Increasing extracellular calcium concentration does not prevent hypotensive effects of verapamil in neonatal swine

Effects of CaCl2 on cardiac function and regional circulatory responses to verapamil (V) infusion were studied in pentobarbital-anesthetized 2-week-old swine. V 100 micrograms/kg (n = 15) or 300 micrograms/kg (n = 15), given as a 2-min intravenous infusion, was repeated after 30 min. Only V was given to 15 of these. The other 15 were given CaCl2 (15 mg/kg) over 2 min, pre-V (protocol A), and over 4 min, 2 min pre-V and during V (protocol B). Positive chronotropic and negative inotropic responses to V were attenuated by CaCl2; hypotensive effects were unaltered. Renal, but not mesenteric and femoral, vasodilation was augmented by CaCl2, CaCl2 alone produced marked positive inotropic and renal vasodilatory effects which contributed to maintenance of the hypotensive effect of V.