A Comparison of the Disappearance Rates of Luteinizing Hormone from Intact and Ovariectomized Rats1

Abstract

Hypophysectomy was performed on intact female rats during the proestrous LH [luteinizing hormone] surge and on ovariectomized rats, and plasma concentrations of LH were measured every 5 min for approximately the next hour. The disappearance rate of LH from ovariectomized rats corresponded to an initial half-life of 23.1 .+-. 2.9 min, which is within the range previously reported for this species. The disappearance of LH from intact rats, corresponded to an initial half-life of 13.7 .+-. 0.7 min. In a 2nd experiment, blood was taken from ovariectomized rats and from intact female rats during the LH surge. The sera were injected i.v. into hypophysectomized female rats (with ovaries intact) bearing chronic venous catheters, and plasma concentrations of LH were measured every 5 min for the next hour. LH from ovariectomized rats disappeared at a rate corresponding to an initial half-life of 22.7 .+-. 2.2 min, while the half-life for LH from proestrous intact rats was 13.4 .+-. 1.2 min. These results suggest a change in the circulating form of LH following ovariectomy, in that LH in the ovariectomized rat is cleared more slowly. It appears that LH is removed from the circulation of the intact rat at a higher rate than was previously reported.