Increased pressor responses to pressor agents in spontaneously hypertensive rats

Abstract

Pressor reactivity to a variety of pressor agents after partial ganglionic blockade induced with hexamethonium was investigated in intact, spinalized and chemically sympathectomized, spontaneously hypertensive rats (SHR). Responses of unanesthetized 6 mo. old SHR to noradrenaline [norepinephrine], phenylephrine and angiotensin after hexamethonium administration (32 mg/kg) markedly exceeded those of unanesthetized, age-matched normotensive Wistar-Kyoto rats (WKR). Responses of anesthetized SHR to noradrenaline after hexamethonium administration (16 mg/kg) were also increased at the hypertensive stages but not at the prehypertensive stages, when compared with those of anesthetized normotensive Wistar rats of respective ages. In spinalized and chemically sympathectomized preparations after hexamethonium administration (16 mg/kg), noradrenaline produced equal increases in blood pressure in 6 mo. old SHR and WKR. The functional sympathetic nervous system is important for the hyperreactivity of intact SHR.