Sex-dependent expression of CYP2C11 in spleen, thymus and bone marrow regulated by growth hormone.

CYP2C11, the most commonly expressed isoform of cytochrome P450 in male rat liver, was measured in spleen, thymus and bone marrow by quantitative real-time PCR and enhanced Western blotting. CYP2C11 concentrations in the lymphoid tissues were a fraction of that observed in liver, but like the liver, were sexually dimorphic (M>F) with mRNA and protein levels in agreement. Although the response to hypophysectomy varied according to tissue and sex, expression levels of CYP2C11 in all measured tissues remained greater in males. Further differences in CYP2C11 expression between liver and lymphoid tissue were observed following restoration of the circulating masculine growth hormone profile in hypophysectomized rats. In contrast to the liver where the renaturalized growth hormone profile elevated CYP2C11 expression in both sexes, the response was opposite in spleen and thymus with isoform concentrations declining in both sexes. Lastly, the divergent response of CYP2C11 between the liver and immune system was examined in cultured splenocytes exposed to different mitogens. In contrast to the dramatic depletion of CYP2C11 reported in proliferating hepatocytes, mitogen-stimulation resulted in a significant elevation in splenocyte CYP2C11 expression. In summary, we report for the first time that thymus, spleen and bone marrow express, albeit nominal, sex-dependent levels of CYP2C11 (M>F) whose regulation appears to be under some hormonal control, but very different from that of the hepatic isoform.