5 h before the beginning of the incubation experiment or during the three preceding days (three daily injections). Depending upon the period during which the pituitary glands had been exposed to OeB LH release induced by LRH was inhibited (negative effect of OeB) or augmented (positive effect). When the glands were incubated in medium containing high K+, only the negative effect of OeB pre-treatment was seen. It is concluded that that part of LRH-induced LH release which is mimicked by high K+ is involved in the negative effect of OeB, but not in its positive effect.

Effect of pretreatment of long-term ovariectomized (OVX) rats with a competitive LRH antagonist on FSH release in vitro

1985 ◽  
Vol 109 (4) ◽  
pp. 481-484
Author(s):  
J. A. M. J. van Dieten ◽  
G. P. van Rees
Keyword(s):  
Specific Effect ◽  
High Concentration ◽  
Ovx Rats ◽  
High K ◽  
Basal Release ◽  
Pituitary Glands ◽  
Lh Release ◽  
Release In Vitro

Abstract. The effect of a single sc injection of an LRH antagonist ((Ac - D - p - Cl - Phe1,2,D-Trp3,D-Phe6,D-Ala10)-LRH, Org 30093) into OVX rats on FSH release 24 h later was studied. Plasma FSH was decreased but pituitary FSH content was not changed. Incubation of the pituitary glands during 4 h resulted in a decreased basal release. FSH release induced by a low concentration of LRH (1 ng/ml) was depressed but that of a high concentration (10000 ng/ml) was augmented in comparison to FSH release induced in control glands. However, pretreatment with the antagonist had no specific effect on FSH release in vitro induced by high K+ or high K+ plus mbcAMP and theophylline, indicating that the changes of pituitary responsiveness to LRH are not caused by those parts of the secretory mechanism which are stimulated by these secretagogues. Moreover, it is concluded that the changes of pituitary LH release induced by administration of an LRH antagonist also concern FSH.

Effect of acute immunoneutralization of endogenous leptin on prolactin and LH secretion during the afternoon of pro-oestrus or in steroid-treated ovariectomized female rats

Reproduction ◽  
2000 ◽  
pp. 39-45 ◽  
Author(s):  
LC Gonzalez ◽  
L Pinilla ◽  
M Tena-Sempere ◽  
C Dieguez ◽  
FF Casanueva ◽  
...  
Keyword(s):  
Prolactin Secretion ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Rabbit Serum ◽  
Normal Rabbit Serum ◽  
Blood Samples ◽  
Lh Release ◽  
Lh Secretion

Recent data indicate that leptin is involved in the control of reproductive function. Experiments were carried out to analyse the role of endogenous leptin in the regulation of LH and prolactin secretion during the afternoon of pro-oestrus and that induced by ovarian steroids in ovariectomized rats. In the first experiment, cyclic female rats were implanted with intra-auricular and intracerebroventricular (i.c.v.) cannulae and, at pro-oestrus, were injected (i.c.v.) with 10 microliters normal rabbit serum or leptin antiserum (at 13:00 and 14:00 h). Blood samples were obtained at 10:00 h and at intervals of 1 h between 13:00 and 20:00 h. In the second experiment, female rats in pro-oestrus were injected with normal rabbit serum or leptin antiserum at 16:00 and 18:00 h and blood samples were taken every 10 min between 18:00 and 20:00 h. In the third experiment, adult female rats that had been ovariectomized 2 weeks before were implanted with intra-auricular and i.c.v. cannulae and treated with oestradiol benzoate (30 micrograms s.c.) at 10:00 h and progesterone (2 mg s.c.) 48 h later. Normal rabbit serum (10 microliters) or leptin antiserum (10 microliters) were injected (i.c.v.) at 13:00 and 14:00 h, and blood samples were obtained at 10:00 h and at intervals of 1 h between 13:00 and 20:00 h. In the fourth experiment, hemipituitaries from ovariectomized steroid-treated female rats were incubated in the presence of leptin116-130 (an active fragment of the native molecule), GnRH or leptin + GnRH. Prolactin and LH secretion during the afternoon of pro-oestrus in females treated with leptin antiserum was similar to that observed in animals injected with normal rabbit serum. In ovariectomized female rats, the steroid-induced LH surge increased slightly after administration of leptin antiserum, whereas the prolactin surge remained unchanged. In vitro, leptin116-130 (10(-5) to 10(-8) mol l-1) inhibited LH secretion and modulated the effect of GnRH on LH release, depending on the concentration of GnRH: leptin116-130 (10(-6) mol l-1) reduced the effectiveness of 10(-7) mol GnRH l-1 and increased that of 10(-9) mol GnRH l-1. In conclusion, these experiments indicate that acute immunoneutralization of endogenous leptin does not interfere with spontaneous or steroid-induced LH and prolactin surges. In addition, the finding that leptin116-130 inhibited LH release and modulated the effectiveness of GnRH in vitro provides evidence of the direct modulatory role of leptin on LH secretion acting at the pituitary.

