Strain differences in distribution of phenylethanolamine N-methyltransferase activity from rat brain and adrenal gland

Phenylethanolamine N-methyltransferase (PNMT) activity was measured in adrenal glands and medulla oblongata from 4 inbred rat strains, Fischer 344, Buffalo, Lewis and Sprague-Dawley rats. Adrenal enzyme activity was markedly different among the strains with the highest in Fischer, followed by Sprague-Dawley, Lewis and Buffalo rats in decreasing order. In medulla oblongata, the PNMT activity of Buffalo rat was the lowest being about one half of that of the other strains. Despite differences in the enzyme activity, immunotitration results indicate that there is no immunochemical difference between adrenal or medulla oblongata PNMT among the strains. Furthermore, the strain differences in the activity are not due to presence of an inactive enzyme, but to the amount of the enzyme. Our preliminary findings by dot blot hybridization, using a ³²P-labeled cDNA probe for PNMT suggest that differences in adrenal and medulla oblongata PNMT activity between Fischer and Buffalo rats are partially due to differences in the amount of PNMT mRNA present.