Abstract

Studies have shown that angiotensin-converting enzyme (ACE) inhibitor treatment in young genetically hypertensive rats prevents the full expression of blood pressure and vascular abnormalities in the adult. This model provides unique conditions with which to study the pathogenesis of altered Ca++ regulation. Normotensive (WKY) rats and stroke-prone spontaneously hypertensive rats (SHRSP) received at 6 to 10 weeks of age either ACE inhibitor (ramipril), hydralazine/hydrochlorothiazide or no treatment. At 17 weeks of age, rats were anesthetized, and vascular tissue was excised. Thoracic aorta challenged with 20 mM caffeine in Ca(++)-free buffer produced a phasic contractile response. The magnitude of this phasic response was used as a measure of Ca++ released from intracellular stores; a direct correlation between this phasic response and systolic blood pressure was observed. A concentration-response curve to Bay K8644 was performed on carotid arteries; a direct correlation of force development to Bay K8644 and systolic blood pressure was observed. All WKY groups showed lower blood pressure and force development in response to Bay K8644 than did SHRSP. Treatment with ramipril reduced blood pressure and force development in response to Bay K8644 in adult SHRSP, although not to levels of WKY rats, whereas WKY rats were unaffected by treatment. These data support the hypothesis that contractile responses to Bay K8644 in carotid arteries and caffeine in aorta parallel changes in systolic blood pressure. We conclude that alteration of Ca++ regulation in hypertension is directly related to elevated blood pressure and mediated by an angiotensin II-sensitive mechanism during development.