Enhanced non-esterified fatty acids and corticosterone in blood plasma of chickens treated with insulin are significantly depleted by reverse T₃: minor changes in hypoglycaemia

Previously, it has been observed that dexamethasone or adrenaline-induced hyperlipaemia in blood of chicken was significantly reduced after administration of reverse triiodothyronine (rT3). The present experiment was performed on chicken to determine the altered circulating non-esterified fatty acids (NEFA) induced by physiologically enhanced endogenous corticosterone and catecholamines may also be influenced by rT3. Rise of both hormones were induced by insulin administration. Changes in circulating glucose, corticosterone and catecholamines were additionally measured. Following insulin injection blood glucose fell on the average by 32.7% below control at 2 h of the experiment. Additional treatment with rT3 (rT3 + insulin group) gradually attenuated this decrease and at 4 and 6 h of the experiment it was 17.1% and 12.9% below control, respectively, suggesting on slight inhibition by rT3 of insulin-stimulated glucose utilization. Exposure to insulin significantly increased NEFA levels to about 670% above control group. Additional treatment with rT3 reduced this increase to 309% of control, suggesting inhibition of lipolysis by rT3. Similar alterations were observed in plasma corticosterone levels. Insulin treatment peaked the corticosterone levels maximally by 507.6% above control. Additional treatment with rT3 abolished this rise in the averages to 194.2% above control, possibly by interaction of rT3 with hypothalamo-adrenal axis. Insulin injection increased plasma catecholamines on the average by 21.5% and 53.4% for adrenaline and noradrenaline respectively. Supplementary treatment with rT3 intensified this rise by 55.6% and 71.6% respectively. The obtained results suggest on inhibitory effect of rT3 on hypoglycaemia, hyperlipaemia and plasma corticosterone concentrations in chickens treated with insulin. Contrary to this, rT3 enhanced the rise of plasma catecholamines due to insulin treatment. The obtained data favour the assumption that hypometabolic properties of rT3 depends mainly upon reduced supply of NEFA as a result of restricted lipolysis and to a lesser extent upon the supply of glucose.