Immunoreactive Luteinizing Hormone Releasing Factor in Rat Pituitary Stalk Blood: Effects of Electrical Stimulation of the Medial Preoptic Area

Abstract

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 suggest 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.

Immunoreactive luteinizing hormone releasing factor (LRF) in pituitary stalk plasma from female rats: effects of stimulating diencephalon, hippocampus and amygdala.

“…Brown-Grant & Raisman, 1972;Sawyer, 1972;van Rees, 1972;Velasco & Rothchild, 1973;Kawakami & Terasawa, 1974). Previous studies from this laboratory have shown that electrical stimulation of the medial preoptic area (Fink & Jamieson, 1976) or median eminence (Sherwood, Chiappa & Fink, 1976) is accompanied by a significant increase in the content of immunoreactive LRF in blood collected from the cut pituitary stalk of rats. The aim of the present work was to determine (1) whether stimulation of other brain areas can cause an increase or decrease in the content of LRF in pituitary stalk blood, and (2) whether other areas of the brain influence the LRF response to electrical stimulation of the medial preoptic area.…”

“…(Margate), were housed and maintained as described by Fink & Jamieson (1976). Only animals which exhibited regular 4 day oestrous cycles were used for experimentation at which time the animals weighed 200-300 g.…”

“…Pituitary stalk blood was collected (Fink & Jamieson, 1976) for 30 min before and 30 min during the application of an electrical stimulus through the electrodes (except for one group subjected to hippocampal stimulation; see Results). The stimulus consisted of 30 see trains (separated by intervals of 30 see) of accurately balanced biphasic square wavepulses with afrequency of 60 Hz, amplitude 500 #A (1 mA peak to peak) and duration (each pulse) 1 msec (Fink & Jamieson, 1976 (-), and the extent of cuts made in animals subjected to long PRS (lines). The latter are based on the positions of the lower edges of the cuts.…”

Hypothalamic Gonadotropin‐Releasing Hormone Secretion: Methodological Aspects of in vitro Systems

“…In recent years both in vivo (1-4) and in vitro (4)(5)(6) methods have been developed to study mechanisms of GnRH secretion directly. Direct measurement of GnRH levels in hypophyseal portal blood in vivo has been achieved by sampling from both conscious (1-3) and anaesthetized (7)(8)(9)(10)(11)(12) animals including the rat (7-lo), monkey (11. 12), sheep (1, 2) and horse (3).…”

Neuroendocrine control of ovarian function in the primate

“…7). Local injections of oestradiol in this area initiate a signal which, when it reaches the median eminence, culminates in a surge of Gn-RH and a subsequent release of LH (Fink & Jamieson, 1976;Goodman, 1978). Interruption of this pathway by deafferentation prevented the oestradiol-positive feedback and resulted in a lack of LH surges and anovulation (Halasz & Pupp, 1969 (Krey et al, 1975;Ferin et al, 1977 (From Ferin et al, 1979.…”