Effect of CRF in the median eminence on gonadotropin levels in conscious female rats

To evaluate whether the median eminence (ME) is the site of action of CRF (corticotropin releasing factor) in inhibiting LH levels in female rats, we have injected CRF (1 nmol) directly into the ME and then measured plasma LH and FSH concentrations in conscious ovariectomized (OVX) rats in the absence or presence of a single dose of estradiol benzoate (EB). CRF caused a significant decrease in plasma LH levels in both OVX and OVX + EB rats at 30 min postinjection, in comparison to the values obtained in animals injected with water only. Injection into the ME of water had no effect on plasma LH levels in either OVX or OVX + EB animals. The results suggest that CRF probably inhibits LH secretion, at least in part by a central action on GnRH release in ME.