EFFECTS OF ANTIHYPERTENSIVE THERAPY WITH ANGIOTENSIN-CONVERTING ENZYME-INHIBITORS OR CALCIUM-ANTAGONISTS ON SPONTANEOUS CYCLIC VASOMOTOR ACTIVITY IN SMALL RESISTANCE ARTERIES OF SPONTANEOUSLY HYPERTENSIVE RATS

Objective: Spontaneous cyclic vasomotor activity can occur in small re sistance arteries in vitro after precontraction with a vasoconstrictor . Calcium and potassium channels and nitric oxide synthesis or release seem to be involved in the genesis of this vasomotor activity. We the refore investigated the effects of chronic antihypertensive therapy wi th calcium antagonists and angiotensin converting enzyme (ACE) inhibit ors on the amplitude and frequency of cyclic vasomotor activity in vit ro in spontaneously hypertensive rats (SHR). Materials and methods: SH R were treated with fosinopril at 25 mg/kg per day or lacidipine at 10 mg/kg per day or nitrendipine at 30 mg/kg per day, from the age of 4 to 12 weeks. Data were compared with those obtained in untreated SHR a nd Wistar-Kyoto (WKY) rats. Half the Fats were killed at 13 weeks of a ge, and the remaining half were killed at 38 weeks of age. The mesente ric small resistance arteries were dissected, mounted on a micromyogra ph and then contracted submaximally with noradrenaline. Acetylcholine was then added to the organ bath. Results: More than 50% of the vessel s showed cyclic vasomotor activity. The frequency and amplitude of thi s activity were greater in SHR than WKY rats after noradrenaline and a fter acetylcholine. At 13 weeks of age (but not at 38 weeks of age), t reatment with a calcium antagonist (either lacidipine or nitrendipine) significantly reduced the frequency and amplitude of the vasomotor ac tivity, probably by interfering with calcium entry. No change was obse rved after fosinopril. Conclusions: Antihypertensive treatment with di fferent drugs may affect cyclic vasomotor activity differently, probab ly by interfering with cellular mechanisms involved in its genesis. Th e effects of calcium antagonists on cyclic vasomotor activity are stil l present after short-term but not after long-term treatment withdrawa l.