Fig. 6.

Myostatin attenuates GH action in primary human hepatocytes. Temporal GH responses were established by treating cells for 24 or 48 h with increasing GH doses and quantifying IGF1 (A) and ALS (B) mRNA using qRT-PCR. (C,D,E) Cells were then costimulated with GH and/or myostatin at the indicated doses (nM) and expression of IGF1, ALS, and IGFBP1 was quantified after 24 and 48 h. In each panel, mean differences for each gene are indicated by different letters, shared letters indicate no difference and comparisons were only made within time periods for a specific gene (AB, n = 6; C-E, n = 12; P ≤ 0.05; one-way ANOVA). (F) A proposed model incorporating GH released from the pituitary (green), MSTN from muscle (red), and IGF1 from the liver, muscle, and bone (blue). Arrows indicate stimulation, blocked lines attenuation. ALS, acid labile subunit; GH, growth hormone; IGF, insulin-like growth factor; IGFBP, insulin-like growth factor binding protein; MSTN, myostatin.