ALTERATION OF SENSITIVITY TO VARIOUS REGULATORS IN THE INTESTINE OF THE EEL FOLLOWING SEAWATER ACCLIMATION

Effects of serotonin (5-HT), methacholine (MCh; a muscarinic acetytcholine receptor agonist), eel atrial natriuretic peptide (eANP) and adrenalin (AD) on the transepithelial potential difference (PD), short-circuit current (Isc) and tissue resistance (Rt) across the intestine were compared between seawater (SW) and freshwater (FW) eels. The dose-response curves and the median effective concentrations (EC(50)) of 5-HT, MCh and eANP were not significantly different between SW and FW eels. However, the SW eel intestine was three times more sensitive to AD than FW eels. Cortisol treatment enhanced the AD sensitivity and bumetanide-sensitive Isc, an indicator of Na+-K+-Cl- cotransport activity. These results suggest that cortisol may synthesize AD receptor and Na+-K+-Cl- cotransport system in the intestine following SW acclimation of eels.