Atrial natriuretic factor and cyclic guanosine monophosphate: Ion transport in rat colon in vitro and in vivo

Abstract The role of atrial natriuretic factor receptors in the colon is uncertain. Accordingly, the effects of atrial natriuretic factor in vivo and in vitro were studied. In vivo perfusion of the colon in Sprague-Dawley rats was used to measure Na + , K + , Cl − , and water transport, while atrial natriuretic factor was infused into the jugular vein at 0.5 or 1.0 μg · kg −1 · min −1 . In vitro experiments in Ussing chambers measured short-circuit current and ion fluxes before and after atrial natriuretic factor administration. Because cyclic guanosine monophosphate is thought to be a second messenger for atrial natriuretic factor, shortcircuit current was also determined before and after exposure to 8-Br-cyclic guanosine monophosphate. Plasma atrial natriuretic factor (atriopeptin III) levels were determined by radioimmunoassay. The in vivo transport of water, sodium, and chloride and the secretion of potassium were not altered by atrial natriuretic factor infusion. In vitro studies showed no change in Na + or Cl − transport or change in short-circuit current. Plasma atrial natriuretic factor concentrations increased from 139 ± 55 pg/mL to 1385 ± 396 pg/mL during infusion, and urine output increased from 12.6 ± 0.5 μL/min to 37.4 ± 2.9 μL/min ( P P = 0.0004) increase in short-circuit current from 1.2 ± 0.2 to 2.9 ± 0.3 μEq · cm −2 · h −1 .