Effect of exogenous urea on urea metabolism in heat stressed swamp buffalo

Abstract

Effect of exogenous urea on urea metabolism in heat stressed swamp buffalo. In buffaloes during normal ambient temperature given exogenous urea infusion intravenously; the heart rate, respiratory rate, packed cell volume, glomerular filtration rate, plasma concentration of electrolyte, protein and creatinine were not significantly affected. The rate of urine flow, fractional urea excretion, urinary potassium excretion and osmolar clearance significantly decreased on the third hour of urea infusion. The decrease of fractional potassium excretion was concomitant with the reduction of the reduction of the rate of urine flow and urine pH. The renal urea reabsorption markedly increased after urea infusion which had the negative correlation to urine flow rate. Before and during urea infusion in heat exposed animals. The rectal temperature, heart rate and respiratory rate significantly increased. No significant changes in GFR, RBF were noted. After urea infusion, the urine flow rate slightly decreased while renal urea reabsorption, urine pH and fractional electrolyte excretion kept constant. During heat exposure, there were marked increases in concentrations of total plasma protein, albumin and plasma creatinine whereas plasma inorganic phosphorus concentration significantly decreased. It is concluded that an increase in renal urea reabsorption during urea infusion in normal ambient temperature depends on urinary electrolyte excretion. Urea alone has limited diuretic ability. The decrease in urinary electrolytes excretion (e.g. K[superscript +] will affect to the reduction of the rate of urine flow by an osmotic diuretic effect. These changes are insufficient to aid renal urea excretion although an increase in the filtered urea has been determined. In heat stressed animals, renal urea reabsorption is not affected by the decrease in the rate of urine flow, but it depends on an increase in the body pool size of nitrogenous substance which will limit renal urea retention.