ROLE OF THE KIDNEYS IN MODIFYING THE RESPONSE TO THE ‘SUSTAINED PRESSOR PRINCIPLE’

Abstract

As previously reported there appears in the blood plasma of cats a pressor substance which presumably emanates from the kidneys as a consequence of decreased blood flow (or blood pressure) within these organs. Unlike other known biologic pressor substances, it possesses the ability to cause a sustained elevation or blood pressure when injected intraven. into cats which have been nephrectomized several hrs. to several days before. Repeated injns. of plasma containing the pressor principle have caused only acute, unsustained rises in blood pressure in normal cats (kidneys intact). In animals from which the kidneys have been acutely removed or excluded from the circulation, the initial pressor responses were unsustained, but with repeated injns. of the plasma sustained responses were ultimately observed. Cats, nephrectomized 6-24 hrs. before, not infrequently exhibited unsustained responses to the first injn. of plasma containing the pressor principle, but the responses to the 2d or 3d injns. were well sustained. The initial responses in cats nephrectomized 48 hrs. before were almost invariably sustained. The failure of certain of the pressor responses to be sustained suggests the possibility that the pressor principle injected into the blood stream may be inactivated or its action otherwise inhibited. In the non-nephrectomized animals, it has not yet been detd. to what extent, if any, ''inactivation'' may have taken place within the kidneys. Other expts. offer supporting evidence for the following hypotheses: the kidneys may secrete an inhibitor of the pressor principle under conditions of normal blood flow (or blood pressure) within these organs; the inhibitor remains in the animal after removal of the kidneys but diminishes progressively as the time following nephrectomy increases; and the inhibitor may be neutralized or exhausted by repeated injns. of plasma containing the sustained pressor principle.