Desensitization of the pituitary gland induced in vivo by luteinizing hormone-releasing hormone (LRH) or by the LRH-analogue buserelin does not affect the autonomous secretion of luteinizing hormone and follicle stimulating hormone as observed in vitro

1984 ◽  
Vol 106 (4) ◽  
pp. 454-458 ◽  
Author(s):  
G. A. Schuiling ◽  
H. Moes ◽  
T. R. Koiter
Keyword(s):  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Normal Level ◽  
Ovariectomized Rats ◽  
Complete Suppression ◽  
Pituitary Glands ◽  
Pre Treatment ◽  
Lh Secretion

Abstract. Three-weeks ovariectomized rats were sc implanted with Alzet® osmotic minipumps which released either LRH or the LRH-analogue buserelin at the rate of 250 ng/h. Control rats were implanted with a silastic 'shampump'. After explantation, 6 days later, the pituitary glands of part of these rats were exposed to the maximally active LRH concentration of 1 μg/ml for a period of 6 h. using a perifusion system. In a second group of rats explantation and perifusion was done not directly, but 5 days after cessation of the I.RH pretreatment. After 6 days in vivo pre-treatment with LRH or with buserelin the pituitary LH and FSH stores were partially depleted, the depletion after buserelin being stronger than after LRH. The pituitary glands of the first group of rats showed rates of both maximally LRH-stimulated and unstimulated (autonomous) LH- and FSH-secretion which were strongly impaired, the impairment after buserelin being stronger than after LRH. In the group with a 5 days interval between in vivo LRH/buserelin pre-treatment and explantation the pituitary LH and FSH stores were restored to the range of pre-treatment levels. Of these pituitaries the autonomous secretion of LH and FSH as well as the maximally LRH-stimulated secretion of FSH was restored to the normal level; the maximally LRH-stimulated secretion of LH, however, remained depressed, indicating that 5 days after cessation of exposure to LRH or to buserelin, and in spite of restored pituitary LH/FSH contents, the sensitivity of the LH releasing system to LRH was still subnormal. The results suggest that the autonomous secretion of LH and FSH as well as the LRH-stimulated secretion of FSH, but not the LRH-stimulated secretion of LH may be dependent on the content of the pituitary LH and FSH stores. Furthermore, after treatment with LRH or buserelin the autonomous secretion of LH may return to a normal level when the sensitivity of the LH releasing system to LRH is still impaired: apparently, the mechanisms underlying the autonomous and the LRH-stimulated LH secretion do not influence each other. It is discussed that in situations in which a complete suppression of the pituitary-gonadal axis is demanded (carcinomata of the breast or the prostate; precocious puberty) desensitization of the pituitary gland with super-active LRH-analogues like buserelin alone is not sufficient, as this does not affect the autonomous secretion of LH and FSH. For total suppression of gonadal activity the pituitary gland must be completely depleted with relatively large doses of analogue.

