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In large animals pulse pressure increases from central to peripheral arteries whereas mean arterial pressure decreases slightly. This haemodynamic pattern has not been verified in small animals, particularly in hypertensive rats before and after administration of antihypertensive drugs.The intra-arterial blood pressure of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) was determined along the aorta in anaesthetized and conscious rats. In anaesthetized rats the study was performed before and after acute intravenous nicardipine administration (30 |ig/kg).Mean arterial pressure was significantly higher in untreated SHR than in WKY rats, and within each strain was quite similar along the aortic tree. Pulse pressure increased significantly from the central to the terminal aorta in WKY rats, principally due to an increase in systolic blood pressure. In SHR pulse pressure did not differ along the aortic tree. Compared with in WKY rats, aortic pulse pressure in SHR was significantly elevated whereas femoral pulse pressure was quite similar. Acute nicardipine administration re-established the pulse pressure gradient in SHR, due to a significant decrease in central aortic pulse pressure with no significant change in femoral pulse pressure.These results suggest, first, that since there are large differences in pulse pressure in the proximal aorta of SHR and WKY rats but only small or negligible differences in the distal aorta, the measurement of pulse pressure may be an available index to differentiate normotensive and hypertensive rats, and secondly, that increased aortic pulse pressure in SHR participates in the increase in cardiac afterload independently of mean arterial pressure, and may be a preferential site of action of antihypertensive agents.