EFFECT OF CRH ON THE PREOVULATORY LH AND FSH SURGE IN THE CYCLIC RAT - A ROLE FOR ARGININE-VASOPRESSIN

The effect of intracerebroventricular (i.c.v.) injection or infusion o f various doses of corticotropin-releasing hormone (CRH) on the LH and FSH surge was studied in pro-oestrous rats supplied with a jugular ve in and an i.c.v. cannula. Additionally, we investigated if arginine va sopressin (AVP) was involved in the CRH-induced alterations to the sur ge of gonadotropins. I.c.v. injection of 10 mu g CRH given 5 min befor e the presumed onset of the LH surge caused a strong inhibition of the LH surge and a slight inhibition of the FSH surge, Three to four h af ter CRH injection, its inhibitory effect diminished. A 6 h i.c.v. infu sion of CRH started 1 h before the presumed onset of the LH surge, cau sed a dose-related inhibition of the LH and FSH surge. Infusion of 1 m u g/h CRH did not suppress the surge of both hormones while infusion o f 5 or 10 mu g/h CRH inhibited the LH surge. Infusion of 10 mu g/h CRH caused a strong suppression of plasma LH during the first 3 h of the LH surge. Despite continuation of CRH infusion, the inhibitory effect disappeared and plasma LH increased to similar levels as in controls a t corresponding points of time of the LH surge. The FSH surge was also suppressed by infusion of 10 mu g/h CRH. The surge of LH and FSH was not affected by a 9-h infusion of 10 mu g/h CRH started 4 h before the presumed onset of the LH surge. This observation also indicates that the inhibitory effect of CRH may last for only 3-4 h, The surge of LH and FSH was not affected by i.c.v. injections of AVP-antiserum. Howeve r, pretreatment with AVP-antiserum prolonged the inhibitory effect of CRH on the LH surge. In conclusion, CRH can inhibit the pro-oestrous L H and to a lesser extent the FSH rise for only 3-4 h after the beginni ng of CRH administration, AVP may play a role in limiting the inhibito ry effect of CRH on LH to 3-4 h.