Testicular Blood Flow and Plasma Concentrations of Testosterone and Total Estrogen in the Stallion after the Administration of Human Chorionic Gonadotropin

The goal Of this study was to investigate for the first time a possible association between plasma concentrations of testosterone and total estrogen and testicular blood flow in the stallion. Correlations between these variables were calculated before and after administration of human chorionic gonadotropin (hCG). Eight mature warmblood stallions received 5,000 IU hCG intravenously, and four stallions received solvent only. Testicular blood flow in the left and right testicular arteries was assessed using colour Doppler sonography by measuring blood flow volume (BEV) and pulsatility index (PI) immediately before (time 0) and 1, 3, 6, 12, 24, 72, 1,20 and 168 h after hCG administration. EDTA blood samples were collected after each examination from a jugular vein to measure plasma testosterone and total estrogen concentrations. After treatment, the BEV increased and was elevated at I h and between 12 and 24 h. The profile of the Pl was contrary to that of the BEV throughout the study period. Following hCG, there and was a biphasic increase in testosterone concentration with maxima between I and 3 h and between 24 and 72 11, and there was a monophasic increase in the total estrogen concentration with a maximum between 6 and 24 h. At time 0, the total estrogen concentration correlated significantly with BEV (r=0.90; P 0.05) but the testosterone concentration did not (P>.05). The testosterone and total estrogen concentrations did not correlate with PI (P>0.05). The total estrogen concentration, but not testosterone, correlated well with BEV after injection of hCG (P<0.05). The results of this study indicated that the testicular blood flow volume of the stallion may be regualted by estrogens, but additional studies are necessary to investigate whether there is a causal relationship.