The effect of secretin on renal haemodynamics in man

Five young males were studied after no overnight fast on 2 separate days with a 3 h intravenous infusion of secretin 2 CU per kg body weight per h in saline and of saline alone. Urinary outputs of water, sodium, potassium, calcium, inorganic phosphate, creatinine and solutes were determined, and the creatinine clearance was calculated. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were determined by constant infusion of [51Cr]EDTA and [125I]o-iodohippurate, respectively. Secretin induced a significant increase in urinary water, sodium, calcium and solute excretion, and a significant decrease in free water clearance. Both creatinine and [51Cr]EDTA clearance rose slightly but non-significantly, whereas [125I]o-iodohippurate increased 2 fold and significantly. This study confirms that secretin has a diuretic effect in man, and it is concluded that this effect is most likely due to impairment of sodium reabsorption in the renal tubule caused by the increase in RPF. Furthermore, this increase in RPF is probably secondary to a direct vasodilatation of the renal arterioles.