Blood pressure adrenoceptors affecting

The diastolic blood pressure is affected mainly by peripheral vascular resistance and the heart rate. The adrenoceptors with the greatest effects on vascular resistance are alpha and beta2 receptors. The systolic pressure is the sum of the diastolic and the pulse pressures. The pulse pressure is determined mainly by the stroke volume (a function of force of cardiac contraction), which is influenced by beta, receptors. 

The decreased work capacity of the in-farcted myocardium leads to a reduction in stroke volume (SV) and hence cardiac output (CO). The fall in blood pressure (RR) triggers reflex activation of the sympathetic system. The resultant stimulation of cardiac 3-adreno-ceptors elicits an increase in both heart rate and force of systolic contraction, which, in conjunction with an a-adren-oceptor-mediated increase in peripheral resistance, leads to a compensatory rise in blood pressure. In ATP-depleted cells in the infarct border zone, resting membrane potential declines with a concomitant increase in excitability that may be further exacerbated by activation of p-adrenoceptors. Together, both processes promote the risk of fatal ventricular arrhythmias. As a consequence of local ischemia, extracellular concentrations of H+ and K+ rise in the affected region, leading to excitation of nociceptive nerve fibers. The resultant sensation of pain, typically experienced by the patient as annihilating, reinforces sympathetic activation. 

SC-30552 (42) given orally to SHR (spontaneously hypertensive rats) lowered blood pressure and caused bradycardia. Tachycardia caused by isoproterenol was not affected by SC-30552, whereas isoproterenol-induced decreases in blood pressure were attenuated. Ganglionic blockade caused by hexamethonium did not affect vasodilatation caused by this CEB. A pA2 value against calcium-induced contractions of rabbit, aortic strips of 7.42 was calculated. These effects suggest possesses some but not 6i- or a-adrenoceptor activity and may depress the SA node. 

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