Effect of Ca2+ deprivation on release of luteinizing hormone induced by luteinizing hormone releasing hormone from female rat pituitary glands in vitro

1982 ◽  
Vol 94 (1) ◽  
pp. 11-20 ◽  
Author(s):  
J. de Koning ◽  
A. M. I. Tijssen ◽  
J. A. M. J. van Dieten ◽  
G. P. van Rees
Keyword(s):  
Protein Synthesis ◽  
Initial Phase ◽  
Phase Response ◽  
Ovariectomized Rats ◽  
Second Phase ◽  
Pituitary Glands ◽  
Lh Release ◽  
Lh Rh ◽  
Intact Rats

Continuous exposure of hemi-pituitary glands from intact female rats to LH releasing hormone (LH-RH) in vitro displayed three phases in the pattern of LH release: during the first hour release of LH was low (first phase response), then it increased to a higher level during the second hour and remained constant during the next 2 h (second phase response), after which there was a refractoriness of LH release (third phase response). The initial phase response of pituitary glands from intact rats was blocked by EGTA (a Ca2+ chelator) but there was a small but significant increase in the rate of LH release during the second phase response. This increase could be prevented by inhibition of protein synthesis by cycloheximide. Cycloheximide and EGTA did not affect basal release of LH by glands from intact rats, neither did EGTA affect the high basal release of LH by glands from ovariectomized rats. However, the LH-RH-induced release of LH from pituitary glands of ovariectomized rats, which did not show the initial phase of low LH release, was completely suppressed by EGTA throughout a 4-h incubation period. The pattern of LH release stimulated by the combination of N6-monobutyryl cyclic AMP and theophylline (mbcAMP/theophylline) showed an initial phase of low LH release lasting 4 h after which it increased. The magnitude of the effect was small compared with the action of LH-RH. As it did with LH-RH, EGTA completely blocked the initial response, but allowed a small increase in the rate of LH release thereafter; this increase could also be blocked by inhibition of protein synthesis. Addition of EGTA to media during pretreatment of pituitary glands from intact rats with either LH-RH or mbcAMP/theophylline did not impair the facilitatory effect of these secretagogues on the responsiveness of the glands to subsequent exposure to LH-RH and cycloheximide and normal Ca2+ levels. The restoration of Ca2+ levels after withdrawal neither affected basal nor LH-RH-induced release of LH. Exclusion of Ca2+ from the media during a 6-h incubation of pituitary glands from intact rats with LH-RH prevented the glands from becoming refractory to subsequent stimulation by LH-RH, which occurs when normal Ca2+ concentrations are present. The results suggested that extracellular Ca2+ is obligatory for LH release and the induction of refractoriness by LH-RH. In contrast, that part of the action of LH-RH which is cyclic AMP-mediated and protein synthesis-dependent is not affected by withdrawal of extracellular Ca2+.

ABSENCE OF AN IMMUNOLOGICALLY DISTINCT FOLLICLE-STIMULATING HORMONE RELEASING FACTOR IN RAT STALK MEDIAN EMINENCE EXTRACTS

1976 ◽  
Vol 68 (1) ◽  
pp. 89-94 ◽  
Author(s):  
M. SHAHMANESH ◽  
S. L. JEFFCOATE
Keyword(s):  
Median Eminence ◽  
Male Rats ◽  
Rabbit Serum ◽  
Normal Rabbit Serum ◽  
Pituitary Tissue ◽  
Rat Pituitary ◽  
Pre Treatment ◽  
Lh Rh ◽  
Dose Levels

