Mechanics and electrolyte composition of arterial smooth muscle in developing dogs.

The effects of age on arterial smooth muscles (SM) mechanics and electrolyte composition were studied during growth and development in six litters of puppies and their mothers from isolated segments of carotid, renal, mesenteric, and iliac arteries. An increase in the maximum wall stress following both norepinephrine (NE) and potassium (K) was found with age at all sites. The ratio of the stress response for K/NE was found to decrease with age. The maximum stress response for both NE and K shifted to lower values of wall strain with age in the same manner that passive stress-strain curves were shifted. The maximum diameter re3 (3 SM activator to SM activator were not significantly altered with age, but they were better maintained at higher transmural pressure in older animals. Chemical analysis indicated "cell" water, Mg, and K contents decreased with age, as did extracellular water, Na, and Cl. Na anhe suggest that changes in SM excitation-contraction coupling occur with age. Passive wall elements appear to interact with the contractile elements in determining wall responses to SM activation.