Abstract

A heterologous RIA for rat GH-releasing factor (rGRF) was established using synthetic rGRF-(l–43)OH for both standard reference and radioiodination with the antiserum produced against human GRF-(l–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 somatostatih (SRIF)-LI. Both rGRF- and SRIF-LI contents (mean ± se; nanograms per 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), whereas rGRF-LI was not detected in the other nuclei of the hypothalamus. A considerable amount of SRIF-LI was contained in the periventricular, ventromedial, and paraventriciilar 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-(l–43)OH and two peaks of SRIF-LI equivalent to SRIF-(l–28) and SRIF-(1–14), respectively. These findings indicate that rGRF-LI is localized in the median eminence and arcuate nucleus in the rat and that rGRF-, SRIF-(l-28)-,and SRIF-(1–14)-LI are present in a 1:2.10:6.29 ratio on a molar basis. (Endocrinology116: 259–262, 1985)

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