Role of Area Postrema in Transgene Hypertension

Abstract

Abstract Transgenic [Tg(+)] rats carrying the mouse Ren -2 d gene [(m Ren -2 d )27] are a newly established monogenetic form of experimental hypertension. To determine whether the area postrema contributes to the development of hypertension in m Ren -2 Tg(+) rats, this circumventricular organ in the fourth ventricle was removed from 5-week-old Tg(+) rats. From weeks 4 through 9, systolic blood pressure was measured weekly by tail-cuff plethysmography in area postrema–lesioned and sham-lesioned Tg(+) rats. Although systolic blood pressure rose markedly in sham-lesioned Tg(+) rats, the increase in systolic blood pressure was significantly attenuated in area postrema–lesioned Tg(+) rats. At 9 weeks of age, a femoral artery was cannulated for the measurement of arterial pressure in awake rats. Mean arterial pressure (MAP) in area postrema–lesioned Tg(+) rats was significantly ( P <.01) lower than that in sham-lesioned rats: 171±7 and 132±5 mm Hg, respectively. Baroreceptor reflex was evaluated by intravenous infusion of sodium nitroprusside. There was no significant difference in baroreceptor reflex sensitivity between the two groups. Intravenous pentolinium (5 mg/kg), used to produce sympathetic ganglionic block, caused significant decreases in MAP in both groups. However, the reduction of MAP in the sham-lesioned group was significantly ( P <.05) greater than that in the area postrema–lesioned group: −73±4 and −48±6 mm Hg, respectively. The ratio of left ventricular weight to body weight in sham-lesioned Tg(+) rats was significantly larger than that of area postrema–lesioned rats. These results suggest that ablation of the area postrema markedly attenuates the development of hypertension in m Ren -2 d Tg(+) rats, and this attenuation may be attributed to decrease in sympathetic outflow.