DL-propranolol inhibits the vascular changes in the rat carotid body induced by long-term hypoxia

Two groups of rats were exposed to hypoxia (10% O2) for 1 and 3 weeks with or without daily injections of DL-propranolol (0.66 mg.kg-1 ip). The structure of the carotid body was analyzed by light microscopical morphometry and the catecholamine content was assayed by high performance liquid chromatography. Exposure to hypoxia induced enlargement of the carotid body due to enhanced vascularity and hypertrophy of glomic and interstitial tissues. The dopamine and norepinephrine content were increased at both 1 and 3 weeks of hypoxia and reached levels 40-50 times those of the controls. The DL-propranolol treatment abolished the vasodilatory effect of hypoxia within the first week but did not prevent the other structural changes or the rise in catecholamine content. The data suggest that 1. the vasodilation elicited by long-term hypoxia may be controlled by beta-adrenoceptors and 2. the structural and biochemical events occurring in rat carotid body during long-term hypoxia do not influence each other and thus seem to be controlled by different mechanisms.