Age-related temporal changes of levels of circulating progesterone in repeatedly pseudopregnant rats.

Abstract

Plasma concentrations of progesterone were measured by radioimmunoassay in spontaneous (old) and induced (young adult) repeatedly pseudopregnant rats. Mean duration of pseudopregnancy was significantly longer at 24 months of age (17.3 ± 0.5 days) than at 10 months (14.0 ± 0.3 days). In both young adult and old rats progesterone concentrations showed tniphasic patterns of change throughout pseudopregnancy with an elevated plateau seen during Days 3-8 and 3-9, respectively, in agreement with the longer duration of the luteal phase in old rats.There was little indication of any gross age-related deficiencies in progesterone levels and the patterns of their changes during pseudopregnancy of old rats. However, a two-way analysis of variance demonstrated a low grade impairment in progesterone plateau values of old rats. The significance of this deficit in terms of decreased progesterone secretion is discussed. Middle-aged rats held an intermediate position for progesterone concentrations, suggesting an age-related evolution in this type of senile deviation of the ovarian cycle.