OESTRADIOL RECEPTORS IN THE RAT ANTERIOR PITUITARY GLAND DURING THE OESTROUS CYCLE: QUANTITATION OF RECEPTOR ACTIVITY IN RELATION TO GONADOTROPHIN RELEASING HORMONE-MEDIATED LUTEINIZING HORMONE RELEASE

1978 ◽  
Vol 76 (2) ◽  
pp. 211-218 ◽  
Author(s):  
K. K. SEN ◽  
K. M. J. MENON
Keyword(s):  
Pituitary Gland ◽  
Binding Sites ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Hormone Release ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Stimulation Of

Specific oestradiol binding to a receptor in nuclear and cytosol fractions of the rat anterior pituitary gland and pituitary responsiveness to gonadotrophin releasing hormone (GnRH) during the oestrous cycle have been studied. To accomplish this, both unoccupied and occupied oestradiol-binding sites in the cytosol and oestradiol-binding sites in the nucleus and total cell were measured during the oestrous cycle. The concentration of unoccupied and occupied sites and total oestradiol binding in the cytosol fluctuated during the cycle. At pro-oestrus, the concentration of cytosol receptor was diminished by about 40% and replenishment occurred during oestrus. On the other hand, a profound increase in concentrations of cellular and nuclear receptors occurred at pro-oestrus. Administration of GnRH significantly stimulated LH release at all stages of the cycle. The maximum stimulation of LH release by GnRH was observed at 13.00 h of pro-oestrus. From these studies, it is concluded that pituitary responsiveness to exogenous GnRH during pro-oestrus parallels the changes in the content of oestrogen receptors in the cytosol and nucleus.

Pituitary and testicular responses in sexually mature bulls after intravenous injections of graded doses of LH-releasing hormone

1984 ◽  
Vol 103 (3) ◽  
pp. 371-376 ◽  
Author(s):  
M. J. D'Occhio ◽  
B. P. Setchell
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Limiting Factor ◽  
Releasing Hormone ◽  
Intravenous Injections ◽  
Gonadotrophin Secretion ◽  
Lh Release ◽  
Lh Releasing Hormone ◽  
Sexually Mature

ABSTRACT The capacity of the anterior pituitary gland and testes in mature bulls (705±9 (s.e.m.) kg body wt, n = 4) to respond to graded doses of LH-releasing hormone (LHRH) was assessed relative to endogenous profiles of LH and testosterone secretion. Endogenous hormone profiles were determined by bleeding bulls at 20-min intervals for 12 h. Responses to LHRH were assessed on successive days after single intravenous injections of 1, 5, 10, 50 or 100 ng LHRH/kg body wt. Blood samples were taken at −40, −20, 0, 10, 20, 30, 40, 60 and 120 min relative to LHRH injection. During a 12-h bleed bulls showed spontaneous pulses of LH and testosterone which had peak amplitudes of 2·6±0·5 μg/l and 44·5 ± 7·1 nmol/l respectively. Respective peak LH (μg/l) and testosterone (nmol/l) responses to LVRH were as follows: 1 ng LHRH (3·0±0·7: 47·3±4·1); 5 ng LHRH (8·0±1·2; 52·8 ± 6·2); 10 ng LHRH (11·1±2·3; 57·7 ± 9·1); 50 ng LHRH (19·2±2·8; 47·9±8·6); 100 ng LHRH (19·1±4·7; 43·9 ±6·4). A dose of 1 ng LHRH/kg produced LH and testosterone responses which were comparable in amplitude to spontaneous peaks in the respective hormone. There was a linear (y = 0·28x+5·72; r = 0·81) increase in the LH response to doses of LVRH between 1 and 50 ng/kg; corresponding testosterone responses showed no relationship with the dose of LHRH. The capacity of the anterior pituitary gland to release amounts of LH eight to ten times in excess of those secreted during spontaneous peaks suggests that (1) there exists a large releasable store of LH in the anterior pituitary gland and (2) hypothalamic LHRH is a limiting factor in gonadotrophin secretion. In contrast to LH release, the androgenic response of the testes to acute gonadotrophic stimulation is determined largely by prevailing steroidogenic activity. J. Endocr. (1984) 103, 371–376

Influence of the characteristics of pulses of gonadotrophin releasing hormone on the dynamics of luteinizing hormone release from perifused sheep pituitary cells

