Hypertension and cardiovascular hypertrophy during chronic catecholamine infusion in rats

Chronic continuous infusion of norepinephrine (NE) or epinephrine (Epi) subcutaneously in rats resulted in rapid elevation of systolic blood pressure (SBP) by 40 mm Hg. Pressure remained high for the duration of the infusion but rapidly returned to control levels after its termination. Pronounced hypertrophy of the thoracic aorta, abdominal aorta and heart was evident within 2 days of the initiation of NE infusion and a plateau was attained by 5 days of infusion. The activity of tissue ornithine decarboxylase (ODC), the rate limiting enzyme in polyamine biosynthesis, was elevated preceeding the onset of tissue hypertrophy, and returned to control levels coincidentally with the cessation of accelerated tissue growth. It is concluded that high blood pressure in this animal model of hypertension is dependent upon the continued presence of exogenous catecholamine, and that pronounced cardiovascular hypertrophy per se is not sufficient to maintain the hypertension. The elevation and decline of vascular ODC activity is consistent with reports that in other tissues an elevation of ODC activity is an obligatory early event in hypertrophy.