A comparative study of prolactin levels in five species of aged female laboratory rodents.

Abstract

Plasma and pituitary concentrations of prolactin (PRL) were determined by radioimmunoassay in younger mature (2–6-month-old) and aged (14–20-month-old) C57BL/6 mice, Chinese hamsters, Syrian hamsters, Mongolian gerbils and Wistar rats. All females exhibited a predominantly leukocytic vaginal smear prior to bleeding. Preliminary tests indicated that PRL in C. hamsters crossreacted to a greater extent with mouse PRL antiserum than with rat PRL antiserum. Gerbil PRL crossreacted with either mouse or rat PRL antisera; however, the parallelism of plasma and pituitary dose-response curves was not statistically identical to standards of either antisera. The assays were conducted using mouse PRL antiserum since gerbil PRL was closest to standard curves of the mouse. PRL levels in the S. hamster were assayed using rat PRL. Circulating plasma levels of PRL were significantly lower (P<0.001) in aged S. hamsters and statistically higher (P<0.001) in senescent rats when compared with those in their younger counterparts. Pituitary levels of PRL were significantly depressed (P<0.001) in aged mice and gerbils compared with levels in younger females. There were no statistical differences in the levels of plasma or pituitary PRL in the two age groups of C. hamsters. These data reflect age-related changes in PRL secretion and emphasize species diversity in the secretion of this hormone among older laboratory rodents.