Plasma melatonin in ewes after ovariectomy.

Six ewes were ovariectomized in late November and kept in natural light with 5 intact controls. LH levels were monitored approximately weekly. On Days 16 and 58 after ovariectomy plasma melatonin was determined at 3-h intervals for 24 h in all the ewes. Plasma melatonin concentrations were greater in the ovariectomized ewes than in the controls especially at 16 days when total 24 h secretion was almost 3 times that in the control ewes. These data indicate that, in the ewe, the gonads exert an inhibitory influence on melatonin secretion.