Effects of Chronic Cortisol Elevation on Cardiac Structure and Function in Zebrafish (Danio rerio)

Abstract

Cardiac deformities are increasingly reported in farmed salmonid fishes. Pathological cardiac hypertrophy is dysfunctional remodelling that includes enlargement of the ventricle and compact myocardium, as well as fibrotic collagen deposition. The current study investigated the effect of chronic cortisol elevation, as a proxy for chronic stress, on zebrafish (Danio rerio) heart structure and function. Compact myocardium thickness and heart size increased in wildtype zebrafish exposed to waterborne cortisol treatment. However, pro-hypertrophic molecular markers did not differ in transcript abundance between treatment groups. Measures of cardiac function were not affected by cortisol exposure, nor was swimming performance. Zebrafish lacking functional expression of the glucocorticoid receptor (GR-KO) had hearts that were smaller and with thinner walls relative to body mass than wildtype fish. However, cardiac function and swimming performance in GR-KO fish were comparable to those of matched wildtype fish. Collectively, these data indicate that the zebrafish heart is capable of maintaining function even as morphology changes.