Effect of secretin on glomerular dynamics in dogs.

These studies were performed to determine whether a role for increased renal plasma flow (RPF) in the regulation of glomerular filtration rate (GFR) could be demonstrated in dogs by infusing the polypeptide hormone secretin, a vasodilator that has been reported to increase GFR. Differences between control and recollection periods were compared by paired t test in five time-control dogs (group 1) and 10 secretin dogs (group 2). In group 2, secretin (100 mU . kg-1 . min-1, ia) significantly increased single-nephron glomerular filtration rate (SNGFR) 11.1 +/- 3.1 nl/min (20%) and glomerular plasma flow 59 +/- 11 nl/min (26%). Similar increases in GFR (26%) and RPF (29%) were observed. Secretin also increased glomerular capillary pressure 5.2 +/- 0.8 mmHg and free-flow proximal tubule pressure 5.5 +/- 1.0 mmHg. Secretin did not significantly affect average effective filtration pressure (EFP) but significantly increased the ultrafiltration coefficient (Kf) 0.74 +/- 0.14 nl . min-1 . mmHg-1. These differences were significantly greater than those observed in group 2. It is concluded that secretin increased SNGFR primarily by an effect on Kf. This is consistent with the marked effect that Kf is predicted to have on glomerular filtration in dogs. The maintenance of EFP agrees with other vasodilator studies and indicates that GFR is only moderately dependent on plasma flow in dogs.