Meeting Abstract
Previously we showed that annetocin, an earthworm member of the oxytocin/vasopressin family of peptides, caused an increase in the contraction rate and amplitude of the isolated crop-gizzard from the earthworm Lumbricus terrestris. Since this experiment examined the response of longitudinal muscles in these organs we decided to examine the effects of these peptides on the circular muscles in the gizzard for comparison. After removal from the worm the gizzard was cut into rings which contained intact circular muscle. One end of the ring was attached to a support in a tissue bath and the other end was connected to a force-transducer. Mechanical contractions were recorded on a computer using an Iworx A/D converter and Labscribe 2 software. Increasing concentrations of peptide were added to the bath and changes in contraction rate and amplitude were used to create log-concentration curves. Annetocin caused an increase in both rate with a threshold of 10-8 M and amplitude with a threshold of 10-9 M. Oxytocin caused an increase in rate with a threshold of 10-7 M and no change in amplitude. Vasotocin caused an increase in both rate with a threshold of 10-8 M and amplitude with a threshold of 10-9 M. Both arg-vasopressin and lys-vasopressin caused an increase in rate with a threshold of 10-6 M and no change in amplitude. These data suggested the following rank in potency: oxytocin>anntecoin =vasotocin>arg-vasopressin=lys-vasopressin. This is similar to the potency rank for the longitudinal muscle of the crop-gizzard: anntecoin>oxytocin> vasotocin =lys-vasopressin=arg-vasopressin. In both cases the receptor prefers the oxytocin like peptides more than the vasopressins. The slight differences in potency may be due to the fact that longitudinal muscle study used both the crop and the gizzard combined.