1983 ◽  
Vol 98 (3) ◽  
pp. 411-421 ◽  
Author(s):  
R. P. McIntosh ◽  
J. E. A. McIntosh
Keyword(s):  
Luteinizing Hormone ◽  
Anterior Pituitary ◽  
Pulse Width ◽  
Pulse Amplitude ◽  
Threshold Value ◽  
Pituitary Cells ◽  
Hormone Release ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

The effects were studied of varying the frequency, width and amplitude of pulses of gonadotrophin releasing hormone (GnRH) on the release of LH from anterior pituitary cells. Dispersed sheep cells supported in Sephadex were perifused with medium for 10 h and stimulated with different constant pulse patterns of GnRH. The timing of release of LH was measured by radioimmunoassay of the effluent fractions. Pulses of GnRH ranging in duration from 2 min every 8 min to 16 min every 128 min, and in concentration from 1·7 pmol/l to 250 nmol/l were applied to the cells, as well as continuous stimulation. Comparisons of differences between LH release patterns among samples of the same preparation of cells were used to demonstrate the effects of different GnRH stimulatory regimes. It was concluded that (1) the frequency of GnRH stimulation was important to the nature of LH release (periods shorter than about 16 min between pulses reduced LH output and caused faster desensitization of response), (2) the pulse width of GnRH input was important (the rising edge of the pulse produced greater LH output per unit of GnRH input than did continued application of GnRH within a pulse and wider pulses combined with shorter periods reduced LH output) and (3) over a threshold value of 5–10 nmol GnRH/1 pulse amplitude had little further influence on LH output or rate of desensitization in dispersed cells. These findings reinforce the hypothesis that the rising edge of the GnRH pulse is the major stimulant to LH release.

Ornithine decarboxylase activity and polyamines in the anterior pituitary gland during the rat oestrous cycle

1985 ◽  
Vol 107 (1) ◽  
pp. 83-87 ◽  
Author(s):  
L. Persson ◽  
M. Nilsson ◽  
E. Rosengren
Keyword(s):  
Pituitary Gland ◽  
Ornithine Decarboxylase ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Ovariectomized Rats ◽  
Oestrogen Treatment ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Lh Releasing Hormone

ABSTRACT The biosynthesis of polyamines, an ubiquitous group of amines shown to be essential for normal cellular growth and differentiation, was studied in the rat anterior pituitary gland during the different stages of the oestrous cycle. The activity of ornithine decarboxylase (ODC), which catalyses the rate-limiting step in the biosynthesis of polyamines, was low during oestrus, metoestrus and dioestrus. However, a marked transitory rise in ODC activity was found in the pituitary gland on the evening of pro-oestrus. The rise in ODC activity was accompanied by an increase in the pituitary content of the polyamines putrescine and spermidine. Ovariectomy did not significantly change the basal ODC activity in the pituitary gland. Oestrogen treatment of ovariectomized rats resulted in a marked stimulation of pituitary polyamine biosynthesis. The largest effects were observed when oestrogen was given as two injections 72 h apart, which gave rise to levels of ODC activity comparable to those observed on the evening of pro-oestrus. The increase in polyamine synthesis in the anterior pituitary gland during pro-oestrus appeared not to be related to the preovulatory secretion of LH or prolactin, since neither LH-releasing hormone nor thyrotrophin-releasing hormone (which induces a secretion of prolactin) affected pituitary ODC activity. The observed biosynthesis of polyamines may be associated with the cellular proliferation which occurs in the anterior pituitary gland at oestrus. J. Endocr. (1985) 107, 83–87

Effect of cortisol on the response to gonadotrophin releasing hormone in the boar

1983 ◽  
Vol 97 (1) ◽  
pp. 75-81 ◽  
Author(s):  
R. M. Liptrap ◽  
J. I. Raeside
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Plasma Cortisol ◽  
Intramuscular Injection ◽  
Anterior Pituitary Gland ◽  
Nacl Solution ◽  
Hormonal Response ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
Different Doses

The effect of intracarotid perfusion of 40 mg cortisol for 1 h on the hormonal response to three different doses of an intramuscular injection of synthetic gonadotrophin releasing hormone (GnRH) was compared to that of GnRH injected during intracarotid perfusion with 0·9% (w/v) NaCl solution in five boars. The increase in production of LH, above basal values, in response to injection of 0·25 μg GnRH midway through perfusion was only slightly greater (P > 0·05) in boars receiving cortisol compared to that when the same boars received saline. When 0·5 μg GnRH was injected midway through perfusion, a significantly greater (P<0·05) increase in production of LH above basal levels occurred during cortisol administration than occurred when saline was given. Injection of 1·0 μg GnRH in boars during cortisol perfusion resulted in significantly greater (P<0·01) production of LH, above basal levels, compared to the increase above basal levels that resulted when this dose of GnRH was given during intracarotid saline treatment. Increases in plasma values of testosterone reflected the increases in levels of LH. The results suggest that acute elevations in plasma cortisol may, under some circumstances, enhance the increased production of LH in the boar by increasing the responsiveness of the anterior pituitary gland to GnRH.

