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

Abstract

The carotid bodies of rats made chronically hypoxic by breathing 12% O 2 in a normobaric chamber (inspired PO 2 91 mmHg) were compared with those of controls. Serial 5-µm sections of the organs were examined using an interactive image analysis system. The total volume of the carotid bodies was increased by 64%. The total vascular volume rose by 103% and was likely due to an increase in size of the large vessels (>12 µm lumen diameter) because the small vessel (5-12 µm lumen diameter) volume did not increase significantly 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 vessel volume was significantly decreased from 7.83 to 6.06%. The large vessel volume must therefore have been increased. The proportion occupied by the extravascular 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 extravascular area per small vessel was increased from 493 to 641 µm 2 or by 30%. In conclusion, the enlargement of the carotid body in chronic hypoxia is most likely due to an increase in total vascular volume, mainly involving the large vessels, and to an increase in extravascular volume. This is in contrast to our previously published findings indicating that in the spontaneous insulin-dependent diabetic rat the enlargement of the carotid body is due solely to an increase in extravascular volume. Some of these data were previously reported in abstract form

Chronic hypoxia‐induced morphological and neurochemical changes in the carotid body

“…They observed many labeled cells in the CB; however, the labeling of cells was too dense to determine whether they were type I cells. On the other hand, some reports claimed that no signs of mitosis of type I cells were detected in rats exposed to 1-4 weeks CH (Pequignot et al, 1984;Clarke et al, 2000). By using bromodeoxyuridine (Brdu), a uridine analog that is stably incorporated into cells undergoing DNA synthesis, we have found hypoxia causes hyperplasia of type I cells in the rat CB (Fig.…”

“…Four to five weeks of CH elicited an approximately 2-4-fold enlargement of the size of the CB (Hanbauer et al, 1981;Kameda et al, 1998). However, in a study by Clarke et al (2000) the total volume of the rat CB was only increased by 64% following 31 days of hypoxia. As the CB is a very small structure and is largely vascularized, variations in values measured may reflect the differences in techniques for tissue preparation.…”

“…The volume of type I cells isolated from newborn rats enlarged 3-4-fold during culture in 6% O 2 for 2-3 weeks, indicating that this change in morphology can occur in the absence of innervation or circulating hormones (Mills and Nurse, 1993). However, a recent study by Clarke et al (2000) does not seem to support this observation. In rats exposed to 31 days hypoxia, they found that the size of type I cells fell in the normal range.…”

“…The vascular volume could increase as many as 10-fold (Laidler and Kay, 1975). This increase may mainly involve the large vessels (Ͼ12 m lumen diameter) (Clarke et al, 2000). The increase of vascularity may also involve the growth of new blood vessels and is likely related to increased expression of vascular endothelial growth factor (VEGF).…”

Chronic intermittent hypoxia-induced vascular enlargement and VEGF upregulation in the rat carotid body is not prevented by antioxidant treatment

“…long-term exposure to sustained hypoxia produces hypertrophy and/or hyperplasia of glomus cells and enlarges the CB size and the vascular area (6,14,20,24,32,45). Indeed, a tenfold increase in the volume of the CB capillaries in hypoxic rats has been reported (6,20).…”