Chronic treatment of rats with D-600 causes a compensatory decrease in the calcium requirement for contractility of vascular smooth and cardiac muscles.
We studied the effects of chronic hypotensive treatment of normotensive Wistar rats (NWR) with methoxyverapamil (D-600) and hydralazine on in vitro contractile response of aortic strips, portal vein strips, and Langendorff-perfused hearts in normal (2.5 mM) and low (0.2 mM) calcium (Ca). Portal vein strips from rats treated with D-600, compared with the same strips from control and hydralazine-treated rats, developed greater spontaneous contractile activity in normal Ca and retained greater responses to norepinephrine (NE) and 80 mM K in low Ca. Aortic strips from all three groups of rats retained similar responses to NE and K in low Ca. Hearts from D-600-treated rats produced less intraventricular pressure (IVP) to isoproterenol (ISO) than hearts from control and hydralazine-treated rats in normal Ca but greater IVP to ISO than hearts from the other two groups of rats in low Ca. Thus, chronic treatment of NWR with D-600 but not with hydralazine resulted in the reduction of Ca requirement for contractile activities of the portal vein and the myocardium.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D005711:Gallopamil / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006830:Hydralazine / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009200:Myocardial Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011169:Portal Vein / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology*
D006830:Hydralazine; D005711:Gallopamil; D014700:Verapamil; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine