Distribution of catechol-O-methyltransferase enzyme in rat tissues

In the present study we show the distribution of catechol-O- methyltransferase (COMT) in various rat tissues with a highly specific antiserum prepared against recombinant rat COMT. Immunoprecipitation and immunocytochemical 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 enzyme was found in most rat tissues. Staining was most intense in the liver and in the kidney, in agreement with previous studies and our immunoblotting results. In the gastrointestinal tract, epithelial cells of the stomach, duodenum, and ileum were immunoreactive for COMT. In pancreas, COMT immunoreactivity was found in insulin-producing β-cells and somatostatin-producing D-cells but not in glucagon-producing α-cells of the islets of Langerhans. In pituitary, COMT immunoreactivity was found in cleft 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 found in epithelial cells of the thyroid gland and in zona glomerulosa of the adrenal cortex. In the brain, brightest immunofluorescence was seen in ependymal cells of the cerebral ventricles and choroid plexus. Weak to moderate immunofluorescence was found in the neuropil of several brain areas, including striatum and cortex. Scattered small neurons in spinal sensory ganglia were also COMT immunoreactive. Previous immunocytochemical studies, enzyme activity determinations, and distribution of the COMT mRNA are in general agreement with the results presented here. The wide distribution of COMT in different tissues suggests an important role for this protein in inactivation of catechol compounds.