DISTRIBUTION OF CATECHOL-O-METHYLTRANSFERASE ENZYME IN RAT-TISSUES

In the present study we show the distribution of catechol-O-methyltran sferase (COMT) in various rat tissues with a highly specific antiserum prepared against recombinant rat COMT. Immunoprecipitation and immuno cytochemical controls confirmed the COMT-specificity of the antibodies . The antiserum detected both the 24 KD soluble and the 28 KD membrane -bound forms of the enzyme. By immunohistochemical staining the COMT e nzyme was found in most rat tissues. Staining was most intense in the liver and in the kidney, in agreement with previous studies and our im munoblotting results. In the gastrointestinal tract, epithelial cells of the stomach, duodenum, and ileum were immunoreactive for COMT. In p ancreas, COMT immunoreactivity was found in insulin-producing beta-cel ls and somatostatin-producing D-cells but not in glucagon-producing al pha-cells of the islets of Langerhans. In pituitary, COMT immunoreacti vity was found in deft cells, in pituicytes of the posterior lobe, and in the anterior lobe, partly in the same cells containing luteinizing hormone (LH). In other endocrine organs, COMT immunoreactivity was fo und in epithelial cells of the thyroid gland and in zona glomerulosa o f the adrenal cortex. Tn the brain, brightest immunofluorescence was s een in ependymal cells of the cerebral ventricles and choroid plexus. Weak to moderate immunofluorescence was found in the neuropil of sever al brain areas, including striatum and cortex. Scattered small neurons in spinal sensory ganglia were also COMT immunoreactive. Previous imm unocytochemical studies, enzyme activity determinations, and distribut ion of the COMT mRNA are in general agreement with the results present ed here. The wide distribution of COMT in different tissues suggests a n important role for this protein in inactivation of catechol compound s.