Fluctuations in Plasma Testosterone Levels in Adult Male Rats and Mice

TLDR

Large, irregular fluctuations in plasma testosterone levels in male rats and mice contrast with the stable levels seen in humans and resemble pulsatile release patterns observed in bulls, rams, and dominance‑related differences in rhesus monkeys. Testosterone concentrations were quantified by radioimmunoassay, and chronic indwelling jugular catheters enabled serial blood sampling every 24 h for 4–8 days and every 30 min for 2–8 h in conscious adult male rats. Individual mice displayed striking variation in plasma testosterone, ranging from below 1 ng/ml to over 30 ng/ml, and even within the same animal, concentrations fluctuated 2– to 5‑fold over time. Endocrinology 92:1223 (1973).

Abstract

Testosterone (T) levels in the plasma of male laboratory rats and mice were measured by radioimmunoassay. There was a striking individual variation with values ranging from less than 1 ng/ml to over 30 ng/ml in mice of the same age and strain housed under identical conditions. Using chronic indwelling catheters inserted into a jugular vein, blood was collected from adult conscious male rats every 24 hr for 4 or 8 days and every 30 min for 2l/2 or 8 hr. Considerable differences in plasma T levels were observed between different animals, and 2– to 5–fold fluctuations of T concentrations in the plasma were detected between samples collected from the same animal at different times. These large and irregular changes in plasma levels of T are unlike the fairly stable levels observed in the human but bear certain resemblance to the pulsatile release of T described in bulls and rams and perhaps also to the social dominance related differences in plasma T levels in Rhesus monkeys. (Endocrinology92: 1223, 1973)