Complex sentence: The endothelium may also regulate the growth patterns of the cardiac muscle cells throughout life, and the endothelins it secretes create an environment in the surrounding tissue fluids that regulates ionic concentrations and states of contractility.
Split into simpler sentences: The endothelium may also regulate the ongoing growth patterns of the cardiac muscle cells. The endothelins it secretes, create an environment in the surrounding tissue fluids that regulates ionic concentrations and states of contractility.