Progesterone regulation of estrogen receptor in the hamster uterus during the estrous cycle.

Abstract

The purpose of this study was to determine serum steroid-uterine receptor relationships during the preovulatory period of the hamster estrous cycle. Methods were developed and validated for the simultaneous measurement of estrogen receptor (Re) and progesterone receptor in cytosol and a KCl extract of the nuclear fraction. Receptor levels (picomoles per g tissue) were determined by Scatchard plot analysis of specific 3H-labeled steroid binding data. Serum 17β-estradiol (E) and progesterone (P) were measured by standard RIA procedures. During the 4-day cycle, nuclear Re increased from day 2 to the morning of day 4 (proestrus) in parallel with rising serum E titers. After the critical period (1300–1400 h) for the ovulatory surge of gonadotropin on day 4, there was a transient surge of serum E and a sustained elevation of serum P. Preovulatory P secretion was associated with P receptor translocation to the nuclear fraction. The E surge was accompanied by cytosol Re depletion, but there was no concomitant inc...