Inhibition of LH Release as Influenced by LRF Infusion

Abstract

Four ovariectomized ewes were infused with LRF (10 mug/hr for 20 hr. Jugular vein blood samples were taken at 30 min intervals. After 16 hr of LRF infusion each animal was given a 1 mg iv injection of LRF. At the end of the 20 hr infusion period, the animals were sacrificed and the pituitary removed. Pituitary and plasma samples were analyzed for LH. Plasma LH concentration reached a peak level of 73 ng/ml, 1.5 hr after starting the LRF infusion. A rapid decline in LH concentration occured for the next 3 hr. The plasma LH concentration declined slowly to preinfusion levels over the next 15.5 hr. A small insigificant rise in plasma LH concentration occured when the animals were given 1 mg of LRF after 16 hr of LRF infusion. At the end of the treatment period pituitary LH concentration varied from 369 to 1360 ng/mg. Two of the four ewes had pituitary LH concentrations similar to untreated ovariectomized ewes. The pituitarys' refractoriness to LRF apparently is not due to depletion of pituitary LH.