PROSTACYCLIN IN SYNTHESIS PULMONARY HYPERTENSION

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In severe pulmonary hypertension, the regulation of vascular tone is altered as well as the normal morphology of the vessels. We have found a relative deficiency in the synthesis of vasodilatory prostaglandins in the arteries but not veins of neonatal calves with hypoxia-induced severe pulmonary hypertension. Since this deficiency can be demonstrated in endothelial and smooth muscle cells and even fibroblasts cultured from vessels, we wish to study the nature of this defect and the mechanisms responsible for this deficiency. Prostacyclin (PGI2) and PGE2 are important for vascular tone regulation and are antiproliferative. We postulate that the pulmonary (and possibly systemic also) hypertensive arteries express a hypertensive cell phenotype. We further postulate that the substantial decrease in the PGI2 synthesis capacity is one important feature of this hypertensive phenotype. Hemodynamic stress (increased pressure, vessel wall stretch) acutely induces a large increase in PGI2 synthesis which is followed by suicide inactivation of the enzyme and because of impaired enzyme regeneration, leads to a chronic decrease in endogenous PGI2 synthesis. We plan to examine the mechanism of impaired PGI2 synthesis in arteries from pulmonary hypertensive calves and rats. (Systemic hypertensive arteries will also be studied). There are likely several components which add up to the impaired PG synthesis of hypertensive vessels. First experiments lead us to believe that in hypertensive cells, a product of the cyclooxygenase impairs or inactivates the function of the PGI2 synthase. We plan to purify the PGI2 synthase from bovine, human, and rat pulmonary vessels, and to measure the mass and activity of the PGI2 synthase in cells from hypertensive arteries. We plan to use polymerase chain reaction (PCR) technology to clone the bovine (and also human) pulmonary endothelial cell PGI2 synthase, to obtain the amino acid sequence, and to examine the transcription of the PGI2 synthase gene in normotensive and hypertensive cells. Hypoxic pulmonary hypertension will be induced in rats, and the lung and pulmonary artery PGI2 synthesis capacity will be assessed in tissues from rats treated with N-acetyl cysteine (to raise glutathione antioxidant defenses), fish oil, or a Ca4++-entry blocker. These strategies may lead to increased endogenous pulmonary vascular PGI2 synthesis, which in turn may protect against vascular remodeling. We also want to examine whether simple mechanical perturbations (vascular ring contraction, stretch, shear stress) cause impairment of PGI2 synthesis by suicide inactivation of the enzyme.