GH1 and familial dilated cardiomyopathy: When Gr-1(+) cells were cultured with 400 pg/ml of activin A, a concentration equivalent to that in the peripheral blood of DCM mice, mRNA and protein levels of GH were significantly downregulated (Figure 6B), suggesting that activin A might be a key mediator of the reduced expression of GH in the Gr-1(+) cells of DCM mice.