Adrenal medullary secretion with splanchnic stimulation in spinal cats

This project was undertaken to determine whether previously observed adrenal medullary hyperactivity that developed following high spinal cord transection in the cat could be explained by increased sensitivity of the synapse between the splanchnic nerve and chromaffin cell. The splanchnic nerve was stimulated in acute (2-3 h; n = 7) or chronic (61-64 days; n = 7), spinally transected (T3) cats that were decerebrate and unanesthetized. Mean arterial blood pressure and adrenolumbar venous blood flow were significantly greater in the chronic animals. Stimulation (30 V; 1 ms pulses) was applied at 3 Hz and 30 Hz to deliver the same number of pulses within 3 min. Adrenal medullary secretion (ng/min) of epinephrine (EPI), norepinephrine (NE), dopamine, neuropeptide Y (NPY), [Met]enkephalin (ENK), and encrypted [Met]enkephalin was determined at baseline and in relation to both patterns of stimulation. With near threshold (3 Hz) stimulation, the following differences were observed between groups: (1) secretion of EPI, NPY, and ENK was significantly greater in the chronic than in the acute animals; and (2) preferential secretion of NE was elicited in the acute animals. These observations suggest that there may be some facilitation of the splanchnic nerve--chromaffin cell synapse that occurs over time following high thoracic spinal cord transection. However, it is likely that central, spinal mechanisms also contribute to adrenal medullary hyperactivity.