CALCIUM REQUIREMENT FOR STIMULATION OF CYCLE AMP ACCUMULATION IN ANTERIOR PITUITARY GLAND BY LH-RH

1975 ◽  
Vol 30 (9) ◽  
pp. 617-618
Author(s):  
P. BORGEAT ◽  
P. GARNEAU ◽  
F. LABRIE
1979 ◽  
Vol 82 (1) ◽  
pp. 71-75 ◽  
Author(s):  
D. T. DAVIES ◽  
J. COLLINS

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.


1978 ◽  
Vol 76 (2) ◽  
pp. 211-218 ◽  
Author(s):  
K. K. SEN ◽  
K. M. J. MENON

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.


1974 ◽  
Vol 62 (3) ◽  
pp. 589-604 ◽  
Author(s):  
G. FINK ◽  
M. S. AIYER

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.


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