Immunoreactive and Biologically Active Growth Hormone-Releasing Factor in the Rat Placenta*

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Abstract
Rat placentas from fetuses of 18 and 20 days of gestation were collected, extracted, and examined for their capacity to stimulate GH release in vitro. The crude extract stimulated, in a dose-dependent fashion, GH release by rat anterior pituitary cells in monolayer culture. The biological and immunological activities retained on antirat GH-releasing factor immunoaffinity columins eluted on Sephadex G-75 (fine) columns with an estimated mol wt of 5000 daltons. Reverse phase HPLC of this material revealed the presence of two forms of GRF activity that eluted with retention times identical to those of synthetic rat GRF and its methionine sulfoxide counterpart [Met(O)27]GRF. The results demonstrate the presence of an immunoreactive and biologically active GRF in the rat placenta that is indistinguishable from rat hypothalamic GRF.