Moreover, functional studies have shown that human lymphocyte membrane receptors are coupled to a G protein,
and via these receptors, melatonin inhibits forskolin-stimulated cyclic AMP (cAMP) production and cyclic GMP (cGMP) production and diacylglycerol (DAG) production[45]. In immunocompetent cells, specific nuclear melatonin-binding sites have been reported in several species,including humans