Comparison of regional vasomotor responses to acetazolamide and CO 2 in rabbit cerebrum and cerebellum, measured by a hydrogen clearance method K. Csete, 1 Z. Vezeke ´nyi, 1 T. Do ´ czi, 2 J. Gy. Papp, 1,3 M. Bodosi 4 and P. Barzo ´ 4 1 Department of Pharmacology and Pharmacotherapy, Albert Szent-Gyo ¨rgyi Medical Centre, University of Szeged, Szeged, Hungary 2 Department of Neurosurgery, University Medical School, Pe ´cs, Hungary 3 Division of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary 4 Department of Neurosurgery, Albert Szent-Gyo ¨rgyi Medical Centre, University of Szeged, Szeged, Hungary Received 19 November 2003, accepted 20 July 2004 Correspondence: K. Csete, Department of Pharmacology and Pharmacotherapy, University of Szeged, Do ´m te ´r 12, PO Box 427, 6701 Szeged, Hungary. Abstract Aim: Many investigators have proved the usefulness of acetazolamide pro- vocation and the carbon dioxide test for assessment of the local cerebro- vascular reactivity by measurement of the regional cerebral blood flow in patients with occlusive cerebrovascular disease. Data originating from a comparison of these two different vasomotor stimuli as concerns the dif- ferences in sensitivity to them in various parts of the central nervous system are scarce. Our aim was to compare the cerebral blood flow responses to hypercapnic and acetazolamide stimuli in different brain regions. Methods: The cerebral blood flow was measured in the cerebrum (cortex and caudate nucleus) and cerebellum (cortex), as measured by a hydrogen clearance method in anaesthetized, artificially ventilated rabbits. Results: In normocapnia, the cerebral blood flow values in the cerebrum and the cerebellum differed significantly. The cerebral blood flow responses to both vasodilatory stimuli were to be significantly higher in the cerebrum than in the cerebellum, but the relative increases, i.e. the mean relative reactivities, were similar in the different regions measured. Conclusion: The regional dissimilarity might explain to some extent the different sensitivities of the various brain areas to sudden blood pressure changes (infarction or haemorrhage). The results further suggest that het- erogeneity in cerebrovascular reactivity should be considered in the assess- ment of vasoreactivity in patients with occlusive cerebrovascular disease. Since the comparison of the carbon dioxide and acetazolamide – induced cerebrovascular reactivities revealed a strong linear relationship, it was concluded that acetazolamide provocation is equivalent to the carbon dioxide test in the evaluation of cerebrovascular reactivity. Keywords acetazolamide, hydrogen clearance method, hypercapnia, rab- bits, regional vasomotor response. In patients with a major extra- or intracranial artery obstruction, cerebral autoregulation ensures that the fall in perfusion pressure is counterbalanced by vaso- dilatation of the cerebral arterioles. Measurement of this cerebrovascular reactivity (CVR) is the key to introducing cerebral revascularization surgery, such as carotid endarterectomy or an external to internal cranial bypass (Piepgras et al. 1990, Ringelstein et al. Acta Physiol Scand 2004, 182, 287–294 Ó 2004 Scandinavian Physiological Society 287