Histological study of kidneys, especially their vascular changes, were carried out with measurement of renin-like activity in kidneys of rats with different types of experimental hypertension for the evaluation of the significance of the renal pressor material in the production and maintenance mechanism of hypertension.
Goldblatt-type hypertension, andrenal regeneration hypertension, coarctation of the aorta, neurogenic hypertension, and experimental nephritis were produced in albino rats and the histological changes and renin-like activity in the kidneys were observed;
(1) In the Goldblatt-type hypertension, in which moderate hypertension was maintained for 2-4 months, the findings were similar to those of human benign nephrocsclerosis. In those with severe hypertension for six month duration or those with rapid blood pressure elevation, the tissue findings were similar to those of human malignant nephrosclerosis. Renal renin increased in clamped kidneys and decreased in the contralateral untreated kidneys.
(2) In the adrenal regeneration hypertension, maintained for six months or more, degeneration, thickening, and stenosis were seen in renal arterioles and small arteries, while the amount of renal renin decreased.
(4) In the coarctation of the aorta for 1-2 month duration, the blood pressure elevation and cardiac hypertrophy were marked, and degeneration, thickening and stenosis of renal arterioles were remarkable. The amount of renal renin showed a slight, insignificant decrease.
(4) In neurogenic hypertension, the blood pressure elevation was variable, and degeneration, thickening, and partial stenosis were observed in small renal arteries. Renal renin were within normal range.
(5) In experimental nephritis the changes in the vacsular wall were usually slight, and the amount of renal renin showed a slight decrease.
There is no direct correlation between hypertension and renin-like activity in the kidneys, and hypertension is maintained without the increase in the renin-like activity. There is, however, some correlation between the renin-like activity and the renal histological changes ; the amount of renin was generally decreassed, in kidneys with marked thickening and stenosis of renal arterioles, while the value of renin was nearly normal when neither thickening nor stenosis were found. On the other hand, in the clamped kidneys with the increased renin-like activity, degeneration of arteriolar wall were found without thickening or stenosis. Therefore, renal pressor system plays a different role in the production and maintenance of high blood pressure in each kind of hypertension. However, it probably plays an indirect role in correlation with the neurogenic and the metablic or other factors.
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