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

The self-priming action of LHRH increases the low pituitary LH and FSH response caused by ovarian factors: observations in vitro

1989 ◽  
Vol 120 (3) ◽  
pp. 439-447 ◽  
Author(s):  
J. de Koning ◽  
A. M. I. Tijssen ◽  
G. P. van Rees
Keyword(s):  
Pituitary Gland ◽  
Priming Effect ◽  
Phase Response ◽  
The Self ◽  
Ovariectomized Rats ◽  
Lag Phase ◽  
Second Phase ◽  
Prolonged Incubation ◽  
Pituitary Glands ◽  
Free Material

ABSTRACT Pituitary glands taken from intact rats on day 2 of dioestrus and incubated with LHRH show a biphasic pattern of LH and FSH release. Initially the release of the gonadotrophins is low (first-phase or lag-phase response), but increases during further incubation with LHRH (second-phase or primed-state response). Removal of the influence of an unidentified ovarian factor either by ovariectomy or prolonged incubation in medium only leads to an increased (lag-phase) response to LHRH. The development of the increased response after prolonged incubation was prevented by the addition of cycloheximide to the media, implicating that this process is dependent upon the synthesis of protein. Steroid-free material (bovine follicular fluid or rat ovarian extracts) prevented the development of this process. In addition, it was shown that steroid-free rat ovarian extracts were also able to induce the development of a lag phase in pituitary glands from ovariectomized rats. Finally, it was found that steroid-free ovarian extracts reversed the self-priming effect of LHRH. The biological activity which reduced the responsiveness of the pituitary gland towards stimulation by LHRH was eliminated after the use of protein-denaturating techniques such as increased temperature or addition of methanol. The presence of this activity in ovaries, did not vary during the oestrous cycle, contrary to inhibin-like activity. Hence the ovarian factor responsible for the low lag-phase response is a protein which is probably not identical to inhibin. It is concluded that a non-steroidal ovarian factor reduces the responsiveness of the anterior pituitary gland to LHRH. This reduced responsiveness can be reversed by LHRH, which is generally recognized as the self-priming effect of LHRH. Journal of Endocrinology (1989) 120, 439–447

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+.

Time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro

1983 ◽  
Vol 96 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Marta E. Apfelbaum
Keyword(s):  
Time Course ◽  
Ovariectomized Rats ◽  
Second Phase ◽  
Hormone Synthesis ◽  
Continuous Release ◽  
Rat Pituitary ◽  
Pituitary Glands ◽  
Secondary Phenomenon ◽  
Two Phases

To study the time-course of release and synthesis of LH, FSH and prolactin, anterior pituitary glands from ovariectomized rats were incubated for different time-intervals between 0 and 4 h. Comparable patterns of release and synthesis of LH and FSH as a function of the incubation time were observed. It was possible to distinguish two phases in the profiles of secretion of both gonadotrophins. During the first phase, from 0–2 h, release was associated with a corresponding decrease of the hormone concentrations within the gland but no overall changes in total LH and FSH production. During the second phase, between 2 and 4 h, a progressive reaccumulation of both gonadotrophins occurred in spite of the continuous release of hormones into the medium, reflecting formation of new immunoassayable material. These results suggest that the increased synthesis ensues as a secondary phenomenon arising from the release of the hormones from the tissue. The time-course of release and synthesis of prolactin showed different dynamics during the course of incubation. High levels of prolactin were released and synthesized when the adenohypophysis was incubated in vitro. Considerably larger amounts of this hormone were found in the medium than in the tissue from the first hour of incubation. After a lag of about 40 min synthesis of prolactin was increased in parallel with its release. This led to the assumption that both prolactin synthesizing and releasing processes occurred simultaneously from the early stages of the incubation. Comparatively, prolactin-secreting cells had a very fast and LH-secreting cells a low rate of turnover; FSH-secreting cells were intermediate between the two. These results indicate that (1) the increase in release of LH, FSH and prolactin into the medium precedes that of hormone synthesis and (2) the initial depletion of the pituitary gland as a result of hormone release could act as a stimulus for synthesis, leading to the reestablishment of hormonal storage levels.

