GDF15 and Myocardial fibrosis: 127). In the pathological state of myocardial fibrosis induced by isoproterenol (ISO), the production of growth differentiation factor 15 (GDF15) was decreased, while the mRNA levels of type I and type III collagen were increased. The phosphorylation of Akt at Ser473 and GSK-3β at Ser9 was decreased with ISO, but ghrelin administration increased the levels of GDF15 mRNA and protein, significantly reversing the downregulation of p-Akt and p-GSK-3β (Ref. 128).