THE EFFECTS OF PRESSOR DRUGS AND OF SALINE KIDNEY EXTRACTS ON BLOOD PRESSURE AND SKIN TEMPERATURE 1

Abstract

An oscillometric method of studying peripheral vascular changes in the unanesthetized, warmed rabbit is descr. Oscillometric determinations of systolic blood pressure in the auricular artery were compared with simultaneous measurements by direct cannulation of the opposite auricular artery. In control expts. the slow injection of 0.9% NaCl soln. produced no significant variations in peripheral circulation. Epinephrine, tyramine, pituitrin, pitressin, guanidine, methylguanidine, dimethylguanidine, ergotoxine and ergotamine elevated blood pressure but always decreased skin temp. with varying degrees of vasoconstriction in the ear of the heated rabbit. The temporary hypertension produced by these substances was associated with a disproportionate increase of peripheral resistance and a decrease of blood flow through the auricular vessels. "Unheated kidney extracts" elevated blood pressure occasion- ally, reduced blood pressure more frequently, and always reduced skin temp. Many of the "unheated kidney extracts" were toxic. Heating the original saline kidney extracts to between 55[degree] and 56[degree]C for 20 min. precipitated considerable protein, and subsequent filtration at or near 55[degree]C produced a clear yellowish solution which elevated blood pressure without diminishing skin temp. and without reducing the amplitude of arterial pulsation. Peripheral blood flow was not measurably decreased at any time during the pressor response; a slight increase of peripheral blood flow could not be excluded by the methods used. In agreement with earlier studies, the pressor activity of kidney extracts was destroyed by heating to 65[degree]C for 20 min.; the pressor substance did not dialyze or pass through an ultrafilter. Saturation of heated (55-56[degree]C) extracts with (NH4)2SO4 yielded a precipitate which, after solution and dialysis, also produced a conspicuous rise of b. p. without diminishing peripheral blood flow. Certain properties of this material are compared with those of "renin" descr. by earlier investigators. Suitably heated kidney extracts, and a protein-like material precipitated from such extracts, were the only pressor substances which elevated b. p. without decreasing peripheral blood flow, a relationship which is characteristic of certain forms of human hypertension.