Distribution of Growth Hormone-Releasing Hormone Like Immunoreactivity in Human Tissue Extracts*

Abstract

A specific RIA for human pancreatic tumor GH- releasing hormone [hpGRH(1-44)NH₂] was developed using an antiserum which recognizes the region (Met²⁷-Leu⁴⁴)NH₂ of hpGRH(1-44)NH₂. This RIA was used to measure GH-releasing hormone-like immunoreactivity (GRH-LI) in various human tissue extracts. The highest concentration of GRH-LI was detected in extract of pituitary stalk with moderate amounts found i n hypothalamus and optic chiasm but none in the cerebrum, cerebellum, medulla oblongata, spinal cord, and anterior pituitary. In peripheral organs appreciable quantities of GRH-LI were found in the pancreas, whereas extracts of thyroid, lung, stomach, duodenum, ileum, colon, adrenal, and kidney contained very low concentrations of GRH-LI. No GRH-LI was detected i n liver and spleen extracts. Gel permeation chromatographic analysis of the tissue extract from the hypothalamus revealed only one peak which eluted at the same position as that of ¹²⁵-I hpGRH(l-44)NH₂. Similar analysis of an extract from the optic chiasm showed one peak at the same position as that of ¹²⁵-I hpGRH(1-44)NH₂ and another peak which eluted after hpGRH(1-44)NH₂.In contrast, an extract from the pancreas contained only one peak which eluted before ¹²⁵I-hpGRH(1-44)NH₂, indicating a possible precursor form of hpGRH(1-44)NH₂. Limite d trypsin digestion of the GRH-LI material from the pancreas, followed by gel permeation chromatographic analysis, yielded a major peak eluting at the same position as that of ¹²⁵I-hpGRH(1-44)NH₂. These results suggest that the GRH- I-hpGRH(1-44)NH₂. LI detected in the hypothalamus most likely corresponds to hpGRH(1-44)NH₂ in structure and that the GRH biosynthesized n i the hypothalamus is transported to the stalk median eminence and stored there for release into the portal vessels.