CORLEY, C.A.*; KRAJNIAK, K.G.: The Effects of Catecholamines on the Isolated Earthworm Crop-gizzard

The isolated crop-gizzard of the earthworm, Lumbricus terrestris, responds to a variety of neurotransmitters including acetylcholine, serotonin, and FMRFamide. Since catecholamines also can affect the motility of digestive tracts in other animals, we decided to examine the effects of the catecholamines dopamine, epinephrine, norepinephrine, and octopamine. The crop-gizzard was removed from the animal, attached to a smooth muscle transducer, and exposed to various concentrations of neurotransmitter. Dopamine caused a biphasic response in both the contraction rate and amplitude. There was a decrease in both contraction rate and amplitude with a threshold of 10^-6 M and an increase in both contraction rate and amplitude with a threshold of 10^-7 M. Both epinephrine and norepinephrine initiated increases in amplitude with a threshold of 10^-8 M and a slight increase in contractile rate throughout the concentration range. Octopamine was found to elicit a biphasic response in rate, characterized by an increase with a threshold of 10^-10 M and a decrease with a threshold of 10^-7 M, and a decrease in overall amplitude (threshold at 10^-8 M). Theses data suggest that the catecholamines may be involved in regulation of earthworm digestive tract smooth muscle. We are currently examining how the crop-gizzard responds to alpha and beta agonists.