Quantitation of uncombined gonadotropin subunits within and released by the rat anterior pituitary

Abstract

Abstract. The release of uncombined gonadotropin subunits by rat anterior pituitaries during an in vitro incubation as well as intracellular concentrations were assessed. Uncombined subunits and native gonadotropins were quantitated by radioimmunoassays after samples were subjected to gel filtration on Sephadex G-100 Superfine. Small, but detectable, amounts of uncombined rat LH β subunit were released under basal conditions. GnRH increased the absolute amount of rLHβ released but did not alter the rLHβ/rLH molar ratio (≈ 0.02). Tissue extracts prepared in aqueous buffer (100 000 × g supernatants) and 0.5% Triton X-100 extracts of the 100 000 × g pellets from the initial homogenization ('pellet extracts') contained larger quantities of uncombined rLHβ as well as elevated rLHβ/rLH molar ratios (≈ 0.10 and ≈ 0.20, respectively). Significant amounts of uncombined rLHα were released and were present in both tissue and pellet extracts. However, when FSH β subunit was quantitated in tissue extracts after gel filtration, all of the immunoreactive materials eluted in the position of native rFSH (FSHβ/rFSH molar ratio < 0.0025). Pellet extracts contained significant amounts of rLHβ, rLH and rLHα but lesser amounts of rFSH suggesting that intracellular gonadotropins are not completely extracted when homogenization is performed in aqueous buffers. Thus, rat anterior pituitaries contain and release significant amounts of the uncombined α subunit, relatively small amounts of uncombined rLHβ and extremely small amounts of uncombined FSHβ, if any.