Cellular morphology in mesenteric resistance vessels from antihypertensive treated spontaneously hypertensive rats

The effects on media smooth muscle cell size of long-term antihypertensive treatment with four different drugs were studied in isolated segments of mesenteric resistance arteries from spontaneously hypertensive rats (SHRs) using an unbiased stereological principle (the "disector"). Young SHRs were treated from age 4 weeks to 24 weeks with metoprolol (130 mg/kg/day), isradipine (42 mg/kg/day), captopril (60 mg/kg/day) or perindopril (1.5 mg/kg/day). At 24 weeks, when all drugs had lowered the blood pressure in SHRs compared to untreated controls (order of efficacy perindopril greater than captopril greater than isradipine greater than metoprolol), random arterial samples were taken from the mesenteric vascular bed close to the intestine and mounted on an isometric myograph, allowing standardized measurements of vascular dimensions. Although, taken together, the four treatments reduced blood pressure as well as the media:lumen ratio of the vessels and the number of cell layers, there was no significant effect of the treatments, taken together, on cell volume, cell number or on the ratio between interstitium and cells. However, cell volume correlated with blood pressure (P less than 0.05), suggesting that the most effective treatments (perindopril and captopril) had inhibited cell growth. It is, however, not clear whether the effect on cell volume was a specific effect of the drugs used, or whether it was only due to the blood pressure reduction.