Spontaneously occurring renal disease in the guinea pig

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Effect of ganglion-blocking agents on renin release in hypertensive patients

In 18 patients with benign essential hypertension, renin release during reduction of arterial pressure due to sodium nitroprusside infusion was measured before and after administration of ganglion-blocking agents (pentolinium or trimethaphan). In 12 patients, renin release induced by reduction in pressure was significantly reduced but not abolished by ganglion blockade. Simultaneously, ganglion blockade significantly reduced renal vascular resistance (RVR) and almost abolished a decrease in renal blood flow (RBF) due to hypotension. In 6 other patients in whom no significant renin release resulted from hypotension, ganglion blockade caused little changes in renin release, RVR or RBF. The results support the hypothesis that renal sympathetic nerve activity is a factor in variations in renin release in patients with essential hypertension.

Following ganglion blockade in the responsive patients, the significant reciprocal correlation between renal venous renin activity and sodium excretion rate shifted but still persisted, suggesting that the renin-releasing mechanism related to sodium excretion may be independent of innervation. On the other hand, the correlation between renin activity and the degree of reduction in pressure was insignificant after ganglion blockade. It is concluded that two intrarenal mechanisms, nerve-dependent and nerve-independent, are involved in renin release due to reduction in pressure.

Ganglion blockade also exerted an inhibitory effect on renin release due to hypotension in 4 normotensive subjects and 5 patients with renovascular hypertension.

Renin release in patients with benign essential hypertension

In 16 of 28 patients with benign essential hypertension, reduction of mean arterial pressure to 75 to 120 mm Hg by infusion of sodium nitroprusside caused significant increase in renin release estimated by the renal-systemic difference of renin activity and renal plasma flow (RPF). The threshold at which renin release increased was shifted to a range that was intermediate between that previously reported for normotensive subjects and that for patients with renovascular hypertension, but the average magnitude of renin release was almost comparable to that in normotensive subjects. In the other 12 patients, no significant renin release occurred during reduction in pressure of comparable degree.

The difference in renin release was difficult to explain by the difference in severity of hypertensive disease or in sodium excretion, but increased renin release was usually associated with a decrease in RBF and a rise in renal vascular resistance, while insignificant release was usually associated with an insignificant change in RBF and a decrease in resistance. The average known duration of hypertension was significantly greater in the unresponsive patients. It is suggested that renal sympathetic nerve activity may be a factor in the variations in renin release in patients with essential hypertension.