Effects of caudal elevation on testicular function in rats. Separation of effects on spermatogenesis and steroidogenesis.

A variety of biologic processes are perturbed when exposed to microgravity (space flight) for more than 7 days, including testicular function. Suspension of rats in a special harness (caudal elevation) to induce thoracic pooling of blood fluids and remove the support function of the hind limbs is used to mimic, on earth, the effects of microgravity encountered during space flight. Typically, this induces cryptorchidism in male rats. Three experiments were conducted to differentiate the effects of caudal elevation (30 degrees angle) and anatomic location of testes on spermatogenesis and steroidogenesis. Rats were subjected to caudal elevation for 7 days using either a tail harness (experiments 1 and 2) or a whole-body harness (experiment 3). Testes of rats fell into the abdominal cavity when a tail harness was used, but ligation of the inguinal canal prevented this repositioning. For rats with abdominal testes, testicular weight was reduced (P less than 0.05) and histology of testes was abnormal; the number of spermatids per gram parenchyma was lower (P less than 0.05) in tail-suspended rats compared with control rats. In contrast, spermatogenesis was not affected by caudal elevation in most rats in which the inguinal canal was ligated or in rats elevated by whole-body harness. Concentrations of testosterone in serum and testicular interstitial fluid were lower (P less than 0.05) in suspended rats, regardless of the method used for caudal elevation or anatomic location of testes. Concentrations of luteinizing hormone in serum were elevated (P less than 0.05) in rats with intra-abdominal testes.(ABSTRACT TRUNCATED AT 250 WORDS)