Rat Placental Luteotropin: Initial Secretion and Luteolytic Quality

Abstract

Absfract. The secretion of placental lactogen begins early in pregnancy. Previous studies indicate that rat placental lactogen (rPL) is secreted from Day 8 of pregnancy and that it is luteolytic as well as luteotrophic. This study establishes the onset of both the luteotrophic and the luteolytic effects of placental lactogen in pregnant rats subject to timed hypophysectomy. Pregnancy was preserved in all groups with the administration of dydrogesterone (9p, 10a-pregna4,6-diene-3,20 dione), a progesterone analog, and diethylstilbestrol, an estrogen analog.Plasma progesterone and 20a-hydroxypregn-4-ene-3-one (20-OHP) were measured in serial serum samples by RIA. The data indicate that rPL is secreted as early in pregnancy as the seventh day. Rats hypophysectomized on Day 6 of pregnancy or later had ovaries that con- 76