Renal function, plasma renin, and spontaneous diuresis in an advanced stage of hypertension in rats

Relationship of renal function and plasma renin level to a spontaneous diuresis in an advanced stage of hypertension was examined in the stroke-prone spontaneously hypertensive rats (SHRSP). For a comparison, it was also investigated in 2 kidney 1 clip (1CR) and 2 kidney 2 clip (2CR) models of renovascular hypertensive rats. The spontaneous diuresis was usually associated with an elevation of plasma renin level and an impairment of renal function in SHRSP and 1CR. In SHRSP, renal plasma flow showed an inverse correlation to the plasma renin level. The diuresis, however, is not prerequisite to the increase in plasma renin or to the renal impairment, since the latter changes were not always accompanied by diuresis. No correlations were found between these factors in 2CR. Remittent diuresis was observed in many 2CRs and 2 SHRSPs with normal renal function, indicating that renal damage underlies the continuous progression of the diuresis observed in most cases of SHRSP and 1CR. Both sodium and potassium balances tended to be negative in 1CR and 2CR in the diuretic phase, whereas potassium alone showed this tendency in SHRSP. The negative balances, if any, were not due to an excessive loss of the electrolytes but attributed mainly to a decrease in intake. The critical level of blood pressure for the spontaneous diuresis was highest in SHRSP and lowest in 1CR. It is probable that an interaction and cooperation between high blood pressure, impaired renal function and high plasma renin participate in the mechanism of the spontaneous diuresis during the development of malignant phase of hypertension of the rat.