Cerebral function during hypotensive haemorrhage in spontaneously hypertensive rats and Wistar Kyoto rats

Studies on cerebral function during cerebral ischaemia are usually performed on conscious animals after ligation of a major vessel supplying the brain. In this work, we studied somatosensory evoked potentials (SEP) in chloralose-anaesthetized Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) during hypotensive haemorrhage, with the main emphasis on the SHR which are more vulnerable. The main purpose was to see whether haemorrhaged SHR could be used for studies of cerebral function during relative cerebral ischaemia in anaesthetized rats. The mean arterial pressure (MAP) was rapidly lowered to 45-50 mm Hg and maintained at that level by adjustments of bleeding and transfusion. This resulted in pronounced sympathetic inhibition and bradycardia in all rats. In SHR, this sympatho-inhibitory response was usually reversed after about 20 min. In one group of hypertensive rats (SHRt, n = 24), MAP was raised to 75 mm Hg by partial re-transfusion, when heart rate (HR) had returned to the pre-bleeding level and MAP was maintained at that level for the rest of the experiment. All the other rats (SHR, n = 12; WKY, n = 11) were kept at 45-50 mm Hg for 32 min, after which WKY were bled further to a MAP of 30 mm Hg for 8 min. SEP amplitudes decreased after haemorrhage in all groups but more so in SHR. In the WKY group, SEP were only modestly attenuated during the first 32 min, but after further bleeding to 30 mm Hg the amplitudes were reduced to the same extent as in SHR. Some SHR showed flat SEP immediately upon haemorrhage and were excluded from the SHRt group.(ABSTRACT TRUNCATED AT 250 WORDS)