Ultrastructural and biochemical evaluation of adrenal medullary hyperplasia and pheochromocytoma in aged bulls.

Abstract

Pheochromocytomas and adrenal medullary hyperplasia were investigated ultrastructurally and by assaying catecholamines in tissue and urine. Three of seven bulls had concomitant thyroid C-cell neoplasms and normal parathyroid glands. Pheochromocytomas were either bilateral or unilateral, and were composed of large chromaffin cells predominantly in the storage phase of the secretory cycle. Two pheochromocytomas were composed of cells with ultrastructural characteristics of the epinephrine-secreting type and contained round secretory granules of low electron density. The norepinephrine-secreting type of chromaffin cell predominated in one pheochromocytoma and had storage granules with an electron-dense, eccentric core and a wide submembranous space. Two pheochromocytomas were composed of a mixture of epinephrine- and norepinephrine-secreting cells. Adrenal medullary hyperplasia in four bulls consisted of multinodular or diffuse areas of hyperchromatic chromaffin cells that were non-encapsulated, and compressed adjacent cortical tissue. Tissue and urinary concentrations of norepinephrine were increased in bulls with adrenal medullary hyperplasia or pheochromocytoma, but urinary vanillylmandelic acid and unconjugated epinephrine levels were not different from those of control bulls with a normal adrenal medulla.