Regional Distribution of Rat Growth Hormone Releasing Factor-Like Immunoreactivity in Rat Hypothalamus*

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Abstract
A heterologous [radioimmunoassay] for rat GH growth factor-releasing factor (rGRF) was established using synthetic rGRF-(1-43)OH for both standard reference and radioiodination with the antiserum produced against human GRF-(1-44) NH2. The regional distribution of rGRF-like immunoreactivity (LI) in rat hypothalamus was examined according to the Palkovits microdissection method and compared with that of somatostatin (STIF)-LI. Both rGRF-and SRIF-LI contents (mean .+-. SE; ng/mg protein) were highest in the median eminence (rGRF, 32.28 .+-. 11.42, SRIF, 109.9 .+-. 19.2) and next most abundant in the arcuate nucleus (rGRF, 3.50 .+-. 0.47; SRIF, 12.88 .+-. 0.60). Only a small amount of rGRF-LI was found in the ventromedial (1.41 .+-. 0.51) and dorsomedial (1.16 .+-. 0.15) nuclei and the anterior hypothalamic area (1.29 .+-. 0.42); rGRF-LI was not detected in the other nuclei of the hypthalamus. A considerable amount of SRIF-LI was contained in the periventricular, ventromedial and paraventricular nuclei and the anterior hypothalamic area, in accordance with other reports. Gel filtration chromatography revealed that hypothalamic extracts contained a major peak of rGRF-LI corresponding to rGRF-(1-43)OH and 2 peaks of SRIF-LI equivalent to SRIF-(1-28) and SRIF-(1-14,) respectively. Evidently rGRF-LI is localized in the median eminence and arcuate nucleus in the rat and that rGRF-, SRIF-(1-28)-and SRIF-(1-14)-LI are present in a 1:2.10:6.29 ratio on a molar basis.