DEMONSTRATION OF BIOLOGICAL-ACTIVITY OF A GROWTH HORMONE-RELEASING HORMONE-LIKE SUBSTANCE PRODUCED BY A PHEOCHROMOCYTOMA

The biological characteristics of a growth hormone-releasing hormone ( GHRH)-like substance produced by a pheochromocytoma were studied. Anal ysis by gel filtration chromatography combined with the use of two dis tinct GHRH antisera that recognize the N- and C-termini of authentic G HRH(1-44)NH2 indicated molecular heterogeneity of the immunoreactive G HRH in the tumor extract, but a component corresponding to GHRH(1-44)N H2 was the predominant form. The biological activity of this immunorea ctive component was assessed in vitro by measuring its ability to indu ce growth hormone release from dispersed rat anterior pituitary cells. At concentrations of 0.125-2.0 nmol/l, the test materials induced a d ose-related increase in growth hormone release from the cells into the incubation medium (range 992 +/- 68-1872 +/- 32 ng . 1.7 x 10(5) cell s-1 . 3 h-1), similar to that observed with synthetic GHRH(1-44)NH, (c ontrol value 640 +/- 30 ng . 1.7 x 10(5) cells-1 . 3 h-1). This sugges ts that immunoreactive GHRH in the tumor has almost the same biologica l activity as the synthetic product and that a combination of pheochro mocytoma and acromegaly is not always fortuitous because both diseases may be caused by a single neoplasm.