Antihypertensive Effect of Diltiazem in Young or Adult Rats of Genetically Hypertensive Strains

The antihypertensive effects of diltiazem were investigated in three different strains of genetically hypertensive rats, i.e. spontaneously hypertensive rats (SHR), stroke prone SHR (SHR-sp) and genetically hypertensive rats (GHR) compared to their respective controls, normotensive Wistar-Kyoto (NT-WKY) and New Zealand strain (NT-NZ). Either adult (3-6 months) or young (4 weeks), conscious rats were used. In adult SHR, SHR-sp and GHR, the percent decrease in blood pressure produced by diltiazem (10, 30 and 100 mg/kg orally (p.o.) or 0.1, 0.3, 1.0 and 3.0 mg/kg intravenously (i.v.)) was greater than in NT-WKY or NT-NZ, while no difference was detected in case of hydralazine (5 mg/kg p.o.). In contrast, the reactivity to diltiazem was not different between the young rats bred from the normotensive and hypertensive rats of both the Japanese and the New Zealand strains. It is concluded that diltiazem is a more effective antihypertensive agent in the hypertensive rats than in the normotensive rats. However, the increased reactivity to this compound in the adult hypertensive rats cannot be readily explained by the known pathogenetic factors leading to their hypertension.