Tissue distribution and molecular forms of a novel pituitary protein in the rat

A sensitive and specific radioimmunoassay (RIA) was developed for a novel pituitary protein that we recently isolated from human and porcine pituitary gland and designated 7B2. By employing this RIA, we were able to detect and assay this novel protein in different rat tissue extracts. The concentrations of 7B2 in rat anterior pituitary lobe, neurointermediate lobe, hypothalamus, adrenal medulla and thyroid gland were 10,400 +/- 804; 6,190 +/- 908; 773 +/- 50; 697 +/- 83 and 1,368 +/- 116 pg/mg tissue (wet weight, n = 10, mean +/- SEM), respectively. However, the concentrations of 7B2 were lower than 30 pg/mg tissue in extracts of pancreas, ileum and colon, and were below the sensitivity of the RIA in extracts of liver, kidney, spleen, lung, adrenal cortex and testis. Gel permeation chromatography of extracts of anterior pituitary lobe, neurointermediate lobe, hypothalamus, adrenal medulla and thyroid gland on Sephadex G-100 revealed that most of the immunoreactive (Ir)-7B2 has an apparent molecular weight of 45,000-50,000. Subsequent dissociation of this Ir-7B2 by polyacrylamide gel electrophoresis containing sodium dodecyl sulfate (SDS) yielded an Ir-7B2 with an apparent molecular weight of around 19,000. In addition, high K+ concentration (50 mM) induced the release of Ir-7B2 from cultured cells of both rat anterior pituitary and neurointermediate lobe. Finally, Ir-7B2 was detected in the neurosecretory granule fraction prepared from porcine neurointermediate lobe. These results indicate that 7B2 may be a novel secretory protein in the pituitary gland.