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It is found that nimodipine induces biphasic changes in the circulation in the midbrain artery: an initial slight and transient reduction gives way to a considerable and long-term increase of the circulation. Nimodipine also boosts the circulation in the common and internal carotid arteries, which coincides in time with, but is shorter than, the first phase of changes in the hemodynamics in the midbrain artery. The findings are not consistent with the common view on the selectivity of the cerebrovascular effect of nimodipine.Key Words: nimodipine; ultrasound method; cerebral circulation; midbrain artery According to published data nimodipine (ND), dihydropiridine calcium antagonist, possesses a selective cerebrovascular activity. Experiments on various animal species (rats, rabbits, monkeys) and with the use of discrete experimental methods have demonstrated the ability of ND to increase the cerebral circulation [1,[5][6][7][8][9]. For a characterization of the vascular effect of ND it is important to study the dynamics of ND-induced changes in the cerebral circulation. Such an approach will advance our understanding on the mechanism of the cerebrovascular effect of ND and will promote both a more judicious use of the preparation in neurological patients and a targeted search for new cerebrovascular preparations. The aim of the present study was to study the effect of ND on the circu- MATERIALS AND METHODSThe experiments were carried out on 30 male Wistar rats weighing 250-300 g under general anesthesia (Nembutal, 40 mg/kg, intraperitoneaUy). The circulation was measured using the ultrasound Doppler technique [2]. Band transducers calibrated in units of the voluime rate of circulation were placed on the right common and internal carotid arteries. The circulation in the right midbrain artery was measured using an ultrasound transducer, which was previously used for a study of the coronary circulation in rats [3]. To this end an openning was made on the right side of the head, the midbrain artery was located by the sound signal, and the optimal position of the transducer was determined. Arterial pressure was measured and the preparation was injected through polyethylene cath-

We compared the effects of a pyrrolidone-pyroglutamic acid composition and nimodipine on blood circulation in the middle cerebral artery in rats. The composition produced a strong effect on blood supply to the brain, stimulated blood flow in the middle cerebral artery (by 60 +/- 9%) and decreased blood pressure (by 25.0 +/- 2.7%). The cerebrovascular effects of this composition differed from those of nimodipine. Nimodipine not only increased middle cerebral artery blood flow, but also decreased cerebral blood flow in the early period after treatment.

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