Identification of luteinizing hormone-like proteins in the ovine pineal gland.

A chemical analysis was instigated to investigate the identity of the luteinizing hormone (LH)-like immunoactivity present in ovine pineal protein homogenates. Isolation of pineal LH-like material was accomplished using a 0.1 M ammonium sulphate (pH 4.0) extraction followed by anion-exchange chromatography. The resulting 3.0 M ammonium sulphate precipitate containing 70% of the LH-like immunoactivity was refractionated by cation-exchange and Sephadex G-100 chromatography. Analysis of the pattern of recovered LH-like immunoactivity in the Sephadex G-100 eluate indicated the presence of molecular weight (MW) less than 60,000 besides MW 21,000 species of LH-like proteins. Bioactivity was tested in the rat Leydig cell steroidogenesis assay. In terms of steroid production, the activity was associated with the MW 21,000 LH-like proteins only. Further purification by CM-Sephadex chromatography and gel permeation HPLC was conducted in order to determine whether the physicochemical properties of pineal LH-like material represented endogenous LH, synthesized and released by the ovine pituitary. It is concluded by a variety of means, including polyacrylamide gel electrophoresis, and amino acid and carbohydrate analyses, that at least two molecular forms of immunoactive LH-like proteins occur in ovine pineal tissue. The MW 21,000 forms showed much similarity with ovine adenohypophyseal LH or with a complex mixture of its subunits. These observations contribute to the understanding of endocrine-endocrine transducing events that may occur in this organ.