Seasonal differences in glucose tolerance and insulin response of pinealectomized pigeons (Columba livia).

The effects of a glucose tolerance test (GTT) and an insulin response test (IRT) on blood glucose levels were evaluated in pinealectomized and nonpinealectomized pigeons during the breeding and nonbreeding months. The tests revealed increased glucose tolerance and insulin sensitivity in pinealectomized birds during the breeding season. In the nonbreeding season, both the pinealectomized and the control birds tended to show more or less similar responses for both GTT and IRT. These changes confirm the anti-insulin role of the pineal in wild pigeons during the breeding season and the possible significance of the pineal gland in modulating seasonal changes in carbohydrate metabolism.