Secretion of melanophore-stimulating hormone (MSH) in long-term cultures of pituitary neurointermediate lobes

Abstract

Neurointermediate lobes from pituitaries of the frog, Rana berlandieri forreri (Rana pipiens, sensu lato), were maintained in organ culture in media with and without serum for up to six months. The cultured tissues were examined periodically by light microscopy and transmission electron microscopy and by bioassay of the melanophore-stimulating hormone (MSH) secreted and present in the culture media. Light-microscopic observations revealed a high degree of preservation of the pars intermedia at four weeks with isolated areas of some glands maintaining histological integrity for the entire six months. Similarly, at the ultrastructural level the cells appeared morphologically intact and to be actively synthesizing and secreting hormone. Bioassays showed the glands to be continuously secreting MSH; however, larger yields of hormone were obtained in media lacking serum. No significant ultrastructural differences between cells grown in the presence or absence of serum were detected. The difference in concentration of MSH between the two groups therefore apparently results from enzymatic degradation of the hormone by the serum. Organ culture of the vertebrate neurointermediate lobe may provide a unique method for the production of large quantities of MSH and for the study of other melanotropic and opiate peptides as they may be synthesized and secreted by the pars intermedia.

Coordinate, equimolar secretion of smaller peptide products derived from pro-ACTH/endorphin by mouse pituitary tumor cells.

“…Two previous reports of secretion by AtT-20 cells found secretion to be continuous for many hours (22,67), as in this study. Because exogenous and endogenous ACTH (53), endorphins (55,60), and melanotropins (57) are sometimes degraded in cultures with half-lives of the order of 10 min to 2 h, a lack of stability after secretion can be confused with a decreased secretory rate . Under the incubation conditions used in these and previous studies (Figs.…”