Morphine alters the levels of growth hormone receptor mRNA and [125I]growth hormone binding in human IM-9 lymphoblasts via a naloxone-reversible mechanism.

The immune system and the neuroendocrine system are functionally interactive. Lymphocytes possess opioid receptors as well as growth hormone receptors (GHR) by which opioids and growth hormone (GH) may modulate immune functions. In this study, we have investigated the effects of morphine on [125I]hGH binding and GHR gene expression in human lymphoblastoid IM-9 cells. Northern blot analysis revealed significantly altered GHR mRNA levels after treatment of the cells with different concentrations of morphine for 12 h. Morphine at 10 microM increased the mRNA levels in a time-dependent biphasic manner, with maximum levels at 6 and 48 h. The receptor protein, measured by [125I]GH binding, showed a time-delayed increase compared with the GHR mRNA changes. Pretreatment with naloxone inhibited the action of morphine, suggesting involvement of classical opioid receptors. The present study demonstrates, for the first time, effects of morphine on GHR mRNA levels and [125I]GH binding in human cultured lymphocytes.