INCREASED PRESSOR RESPONSIVENESS OF FEMORAL ARTERIES TO EXOGENOUS NOREPINEPHRINE IN RENAL HYPERTENSIVE DOGS MEDIATED THROUGH ALPHA-2-ADRENOCEPTORS

Changes of perfusion pressure induced by femoral arterial perfusion of norepinephrine (NE) were studied in renal hypertensive dogs made with the method of wrapping both kidneys. The NE threshold dose which indu ced perfusion pressure increase was lower in hypertensive dogs than th at in normotensive dogs. The NE pressor response in low concentration (1, 2, 10 ng . kg-1) was increased in hypertensive dogs, after alpha2 adrenoceptors antagonized by idazoxan this increased response had been eliminated. These suggested that increased vasoconstriction by exogen ous NE in hypertensive dogs was mediated through the increased reactiv ity of postsynaptic alpha2, adrenoceptors to NE.