Regulation by ovarian factors of the LHRH-induced LH response in pituitary glands in situ or grafted under the kidney capsule in intact and ovariectomized rats

1989 ◽  
Vol 123 (1) ◽  
pp. 41-45 ◽  
Author(s):  
J. A. M. J. van Dieten ◽  
J. de Koning ◽  
G. P. van Rees
Keyword(s):  
Pituitary Gland ◽  
High Rate ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Lag Phase ◽  
Kidney Capsule ◽  
Pituitary Glands ◽  
Lh Release ◽  
Secretory Products

ABSTRACT When pituitary glands from intact female rats are incubated with LHRH, the resulting LH release shows a biphasic pattern: an initial low rate of LH release (lag phase) is followed by a high rate. When pituitary glands from long-term ovariectomized rats are incubated, the rate of LH release is high throughout stimulation with LHRH. The disappearance of the lag phase might be due to increased LHRH release after ovariectomy and/or the disappearance of ovarian factors. To distinguish between these possibilities, pituitary glands which had been exposed to endogenous LHRH (pituitary glands in situ) or which had been unexposed to endogenous LHRH (pituitary glands transplanted under the kidney capsule) were incubated in the presence or absence of LHRH. Biphasic LH secretion patterns were observed during incubation with LHRH with the animal's own pituitary gland and with the transplanted pituitary gland from intact, but not from ovariectomized rats. Thus the disappearance of the lag phase after ovariectomy results from the absence of ovarian secretory products, rather than from increased release of LHRH. Journal of Endocrinology (1989) 123, 41–45

INFLUENCE OF STEROID SEX HORMONES ON THE F. S. H.-RELEASE BY RAT HYPOPHYSES IN VITRO

1961 ◽  
Vol 36 (4) ◽  
pp. 485-497 ◽  
Author(s):  
G. P. van Rees
Keyword(s):  
Sex Hormones ◽  
Female Rats ◽  
Male Rats ◽  
Intact Female ◽  
Intact Male ◽  
Incubation Experiments ◽  
Rat Pituitary ◽  
Pituitary Glands ◽  
Steroid Sex Hormones

ABSTRACT The hypothesis that steroid sex hormones influence pituitary F. S. H. by independent actions on its production and capacity of the gland to release it has been investigated by means of incubation experiments. During incubation, rat pituitary glands released considerable amounts of F. S. H. into the medium. Inactivation of F. S. H. during incubation could not be demonstrated; once (in females) some production of F. S. H. was even observed. The amount of F. S. H. which is released into the medium is influenced by the quantity of F. S. H. stored in the hypophyses. Hypophyses from male rats pretreated with oestradiol released relatively more F. S. H. into the medium than hypophyses from control animals. On the other hand, pretreatment with testosterone caused the pituitary glands to release less F. S. H. into the medium. In agreement with these results, hypophyses from intact male rats released relatively less F. S. H. than hypophyses from intact female rats. These facts support the hypothesis that androgens depress pituitary F. S. H.-secretion by inhibiting the capacity to release it, while oestrogens, which can even promote this property of the pituitary gland, also act by directly inhibiting its production.

Hypothalamic dopamine and catechol oestrogens in rats with spontaneous pituitary tumours

1983 ◽  
Vol 96 (2) ◽  
pp. 347-352 ◽  
Author(s):  
R. A. Prysor-Jones ◽  
J. J. Silverlight ◽  
J. S. Jenkins
Keyword(s):  
Pituitary Gland ◽  
Plasma Prolactin ◽  
Pituitary Tumours ◽  
Dopamine Concentration ◽  
Rat Pituitary ◽  
Pituitary Glands ◽  
Normal Rat ◽  
Old Rats ◽  
Hypothalamic Dopamine

Dopamine concentration within the hypothalamus and its depletion after the administration of α-methyl-para-tyrosine were measured in young rats and compared with values obtained in aged animals with and without spontaneously occurring pituitary tumours. Old rats had significantly reduced hypothalamic dopamine concentrations and there was less depletion of dopamine compared with young animals but there were no differences between tumorous and non-tumorous animals. Hyperprolactinaemia induced in young animals caused a much greater depletion of hypothalamic dopamine than in old tumorous rats with comparable plasma prolactin concentrations. The catechol oestrogen 2-hydroxyoestradiol inhibited the release of prolactin from normal rat pituitary glands in vitro but measurement of catechol oestrogens in the hypothalamus showed no differences between young and old tumorous or non-tumorous rats. It is concluded that reduced dopamine concentration and an impaired response to hyperprolactinaemia in old rats may facilitate the growth of prolactin-secreting tumours arising in the pituitary gland.

Influence of gonadal steroids on the time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro

1983 ◽  
Vol 96 (2) ◽  
pp. 171-179 ◽  
Author(s):  
Marta E. Apfelbaum
Keyword(s):  
Time Course ◽  
Follicle Stimulating Hormone ◽  
Gonadal Steroids ◽  
Regulatory Mechanisms ◽  
Ovariectomized Rats ◽  
Hormone Synthesis ◽  
The Third ◽  
Rat Pituitary ◽  
Pituitary Glands

