Studies on renin release in vitro

1) Measurements of renin secretion from single arterioles at time intervals down to 20 seconds showed that the renin secretion is episodic, the amount of renin released during each episode corresponding to the estimated content of one secretory granule. 2) A decrease in osmolality elicits episodic release of renin from single arterioles, stimulates renin release from isolated glomeruli transiently, and is associated with swelling of the secretory granules and formation of contacts between granules and the plasmalemma. 3) Increases in osmolality produce sustained inhibition of the renin secretion, and prevents swelling of the organelles of the juxtaglomerular epithelioid cells. 4) Treatment of isolated glomeruli with weak permeable bases has a biphasic effect on renin release: an initial transient stimulation, which can be blocked with sucrose, and a delayed inhibition which may be associated with an increase in intracellular pH. 5) Results with the monovalent cation ionophores nigericin and monensin, are similar to those obtained with weak permeable bases, and suggest that their effects are due to swelling and alkalinization of acidic cellular organelles. 6) A decrease in the extracellular calcium concentration results in sustained stimulation of renin secretion to a variable level dependent on the season. 7) After stimulation with a low extracellular calcium concentration, the sensitivity of secretion rate to osmotic stimuli is proportionally increased. A high extracellular osmolality blocks the stimulatory effect of a low calcium concentration. 8) Renin release is not correlated to the release of adenylate kinase.