Representative images of zebrafish heart post cryoinjury. (A) A super cooled probe was used to cause a cryoinjury to the ventricle in anesthetized zebrafish. The heart was then sampled at specific days post injury (dpi), sectioned along the longitudinal axis and stained with Picrosirius Red to identify the injury site. (B) Brightfield images of ventricular sections at 1-, 7-, and 10-dpi showing the injury site (is) near the apex of the ventricle (v). (C) The brightfield image at 7-dpi shows the yellow fibrin clot (fc) surrounded by brightly stained red collagen (co). (D) The polarized image highlights the densely packed (orange) collagen in the regions surrounding the faint green fibrin in the 7-dpi section. Healthy tissue of the spongy myocardium (sm) and the compact myocardium (cm) can be seen to the left of the injury site. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

The influence of T3 exposure on the median Young's modulus values of zebrafish myocardium following injuring. N = 6 samples, with 3–6 scans per section. Values are presented as mean ± S.E.M. Statistical differences between mean values for the control group are indicated using capital letters and those for the treatment group are indicted with lowercase letters. Two mean values within the same group that do not share the same letter are statistically different. Asterisks indicate a difference between treatment and control at the same time point. Statistical significance was determined through a two-way ANOVA followed by a Tukey post-hoc test (p < 0.05).

The influence of T3 exposure on the expression of various genes in the zebrafish ventricle following cryoinjury. Gene expression is normalized to ef1a. Orange bars represent the control group and green bars represent the T3 exposed group. Values are presented as mean ± SEM. Pairs of bars indicated with dissimilar letters on the same panel are different from each other through time (p < 0.05). Overall differences in the expression of vimentin and mpeg1 between treatment and control groups at all sampling points are indicated in the top right corner of the relevant panel (p < 0.05). An asterisk represents a difference between treatment and control at a specific time point (p < 0.05). Significance was determined through a two-way ANOVA followed by a Tukey post-hoc test (p < 0.05). N = 4–7 individual ventricles. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

The influence of T3 exposure on the expression of select genes and type I collagen in cultured trout cardiac fibroblasts. Panels A-D) Relative expression of col1a1, mmp2, timp2 and mmp9, respectively, normalized to β-actin. E) The expression levels of type I collagen normalized to total protein in cardiac fibroblasts. Fibroblasts were exposed to 0 nM, 10 nM or 70 nM T3. F) Representative image of western blot stained for type I collagen. N = 3–4 cell lines, each individual cell line is composed of the mean of 4 cell passages. IC = internal control.