Brain Research, 159 (1978) 149-159 149 © Elsevier/North-Holland BiomedicalPress EARLY INCREASE IN PHENYLETHANOLAMINE-N- METHYLTRANSFERASE ACTIVITY IN A NEW STRAIN OF SPONTANEOUSLY HYPERTENSIVE RATS BERNARD RENAUD, SOIZIC FOURNII~RE, LUC DENOROY, MADELEINE VINCENT, JEAN-FRAN(~OIS PUJOL and JEAN SASSARD D~partement de Physiologie et Pharmacologie and (J.-F.P.) D~partement de Mddecine Expdrimentale (INSERM U 171) Universitd Claude Bernard, 69008 Lyon (France) (Accepted April 13th, 1978) SUMMARY By repeated inbreeding, 2 strains of spontaneously hypertensive and normo- tensive rats have been simultaneously selected. The activities of tyrosine hydroxylase and phenylethanolamine-N-methyltransferase were determined in various central catecholaminergic nuclei (C1, C2, A6 and AD) and in two peripheral tissues (adrenal glands and superior cervical ganglion). These assays were performed on rats belonging to the normotensive or the hypertensive strain at 3 ages which characterize the development of hypertension (5, 9 and 21 weeks). Except for a decrease in the C1 region of 9-week-old rats, no significant change in tyrosine hydroxylase activity occurred in central or peripheral structures of the spontaneously hypertensive rats when compared to the normotensive rats. In contrast, the activity of the phenyletha- nolamine-N-methyltransferase (PNMT), was increased in the C2 adrenergic group of the medulla obiongata in young spontaneously hypertensive rats: -F 43 % (P < 0.001) at 5 weeks of age and -F 32% (P < 0.001) in 9-week-old rats. However, there was no significant difference between the 21-week-old rats. No modification of the PNMT activity was found in the C1 adrenergic group of the medulla oblongata. PNMT activity was increased significantly in the adrenal glands of 5-week-old hypertensive rats (~ 22 ~, P < 0.001). By 9 weeks, the difference in PNMT activity in the adrenals was no longer significant. Thus, in young rats of the hypertensive strain, there was an increase in the capacity to synthetize adrenaline in the C2 area of the medulla oblongata and in the adrenal glands. While the enzymatic change present in the adrenals seems to be specific to this new strain of hypertensive rats, the elevation of PNMT activity in a specific region of the medulla oblongata (C2 group) is a characteristic common to at least two independently derived strains of genetically hypertensive rats.