Analogs of phosphatidylcholine: alpha-adrenergic antagonists from the renal medulla

Antihypertensive polar renomedullary lipid (APRL), a conglomerate of 1-0-alkyl-2-acetoyl-glycero-3-phosphocholine analogs, ws tested in 4- to 6-week-old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats using microcirculatory techniques. APRL (0.5 ug/ml), when added to the solution bathing the cremaster muscle, caused significant changes in the diameter, red blood cell velocity, and blood flow in both groups of rats, for arterioles and venules. Arteriolar changes in diameter were significantly greater (p less than 0.05) in SHR than in WKY. Micropipette application of APRL indicated a dose-dependent response for arterioles and venules in both groups. Moreover, the potent nature of this compound was demonstrated. Relative potency of APRL given intravenously was tested in 10- to 12-week-old SHR and WKY. The response curve was shifted significantly to the left for SHR (p less than 0.01). APRL interaction with known controllers of blood flow was tested in SHR. Blockade of cholinergic, beta-adrenergic, or histaminergic receptors did not inhibit APRL action. blockade of prostaglandin or bradykinin synthesis did not prevent depression of blood pressure by APRL. APRL (40 ug/kg) inhibited (p less than 0.001) the pressor response to norepinephrine (1-10 ug/kg) but not to angiotensin II (4 ug/kg). The present study provides direct evidence that APRL is a vasodilator with increased potency in SHR hypertension. The acute vascular response may be mediated by alpha-adrenergic antagonism.