SUMMARY Rat stalk median eminence (SME) extract was incubated with various quantities of an antiserum raised against synthetic luteinizing hormone releasing hormone (LH-RH) and the resulting material was used at two or more dose levels to stimulate release of LH and FSH from anterior pituitary tissue, obtained from male rats, incubated in vitro. The resulting dose–response lines were used to obtain the LH- and FSH-releasing potency of the material, expressed as a percentage of SME extract pre-incubated with normal rabbit serum. Treatment with various doses of antiserum reduced LH-releasing and FSH-releasing potencies to a similar extent. Stalk median eminence extract and synthetic LH-RH were incubated with antiserum and directly compared in the same experiment in vitro. The changes in LH and FSH release caused by pre-treatment with antibody were similar for SME extract and synthetic LH-RH. In a final experiment, SME extract was passed through a column of Sepharose 2B particles to which was coupled anti-LH-RH antibody. The resulting material, when mixed with synthetic LH-RH and used to stimulate rat pituitary tissue in vitro caused a similar increase in the LH- and FSH-releasing potencies of the synthetic decapeptide. It is concluded that rat SME extract contains a single releasing factor for LH and FSH immunologically indistinguishable from synthetic LH-RH.

scholarly journals Exocytotic protein components in rat pituitary gland after long-term estrogen administration

1999 ◽  
Vol 161 (2) ◽  
pp. 323-331 ◽  
Author(s):  
G Majo ◽  
MJ Lorenzo ◽  
J Blasi ◽  
F Aguado
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Pituitary Cells ◽  
Fischer 344 Rats ◽  
Fischer 344 ◽  
Anterior Pituitary Cells ◽  
Pituitary Glands ◽  
Protein Components

Recently, a set of proteins involved in the docking and fusion machinery of secretory organelles has been identified in anterior pituitary cells. In this study we analyzed, by Western blotting and immunocytochemistry, the expression of several proteins involved in exocytosis after long-term administration of 17beta-estradiol (E2) in Fischer 344 rats. No differences were observed in the amount of synaptosomal-associated protein of 25 kDa, synaptobrevin 2, syntaxin 1, synaptotagmin I and Rab3a in total brain homogenates from treated rats after E2 administration. In striking contrast, the levels of all of these exocytotic proteins, including cellubrevin, were notably decreased in pituitary glands of E2-treated rats. In addition, no differences were observed in the in vitro basal and 8-Br-cAMP-induced prolactin (PRL) release between pituitary cells from control and E2-treated rats, whereas TRH-induced PRL release in anterior pituitary cells from E2-treated animals was higher than in control donors. In conclusion, this study shows that protein components of the exocytotic machinery are specifically down-regulated in the pituitary gland of E2-treated Fischer 344 rats.

Effect of serotonin on basal and TRH-induced release of prolactin from rat pituitary glands in vitro

1987 ◽  
Vol 114 (4) ◽  
pp. 565-571 ◽  
Author(s):  
Marta E. Apfelbaum
Keyword(s):  
Culture Medium ◽  
Blocking Agent ◽  
Ovariectomized Rats ◽  
Rat Pituitary ◽  
Incubation Periods ◽  
Basal Release ◽  
Pituitary Glands ◽  
Specific Receptors ◽  
Different Doses

Abstract. The effect of serotonin on the release of prolactin (PRL) was studied in vitro. Anterior hemipituitary glands from ovariectomized rats were incubated for 1 h in the presence of different doses of serotonin. Serotonin added into the culture medium caused a significant increase in basal PRL release. The effect was dose-related between 10 and 30 nmol/l serotonin, but responsiveness declined towards basal levels with higher concentrations. When studied as a function of incubation time, basal release of PRL was significantly increased up to 1 h but decreased thereafter. Serotonin also enhanced the release of prolactin induced by 30 nmol/l thyrotropin-releasing hormone (TRH), at all doses tested. A serotonin concentration of as little as 30 nmol/l was already effective. A significant response was seen at 15 min and further increases occurred during the following incubation periods. Serotonin (approximately EC50 4.6 × 10−8 mol/l) was less potent than TRH (EC50 about 1.2 × 10−8 mol/l) to increase basal PRL release. On the other hand, the indole amine appeared to act with similar potency in stimulating PRL release both basal and TRH-induced. In addition, the combined effect of the releasing agents was found to be additive. These results suggest that serotonin and TRH could act through separate mechanisms. Methysergide, a serotoninergic blocking agent, had no effect on the in vitro PRL release either basal or TRH-induced, but it completely blocked that evoked by serotonin suggesting that serotonin may interact with specific receptors on the lactotropes. These findings clearly demonstrate that serotonin may stimulate the release of PRL by acting directly at the pituitary gland level.

