Effects of Senescence on Vascular Smooth Muscle in the Yellow Mud Turtle "Kinosternon flavescens" (Family "Kinosternidae")

Abstract

Current literature suggests that reptiles do not undergo senescence and certainly do not age in a manner similar to mammals. This study examines age-related changes in reptilian arteries to evaluate similarities to age-related changes in mammals. Arterial sections from a wild population of turtles ranging in age from 6 to 3% years were examined histologically. Connective tissue-stained arteries showed statistically significant deposition of connective tissue in the tunica media with advancing age, consistent with senescent mammalian arteries. Living rings of arterial tissue from the same turtles were stimulated with potassium chloride, phenylephrine, acetylcholine, and isoproterenol to identify physiological responses in the vascular smooth muscle. No statistically significant changes in response related to aging were observed. Contractions were produced by acetylcholine, a feature typical of "Pseudemys scripta" and not of mammals. Isoproterenol did not produce contractions suggesting "K. flavescens" lack beta-2 receptors or these receptors do not operate similarly to mammals. The lack of decrease in arterial responsiveness in senescent arteries suggests that turtles may possess a mechanism for increasing myofibril strength in the presence of decreased myofibril mass and increased connective tissue.