Adrenal medullary and cortical blood flow during hemorrhage

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Abstract
We used a radiolabeled microsphere technique to measure adrenal medullary and cortical blood flow during hemorrhagic hypotension. Twenty pentobarbital-anesthetized, ventilated, adult mongrel dogs were bled into a pressurized bottle system to reduce and maintain mean arterial blood pressure at 100, 80, 60, or 40 mmHg (n = 5/group). Blood flow was measured prior to and 2, 5, 10, 15, and 25 min posthemorrhage. Adrenal medullary blood flow increased markedly (100-400%) at all levels of hemorrhage. In contrast, decreases in cortical blood flow were observed (approximately 50%) with hemorrhage to 80, 60, and 40 mmHg. Cortical blood flow returned to control levels at 25 min, except in the 40-mmHg group. Whole adrenal gland blood flow showed early, transient decreases, consistent with the fact that the adrenal cortex comprises the bulk of the gland, but it did not precisely reflect either cortical or medullary blood flow changes. Since this method for measuring adrenal medullary and cortical blood flow was developed for the current experiment, extensive evaluation of the technique was performed (n = 31 animals). These studies included demonstration that injection of 4 X 10(6) microspheres results in sufficient numbers of microspheres in the adrenal medulla and cortex to permit estimation of blood flow (greater than or equal to 400 spheres/sample), that 15-micron spheres are almost completely entrapped in the adrenal gland (greater than 98%), that multiple injections of microspheres (n = 5) do not alter blood flow, and that streaming of microspheres does not appear to occur to any significant extent in this vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)