Measurement of plasma LH concentrations in aged male rodents by a radioimmunoassay and a radioreceptor assay.

Abstract

Circulating plasma concentrations of LH from young mature (3-4 months old), middle-aged (15-18 months old) and aged (31-32 months old) male C57BL/6 mice, Syrian hamsters (3-4, 19-20 and 24-25 months old), Fischer 344 rats (3-4, 18-19 and 28-29 months old), Chinese hamsters (3-4, 19-20 and 29-30 months old) and Mongolian gerbils (3-4 and 19-22 months old) were analysed using a radioimmunoassay (RIA) and a radioreceptor assay (RRA). Male rats exhibited the greatest changes with advancing age: the oldest rats had an almost undetectable quantity of plasma LH, as measured by both assays. In contrast, the oldest male Syrian hamsters had significantly higher levels of LH than did younger animals. A significant decrease occurred in the amounts of LH detectable by RRA in middle-aged Chinese hamsters which was not evident with the RIA. There were no statistically significant differences in LH levels of C57BL/6 mice and gerbils with increasing age. The mean RRA:RIA ratios indicated that age-related differences in LH concentrations resulted from physiological changes in the secretion or the metabolic clearance of LH and not from changes in the biological potency of LH.