Heterogeneous response patterns of aortae to norepinephrine.

Concentration-contractile response curves for the thoracic (TA) and abdominal (AbA) aortae from spontaneously hypertensive (SHR) and normotensive control (WKY) rats were determined using adrenergic agonists. The concentrations of epinephrine (E) and norepinephrine (NE) necessary to produce a maximum response in the WKY TA were 7.07 x 10(-7) M and 1.68 x 10(-6) M, respectively. At greater concentrations TA responded with progressive relaxation. When similarly tested, SHR TA responded with significantly less relaxation. The concentrations of E and NE necessary to produce a maximum response in the WKY AbA were greater than 1.0 x 10(-5) M. No significant relaxation occurred at greater concentrations. The relaxation responses of the SHR AbA were no different than their normotensive controls. When propranolol was used the results suggested that relaxation is mediated by the beta-adrenoreceptor. The use of the beta 2-agonist, salbutamol, confirms the hypothesis that relaxation occurring in response to high concentrations of NE and E is partly a beta 2-adrenoeceptor phenomenon, and that this beta 2-adrenergic response decreases with early hypertension in TA. The different response patterns produced may partially account for the diversity of results regarding vascular sensitivity to vasoactive agents in the literature.