Calcium antagonists and vasoconstrictor effects in intracerebral microarterioles

The purpose of this work was to study the contractile activity of intracerebral microarterioles and their sensitivity to the calcium antagonist nimodipine. Potassium depolarization evoked contraction and rhythmic activity that was blocked by nimodipine (IC50 0.08 nM). High concentrations of noradrenaline and prostaglandin F2 alpha were needed to elicit a contractile response. Intracerebral microarterioles were very sensitive to endothelin (ED50, 0.2 nM). The contractions evoked by concentrations of endothelin lower than or equal to ED50 were relaxed by nimodipine, which also blocked the amplified response to potassium chloride depolarization occurring with subthreshold concentrations of endothelin. We discuss these observations in relation to brain ischemia.