Time course of inhibition of synthesis and basal release of FSH from pituitary glands of female rats by bovine follicular fluid in vitro

1982 ◽  
Vol 101 (4) ◽  
pp. 501-506 ◽  
Author(s):  
A. A. J. Jenner ◽  
J. de Koning ◽  
G. P. van Rees
Keyword(s):  
Follicular Fluid ◽  
Time Course ◽  
Mechanisms Of Action ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Intact Female ◽  
In Vitro Technique ◽  
Basal Release ◽  
Pituitary Glands

Abstract. Inhibin-like activity in steroid-free bovine follicular fluid (bFF) is demonstrated using an in vitro technique with hemi-pituitary glands from intact female (second day of dioestrus) and ovariectomized rats: synthesis as well as basal release of FSH, but not of LH, are inhibited profoundly. The results confirm and extend data from other investigators on the action of inhibin-like material. The effect of the inhibin-like activity is shown to be reversible, as synthesis and the rise of basal release are restored when bFF is withdrawn from the incubation medium. Synthesis of FSH seems to be inhibited earlier than basal release, and it is suggested that the inhibin-like material acts only directly on FSH synthesis. Some possibilities of the mechanisms of action of inhibin-like activity are discussed.

The involvement of ovarian factors in maintaining the pituitary glands of female rats in a state of low LH responsiveness to LHRH

1987 ◽  
Vol 112 (2) ◽  
pp. 265-273 ◽  
Author(s):  
J. de Koning ◽  
A. M. I. Tijssen ◽  
G. P. van Rees
Keyword(s):  
Pituitary Gland ◽  
Phase Response ◽  
The Self ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Lag Phase ◽  
Second Phase ◽  
Rat Pituitary ◽  
Pituitary Glands

ABSTRACT The effects of discontinuation and restoration of ovarian influences on the pituitary LH response to LHRH in vitro were investigated. When female rat pituitary glands taken on day 2 of dioestrus were incubated with LHRH the release of LH was low during the first hour (lag phase response) and afterwards a progressive, protein synthesis-dependent increase took place (second phase response), this being the self-priming action of LHRH. Short-term discontinuation (less than 1 day) of ovarian influences on the rat pituitary gland in vivo (ovariectomy) or in vitro (incubation in medium only) resulted in an increased LHRH-induced LH response during the lag phase. The biphasic LH response or the self-priming action of LHRH disappeared completely after long-term discontinuation of ovarian influences on the pituitary gland, LH release being at its maximum from the start of the incubation. The biphasic response was reinstated when ovaries were implanted under the kidney capsules of ovariectomized rats. Auto-implantation of an ovary into the spleen immediately after bilateral ovariectomy did not, however, prevent the disappearance of the LHRH self-priming action. Ovarian activity responsible for the presence of the low LH response during the lag phase was thus effectively removed by the liver, but inhibin-like activity suppressing serum FSH levels remained present. Silicone elastomer implants (s.c.) containing oestradiol-17β, implanted for 4 weeks, did not reverse the loss of the biphasic LH response to LHRH. It is concluded that liver-labile factors released by the ovaries keep the pituitary gland in a state of low responsiveness to LHRH. By giving a sufficiently high LHRH stimulus this inhibitory effect is neutralized and transition to a highly responsive state can be achieved. The ovarian factor(s) is not identical to inhibin or oestradiol-17β. J. Endocr. (1987) 112, 265–273

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