Effects of Hypoxia on Tyrosine Hydroxylase Activity in Rat Carotid Body

Tyrosine hydroxylase (TH) activity was measured in the carotid body. superior cervical ganglion and adrenal glands of the rat under normal conditions and at 48 h following exposure of the animals for 1‐3 h in a low O2 atmosphere. Basal TH levels were 5‐6 nmol/h/mg tissue for both the carotid body and the ganglion. Forty‐eight hours after hypoxia, there was an increase in enzyme activity in both tissues which paralleled the severity of the hypoxia but was greater in the carotid body than the superior cervical ganglion. Thus, following exposure to 5% O2 in N2 for two 30‐min periods (20‐min interim), TH activity had increased by 50% in the carotid body and 33% in the ganglion; after exposure to 10% O2 in N2 for 3 h (continuous), TH levels were increased by 37% in the carotid body and 12% in the ganglion. In the adrenal gland, basal TH activity was 3.42 ± 1.87 nmol/h/mg tissue, and this value was unchanged following either level of hypoxia.