Testosterone concentrations in testicular interstitial fluid collected with a push–pull cannula or by drip-collection from adult rats given testosterone or aminoglutethimide

Abstract

ABSTRACT This study was designed to investigate the differences in testosterone concentrations measured in testicular extracellular interstitial fluid obtained with a push–pull cannula or by post-mortem drip-collection. In the first experiment, testosterone-filled silicone elastomer capsules (2–16 cm lengths) or empty 2 cm capsules were implanted s.c. in adult male rats for 1 week. Animals were then anaesthetized and interstitial fluid was collected with a push–pull cannula for 1 h from one testis in each animal. Testicular and peripheral venous blood were then sampled and supernatant fluid was collected from the dispersed cells of the same testis. The contralateral testis in each animal was removed, and post-mortem interstitial fluid obtained by drip-collection for 20 h at 4 °C. In animals given empty capsules, testosterone concentrations in drip-collected interstitial fluid were significantly (P < 0·01) greater than testicular and peripheral venous blood levels, testicular fluid levels, and levels in interstitial fluid calculated from push–pull cannula samples. The concentrations of testosterone calculated in interstitial fluid collected with a push-pull cannula were never significantly greater than testicular venous blood levels. In animals with testosterone-filled capsules, testosterone concentrations measured in drip-collected interstitial fluid were similar to those calculated from push–pull cannulae samples, and to testicular venous blood levels. In a second experiment, a group of adult male rats was pretreated with aminoglutethimide to block steroidogenesis. Two hours later, interstitial fluid was drip-collected from the testes of these animals and from a group of vehicle-treated controls. For each animal, one testis was placed on ice and interstitial fluid collected for only 10 min, while the contralateral testis was kept at 4 °C and interstitial fluid collected for 20 h. In control animals, testosterone concentrations in interstitial fluid collected for 20 h were significantly (P < 0·01) greater than those in interstitial fluid collected for 10 min. In animals pretreated with aminoglutethimide, testosterone concentrations at 10 min and 20 h were not significantly different, and did not differ from those in control samples collected for 10 min. We believe these results support earlier suggestions that the post-mortem drip-collection technique may give misleading results, and indicate that testosterone synthesis and secretion continues after isolation of the testis. This may also be the case with other Leydig cell products. Journal of Endocrinology (1989) 121, 303–309