Evidence that luteinizing hormone from the maternal pituitary gland may promote antepartum release of relaxin, luteolysis, and birth in rats.

Abstract

The role of the maternal pituitary gland and LH in the regulation of the release of relaxin from the onset of the light phase on day 21 of pregnancy (day 21) until delivery (herein designated the antepartum period) was examined in rats. Serum relaxin levels were determined in rats hypophysectomized (HYPOX) or sham hypophysectomized (SHAM) on day 14. In SHAM rats, the elevated serum relaxin levels that occurred during the light phase of days 21 and 22 coincided with a rapid decline in serum progesterone to basal levels, and relaxin levels then declined markedly throughout the 18- to 24-h before delivery. During the antepartum period HYPOX rats differed from SHAM rats in the following ways: 1) mean serum relaxin levels were higher immediately before the antepartum period (day 20) and remained at the maximal levels the sham-operated animals experienced throughout the ensuing antepartum period; 2) elevations in relaxin levels generally occurred in individual rats; however, they usually occurred later than day...