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

Effect of CaCl₂ on cardiac function and regional circulatory responses to verapamil (V) infusion were studied in pentobarbital-anesthetized 2-week-old swine. V 100 μg/kg (n = 15) or 300 μg/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.