Corticotropin-releasing factor and vasopressin production in the rat pituitary tumor 7315a: biochemical and immunohistochemical studies.
In order to investigate the production and secretion of hypothalamic factors by the prolactin and proopiomelanocortin (POMC)-derived, peptide-producing, transplantable rat pituitary tumor 7315a, we determined the concentrations of corticotropin-releasing factor (CRF)- and vasopressin (AVP)-like immunoreactivities (IR) in the tumor extracts [14.0 +/- 1.6 (SE) and 4.2 +/- 0.9 pmol/g, respectively] and incubation media (0.26 +/- 0.01 and 0.07 +/- 0.01 pmol/10(7) cells/h, respectively). Total peptide content correlated well with tumor weight. Moreover, there is a very good correlation between the CRF and AVP IR, but not as good between CRF or AVP IR and POMC peptide IR tumor contents. Tumor extracts were chromatographed on Sephadex G-75 and compared with chromatograms of stalk median eminence (SME) extracts from normal Buffalo rats. CRF IR in tumor chromatograms gave an unusual pattern of peaks. About 31% of the total CRF IR was eluted in the high molecular weight region. The major portion of CRF IR was located in a wide region of lower molecular weight. The AVP radioimmunoassay revealed a similar pattern of peaks in tumor and SME chromatograms. A propressophysin-like peak and a smaller peak coeluting with synthetic AVP were detected. Immunohistochemical staining of consecutive sections of the tumor indicated that AVP and CRF are often found in the same cell, but the CRF and AVP-producing cells are clearly distinct from the POMC peptide-producing cells.