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.

The diuretic effect of secretin in man.

Six young healthy male students were studied with an intravenous infusion of 50 ml/h saline for three 2 h periods. In the second 2 h period pure natural secretin was added to the saline infusion in a dose of 2 CU/kg . h. Urine was collected separately in the three 2 h periods, and blood was drawn every 1 h. Urinary water, sodium, potassium, chloride, calcium, creatinine and solute excretion increased significantly during the 2-h secretin period. The clearance of sodium, potassium, chloride, calcium and solutes as a percentage of glomerular filtration rate (creatinine clearance) increased significantly, whereas tubular reabsorption of sodium as a percentage of filtrated sodium decrased significantly during secretin infusion. Even though plasma secretin remained elevated in the first half of the last 2 h control period, no diuretic effect was noted in this period. It would appear therefore that the diuretic effect of secretin most likely is a pharmagological effect only.