SUMMARY The New England Deaconess Hospital (NEDH) rat provides a ratable model with which to study pbeochromocytoma (P); 59% of male rats 700 to 900 days old and 81% of those 900 days or older dereloped spontaneous P. One transplantable P (P259), when implanted into other NEDH rats, markedly increased plasma norepiuephrine and dopamine as well as blood pressure, and usually caused death within 4 weeks. Even without P, about 83% of NEDH rats became hypertensive by 13V4 weeks of age and remained moderately hypertensive until 2 years of age when some animals developed spontaneous P and hypertension became severe. Whether a common mechanism Is responsible for early appearance of hypertension and later development of P remains to be determined. Hypopfaysectomized NEDH rats remained normotensire or slightly hypotenslve despite marked elevations of plasma norepinephrine and dopamine caused by P259 implantation; furthermore, survival was prolonged to 3 months. Catecholamine concentrations in plasma and RBC were usually quite similar, indicating that red blood cells play a significant role in inactivating circulating catecholamines. Unlike the normal adrenal, P259 in NEDH rats contains mainly norepinephrine and dopamine with little epinephrine; it appears that P259 is deficient in the enzyme pbenylethanolaniine-N-methyltransferase (PNMT), which converts norepinephrine to epinephrine. Why hypophysectomy prevents hypertension and prolongs life in rats with P259 implants is unclear; adrenal cortical and thyroid deficiency may play a role. Preliminary observations indicate that hypophysectomy can prevent spontaneous development of P in NEDH rats. T HE New England Deaconess Hospital (NEDH) rat (Wistar related) provides a valuable model for studying pheochromocytoma (P). Spontaneous P occurs in NEDH rats especially with aging. P almost always arises in the adrenal medulla and about 50% occur bilaterally; very rarely it occurs in the organ of Zuckerkandl. Others'-* have reported an increased incidence of P in Wistar rats, up to 85% in old males.1 Warren and Chute* established a transplantable P (P259) from a spontaneous P. When implanted in NEDH rats (other strains reject P259) it will grow rapidly and secrete catecholamines; it causes hypertension, cardiovascular lesions, weight loss, and death usually within 1 month.
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