Possible functions of oxytocin/vasopressin-superfamily peptides in annelids with special reference to reproduction and osmoregulation

Annetocin is an earthworm oxytocin-related peptide that we previously isola ted from the whole body of a lumbricid earthworm Eisenia foetida. We have r eported that annetocin induces egg-laying-like behaviors in E. foetida and a gnathobdellid leech, Whitmania pigra, when it is injected into the respec tive animals. The present study was undertaken to probe physiological funct ions of invertebrate oxytocin-vasopressin-superfamily peptides with special reference to reproductive and osmoregulatory events in which vertebrate pe ptides of this superfamily are involved. Annetocin, Lys-conopressin (a leec h vasopressin-related peptide) and two analog peptides, [Tyr(3)]-annetocin (Y-3-annetocin) and [Phe(3)]-annetocin (F-3-annetocin), were compared for t heir activities to induce egg-laying-like behavior and to change body weigh t as a measure of water balance in the leech W. pigra. injection of annetoc in, Lys-conopressin, and F-3-annetocin caused both egg-laying-like behavior and reduction of body weight in the animals, but Y-3-annetocin induced nei ther. Furthermore, leeches in the non-breeding season-responded to peptides less conspicuously than those in the breeding season. Such a concomitant i nduction of egg-laying-like behavior and body-weight reduction suggests tha t these two phenomena are unitary and might be accounted for by the fact th at egg-laying in leeches and earthworms is accompanied by secretion of a la rge quantity of mucus, which should significantly contribute to body-weight loss. J. Exp. Zool. 284:401-406, 1999. (C) 1999 Wiley-Liss, Inc.