The effect of pinealectomy on plasma levels of thyroid hormones in pigeons reared under different photoperiods.

The effects of pinealectomy on plasma T3, T4 and free T4 concentrations were studied for about 10 weeks in pigeons maintained either under a constant short photophase or in a regime where a long photophase was replaced by a short one during the experiments. The results indicate that, regardless of the photoperiod, no clear functional relationship can be found between the avian pineal gland and thyroid function, although a transitory increase in T4 levels was seen in both pinealectomized and sham-operated birds shortly after the operations.