Effect of corticotropin releasing factor (CRF) in the median eminence on gonadotropins in ovariectomized rats with or without steroid priming: dose-response study.

We determined the dose-response relationship and examined the time related effect of CRF (corticotropin releasing factor) injected directly into the median eminence (ME) on LH and FSH secretion in conscious female rats of different steroid status. Doses of 0.25, 0.75, 1, and 1.5 nM CRF dissolved in 1 microliter of water were injected into the ME in 5 experimental groups of rats: Short-term (2 days) ovariectomized (sOVX); long-term (3-4 weeks) ovariectomized (lOVX); lOVX primed by estradiol benzoate (EB) 4 h before the experiment (lOVX+E); lOVX primed by EB 36 h before the experiment (lOVXE) and lOVX primed by EB 72 h and progesterone 6 h before experiment (lOVXP). Blood was collected at 30, 60, 90, and 120 min postinjection to determine LH and FSH by RIA. CRF at the doses of 0.75, 1, and 1.5 nM significantly decreased serum LH levels in all groups. The dose of 0.25 nM CRF was ineffective. The highest dose (1.5 nM) of CRF had no effect on serum FSH levels. The results suggest that CRF inhibits LH secretion, at least in part, by a central action of GnRH release in the ME, and that this effect is independent of the estrogen/progesterone status of the animal.