ISOVOLEMIC HEMODILUTION NORMALIZES THE PROLONGED PASSAGE OF RED-CELLSAND PLASMA THROUGH CEREBRAL MICROVESSELS IN THE PARTIALLY ISCHEMIC FOREBRAIN OF RATS

The objective of this study was to determine whether hemodilution coul d normalize the mean transit times of red blood cells (Tr) and plasma (Tp) through cerebral microvessels in a partially ischemic brain. Wist ar-Kyoto (WKY) rats, aged 30-40 weeks, were divided randomly into thre e groups. The first group was the nonocclusion, nonhemodilution (NN) n ormal control group. The second group was the occlusion, nonhemodiluti on (ON) group, in which animals were treated with bilateral carotid ar tery ligation. The third group was the occlusion-hemodilution (OH) gro up, in which animals were treated with bilateral common carotid artery ligation and, then, isovolemic hemodilution by replacing blood with t he same volume of 3% modified fluid gelatin. Local cerebral blood flow (1CBF) and microvascular volumes of red blood cells (Vr) and plasma ( Vp) in 14 brain structures were measured using C-14-iodoantipyrine, ir on-55-labeled red blood cells, and C-14-inulin, respectively. The amou nt of oxygen delivered to local brain structures (OD), cerebral microv ascular blood volume (Vb), mean transit time of blood (Tb), Tr, and Tp through cerebral microvessels were calculated from the data. Two hour s after carotid artery ligation, 1CBF decreased by similar to 38% in f orebrain structures, 22% in rostral hindbrain areas, and 8% in the cau dal hindbrain (29% for all 14 structures). The decreases in ODs were p arallel with those of 1CBFs, at 33, 17, and 2% in the three regions, r espectively (24% for all structures). In contrast, Vb increased by 68, 37, and 16% in the three regions, respectively (48% for all structure s). Tr and Tp were markedly prolonged (180% for Tr and 154% for Tp) in the forebrain regions, moderately (91% for Tr and 73% for Tp) in the rostral hindbrain, and mildly (60% for Tr and 13% for Tp) in the cauda l hindbrain, with a mean increase of 136% for Tr and 111% for Tp in al l structures. When data in the OH and NN groups were compared, 1CBF va lues tended to be slightly higher and Vb values were significantly hig her (p < 0.05) in the OH group. ODs in the eight forebrain structures were all significantly less (p < 0.05) in the OH group than the NN gro up. Tr and Tp values in the forebrain were similar between the OH and the NN groups. In conclusion, occlusion of the bilateral common caroti d arteries in WKY rats causes partial forebrain ischemia, in which bot h Tr and Tp are prolonged. These prolongations of Tr and Tp can be nor malized by isovolemic hemodilution. However, the ischemic forebrain re mains hypoxic after hemodilution.