[Effect of calcium antagonists on ureteral contractile activity in experiment]

Dihydropiridine (nifedipine), phenilalkilamine (isoptin) and a novel domestic calcium channel blocker A-29 were studied for effects on motor activity of an isolated segment of a rabbit ureteral upper-third. Strength of muscular contractions (134 measurements) was evaluated in per cents to the baseline level. Tonic reaction and its duration were measured. Calcium antagonist action on ureteral contractile activity was studied by changes in contractile power in concentration rage from 10(-9) to 10(-5) M/l. Beginning from 10(-9) M/l concentration of all the drugs studied there was a gradual decline of the initial contractile activity of the ureter. The following concentrations of calcium antagonists significantly reduced the amplitude of phasic contraction, whereas therapeutic concentrations--by more than 40%. In elevation of the concentration in some cases washing of the isolated ureteral segment with Krebs' solution failed to reestablish tonic reaction. Only A-29 spontaneous contractile activity recovered after washing. The maximal effect was achieved with nifedipin and A-29 in concentrations 10(-5) M/l. Thus, calcium antagonists change contractile activity of smooth muscle cells of the ureter with a dose-dependent effect making it possible to use calcium antagonists for inhibition of contractile ureteral activity in clinical practice.