The biological characteristics of a growth hormone-releasing hormone (GHRH)-like substance produced by a pheochromocytoma were studied. Analysis by gel filtration chromatography combined with the use of two distinct GHRH antisera that recognize the N- and C-termini of authentic GHRH(1–44)NH2 indicated molecular heterogeneity of the immunoreactive GHRH in the tumor extract, but a component corresponding to GHRH(1–44)NH2 was the predominant form. The biological activity of this immunoreactive component was assessed in vitro by measuring its ability to induce growth hormone release from dispersed rat anterior pituitary cells. At concentrations of 0.125–2.0 nmol/l, the test materials induced a dose-related increase in growth hormone release from the cells into the incubation medium (range 992±68–1872±32 ng·1.7×105 cells−1·3 h−1), similar to that observed with synthetic GHRH(1–44)NH2 (control value 640±30 ng·1.7× 105 cells−1·3 h−1). This suggests that immunoreactive GHRH in the tumor has almost the same biological activity as the synthetic product and that a combination of pheochromocytoma and acromegaly is not always fortuitous because both diseases may be caused by a single neoplasm.
