ALPHA(1)-ADRENOCEPTOR SUBTYPES MEDIATING ANTINATRIURESIS IN WISTAR AND STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

This study examined the alpha(1)-adrenoceptor subtypes involved in med iating adrenergically induced Na+ reabsorption in the kidney of pentob arbitone anaesthetised Wistar and stroke-prone spontaneously hypertens ive rats (SHRSP). Close renal-arterial phenylephrine (50-100 mu g kg(- 1) h(-1)) administration in Wistars, with regulated renal perfusion pr essure, caused small reductions in renal haemodynamics but large reduc tions, of 35%, 64% and 57% (all P < 0.05), in urine volume, absolute a nd fractional Na+ excretions. The magnitude of these excretory respons es to phenylephrine were similar in the presence of the alpha(1B)-adre noceptor alkylating agent, chloroethylclonidine (10 mu g kg(-1) h(-1)) , but were blocked during administration of the alpha(1A)-adrenoceptor antagonist, 5-methylurapidil (10 mu g kg(-1) h(-1)). Phenylephrine in fusion in the stroke-prone spontaneously hypertensive rats caused chan ges in renal haemodynamics and fluid excretion of comparable magnitude to that achieved in Wistars which was blocked by 5-methylurapidil but not chloroethylclonidine. These observations suggest that in Wistar a nd stroke-prone spontaneously hypertensive rats the adrenergically ind uced Na+ reabsorptive responses are mediated by alpha(1A)-adrenoceptor s.