Abstract
A tail-suspension (TS) rat model used to simulate microgravity was tested for its effects on the anatomy, cell structure, and function of the testis and epididymis in sexually mature male rats. Rats suspended for 7 days without inguinal canal ligation exhibited a significant (P less than or equal to 0.05) reduction in testis weight compared with controls (1.55 +/- 0.04 to 1.1 +/- 0.02 g). Except for the liver, epididymis, and adrenals of TS rats and TS rats allowed to recover for 7 days, no significant (P less than or equal to 0.05) change was observed in the weight of other body and accessory sex organs. A histological examination of the testes and epididymides of model animals revealed disorganized seminiferous tubules and accumulation of large multinucleated cells and spermatids in the lumen of the epididymis. A significant (P less than or equal to 0.05) increase in serum luteinizing hormone (53.1 +/- 6.7 to 66.2 +/- 10.1 ng/ml) and follicle-stimulating hormone (257 +/- 25 to 305 +/- 38 ng/ml) was observed in TS nonligated rats, whereas serum prolactin and testosterone levels were observed to decline from 8.3 +/- 1.3 to 5.1 +/- 0.29 and 7.1 +/- 1.3 to 3.8 +/- 0.25 ng/ml, respectively. Decreases in testis protein content and testosterone levels of the testis, interstitial fluid, and epididymis were also observed in model animals. These data demonstrate that the suspension procedure used in the National Aeronautics and Space Administration TS model results in the testis and epididymis translocating into the abdominal cavity, causing cellular degeneration and organ dysfunction.