Free and conjugated catecholamines and metabolites in cat urine after hypoxia

Catecholamine and metabolite excretion was studied in the cat after 6 h of 7.5% O2 hypoxia. Norepinephrine (NE) release from sympathetic nervous endings was strongly activated, whereas epinephrine (E) excretion was only slightly increased. A noteworthy result was the increase of dopamine (DA) and its metabolites [3-methoxytyramine (MT); 3,4-dihydroxyphenylacetic acid (DOPAC)] in urine samples. This increased release does not seem to originate from the central nervous system, but rather from peripheral dopaminergic structures; available knowledge on peripheral DA suggests that the hypoxia-induced DA release might be partly related to chemosensory or renal function. Indeed, in addition to enhanced DA and NE excretion, we observed an increase in sodium excretion that correlated with both DA and NE. Analysis of free and conjugated urinary metabolites showed that only free NE and both free and conjugated normetanephrine were increased in urine after hypoxic stress. Among DA metabolites, conjugated DOPAC was the main DA metabolite in the basal state and after hypoxia. Both the free and the conjugated forms of DA, MT, and DOPAC were increased by hypoxia.