Administration of testosterone to wether lambs: effects on protein and energy metabolism and growth hormone status

The effects of episodic infusion of testosterone into the vascular system on energy expenditure, nitrogen retention and whole body protein synthesis (determined from [1-14C]leucine kinetics) were studied in castrated male lambs under conditions of controlled food intake. Comparisons were made between a 10-day control period and a 10-day treatment period for each lamb. Infusion of testosterone produced a significant increase in heat production, but the magnitude (198 kJ/day, +2.5%) was less than the differences in energy expenditure expected between entire and castrated male ruminants. The retention of nitrogen improved by 1.24 g/day (+22%) in response to the administration of androgen, and this was accompanied by a decrease in amino acid oxidation. Total protein synthesis also declined, and the anabolic nature of testosterone supply must, therefore, be effected through a reduction in the breakdown of protein, the mechanism being similar to that proposed for certain anabolic steroids and the beta-agonist, clenbuterol. Contrary to other reports, the presence of testosterone had no effect on the plasma concentration of GH.