Phenylephrine-induced hypertension does not improve outcome after closed head trauma in rats

Phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) is reported to increase cerebral perfusion pressure and collateral flow to ischemic areas of the brain in a rat model of focal cerebral ischemia. In the present study, we examined whether phenylephrine-induced hypertension of similar magnitude and duration was beneficial in a rat model of closed head trauma (CHT). Forty-eight rats were randomized into four experimental conditions: CHT at time 0 min (yes/no), plus phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) at 65 min (yes/no). CHT was delivered using a weight-drop device (0.5 J). Outcome measures were neurological severity score (NSS) at 1, 4, and 24 h, and brain tissue specific gravity (microgravimetry) and injury volume (2,3,5-triphenyltetrazoium chloride) at 24h. After CHT, NSS at 24h (median +/- range) and brain tissue specific gravity (mean +/- so, injured hemisphere) were 7 +/- 2 and 1.033 +/- 0.007 without phenylephrine and 8 +/- 2 and 1.035 +/- 0.005 with phenylephrine (P = 0.43), respectively. Tissue injury volume (mean +/- so) was 335 +/- 92 mm(3) without phenylephrine and 357 +/- 154 mm(3) with phenylephrine (P > 0.62). The results of our study indicate that postinjury treatment with 15 min of phenylephrine-induced hypertension does not attenuate brain edema, reduce tissue injury volume, or improve neurological outcome after CHT in rats. Implications: Phenylephrine-induced hypertension is reported to increase cerebral perfusion pressure and blood flow in a rat model of focal cerebral ischemia. In our study, phenylephrine-induced hypertension did not decrease brain edema or tissue injury volume or improve neurological outcome in a rat model of closed head trauma.