Response of C-6 glioma to isoproterenol and papaverine in vivo depends on ?-adrenergic receptor density

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Abstract
Rat C‐6 glioma serves as an experimental model for human glioma. C‐6 glioma cells carried to high culture passages in medium containing 10% fetal bovine serum when injected in vivo are unresponsive to treatment with the β‐adrenergic agonist isoproterenol and the phosphodiesterase inhibitor papaverine. When C‐6 glioma cells are kept in culture in serum‐containing medium, β‐adrenergic receptor density falls and, concomitantly, ability to accumulate cyclic adenosine monophosphate in response to stimulation with catecholamines declines. Responsiveness to treatment in vivo with a β‐adrenergic agonist was restored when C‐6 glioma cells were cultured in serum‐free defined medium prior to systemic injection into rats. Culturing of C‐6 glioma cells in serum‐free medium significantly increases the number of β‐ adrenergic receptors when compared with C‐6 glioma cells grown in serum‐containing medium.