DISTRIBUTION OF ENKEPHALIN IMMUNOREACTIVITY IN SYMPATHETIC PREVERTEBRAL GANGLIA AND DIGESTIVE-TRACT OF GUINEA-PIGS AND RATS

The aim of the present study was to determine the distribution of meth ionine-enkephalin (ME) and leucine-enkephalin (LE) immunoreactivity in the sympathetic prevertebral ganglia (coeliac plexus and inferior mes enteric ganglion) and in the myenteric plexus-muscular layer complex o f the digestive tract in guinea-pigs and rats. This study was performe d using the same immunological approaches including radioimmunoassays and HPLC characterization as those used previously on cats in order to be able to make inter-region and inter-species comparisons. In rat an d guinea-pig prevertebral ganglia, the distributions of the enkephalin immunoreactivities were comparable and were characterized by a low ME /LE concentration ratio, of less than 1. In the digestive tract of rat s, the enkephalin immunoreactivities were homogeneously distributed, w hereas in guinea-pigs, they were found to be very low in the lower oes ophageal sphincter and high in the duodenum. In both species, the ME/L E concentration ratio was around 2. The ME/LE concentration ratio dete rmined in the present study in peripheral nervous structures was much lower than that determined previously in the rat brain. Radioimmunoass ay and biochemical data might indicate that different mechanisms are r esponsible for the processing and/or degradation of enkephalins in the central and peripheral nervous systems. The present study provides fu rther evidences that there are tissue- and species-dependent differenc es in the distribution of enkephalin immunoreactivities. These differe nces should be taken into consideration when dealing with the effects and the role of enkephalins in the nervous control of intestinal motil ity in mammals.