The aim of this study was to investigate the cardiovascular effects of long-term treatment with nifedipine in two distinct stages of early ontogenesis in spontaneously hypertensive rats (SHR). Four- and eight-week-old SHR and age-matched normotensive Wistar rats were treated with nifedipine (50 mg/kg/day) for four weeks. Systolic blood pressure was measured weekly by the tail-cuff technique. At the end of the treatment the animals were sacrificed and rings of their mesenteric arteries were suspended in organ baths and connected to a force-displacement transducer for measuring their reactivity under isometric condition. Neurogenic contractile responses were elicited by electrical stimulation of perivascular adrenergic nerves. We found that treatment with nifedipine prevented the elevation of blood pressure and decreased the relative heart weight values in SHR of both age groups. No changes in these parameters due to nifedipine were detected in Wistar rats. Adrenergic contractions in mesenteric arteries were decreased in nifedipine-treated SHR, particularly at 12th week; in contrast, arteries from 12-week-old Wistar rats treated with nifedipine became more sensitive to endo- and exogenous noradrenaline and responded with enhanced contractions. We conclude that nifedipine administration prevented the rise of blood pressure similarly in both stages of spontaneous hypertension development; however, it decreased the sympathoadrenergic vasoconstriction more effectively in 12-week-old SHR in which the initial blood pressure was already partially elevated.
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