POSSIBLE PRIMING EFFECT OF LUTEINIZING HORMONE RELEASING HORMONE ON THE ANTERIOR PITUITARY GLAND IN THE JAPANESE QUAIL AND THE STIMULATION OF SECRETION OF FOLLICLE-STIMULATING HORMONE

1979 ◽  
Vol 82 (1) ◽  
pp. 71-75 ◽  
Author(s):  
D. T. DAVIES ◽  
J. COLLINS
Keyword(s):  
Pituitary Gland ◽  
Japanese Quail ◽  
Anterior Pituitary ◽  
Follicle Stimulating Hormone ◽  
Anterior Pituitary Gland ◽  
Luteinizing Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Lh Rh ◽  
Lh Releasing Hormone ◽  
Stimulation Of

SUMMARY After the i.m. injection of 10 μg synthetic LH releasing hormone (LH-RH) into Japanese quail the levels of LH and FSH in plasma rose significantly within 2 min. The increased level of LH declined rapidly but that of FSH was maintained for the duration of the experiment. To determine whether the anterior pituitary gland is primed by LH-RH a double injection schedule was adopted. It would appear that, while endogenous LH-RH may prime the avian pituitary gland slightly, synthetic LH-RH is ineffective.

GONADOTROPHIN SECRETION AFTER ELECTRICAL STIMULATION OF THE PREOPTIC AREA DURING THE OESTROUS CYCLE OF THE RAT

1974 ◽  
Vol 62 (3) ◽  
pp. 589-604 ◽  
Author(s):  
G. FINK ◽  
M. S. AIYER
Keyword(s):  
Electrical Stimulation ◽  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Preoptic Area ◽  
Medial Preoptic Area ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Early Afternoon ◽  
Stimulation Of

SUMMARY The responsiveness of the hypothalamo-hypophysial axis to electrical stimulation of the medial preoptic area was tested at various times during the oestrous cycle of the rat. Animals were anaesthetized with sodium pentobarbitone, and glass-insulated bipolar platinum electrodes were stereotaxically implanted in the medial preoptic area. The stimulus consisted of accurately balanced biphasic rectangular pulses, height 500 μA, duration 2 ms and frequency 60 Hz, applied in trains of 30 s intervals. The concentration of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in blood samples withdrawn from the external jugular vein immediately before and at frequent intervals up to 1 h after application of the stimulus was determined by radioimmunoassay. In all animals the stimulus was applied for a period of 15 min, for it was found that under these conditions the profiles of LH and FSH produced in individual animals were similar to those which followed the i.v. injection of 50 ng synthetic luteinizing hormone releasing factor (LH-RF)/100 g body wt, the minimal ovulatory dose of LH-RF in our laboratory. Both for LH and FSH, the profiles of responsiveness of the hypothalamo-hypophysial axis to electrical stimulation through the oestrous cycle resembled closely the profile of responsiveness of the anterior pituitary gland to LH-RF administered intravenously. There was a relatively gradual increase in pituitary sensitivity, in terms of the mean maximal increments, between the early afternoon of dioestrus and pro-oestrus, followed by an abrupt and marked rise which reached a peak at 18.00 and 21.00 h of pro-oestrus for LH and FSH, respectively. Sensitivity of the hypothalamo-hypophysial axis declined through oestrus and metoestrus reaching a nadir at 13.30 h of dioestrus. While these results do not exclude a change in sensitivity of the neural component of the hypothalamo-hypophysial axis during the oestrus cycle, they do indicate that the timing and magnitude of changes in sensitivity of the anterior pituitary gland to both endogenous and exogenous LH-RF are similar. This raises the possibility that a marked increase in the secretion of LH-RF during the afternoon of pro-oestrus may not be necessary for the occurrence of the surge of LH and FSH, for conceivably the latter could depend on a change in sensitivity of pituitary gonadotrophs to constant or only slightly increased levels of LH-RF in hypophysial portal blood. Our findings are compared with those of workers who have employed electrochemical stimulation of the preoptic area.

