We first examined the activities of extracellular signal-regulated kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs) in the aorta of hypertensive rats. In Dahl salt-sensitive (DS) rats, chronic hypertension caused by a high-salt diet was followed by sustained activation of aortic p42ERK and p44ERK. p46JNK and p55JNK activities were also increased in hypertensive DS rats, but returned to control levels earlier than ERKs, suggesting that ERKs and JNKs may be independently activated in hypertensive rats. In stroke-prone spontaneously hypertensive rats (SHRSP) which spontaneously develop hypertension under a low salt-diet, aortic p42ERK and p44ERK activities were progressively increased with the development of hypertension, compared with control normotensive rats. p46JNK and p55JNK activities in SHRSP were increased, with a different time course from ERKs. Thus, we first demonstrated that ERKs and JNKs activities are chronically and differentially increased in the aorta of hypertensive rats, suggesting the involvement of these kinases in hypertensive vascular diseases. (C) 1997 Academic Press.