Sympathetic control of adrenal secretion of enkephalins after hemorrhage in awake dogs

Adrenomedullary secretion of methionine (Met)-enkephalin and of leucine (Leu)-enkephalin was measured in awake trained dogs subjected to 10 or 20% hemorrhage. Enkephalin secretory rates increased in proportion to the magnitude of hemorrhage with the ratio of Met-enkephalin to Leu-enkephalin being ~4:1. Arterial concentrations of enkephalins reflected adrenal secretion only in dogs exhibiting the largest secretory responses to hemorrhage. Cross-correlation analysis of 12 individual experiments showed that Met-enkephalin and epinephrine secretory rates were maximally correlated at 0-min delay, suggesting that enkephalins are cosecreted with catecholamines. The molar ratio in adrenal venous blood of epinephrine to Met-enkephalin ranged from 480 ± 50 to 570 ± 60. Chronic denervation of the adrenal by removing thoracic and lumbar splanchnic nerves prevented the Met-enkephalin and catecholamine secretory responses to hemorrhage. These data show that the adrenal medulla secretes enkephalins in response to stimuli activated by hemorrhage. These findings suggest that secretion of opiate-like peptides into the peripheral circulation may be a component of the sympathetic response to trauma.