INCREASED ADRENAL CATECHOLAMINE TURNOVER IN RATS BEARING PHEOCHROMOCYTOMA

A rat model of pheochromocytoma (PHEO) was used to study various amine s and their possible role in either promoting or protecting against hy pertension associated with this condition. Rats were inoculated with P C-12 cells. After 3 and 6 weeks, urine samples were collected and the catecholamine concentrations were measured. Urinary norepinephrine (NE ) and dopamine (DA) was increased 15- and 8-fold, respectively, after 3 weeks and 60- and 23-fold, respectively, after 6 weeks. Epinephrine (EPI) was not significantly changed after 3 weeks but was increased by 48% at 6 weeks. The urinary excretion of 3-methoxy-4-hydroxyphenylgly col (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), metabolites of NE and EPI, were also significantly elevated, but the corresponding metaboli te of octopamine, p-hydroxyphenylglycol, was not significantly changed . One to two weeks later, following pentobarbital anesthesia, measurem ent of the heart rate revealed a significant increase in the tumor-bea ring rats but the blood pressure was not significantly increased. Plas ma catecholamine measurements showed the greatest increase in DA, 812- fold; NE was increased 158-fold and EPI was increased 35-fold. Adrenal DA levels were increased and NE and EPI were decreased, suggesting th at the adrenal medulla has an increased catecholamine turnover.