Smooth muscle growth in the mature rat: role of sympathetic innervation.
The role of sympathetic innervation in maintaining smooth muscle structure and function was investigated in the mature rat. Superior tarsal muscle volume, smooth muscle cell nuclear size and packing density, and alpha-adrenoceptor-mediated contractions were assessed in Sprague-Dawley rats at 3 months of age, and in rats at 6 months of age in which one muscle had intact sympathetic innervation and the contralateral mate was sympathectomized at 3 months. Body weight was stable between 3 and 6 months. In contrast, both maximum contraction and muscle volume increased by more than 50% in the innervated organ, while chronic sympathectomy prevented these increases. Both nuclear packing density and nuclear size increased with age. The greater packing density was abolished by sympathectomy, but nuclear enlargement was not. Adrenoceptor supersensitivity was not observed, although the agonist dose producing 50% maximum contraction varied as a function of contractile capacity. It is concluded that superior tarsal smooth muscle growth continues independently of changes in body weight in the mature rat. Structural and functional deficits observed following chronic sympathetic denervation of this muscle are attributable to prevention of growth rather than regressions in size and contractile capacity.
Smith
P G
PG
Department of Physiology, University of Kansas Medical Center, Kansas City 66103.
Venkataraman
P
P
Reddy
H
H
D000375:Aging / Q000502:physiology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D008729:Methoxamine / Q000494:pharmacology; D009119:Muscle Contraction; D024510:Muscle Development; D009130:Muscle, Smooth / Q000033:anatomy & histology / Q000254:growth & development* / Q000294:innervation; D051381:Rats; D011919:Rats, Inbred Strains; D013562:Sympathectomy; D013564:Sympathetic Nervous System / Q000502:physiology*
D008729:Methoxamine