Effects of trimazosin and prazosin on blood pressure and on pressor responses to phenylephrine in rats.
As part of an ongoing investigation into the cardiovascular properties of trimazosin, 99 male Sprague-Dawley rats were anesthetized and cannulas were placed in jugular veins for administration of drugs. The rats were injected with phenylephrine and then treated with either solvent, diazoxide, prazosin, or trimazosin. Blood pressure and heart rate were measured by a pressure transducer and a biotachometer, respectively; both were recorded continuously. Preliminary results indicate that trimazosin was less potent but more efficacious in lowering blood pressure than was prazosin and caused less blockade of the alpha-1-adrenoceptors even when its hypotensive effect exceeded that of prazosin. The differences in hypotensive potency and in alpha-1-receptor blockade are consistent with the fact that trimazosin has less affinity than does prazosin for alpha-1-receptors in vitro. The greater efficacy of trimazosin, compared to prazosin, is further evidence that in addition to alpha-1-receptor blockade, another mechanism contributes to the hypotensive effect of trimazosin. This mechanism has yet to be elucidated.
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects*; D003981:Diazoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology*; D011311:Pressoreceptors / Q000187:drug effects*; D011799:Quinazolines / Q000494:pharmacology*; D051381:Rats; D012997:Solvents / Q000494:pharmacology
D000959:Antihypertensive Agents; D010879:Piperazines; D011799:Quinazolines; D012997:Solvents; D010656:Phenylephrine; C005185:trimazosin; D003981:Diazoxide; D011224:Prazosin