Water metabolism in the eel acclimated to sea water: from mouth to intestine.

Eels seem to be a suitable model system for analysing regulatory mechanisms of drinking behavior in vertebrates, since most dipsogens and antidipsogens in mammals influence the drinking rate in the seawater eels similarly. The drinking behavior in fishes consists of swallowing alone, since they live in water and water is constantly held in the mouth for respiration. Therefore, contraction of the upper esophageal sphincter (UES) muscle limits the drinking rate in fishes.

Central effects of various ligands on drinking behavior in eels acclimated to seawater.

Intracranial injection of eel angiotensin II (eANG II, 5x10(-13)-5x10(-8) mol), acetylcholine (ACh, 5x10(-12)-5x10(-9) mol), substance P (5x10(-10) mol) and isoproterenol (a beta-adrenoceptor agonist, 5x10(-11)-5x10(-9) mol) enhanced water intake in the seawater eel. The effects of eANG II, ACh and isoproterenol were dose-dependent. By contrast, water intake was inhibited by intracranial injection of eel atrial natriuretic peptide (eANP, 5x10(-13)-5x10(-10) mol), serotonin (5-HT, 5x10(-12)-5x10(-8) mol), ghrelin (5x10(-12)-5x10(-10) mol), gamma-amino butyric acid (GABA, 5x10(-11)-5x10(-8) mol), prolactin (PRL, 5x10(-10)-5x10(-9) mol), arginine vasotocin (AVT, 5x10(-12) mol), vasoactive intestinal peptide (VIP, 5x10(-11) mol), noradrenaline (5x10(-9) mol l(-1)) and phenylephrine (alpha-adrenoceptor agonist, 5x10(-11)-5x10(-9) mol).