Regulation of renal function in hypothermia

Abstract

During steady-state body temperature of 25 C in the anesthetized dog many renal functions are reduced in parallel. All measured urinary constituents approach their plasma concentrations. Reabsorption of the major ions is reduced but some distal segment reabsorption of salt remains and urea reabsorption is actually increased. A greater percentag of filtered water appears in the urine but there is still some effect of ADH [anti-diuretic hormone] on net water excretion. Renal plasma flow (CPAH) and glomerular filtration rate (creatinine) are reduced proportionately so that filtration fraction is unaffected. Although TmPAH [thermal dissociation rate of paramino-hippurate] is considerably smaller and there is more splay in the PAH titration curve, tubular perfusion (effective renal blood flow/TmPAH) is unchanged from control (37 C) value. Renal O2 consumption falls 58% but renal blood flow/VO2 [O2 uptake] is constant at the 2 temperatures. The Na/O2 ratio, calculated from this and earlier data, shows no essential difference in the "cost" of Na reabsorption at 37 or 25 C.