Effect of altered thyroid and adrenal activity on the seasonal reproduction of the Indian palm squirrel, Funambulus pennanti

TLDR: Thiouracil and metyrapone administered during the progression phase of the annual reproductive cycle inhibited gonadal development in the Indian palm squirrel and led to normal gonadal regression during the late breeding phase.

Abstract: Thiouracil and metyrapone administered during the progression phase of the annual reproductive cycle inhibited gonadal development in the Indian palm squirrel, Funambulus pennanti. In a further experiment, these drugs led to normal gonadal regression during the late breeding phase. Thyroxine and corticosterone treatment, on the other hand, maintained the gonads continuously in breeding condition, unlike those of controls, which exhibited characteristic post-reproductive regression. Since hypofunction of the thyroid and adrenal glands had inhibitory effects on the initiation of seasonal gonadal growth, and hyperactivity affects post-reproductive regression, it is suggested that an optimal level of hormones is required for the normal breeding cycle in this subtropical mammal. The results are discussed in terms of an interrelationship between the seasonal thyroid, adrenal, and gonad cycles under natural conditions.