Long-term testicular responses to blinding in rats

Gonadal responses to the blinding of one month old rats have been studied at 1,2,3,5,7,9, and 12 month intervals post-surgically. Testosterone in both testicular vein and peripheral venous plasma was measured by radioimmunoassay and spermatogenesis was evaluated by means of differential germ cell counting. The weights of endocrines and accessory sex glands were routinely recorded.Blinding was without effect upon gametogenic function of the testis, at all intervals of study. Testicular venous levels of testosterone in intact rats showed a ‘post-pubertal spurt’ followed by a more pronounced ‘seasonal peak’ and the latter was paralleled by a similar peak in peripheral testosterone. Blinding led to suppression of the post-puberal surge in testicular secretion but testicular vein levels of the hormones were not significantly altered from control values for the remainder of the investigation. In contrast, testosterone concentrations in peripheral plasma of blinded rats were more consistently lower than in control animals until 12 months post-surgery. Atrophic responses of the accessory sex glands to blinding occurred during the initial periods of the study but these had totally disappeared by 9 months. Taken together, the results illustrate a somewhat small degree of gonadal dependency upon photic input in the male rat, particularly when compared with responses reported for the hamster subjected to similar experimental conditions.