EFFECTS OF ENDOTHELIN ON FLUID AND NACL ABSORPTION ACROSS THE JEJUNUMIN ANESTHETIZED DOGS

The aim of the present study was to investigate the effects of endothe lin (ET) on fluid and NaCl absorption across the jejunum. Dogs were an esthetized with pentobarbital sodium (30 mg/kg i.v.). Polyethylene cat heters were placed in the superior mesenteric arteries and portal vein for infusions and to measure arterial and portal venous pressure. Sup erior mesenteric arterial blood flow was continuously measured with an ultrasonic flow probe. A 30-cm-long jejunal loop was made at 10 cm fr om the duodenal fossa. Infusion of saline, ET-1, ET-3, or phenylephrin e (PE) was initiated 10 min before pouring the test solution into the jejunal loop and continued for 25 min. The net fluid (7.2 +/- 0.9 ml, mean +/- SE, n = 8), Na+ (1.1 +/- 0.1 mEq), and Cl- (1.1 +/- 0.2 mEq) absorption during saline infusion was not significantly different from those (7.0 +/- 1.0 ml, 1.1 +/- 0.1 mEq, and 1.1 +/- 0.2 mEq) during E T-1 infusion but was significantly decreased to 4.8 +/- 0.6 ml, 0.7 +/ - 0.1 mEq, and 0.7 +/- 0.1 mEq by ET-3 infusion. ET-1 increased the me senteric vascular resistance by 84.7 +/- 23.4% and ET-3 by 64.3 +/- 7. 5%. To study the underlying mechanisms, the absorption experiment was performed after the increase in vascular resistance and administration of nitric oxide (NO) synthase inhibitor. We increased the resistance by 127.8 +/- 12.6% with PE and found no effect. Pretreatment with NO s ynthase inhibitor did not influence the decreased absorption induced b y ET-3. In conclusion, ET-3 suppresses jejunal absorption. This is not due to an increase in vascular resistance, and NO is not involved in this mechanism.