Ontogeny of vascular smooth muscle responsiveness in the postweaning rat.

This study investigated the ontogeny of contractile and relaxation responses in aortic and tail artery preparations from 3-, 7-, and 11-week-old male Sprague-Dawley rats. Contractile responses to norepinephrine, serotonin, KCl, electrical stimulation, and potassium-free physiological solution were significantly increased in vascular smooth muscle from 3-week-old rats when compared to 7- and 11-week-old rats. Endothelium-dependent acetylcholine-induced relaxation and beta-adrenoceptor mediated isoproterenol-induced relaxation were significantly attenuated with maturation. These data demonstrate that significant changes occur in aortic and tail artery smooth muscle responsiveness during the postweaning maturational period of the rat. The alterations may have significant implications with regard to cardiovascular and thermoregulatory function as well as the age of the animal when utilized as an experimental model for identifying pathogenic mechanisms involved in various disease states such as hypertension. As such, further studies are warranted to determine if similar ontogenic changes in vascular function occur at the level of the resistance vessel.