Changes in biogenic amine synthesis and turnover induced by hypoxia and/or foot shock stress I. The adrenal medulla

Summary

Hypoxia, with or without hypercapnia, was induced by exposing rats to various gas mixtures for 45 min. In addition, some of the rats were exposed to electrical foot shocks for 15 min. Rats were either untreated by drugs or received inhibitors of catecholamine synthesis or metabolism. The adrenals and blood plasma were analyzed for dopa, and the adrenals for dopamine (DA) and adrenaline + noradrenaline.

Adrenal DA was elevated by severe (6 % O₂) but was slightly decreased by moderate hypoxia (8 % O₂). The addition of 5 % CO₂ to 8 % O₂ caused a moderate increase in DA. Foot shock stress raised adrenal DA under normoxia and the effect was markedly potentiated by moderate hypoxia. The accumulation of dopa in the adrenals of animals treated with 3-hydroxybenzylhydrazine (NSD 1015), an inhibitor of the aromatic amino acid decarboxylase, was closely correlated to the levels of adrenal DA in the corresponding experimental groups receiving no drug treatment, supporting the usefulness of adrenal DA as an indicator of catecholamine synthesis. In NSD 1015-treated rats dopa was found in the plasma and levels were increased after foot shock stress.

The data indicate that moderate hypoxia may retard the conversion of tyrosine to dopa, which may be related to the O₂ requirement of this reaction. However, this effect can be overcome by neurogenic stimuli, presumably via an activation of adrenal tyrosine hydroxylase. Apparently such stimuli are induced by foot shock stress, severe hypoxia, hypercarbia and most markedly, by the combination of shock stress and hypoxia.