Rat intermediate lobe in culture: dopaminergic regulation of POMC biosynthesis and cell proliferation.

The effects of the selective D-2 selective agonist, quinpirole, on biosynthesis of proopiomelanocortin (POMC) and cell proliferation rate of cultures of rat intermediate lobe (IL) have been examined. Primary cultures of rat IL were prepared by mechanically dispersing IL lobules in medium. Following a six day incubation, approximately 25% of the cells settled onto the culture plate and began to extend into a monolayer. Quinpirole markedly reduced immunoreactive beta-endorphin levels in the medium and POMC mRNA in both the attached and floating lobules. The incorporation of 35S-methionine into 32 kDa POMC, a 18-22 kDa complex of proteins, a 16 kDa protein and a 15 kDa protein was decreased significantly in both the attached and floating lobules. In contrast, the proliferation in the floating, but not the attached, cells was inhibited by quinpirole. The floating IL lobule appears to provide a reasonably faithful model of the dopaminergic regulation of IL function in vivo, while the attached IL cells may provide an interesting tool to study the regulation of IL cell proliferation.