Interference of pentobarbitone with the contraction of vascular smooth muscle in goat middle cerebral artery

Pentobarbitone (10−5 to 10−3 M) decreased the basal tone of vascular smooth muscle of goat middle cerebral artery in a dose‐dependent manner as well as relaxing established contractions induced by noradrenaline (NA) (10−5 M), 5‐hydroxytryptamine (5‐HT) (10−5 M) and KCl(120 mM). Preincubations with pentobarbitone reduced the contractions evoked by these three agents in a dose‐dependent way. It also decreased Ca2+‐induced contractile responses in K+‐depolarized arteries and 5‐HT‐Ca2+ and NA‐Ca2+ contractions dose‐dependently. Contractions induced by K+ were more sensitive to the depressant actions of the drug than those produced by NA and 5‐HT. The small contractions evoked by K+ and 5‐HT in Ca2+‐free medium were also reduced in its presence. The antagonism Ca2+‐pentobarbitone was insurmountable. These results suggest that the drug interferes with Ca2+ entry and Ca2+ release from cell stores, and therefore with the smooth muscle contractions.