In vivo patterns of circulating steroids in adult male rats. IV. Evidence for rapid oscillations in testosterone in normal and totally parenterally nourished animals.

In vivo patterns of circulating testosterone (T) were investigated in stock fed controls and parenterally nourished (TPN) rats. Rats were sampled at 2 minute intervals for 30 minutes via a jugular cannula. Both groups exhibited a rapid oscillatory T pattern. In the control group, T concentrations at any specific time interval exhibited large differences with coefficients of variation (17-88%). In TPN rats this variation was 34-79%. Moreover, the mean T concentration of all samples obtained during the 30 minute period for each individual animal ranged from 1.3 +/- 0.1 (S.E.M.) to 3.5 +/- 0.3 (S.E.M.) ng/ml in controls and 1.3 +/- 0.1 (S.E.M.) to 2.0 +/- 0.2 (S.E.M.)ng/ml in controls and 1.3 +/- 0.1 (S.E.M.) to 2.0 +/- 0.2 (S.E.M.) ng/ml for TNP rats respectively. The mean coefficient of variation in control animals, however, was twice that of TPN rats, indicating that variation in basal T may be minimized during intravenous feeding. The occurrence of rapid oscillations in T of both stock and parenterally fed animals shows that nutritional regimen does not affect this phenomenon.