Quantitative Changes of Maximum Contractile Response to Norepinephrine in Mesenteric Arteries from Spontaneously Hypertensive Rats During the Development of Hypertension

Maximum contractile responses of mesenteric arterial strips from spontaneously hypertensive rats (SHR) to norepinephrine (NE) were determined at all stages of hypertension (6-30 weeks of age), and data compared with findings in normotensive Wistar-Kyoto rats (WKY). Although the maximum responses to NE in the strips from both 6- and 14-week-old SHR--that is, before and after the development of elevated blood pressure--were significantly greater than those in the strips from age-matched WKY, the ratio of the maximum contraction induced by NE to that by KCl (NE/K+ ratio) was increased only after the development of hypertension. The difference in the NE/K+ ratio was also apparent in strips of femoral artery from 14-week-old rats but not in strips of thoracic aorta. The angiotensin II/K+ ratios in the three arterial strips, which were significantly decreased with advancing age of the rats, were not significantly different between the SHR and WKY. There was a good correlation between the NE/K+ ratios in the mesenteric arterial strips and the blood pressures of both SHR and WKY. It is concluded that the NE/K+ ratio in the mesenteric arterial strips was in good agreement with the onset of hypertension in SHR.