Renin stimulation by isoproterenol and theophylline in the isolated perfused kidney

The intrarenal mechanisms of renin release were studied in the isolated perfused rabbit kidney during stimulation by isoproterenol, 0.01 μg/kg per min, and by theophylline, 0.87 mg/kg per min. In the absence of urinary flow during the early stages of perfusion, isoproterenol caused a 17% increase of renal vein serum renin concentration (RVSRC) (P < 0.001) without changing renal blood flow, renal vascular resistance, or serum potassium. dl-Propranolol, 2.0 mg/kg per min, abolished this isoproterenol induced renin release. A moderate reduction in perfusion pressure prior to the infusion of isoproterenol resulted in a marked additional stimulation of renin release. Studies during and following ureteral occlusion demonstrated that theophylline stimulates renin release by decreasing renal vascular resistance, whereas the concomitant increase in sodium transport to the macula densa exerted an opposite effect. dl Propranolol did not affect theophylline induced renin secretion. It is concluded that single exogenous stimuli may activate more than one intrarenal mechanism simultaneously. Isoproterenol has a direct renin stimulatory effect on intrarenal beta adrenergic receptors that may be reinforced by baroreceptor stimulation. Theophylline stimulates renin via a baroreceptor mechanism, with simultaneous renin suppression via a sodium macula densa effect.