The effect of testosterone on regional blood flow in prepubertal anaesthetized pigs

This work was undertaken to study the effects of testosterone on the coronary, mesenteric, renal and iliac circulations and to determine the mechanisms of action involved. In prepubertal pigs of both sexes anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary, superior mesenteric, left renal and left external iliac blood flow caused by intra-arterial infusion of testosterone were assessed using electromagnetic flowmeters. Changes in heart rate and arterial blood pressure were prevented by atrial pacing and by connecting the arterial system to a pressurized reservoir containing Ringer solution. In 12 pigs, intra-arterial infusion of testosterone for 5 min to achieve a stable intra-arterial concentration of 1 μg1^-1 increased coronary, mesenteric, renal and iliac blood flow without affecting the maximum rate of change of left ventricular systolic pressure (left ventricular (dP/dt_max) and filling pressures of the heart. In a further five pigs, a concentration-response curve was obtained by graded increases in the intra-arterial concentration of the hormone between 0.125 and 8 μg1^-1. The mechanisms of these responses were studied in the 12 pigs by repeating the experiment after haemodynamic variables had returned to the control values before infusions. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the responses caused by intra-arterial infusion of testosterone performed to achieve a stable intra-arterial concentration of μg 1^-1. In the same pigs and in the remaining six pigs, the increases in coronary, mesenteric, renal and iliac blood flow caused by intra-arterial infusion of testosterone performed to achieve a stable intra-arterial concentration of 1 μg 1^-1 were prevented by intra-arterial injection of N^w-nitro-L-arginine methyl ester. The present study shows that intra-arterial infusion of testosterone dilated coronary, mesenteric, renal and iliac circulations. The mechanism of this response involved the release of nitric oxide.