Suppressive effect of estradiol (E2) on pulsatile release of luteinizing hormone (LH) in ovariectomized ewes during anestrus

Twelve ewes were ovariectomized during anestrus and randomly allocated in to two groups. Experimental group was implanted with E₂, and control group was not. Jugular blood samples were drawn every 5 to 10 minutes through an indwelling jugular cannula for 8 to 9 hous. The plasma samples were radioimmunoassayed for LH. The mean LH basal level （MBL） and pulse amplitude （PA） in experimental group were significantly lower than those in control group, hut the LH pulse frequency was not. There was a positive relationship between MBL and PA. It is. concluded that implanted E₂ suppresses LH release at pituitary level, mainly by blocking the reponse of LH to Gn RH, and that the decrease of MBL probably is due to the suppressive effect of E₂.