All dogs with spontaneous hypertension exhibited normal renal plasma flow and glomerular filtration rate.

Clearances on nephrogenic hypertensive dogs revealed that some exhibited normal kidney function, while others had significant depression of renal plasma flow and glomerular filtration rate. In the latter, the filtration fraction may or may not be elevated.

Serial renal clearances were done at intervals on 3 dogs with spontaneous hypertension during their 3rd year of known hypertension. They exhibited no tendency to develop impaired renal function in the face of prolonged benign hypertension.

Serial renal clearances on nephrogenic hypertensive dogs revealed no tendency for kidney function to become progressively impaired. This was true, whether the immediate postoperative clearance values were normal or depressed. It was also true regardless of the duration of the hypertension.

It is suggested that mechanisms other than elevated blood pressure per se operate to produce progressive kidney damage and impairment of renal function.

No tendency was revealed over the course of a year or more for the kidney function to improve in Goldblatt dogs exhibiting depressed clearances immediately postoperatively. This is interpreted as evidence against the postoperative development in persistently hypertensive Goldblatt dogs of a renal collateral circulation sufficient to augment significantly effective renal blood flow.

Pathological studies on 2 dogs with spontaneous hypertension revealed slight to moderate chronic focal lesions in the kidneys, and bilateral adrenal cortical adenomatous hyperplasia. Both lesions may have no pathogenetic significance.

In accord with previous observations, autopsies on 3 Goldblatt dogs revealed minimal renal changes in one, and unilateral kidney atrophy with contralateral hypertrophy in the 2 others. The adrenals were normal.

In general, data on renal clearances showed correlation with postmortem kidney findings. However, normal renal clearances are found in the presence of anatomically abnormal kidneys.

The findings in canine spontaneous and nephrogenic hypertension are compared and contrasted with data obtained in human essential hypertension. Pathogenetic relationships are discussed.