Enzymatic Synthesis of Growth Hormone Releasing Factor (GH-RF) by Rat Incubates and by Extracts of Rat and Porcine Hypothalamic Tissue 1

Abstract

Summary

Incubations of rat hypothalamic fragments and of extracts of rat and porcine hypothalamic tissue found previously to synthesize thyrotropin releasing hormone (TRH), luteinizing hormone releasing factor (LRF) and prolactin releasing factor (PRF) have been used to study the biosynthesis of growth hormone releasing factor (GH-RF). To demonstrate synthesis, GH-RF was measured by the elevation of radioimmunoassayable growth hormone in the estrogen-progesterone-reserpinized male rat. GH-RF is synthesized by rat hypothalamic fragments incubated in Krebs-Ringer bicarbonate buffer under an atmosphere of 95% oxygen and 5% carbon dioxide and by extracts of rat and porcine hypothalamic tissue in the presence of amino acids, ATP and Mg²⁺. This synthesis is not blocked by puromycin, indicating that the synthesizing system may not be ribosomal dependent. Further proof of a nonribosomal mechanism comes from the fact that a ribosomal-free extract also synthesizes GH-RF. From these observations, it may be concluded that GH-RF is also formed enzymatically by a nonribosomal mechanism.