Adrenal blood flow was measured during hemorrhagic
hypotension in
pentobarbital-anesthetized dogs using the radioactive-
microsphere technique. A decrease in adrenal vascular resistance occurred during
hemorrhage that was sufficient to maintain adrenal blood flow at prehemorrhage levels even with a decrease in mean arterial blood pressure (MABP) to as low as 50 mmHG. Blockade of alpha- and
beta-adrenergic receptors, H1- and H2-histamine receptors, and
prostaglandin synthesis all decreased resting adrenal blood flow. However, blood flow did not decrease further with
hemorrhage subsequent to these interventions. Neither
cholinergic blockade (
muscarinic) alone nor ganglionic blockade subsequent to
cholinergic blockade changed adrenal blood flow. However, ganglionic blockade alone increased adrenal blood flow.
Hemorrhage subsequent to
hypophysectomy also did not change blood flow to the adrenal. These data suggest that the maintenance of adrenal blood flow during hemorrhagic
hypotension to 50 mmHg MABP is independent of the autonomic nervous system,
prostaglandin synthesis,
histamine receptors, or an intact pituitary-adrenal axis, even though all of these systems do influence adrenal blood flow.