Effects of perfusion flow rate, prostaglandin F2α, phenylephrine, and serotonin on isolated, perfused brains of spontaneously hypertensive rats

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F_2α (PGF_2α) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 ± 3mm Hg(n = 11) in SHR and 32 ± 2mm Hg(n = 12)in WKY(P < 0.005). The perfusion pressures at all flow rates tested (2.5−6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to sertonin compared with phenylephrine and PGF_2α. EC₅₀ values (−logM) for serotonin in the perfused brains of SHR and WKY were 7.0 ± 0.06 (n = 10)and6.5 ± 0.06 (n = 11), respective (P < 0.01). There were no differences in EC₅₀ values for phenylephrine or PGF_2α between SHR and WKY. Exogenous serotonin and phenulephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF_2α was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY, and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.