SPONTANEOUS AND RENAL HYPERTENSIVE RATS - RESPONSIVENESS OF ISOLATED RIGHT AND LEFT ATRIA TO NORADRENALINE, ISOPRENALINE AND METHOXAMINE

The adrenergic responsiveness of right and left atria isolated from sp ontaneously hypertensive rats (SHR) and renal hypertensive rats (RHR) was studied. Right atria isolated from SHR showed subsensitivity to th e chronotropic effect of noradrenaline (21.3-fold at the EC(50) level, P<0.05) and isoprenaline (12.0-fold, P<0.05). However, atria isolated from RHR did not exhibit any significant alteration (P>0.05) in sensi tivity to the chronotropic effect of noradrenaline or isoprenaline. Ch ronotropic responsiveness to theophyline was not altered in right atri a isolated from SHR or RHR. alpha(1)-Mediated inotropic responses to n oradrenaline and methoxamine were blunted in left atria isolated from SHR. Left atria isolated from RHR showed supersensitivity to the inotr opic effect of noradrenaline (5.4-ford at the EC(50) level, P<0.05) an d subsensitivity to the inotropic effect of methoxamine (6.0-fold, P<0 .05). It is concluded that the present results could, at least partial ly, explain the reduced cardiac output observed during established hyp ertension in SHR and the increased cardiac output observed in the init ial phase of renal hypertension in RHR.