INFLUENCE OF LONG-TERM HYPOXIA ON TYROSINE-HYDROXYLASE IN THE RAT CAROTID-BODY AND ADRENAL-GLAND

Tyrosine hydroxylase (TH) protein was measured in the carotid body and adrenal gland of rats exposed to normobaric hypoxia (10% O2 in nitrogen) for 3, 7, 14 or 22 days. After 22 days of hypoxia, a gradual increase in TH protein content was observed in the carotid body and in the adrenal gland, reaching 168% and 148% of the normoxic controls, respectively. To determine if the increase in TH protein content in the carotid body could alter catecholamine biosynthesis, in vitro TH activity and catecholamine turnover were measured in rats submitted to hypoxia for 14 days. TH activity was increased by 11.2-fold, while the turnover of dopamine and norepinephrine was increased by 14.8- and 5.4-fold, respectively. The data show that long-term hypoxia exerts a stimulatory influence on TH protein in the carotid body and adrenal gland in addition to an elevation in dopamine and norepinephrine biosynthesis in the carotid body.