ADRENAL EPINEPHRINE AND NOREPINEPHRINE RELEASE TO HYPOGLYCEMIA MEASURED BY MICRODIALYSIS IN CONSCIOUS RATS

Experiments were conducted in conscious male rats to determine whether hypoglycemia induced by insulin administration preferentially stimula ted epinephrine (Epi) or norepinephrine (NE) adrenal medullary chromaf fin cells. The release of Epi and NE from the adrenal medulla was cont inuously monitored using a microdialysis probe of novel design that ha d been inserted in the adrenal medulla similar to 16 h before the admi nistration of insulin. Following insulin, 3 U/kg iv, blood glucose dec lined and dialysate Epi levels rose. No measurable increment in dialys ate NE was obtained. Similarly, plasma Epi increased with no detectabl e change in NE. Patterns of dialysate and plasma catecholamine changes were similar in two groups of animals that had been fed or fasted ove rnight before insulin treatment. However, the magnitude of the Epi inc rease was greater in the fasted animals. After recovery of the blood g lucose concentration to preinsulin levels, dialysate and plasma catech olamine concentrations returned to control values. These experiments c learly demonstrate that adrenal medullary chromaffin cells that produc e Epi are preferentially stimulated in response to insulin-induced hyp oglycemia.