Effect of the calcium antagonist nimodipine on local cerebral blood flow: relationship to arterial blood pressure.

The effect of the calcium antagonist nimodipine on local CBF in 31 regions of the CNS was studied with the [14C]iodoantipyrine autoradiographic technique in lightly anaesthetised, mechanically ventilated rats. Continuous intravenous infusion of nimodipine (1, 2, or 4 micrograms kg-1 min-1) produced a dose-dependent reduction in MABP (reduced by 26 +/- 2% after 30 min of nimodipine, 4 micrograms kg-1 min-1) and a significant elevation in plasma glucose concentration (increased by 44 +/- 2% after 30 min of nimodipine, 4 micrograms kg-1 min-1). Local CBF was increased significantly during infusions of nimodipine (1 microgram kg-1 min-1) in 9 of the 31 regions examined (including the cerebral cortex, hippocampus, hypothalamus, and most thalamic nuclei). In contrast to the increases in CBF observed in forebrain regions, no significant increases in CBF were observed during nimodipine infusions in regions of the lower brainstem, cerebellum, and pons or in myelinated fibre tracts. The proportionately greatest increases in local CBF were observed during infusions of the lowest dosage of nimodipine (1 microgram kg-1 min-1), suggesting either that this dosage provokes maximum cerebrovascular relaxation or that effects of increasing concentrations are counteracted by the concomitant systemic hypotension.