Quantitative studies of the vasculature of the carotid body in the chronically hypoxic rat

The carotid bodies of rats made chronically hypoxic by breathing 12% O-2 in a normobaric chamber (inspired PO2 91 mmHg) were compared with those of co ntrols. Serial 5-mu m sections of the organs were examined using an interac tive image analysis system. The total volume of the carotid bodies was incr eased by 64%. The total vascular volume rose by 103% and was likely due to an increase in size of the large vessels (>12 mu m lumen diameter) because the small vessel (5-12 mu m lumen diameter) volume did not increase signifi cantly while the small vessel density tended to decrease. The extravascular volume was increased by 57%. Expressed as a percentage of the total volume of the organ, the total vascular volume did not change, but the small vess el volume was significantly decreased from 7.83 to 6.06%. The large vessel volume must therefore have been increased. The proportion occupied by the e xtravascular volume was virtually unchanged (84 vs 82%). In accordance with these findings, the small vessel endothelial surface area per unit carotid body volume was diminished from 95.2 to 76.5 mm(-1), while the extravascul ar area per small vessel was increased from 493 to 641 mu m(2) or by 30%. I n conclusion, the enlargement of the carotid body in chronic hypoxia is mos t likely due to an increase in total vascular volume, mainly involving the "large" vessels, and to an increase in extravascular volume. This is in con trast to our previously published findings indicating that in the spontaneo us insulin-dependent diabetic rat the enlargement of the carotid body is du e solely to increase in extravascular volume.