THE EFFECTS ON RENAL RESISTANCE TO BLOOD FLOW OF RENIN, ANGIOTONIN, PITRESSIN AND ATROPINE, HYPERTENSION, AND TOXEMIA OF PREGNANCY 1

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Abstract
Previously derived formulas for resistance to blood flow of the afferent and efferent arterioles of the kidney have been applied to data in the literature. It appears that dialectic reasoning concerning the predominance of afferent or efferent arteriolar constriction frequently leads to incorrect conclusions. Renal homeostasis is discussed and it is considered likely that the resistance of the afferent arterioles varies with blood pressure changes so as to preserve renal function. Pitressin caused no consistent change in glomerular intra-capillary pressure, total effective renal arteriolar resistance, or in the afferent-to-efferent arteriolar resistance ratio in unanesthetized dogs. Atropine added to pitressin increased total effective arteriolar renal resistance, with afferent arteriolar constriction predominating in unanesthetized dogs. Renin infused into unanesthetized dogs increased glomerular intra-capillary pressure and. total arteriolar resistance with neither afferent nor efferent constriction predominating consistently. Angiotonin acted rather similarly, but conclusions concerning it are subject to some doubt. In one human subject, angiotonin caused constriction of both sets of arterioles with afferent constriction predominating. Afferent arteriolar constriction outweighed efferent constriction more than is normal in all of the 17 cases of essential hypertension studied. A specific renal effect is the probable cause of the low filtration fraction seen in late severe toxemia of pregnancy. There is inadequate evidence to decide how much of this effect is primarily constriction of the efferent arterioles and how much, if any, is change in the permeability of the glomerular membrane to water and/or inulin and other sugars.