These data indicate that the sex difference in myointimal proliferation after vascular injury is estrogen dependent. C-myc gene expression is greater in the undamaged carotid artery of the male than in that of the female, and the responsiveness of this gene to balloon injury of the artery is more rapid and more robust in the male than in the female rat. These findings have direct implications for the prevention and treatment of vascular disease in humans.

The current study examined the effects of bosentan, an orally active antagonist of endothelin-A and -B receptors, on the development and maintenance of hypoxia (10% O2)-induced pulmonary hypertension and vascular remodeling in the rat. Pretreatment with bosentan (100 mg.kg-1.day-1, 1 gavage/day for 2 days) completely blocked the pulmonary vasoconstrictor response to acute hypoxia. Chronic bosentan treatment (100 mg.kg-1.day-1 po in the food) instituted 48 h before hypoxic exposure prevented the subsequent development of pulmonary hypertension, attenuated the associated right heart hypertrophy, and prevented the remodeling of small (50-100 microns) pulmonary arteries without altering systemic arterial pressure. Institution of bosentan treatment (for 4 wk) after 2 wk of hypoxia produced a significant reversal of established hypoxia-induced pulmonary hypertension (from 36 +/- 1 to 25 +/- 1 mmHg), right heart hypertrophy, and pulmonary vascular remodeling despite continuing hypoxic exposure. These findings support the hypothesis that endogenous endothelin-1 plays a major role in hypoxic pulmonary vasoconstriction and/or hypertension, right heart hypertrophy, and pulmonary vascular remodeling and suggest that endothelin-receptor blockade may be useful in the treatment of hypoxic pulmonary hypertension humans.

To test the hypothesis that endothelin (ET)-1 synthesis and ET receptor levels are increased selectively in the lung of rats with chronic hypoxic pulmonary hypertension, the current study examined the effects of exposure to chronic hypoxia (10% O2, 1 atm, 4 wk) on pulmonary arterial pressure, ET-1 levels in plasma and lung, and ET-1 and ETA and ETB receptor mRNA levels in lung, heart, pulmonary artery, aorta, kidney, spleen, and liver. Hypoxic exposure was associated with increases in pulmonary arterial pressure, plasma ET-1 levels, ET-1 mRNA in lung and pulmonary artery, and ET-1 stores and ETA and ETB receptor mRNA levels in lung. In thoracic aorta and the four heart chambers, ETA and ETB receptor mRNA levels were increased, but ET-1 mRNA levels were unchanged from air control levels. No change in ET-1 or ET receptor mRNA levels was seen in organs perfused by the systemic vascular bed, except in liver, where ETA receptor mRNA levels were decreased. The findings of concomitant increases in gene transcript levels for ET-1 and the ETA and ETB receptors in lung, but not in the great vessels or any other organ examined, are consistent with the hypothesis that increased ET-1 synthesis in the lung contributes to pulmonary vascular remodeling and the maintenance of chronic hypoxic pulmonary hypertension.

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