Effects of intrathecal administration of thyrotropin releasing hormone and its analogue, DN1417, on plasma glucose and catecholamine levels in conscious rats.

Effects of intrathecal (i.t.) administration of TRH and the TRH analogue, DN1417, on plasma catecholamines and glucose levels were studied in conscious male rats. The i.t. administration of TRH (0.6 and 3 nmol) at the T8-10 vertebral level resulted in a dose-related increase in epinephrine (E), norepinephrine (NE), and glucose levels, which was suppressed by prior administration of the ganglionic blocker, hexamethonium (1.5 mg/100 g b. wt.). I.t. administration of TRH (3 nmol) caused small increases in plasma E and glucose at the C7-T1 vertebral level, but it did not change plasma E, NE and glucose levels at the sacral level. DN1417 (3 nmol) administered i.t. at the T8-10 or C7-T1 vertebral level had a more potent and long-lasting effect in stimulating the release of E than TRH. These findings suggest that TRH may act on sympathetic preganglionic neurons at the T7-10 spinal levels and stimulate the release of catecholamines from the adrenal medulla.