RGS2 inhibits norepinephrine- and isoproterenol-dependent elevation of N-acetylserotonin, melatonin and cAMP in pinealocyte culture media. Pineal cells were stimulated by a range of concentrations of norepinephrine (A and C) or isoproterenol (B and D). Significant inhibition of melatonin and N-acetylserotonin production by RGS2 occurred at concentrations of 10−9–10−6 and 10−8–10−6 M norepinephrine, respectively (A and C, P < 0.05, one-way ANOVA, Control vs RGS2-infected cells at the same concentration of norepinephrine, n = 3 each). Significant inhibition of both melatonin and N-acetylserotonin production by RGS2 was found at the concentrations of 10−9–10−8 M isoproterenol (B and D, P < 0.05, one-way ANOVA, Control vs RGS2-infected cells at the same concentration of isoproterenol, n = 3 each). (E) Norepinephrine stimulation of cAMP content of media was decreased in cultures of cells in which RGS2 was overexpressed (P < 0.05, one-way AVNOVA, Control vs RGS2-infected cells at 10−5 µM norepinephrine, n = 3 each). For further details see Section 2.