The effect of the gonadal steroids on the time-course of release and synthesis of LH, FSH and prolactin was studied in vitro. Pituitary glands from ovariectomized rats were incubated for four sequential periods of 1 h in the presence or absence of 1·84 μmol oestradiol-17β/l, 3·44 μmol 5a-dihydrotestosterone/l or 31·80 μmol progesterone/l. The rate of release of LH was not affected by oestradiol or dihydrotestosterone, but was enhanced by progesterone after the third period of incubation. Synthesis of LH was increased by the three steroids tested, from 1 to 4 h of incubation, the effect being more marked for oestradiol than for the other steroids. The rate of release of FSH was depressed after 3 h whereas its synthesis was increased between 1 and 2 h, only in the presence of dihydrotestosterone. Synthesis of FSH was also stimulated by oestradiol after 2 h incubation but its release was not affected. Progesterone showed no effect on either the release or the synthesis of FSH. Although oestradiol and dihydrotestosterone induced a rise in both LH and FSH synthesis, the onset, magnitude and duration of the responses were different, indicating separate regulatory mechanisms. Oestradiol stimulated the rates of both release and synthesis of prolactin. The effect was already evident after 1 h of incubation and increased thereafter. On the contrary, progesterone treatment inhibited the release and synthesis of prolactin. The rate of synthesis decreased after 1 h of incubation, whereas release was depressed after 3 h. Dihydrotestosterone had no effect on the release and synthesis of prolactin. The evidence provided by this study indicates that the effect of the steroid hormones in vitro was predominantly on the synthesis of LH, FSH and prolactin. When changes in release of LH, FSH and prolactin occurred they were always preceded by alterations in hormone synthesis.

GONADOTROPHIN RELEASE IN VITRO, IN THE PRESENCE AND ABSENCE OF LUTEINIZING HORMONE RELEASING HORMONE, BY PITUITARY GLANDS FROM OVARIECTOMIZED AND SHAM-OPERATED IMMATURE FEMALE RATS OF VARIOUS AGES

1981 ◽  
Vol 88 (3) ◽  
pp. 375-379
Author(s):  
J. DULLAART
Keyword(s):  
Female Rats ◽  
Ovariectomized Rats ◽  
Immature Female ◽  
Releasing Hormone ◽  
Incubation Experiments ◽  
Immature Rats ◽  
Pituitary Glands ◽  
Lh Releasing Hormone

Hemipituitary glands of immature female rats, aged 10, 15, 20, 25, 30 and 35 days and either ovariectomized or sham-operated 5 days earlier, were incubated for 2 h in vitro with or without LH releasing hormone. Concentrations of LH and FSH were determined at the end of the incubations in the incubation media and in the hemipituitary glands, and also in the sera collected at the beginning of the incubation experiments. Results showed that in many instances gonadotrophin release was higher after incubation of glands of ovariectomized rats than with glands of control animals. However, these effects of ovariectomy were much smaller than those observed in vivo and were generally absent in rats of less than 20 days of age. It was concluded that ovariectomy may change the secretory characteristics of the gonadotrophic cells of immature rats but that such changes were largely restricted to immature rats older than 20 days.

PREPARATION AND CHARACTERIZATION OF ANTISERUM TO PURIFIED GONADOTROPHINS FROM RAT PITUITARY GLANDS

1967 ◽  
Vol 54 (2) ◽  
pp. 311-327 ◽  
Author(s):  
B. Lunenfeld ◽  
Aliza Eshkol ◽  
G. Baldratti ◽  
G. K. Suchowsky
Keyword(s):  
Mature Female ◽  
Female Rats ◽  
Mouse Serum ◽  
List Type ◽  
Mouse Uterus ◽  
Rat Serum ◽  
Rat Pituitary ◽  
Pituitary Glands ◽  
Normal Human

ABSTRACT Antiserum to a gonadotrophic extract of rat pituitary glands was prepared and investigated: In specific assays the antiserum neutralized rat FSH and LH, as well as the total gonadotrophic effect measured by the mouse uterus test. The antiserum did not counteract the gonadotrophic activity of HMG and HCG, but inhibited endogenous mouse gonadotrophins. The antiserum interrupted the continuous oestrous cycle in androgen sterilized rats. When antiserum was injected into mature female rats starting on the day of cornification, the leucocytic smear appeared within 24 hours and persisted for the duration of the injections. Immunoelectrophoretic studies with the antiserum revealed formation of precipitation lines with the antigen used for immunization and with rat serum. The antiserum cross-reacted in vitro with mouse serum. No precipitin lines were observed,against normal human serum, human menopausal gonadotrophins or human chorionic gonadotrophin. The response of antiserum treated immature mice and rats to human gonadotrophins is described. Interpretation of these findings is based on previous observations in hypophysectomized animals. The possible use of animals immunologically deprived of endogenous gonadotrophins for the study of the response to specific human gonadotrophins is discussed. The significance of substituting hypophysectomized animals for antiserum treated rodents is outlined.

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.

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