Biphasic effect of hypoxia on adrenal catecholamine content.

STEINSLAND, ODD S., STANLEY S. PASSO, AND GABRIEL G. NAHAS. B@hasic effect of hypoxia on adrenal catecholamine content. Am. \ J. Physiol. 2 18(4) : 995-998. 1970.-The adrenal catecholamine content of guinea pigs and rats exposed to 7.5 y0 oxygen in nitrogen for periods of 4, 8, and 12 hr decreased significantly ( -40% after 12 hr). With more prolonged exposure, adrenal catecholamine content increased, reaching control levels between 20 to 38 hr after onset of hypoxia. In another series of experiments, inhibition of catecholamine synthesis was produced by administering amethyl-L-tyrosine. Inhibition of synthesis in animals breathing air resulted in a slow decline in adrenal catecholamine levels ( -9.1 y0 after 12 hr and -24.2 y0 after 28 hr); in rats exposed to hypoxia there was 54 and 71 y0 depletion of the adrenal medullary content after 12 and 28 hr, respectively. The return to essentially normal catecholamine levels after prolonged hypoxic exposure involves, therefore, an increased rate of synthesis; this increased rate of synthesis occurs mainly in the late phase of hypoxia. The delayed increase in synthesis was apparent in animals removed from the hypoxic environment and permitted to recover in room air. The establishment of a rate of synthesis that will restore and maintain catecholamine content at normal levels might be one of the adaptive processes to hypoxia.