Effect of CRH on the preovulatory LH and FSH surge in the cyclic rat: a role for arginine vasopressin?

Abstract

The effect of intracerebroventricular (i.c.v.) injection or infusion of various doses of corticotropin-releasing hormone (CRH) on the LH and FSH surge was studied in pro-oestrous rats supplied with a jugular vein and an i.c.v. cannula. Additionally, we investigated if arginine vasopressin (AVP) was involved in the CRH-induced alterations to the surge of gonadotropins. I.c.v. injection of 10 micrograms CRH given 5 min before 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 after CRH injection, its inhibitory effect diminished. A 6'h i.c.v. infusion of CRH started 1 h before the presumed onset of the LH surge, caused a dose-related inhibition of the LH and FSH surge. Infusion of 1 micrograms/h CRH did not suppress the surge of both hormones while infusion of 5 or 10 micrograms/h CRH inhibited the LH surge. Infusion of 10 micrograms/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 at corresponding points of time of the LH surge. The FSH surge was also suppressed by infusion of 10 micrograms/h CRH. The surge of LH and FSH was not affected by a 9-h infusion of 10 micrograms/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. However, pretreatment with AVP-antiserum prolonged the inhibitory effect of CRH on the LH surge. In conclusion, CRH can inhibit the pro-oestrous LH and to a lesser extent the FSH rise for only 3-4 h after the beginning of CRH administration. AVP may play a role in limiting the inhibitory effect of CRH on LH to 3-4 h.