Pro-oestrous-specific role for polyamines in mediating the secretion of prolactin induced by thyrotrophin-releasing hormone in the rat

1993 ◽  
Vol 137 (1) ◽  
pp. 133-139 ◽  
Author(s):  
G. A. Wynne-Jones ◽  
A. M. Gurney
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Prolactin Secretion ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Male Rats ◽  
Pituitary Cells ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone

ABSTRACT The activity of ornithine decarboxylase (ODC) in the rat anterior pituitary gland varies during the oestrous cycle, with a rise in activity seen at pro-oestrus. This enzyme, which is rate-limiting for the synthesis of the polyamines, can be specifically and irreversibly blocked by α-difluoromethylornithine (DFMO). A previous study showed that when this drug was administered to rats in vivo on the afternoon of pro-oestrus, it suppressed the normal surge in plasma prolactin levels that occurred later that day. The effect of DFMO was associated with reduced levels of putrescine in the anterior pituitary gland, suggesting that ODC activity in the lactotroph might be involved in the prolactin surge. We have examined the effects of DFMO on the secretion of prolactin from anterior pituitary cells, isolated either from male rats or from females at different stages of the oestrous cycle. The drug was found to reduce prolactin secretion stimulated by thyrotrophin-releasing hormone (TRH), but only in cells isolated from pro-oestrous animals and only for 2 days after cell isolation. Basal secretion was unaffected by DFMO. The results imply that ODC is important for TRH-stimulated prolactin secretion at pro-oestrus, and it is specific for pro-oestrus. The prolactin surge could therefore be influenced by this ODC-dependent effect of TRH. The pro-oestrous-specific response to TRH may be a consequence of the increased ODC activity seen at this time. Alternatively, the increased ODC activity could be a consequence of coupling to TRH receptors, which are known to increase in number at pro-oestrus. Journal of Endocrinology (1993) 137, 133–139

THYROTROPHIN RELEASING HORMONE-INDUCED GROWTH HORMONE AND PROLACTIN RELEASE: PHYSIOLOGICAL STUDIES IN INTACT RATS AND IN HYPOPHYSECTOMIZED RATS BEARING AN ECTOPIC PITUITARY GLAND

1977 ◽  
Vol 72 (3) ◽  
pp. 301-311 ◽  
Author(s):  
A. E. PANERAI ◽  
IRIT GIL-AD ◽  
DANIELA COCCHI ◽  
V. LOCATELLI ◽  
G. L. ROSSI ◽  
...  
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Time Lapse ◽  
Anterior Pituitary Gland ◽  
Plasma Prolactin ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Clear Cut ◽  
Urethane Anaesthesia ◽  
Releasing Effect

SUMMARY To determine how the sensitivity of the ectopic anterior pituitary gland to the GH-releasing effect of thyrotrophin releasing hormone (TRH) might be affected by the time lapse from transplantation, TRH (0·15 and 0·6 μg) was injected i.v. into hypophysectomized (hypox)-transplanted rats under urethane anaesthesia 1,3, 8,15, 30 and 60 days after transplantation, and plasma samples were taken 5 and 10 min later. Baseline GH values gradually decreased with time from about 16·0 ng/ml (1 day) to about 3·0 ng/ml (30 and 60 days). The TRH-induced GH release was absent 1 day after transplantation, present only with the higher TRH dose 3 and 8 days after transplantation, and clearly elicitable, also with the lower TRH dose (0·15 μg), from 15 up to 60 days. Determination of plasma prolactin concentrations showed a decline from about 85·0 ng/ml (1 day) to about 32·0 ng/ml (8 days); subsequently (15–60 days) prolactin values stabilized. Plasma prolactin levels increased 15 and 60 days after transplantation only when a dose of 0·6 μg TRH was given. In intact weight-matched rats, TRH induced a GH response only at the dose of 1·2 μg while a short-lived but clear-cut prolactin response could be obtained even with the 0·3 μg dose. The present results indicate that: (1) disconnexion between the central nervous system and the anterior pituitary gland greatly enhances GH responsiveness while blunting prolactin responsiveness to TRH; (2) the sensitivity of the anterior pituitary gland to the GH-releasing effect of TRH increases with time from transplantation; (3) TRH is a more effective prolactin-than GH-releaser on the pituitary gland in situ.

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