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Rat intermediate lobe in culture: dopaminergic regulation of POMC biosynthesis and cell proliferation
D R Gehlert1, J F Bishop, M P Schafer
1Experimental Therapeutics Branch, National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
Abstract:
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.
Insights
The D-2 agonist quinpirole reduces proopiomelanocortin (POMC) biosynthesis and beta-endorphin levels in rat intermediate lobe cultures. Quinpirole also inhibits cell proliferation in floating, but not attached, intermediate lobe cells.
Area of Science:
- Neuroendocrinology
- Cell Biology
Background:
- The intermediate lobe (IL) of the pituitary gland produces proopiomelanocortin (POMC)-derived peptides, including beta-endorphin.
- Dopaminergic regulation plays a crucial role in controlling IL function.
- Understanding the mechanisms of POMC biosynthesis and IL cell proliferation is essential for neuroendocrine research.
Purpose of the Study:
- To investigate the effects of the D-2 selective agonist quinpirole on POMC biosynthesis and cell proliferation in rat IL cultures.
- To determine whether quinpirole differentially affects attached and floating IL cells.
- To evaluate the utility of IL cell cultures as models for studying dopaminergic regulation and cell proliferation.
Main Methods:
- Primary cultures of rat intermediate lobe (IL) cells were established.
- Mechanical dispersion of IL lobules was used to create cultures.
- Immunoreactive beta-endorphin levels and POMC mRNA were measured.
- Incorporation of 35S-methionine was used to assess protein synthesis.
- Cell proliferation rates were determined for both attached and floating cell cultures.
Main Results:
- Quinpirole significantly reduced immunoreactive beta-endorphin levels in the medium.
- POMC mRNA levels were decreased by quinpirole in both attached and floating lobules.
- Protein synthesis, including that of POMC, was significantly reduced by quinpirole.
- Quinpirole inhibited cell proliferation in floating IL lobules but not in attached cells.
Conclusions:
- The floating rat IL lobule culture system serves as a valid model for studying in vivo dopaminergic regulation of IL function.
- Attached rat IL cells may offer a valuable tool for investigating the regulation of IL cell proliferation.
- Dopamine D-2 receptor agonism impacts both POMC peptide production and cell proliferation in the rat intermediate pituitary.