Neural influences and norepinephrine sensitivity in the rat portal vein

Experimental evidence suggests that innervation can exert a long-term control and modulation on effector cell homeostasis. These trophic influences are known to occur between the motor innervation and skeletal muscles, tissues in which these phenomena have been well studied. A similar picture is also emerging to indicate that smooth muscles may be subjected to a neurotrophic influence. The present paper reviews and presents data obtained after chemical sympathectomy of rat portal vein with 6-hydroxydopamine. Basically three experimental protocols were utilized: 1) studies before and after complete in vitro denervation, using the vessel as its own control; 2) in vivo sympathectomy followed by in vitro studies at various times thereafter; and 3) experiments in which the veins were denervated in vitro, placed in organ culture, and treated with either norepinephrine (NE) or the vehicle. The results indicate that in rat portal vein the sympathetic innervation normally exerts a trophic influence mediated, at least in part, by NE. This evidence is discussed in relation to other smooth muscles insofar as supersensitivity mechanisms and other possible effects triggered by transmitter withdrawal. The discussion is extended to encompass ways by which NE could exert its effects, and the possibility of other trophic factors.