Effect of water deprivation, desmopressin (DDAVP) infusion, and oral loads of water, Na + and NH 4+ on urinary excretion of epidermal growth factor in the rat

Abstract

Epidermal growth factor (EGF) is synthesized in the kidneys and excreted in urine. Administration of exogenous EGF modulates the reabsorption of Na + and the vasopressin stimulated reabsorption of water in the collecting tubules. In order to clarify whether this reflects a physiological role for urinary EGF we examined the effects of changes in the oral loads of water, Na + and NH 4 + as well as the effect of infusion of the vasopressin analogue, desmopressin (DDAVP) on the endogenous urinary EGF excretion in the rat. Water deprivation for 48 h reduced the urinary excretion of EGF by 25% and the urinary EGF/creatinine ratio by 8%. Also, urinary volume, Na + excretion, and urinary pH were reduced by water deprivation. Infusion of DDAVP, low plasma vasopressin induced by polydipsia, and changes in the renal excretion of Na + and H + did not affect the urinary excretion of EGF. In conclusion: it seems unlikely that nephrogenous EGF excreted in the urine plays a physiological role in the regulation of the renal excretion of Na + and H + and in the vasopressin stimulated reabsorption of water in the rat. However, since water deprivation reduced the urinary excretion of EGF it remains possible that urinary EGF plays a role in the complex physiological response to dehydration.