The effects of a hyperosmotic challenge in vivo on tissue composition of rat cardiac and skeletal muscle.

The effects of hyperosmotic stress under both acute and chronic conditions were investigated in two types of rat muscle tissue: cardiac and skeletal. Under acute conditions of a 4-h infusion, both types of muscle behaved as osmometers. However, under chronic hyperosmotic stress (several days), skeletal muscle behaved as predicted as an osmometer, but cardiac muscle did not. The levels of free amino acids in this tissue increased markedly--in particular, taurine. This phenomenon is discussed with respect to the capacity of this tissue for volume regulation.