MECHANICAL-STRESS OF THE CAROTID-ARTERY AT THE EARLY PHASE OF SPONTANEOUS HYPERTENSION IN RATS

Common carotid artery (CCA) hypertrophy has long been recognized in th e neonatal period of development in spontaneously hypertensive rats (S HR), but the mean circumferential and shear stresses acting on the art erial wall have never been investigated in vivo. We investigated intra -arterial blood pressure in conscious rats, CCA diameter (echotracking techniques), blood flow velocity (pulsed Doppler), wall thickness (hi stomorphometry), and ganglionic blockade (hexamethonium) in Wistar rat s and SHR at 5 and 12 weeks of age. During this interval, weight gain was identical in the strains, whereas the increase in wall thickness a nd blood pressure was greater in SHR. CCA diameter was identical at we ek 5 and increased similarly at week 12 in both strains. During gangli onic blockade, a larger diameter was observed in SHR at week 5 for the same BP level, whereas equivalent values were observed at week 12. Bl ood flow velocity decreased with age but to a significantly greater ex tent in SHR. Mean circumferential stress and shear stress index were i dentical in both strains at week 12. However, from weeks 5 to 12, mean circumferential stress increased with age similarly in both strains, whereas the age-related decrease in mean shear stress index was much g reater in SHR than Wistar rats. Thus, despite a higher blood pressure, SHR exhibit the same carotid diameter as Wistar rats during early dev elopment. Because the kinetics of shear stress are different in both s trains, altered flow-dilatation mechanisms, and possibly resulting end othelial dysfunction, may be involved in the diameter changes.