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 The concentration of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in blood samples withdrawn from the external jugular vein immediately before and at frequent intervals up to 1 h after application of the stimulus was determined by radioimmunoassay.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.

CHANGES IN THE SENSITIVITY OF THE PITUITARY GLAND TO LUTEINIZING HORMONE RELEASING FACTOR DURING THE OESTROUS CYCLE OF THE RAT

1974 ◽  
Vol 60 (1) ◽  
pp. 47-64 ◽  
Author(s):  
M. S. AIYER ◽  
G. FINK ◽  
FENELLA GREIG
Keyword(s):  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Critical Period ◽  
Standard Dose ◽  
Fold Increase ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Early Afternoon ◽  
Conscious Animals

SUMMARY The responsiveness of the anterior pituitary gland to synthetic luteinizing hormone releasing factor (LH-RF) was tested at various times of the oestrous cycle of the rat in order to assess the relative importance of changes in pituitary sensitivity in the timing and magnitude of the preovulatory surge of luteinizing and follicle-stimulating hormones (LH and FSH). The minimal dosage of LH-RF which consistently induced ovulation in rats anaesthetized with sodium pentobarbitone (Nembutal) immediately before the critical period of pro-oestrus was 50 ng/100 g body weight, and this was used as the standard dose throughout the study. The LH-RF was injected either intravenously into animals anaesthetized with Nembutal 30 min to 1 h before, or into conscious animals through a cardiac catheter which had been inserted several days before. Most experiments were carried out on rats which had exhibited regular 4-day oestrous cycles, although results from animals with 5-day cycles are also presented and discussed. Blood samples were taken immediately before and at frequent intervals after the injection of LH-RF, and the concentrations of LH and FSH in these samples were determined by radioimmunoassay. With respect to the secretion of LH, in both anaesthetized and conscious animals with regular 4-day cycles a tenfold increase in pituitary sensitivity occurred between the early afternoon of dioestrus and pro-oestrus. This was followed by a marked (50-fold) increase which reached a peak at 17.00–18.00 h of pro-oestrus. The phase of marked increase in sensitivity appeared to commence at about the time of the onset of the pre-ovulatory surge of LH and continued for some hours after. Pituitary sensitivity then declined through oestrus and metoestrus, reaching a nadir at 14.00 h of dioestrus. From 15.00 to 22.30 h of pro-oestrus there was a significant positive correlation between the pre-injection levels of and maximal increments in plasma LH, and this, together with the fact that the marked increase in sensitivity could be abolished by administering Nembutal before the critical period, raised the possibility that endogenous LH-RF, presumably secreted in greater amounts during the early afternoon of pro-oestrus, may exert a priming effect on the anterior pituitary gland. Pituitary responsiveness to LH-RF with respect to the secretion of FSH was also at its highest at 17.00–18.00 h of pro-oestrus. However, in contrast to LH, the mean level of FSH before injection reached a peak at 05.00 h of oestrus, 11 h after the maximum FSH response to LH-RF. These results suggest that a change in pituitary sensitivity to LH-RF may play an important role in determining the magnitude of the pre-ovulatory surge of LH, but it would appear that the timing and duration of the surge depend on other factors as well. The relationship between the secretion of LH and ovulation is discussed with respect to the finding that there appeared to be no correlation between the number of ova shed and the maximal levels of plasma LH after injection.

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.

IMMUNOREACTIVE LUTEINIZING HORMONE RELEASING FACTOR IN RAT PITUITARY STALK BLOOD: EFFECTS OF ELECTRICAL STIMULATION OF THE MEDIAL PREOPTIC AREA

1976 ◽  
Vol 68 (1) ◽  
pp. 71-87 ◽  
Author(s):  
G. FINK ◽  
M. G. JAMIESON
Keyword(s):  
Electrical Stimulation ◽  
Preoptic Area ◽  
Free Acid ◽  
Medial Preoptic Area ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Pituitary Stalk ◽  
Male And Female ◽  
Male And Female Rats ◽  
Stimulation Of

SUMMARY Blood was collected from the cut pituitary stalk of male and female rats before and during the application of an electrical stimulus to the medial preoptic area. The plasma was assayed for immunoreactive LH releasing factor (RF) by a double antibody radioimmunoassay using a specific antiserum raised in rabbits against the free acid derivative of the decapeptide LH-RF conjugated to bovine serum albumin. The decapeptide (used as a standard) and pituitary stalk plasma cross-reacted in a similar manner with the antiserum. Stimulation of the preoptic area increased significantly the amount of LH-RF in pituitary stalk plasma in both male and female rats. The increase in LH-RF was linearly related to the strength of the stimulating current, and the amount of LH-RF liberated diminished on cessation of the stimulus. The concentration of LH-RF in pituitary stalk plasma from female rats was significantly greater than that in jugular venous plasma. The magnitudes of the mean increments of LH-RF in pituitary stalk plasma (stimulation minus pre-stimulation values) at various times of the oestrous cycle in female rats suggests that between 18.00 h of dioestrus and 13.00 h of pro-oestrus there is an increase in sensitivity of the LH-RF secretory mechanism to electrical stimulation. However, the increments decreased in magnitude between 13.00 and 18.00 h of pro-oestrus, indicating that the marked increase in responsiveness of the hypothalamo-hypophysial system to electrical stimulation which occurs during this period is due mainly to a change in sensitivity of the pituitary gonadotrophs to LH-RF. The LH-RF in pituitary stalk plasma collected before application of the stimulus was higher at some of the times examined during pro-oestrus than at other times of the oestrous cycle. A higher level of the secretion of the factor may be important for the full development of the priming effect of LH-RF and, consequently, the marked increase in responsiveness of the pituitary gland which occurs during the afternoon of pro-oestrus.

Relationship between endogenous opioids and the oestrous cycle in the rat

1984 ◽  
Vol 100 (3) ◽  
pp. 271-275 ◽  
Author(s):  
G. K. Hulse ◽  
G. J. Coleman ◽  
D. L. Copolov ◽  
J. A. Clements
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Ovarian Hormones ◽  
Endogenous Opioids ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Neurointermediate Lobe ◽  
Response To Stress ◽  
Induced Changes

ABSTRACT The aim of this study was twofold: (1) to document changes in levels of immunoreactive β-endorphin (Ir-β-EP) in the hypothalamus, anterior pituitary gland, neurointermediate lobe and plasma during the oestrous cycle of the rat and (2) to investigate stress-induced changes in plasma Ir-β-EP at different stages of the oestrous cycle. Evidence was found that Ir-β-EP levels in the hypothalamus, anterior pituitary gland and plasma are not constant during the oestrous cycle and that the Ir-β-EP response to stress is a function of the phase of the oestrous cycle at which stress is applied. It is suggested that fluctuations in ovarian hormones may influence oestrous Ir-β-EP levels both under normal conditions and after exposure to stress. J. Endocr. (1984) 100, 271–275

Discovery of the luteinizing hormone of the anterior pituitary gland

2004 ◽  
Vol 287 (5) ◽  
pp. E818-E819 ◽  
Author(s):  
H. Maurice Goodman
Keyword(s):  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Anterior Lobe ◽  
Anterior Pituitary Gland ◽  
Luteinizing Hormones ◽  
Historical Significance ◽  
Classic Paper

This essay looks at the historical significance of an APS classic paper that is freely available online: Fevold HL, Hisaw FL, Leonard SL. The gonad stimulating and the luteinizing hormones of the anterior lobe of the hypophesis. Am J Physiol 97: 291—301, 1931 ( http://ajplegacy.physiology.org/cgi/reprint/97/2/291 ).

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