Effects of reflex stimuli on blood flow to the adrenal medulla.

The goal of this study was to examine changes in blood flow to the adrenal medulla during reflex stimuli that release catecholamines. Adrenal blood flow was measured with microspheres during exercise in conscious dogs and during bicuculline-induced seizures in anesthetized dogs. In awake dogs, blood flow to the adrenal cortex and adrenal medulla was 310 +/- 48 and 1,613 +/- 258 (SE) ml.min-1.100 g-1, respectively. Blood flow to the cortex and medulla was not affected by moderate exercise. Anesthesia (pentobarbital sodium) reduced blood flow to the adrenal cortex and medulla to 158 +/- 12 and 243 +/- 24 ml.min-1.100 g-1, respectively. In anesthetized dogs, seizures markedly increased blood flow to the adrenal medulla (282 +/- 68 to 1,257 +/- 128 ml.min-1.100 g-1), and this response was blocked by sectioning the greater splanchnic nerve. Vasodilator responses of the adrenal medulla to adenosine were not impaired by adrenal denervation. Blood flow to the adrenal cortex was not affected by seizures but increased in response to intravenous adenosine. These findings suggest that 1) anesthesia decreases adrenal blood flow, particularly to the adrenal medulla, and 2) reflex stimuli that release catecholamines can produce selective increases in blood flow to the adrenal medulla.