Structure and function of the carotid body in New Zealand genetically hypertensive rats

Morphology of the carotid body and the ventilatory response to hypoxia were compared in New Zealand genetically hypertensive rats and 'normotensive' control rats from the same genetic stock. Hypertensive rats grew more slowly, had higher blood pressure from 6 weeks of age and developed left ventricular hypertrophy. Carotid bodies of both groups were similar in size but larger than those of a common Wistar strain. Intimal damage and proliferation were seen in 1st- and 2nd-order branches of the carotid body artery in hypertensive rats and point-counting showed that the volume proportion of Type 1 cell nuclei and vascular lumen was reduced and vascular wall increased. In age-matched anaesthetized rats, minute ventilation per 100 g was greater in hypertensives than 'normotensive' when inspiring O2 concentrations of 30, 21, 18, 15, 12, 10 and 8%. However, at each inspired O2 concentration, arterial Pa.O2 was higher and Pa.CO2 lower in hypertensive than in 'normotensive' rats. Hypertensive rats were hyperventilating. The shape of the ventilation/O2 tension curve was similar in hypertensive and 'normotensive' rats; thus carotid body sensitivity to hypoxia was probably unchanged. Possible causes of hyperventilation and the relation of carotid body morphology to hypertension are discussed.