Suppression of isoprenaline-induced increase in plasma renin concentration by vasoconstrictors in rats with nonfunctioning Macula densa.

The mechanism of the increase in plasma renin concentration caused by the beta-sympathomimetic agent isoprenaline has been further investigated. Rats were pretreated by occluding the left renal artery for 2 hrs, thus rendering the macula densa cells of this kidney nonfunctioning. After contralateral nephrectomy infusion of isoprenaline (1.5 mug/kg min) still caused a strong increase in plasma renin concentration. This increase was significantly suppressed by simultaneous infusion of angiotensin II (1.0 mug/kg min). The alpha-sympathomimetic amine phenylephrine (60 mug/kg min) or octapressin (10 mU/kg min). The results exclude any mediator-role of the macula densa receptors in the isoprenaline-induced release of renin. The possibility of a stimulation of renin release via the baroreceptors or a direct "secretomotoric" action of isoprenaline is discussed.