Calcium antagonists: effects on cerebral blood flow and blood-brain barrier permeability in the rat

1 Because they affect isolated cerebral arteries, some calcium antagonists have been studied on the intact cerebral circulation of the rat.

2 Global cerebral blood flow (¹³³Xe clearance technique) was measured in anaesthetized rats. Neither perhexiline (0.1 μg/kg to 1.0 mg/kg, i.v.) nor diltiazem (0.06-0.6 mg/kg, i.v.) had any significant effect on resting cerebral blood flow when measured 5 min after each dose. A high dose of nifedipine (1.0 mg/kg, i.v.) was administered during induced hypocapnia. Nifedipine failed to modify the hypocapnic vasoconstriction of the cerebral vasculature when compared to vehicle-treated rats.

3 The possibility of discrete changes in regional cerebral blood flow was investigated. Local cerebral blood flow was measured in a number of brain regions by the [¹⁴C]-ethanol technique 15 min after the administration of nifedipine (20 or 100 μg/kg, i.v.). Nifedipine had no apparent effect on regional blood flow in the rat brain.

4 Acute arterial hypertension increases protein leakage into the brain, a phenomenon susceptible to drugs that act on endothelial pinocytosis which is known to be calcium-dependent. The increase in protein extravasation, induced by the intravenous administration of either angiotensin II or adrenaline, was unchanged in rats previously treated with either nimodipine (20 μg/kg, i.v.) or nifedipine (50 μg/kg, i.v.) when dissolved in ethanol alone. However, nifedipine (20 μg/kg, i.v.) when dissolved in a solution of polyethylene glycol and ethanol further enhanced the hypertension-induced increase in brain albumin permeability.

5 In conclusion, we have been unable to demonstrate any apparent effects of various calcium antagonists on the intact cerebral circulation of the rat, despite the number of different experimental models used.