Effects of exogenous urea infusion on glucose metabolism in acute heat stressed swamp buffaloes

Abstract

Effects of exogenous urea infusion on glucose metabolism in acute heat stressed swamp buffaloes. Five buffaloes kept in normal ambient temperature showed no significant changes in the heart rate, respiratory rate, packed cell volume, glucose turnover rate, glucose pool size, glucose clearance, glomerular filtration rate (GFR), effective renal plasma flow (ERPF), plasma concentration of electrolytes, protein and creatinine during intravenous infusion of urea for 4 h. The rate of urine flow, fractional urea excretion, urinary potassium excretion and osmolar clearance significantly decreased on the 4 h. of urea infusion. The decrease of fractional potassium excretion was concomitant the reduction of the rate of urine flow and urine pH. The renal urea reabsorption markedly increased during urea infusion. In animals exposed to heat, the rectal temperature, heart rate and respiratiory rate significantly increased. The turnover rate of both U-[superscript 14]C glucose and 3-[superscript 3]H glucose markedly increased while the reduction of glucose carbon recycling was observed. Plasma glucose concentration significantly increased during heat exposure but no significant changes in GFR and ERPF were noted. An intravenous infusion of urea in heat exposed animals caused the reduction of qlucose turnover rate and glucose clearance while plasma glucose concentration progressively increased. Glucose carbon recycling slightly increased during exogenous urea infusion. The rate of urine flow decreased while renal urea reabsorption, urine pH and fractional electrolyte excretions showed no significant changes. During heat exposure, there were marked increases in concentrations of total plasma protein and plasma creatinine whereas plasma inorganic phosphorus concentration significantly decreased. It is concluded that glucose production and utilization increased in animals exposed to heat but the interference of utilization occurred during urea infusion. An increase in renal urea reabsorption during urea infusion in buffaloes kept in normal ambient temperature depends on the rate of urine flow which affect by an osmotic diuretic effect of electrolytes. The limitation of renal urea reabsorption in heat stressed animals would be attributed to an increases in either plasma pool size of nitrogenous substance or body metabolism.