The effects of glucagon and insulin on plasma thyroid hormone levels in fed and fasted domestic fowls

Abstract

1. 1. Glucagon injection (50 μg kg −1) produced a biphasic response in plasma thyroxine (T 4) level in both fed and fasted chickens. An initial inhibition was followed by an increase to levels above control value. 2. 2. Glucagon reduced plasma triidothyronine (T 3) possibly as a consequence of inhibition of peripheral monodeiodination. This inhibition persisted in fasted animals despite a glucagon induced hyperglycaemia. 3. 3. Insulin injection (4 IU kg −1) decreased plasma T 4 concomitant with a profound hypoglycaemia. These effects were more pronounced in fasted birds. 4. 4. Insulin induced hypoglycaemia was associated with decreased plasma T 3 probably as a consequence of reduced thyroidal T 4 secretion and reduced peripheral monodeiodination. 5. 5. Glucagon and insulin may play direct or indirect roles in the regulation of thyroid hormone secretion and metabolism in the domestic fowl.