Testosterone and androstenedione profiles in the blood of domestic tom-cats

Testosterone and androstenedione were measured in the blood of four mature, intact tom-cats. Samples were collected from an indwelling jugular catheter once an hour for 24 h, and at more frequent intervals after a number of experimental procedures. Testosterone and androstenedione concentrations have a pattern of episodic release over a 24-h period but no diurnal rhythm was evident. The range of testosterone concentration was 0–23.5 ng/ml and androstenedione concentration 0–35.7 ng/ml. There was evidence of some seasonal influence on testosterone concentration, it being low in the period of reduced sexual activity (Jan–March) and high in the period of peak sexual activity (Aug).Sexual stimulation did not cause a rise in testosterone concentration as it was already high, but androstenedione concentration was significantly increased.Castration produced an immediate decrease in testosterone to baseline concentrations of 0–0.5 ng/ml but the concentration of androstenedione was variable and it is probable that a substantial amount of androstenedione is contributed from another source (possibly from the adrenals).