Differential relaxing response of various arterial smooth muscles of dogs to nifedipine.

Differences in the relaxing effects of nifedipine, a so-called calcium antagonist, were studied in smooth muscle from different arteries of dogs. The common carotid artery (Car A), celiac artery (Cel A), superior mesenteric artery (SMA), renal artery (RA), femoral artery (FA), and coronary artery (Cor A) were helically cut, and their developed isometric tensions were recorded. High potassium contraction was induced in these strips, and, at the peak of developed tension, nifedipine (10(-6) M) was added. Relaxation curves induced by nifedipine were analyzed by a curve fitting method into two to three exponentials. The general form of the equation is At equal 2 or 3 sigma i = 1 A0ie-kit. The k value shows the rate of relaxation; i.e., the larger the value the faster the relaxation. The relaxation was faster in the order of RA, SMA, Cor A, Cel A, Car A, and FA. The value of (A0i/2 or 3 sigma i = 1 A0i) X 100 shows the fraction of tension in each component of the relaxation curve A0ie-kit. The fraction of tension distributed to the faster relaxation exponentials [A02e-k2t(+A03e-k3t)] in each smooth muscle was larger in the order of RA, SMA, Cor A, Car A, FA, and Cel A.