We have used a push pull cannula to collect interstitial fluid from the testes of anaesthetized rats at various times after a single injection of human chorionic gonadotrophin (hCG; 50 IU), and compared the levels of testosterone in this fluid with the levels in testicular and peripheral venous blood collected at the same times. Following hCG injection, significant increases in testosterone concentrations were observed in all fluids with notable peaks occurring in interstitial fluid at 2, 8 and 24 h, in testicular venous blood at 2, 8 and 30 h, and in peripheral venous blood at 2, 8, 24 and 72 h. The results demonstrate for the first time that changes in testosterone concentrations in interstitial fluid can be different from those in testicular venous blood. In addition, when testosterone levels in interstitial fluid were compared with levels in testicular venous blood at each time-point, the results suggested that the partitioning of testosterone between these two compartments can be regulated. Furthermore, the changes in both interstitial fluid and testicular venous blood levels of testosterone do not always parallel those in peripheral venous blood, suggesting that changes in testicular blood flow and peripheral clearance rates of testosterone may also be important in the control of circulating testosterone concentrations.
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Maddocks et al. (1989) studied this question.