AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 1 331-R336, Copyright © 1997 by American Physiological Society

ARTICLES

Effects of alpha-adrenergic stimuli on mesenteric collecting lymphatics in the rate

J. N. Benoit
Department of Physiology, University of South Alabama College of Medicine, Mobile 36688, USA.

The present study examined the effects of alpha 1- and alpha 2-adrenergic stimuli on rat mesenteric collecting lymphatics in vivo. Sprague-Dawley rats were anesthetized, and the mesentery was prepared for intravital microscopic study. Mesenteric collecting lymphatic diameter was continuously monitored by using a computerized video tracking system, and indexes of lymphatic pumping (e.g., contraction frequency, stroke volume, ejection fraction, and muscle shortening velocity) were determined from the diameter record. Contractile activity was monitored before and during the administration of various adrenergic agonists and antagonists. The receptor antagonists prazosin (alpha 1) and yohimbine (alpha 2) did not significantly alter baseline diameter or contractile activity, which suggests that lymphatics possess no basal adrenergic tone. Norepinephrine and phenylephrine (01-1.0 microM) produced dose-dependent increases in frequency and decreases in diameter. Lymphatic pump flow increased in direct proportion to frequency, because stroke volume did not change. The changes in lymphatic pumping produced by 1 microM norepinephrine were completely blocked by prazosin or phentolamine and only partially blocked by yohimbine. The alpha 2-adrenoceptor agonist (alpha-methyl-norepinephrine) produced no changes in lymphatic activity. This latter observation suggests that a role for postjunctional alpha 2-adrenoceptors in modulating mesenteric lymphatic smooth muscle is unlikely. The results of these studies support the existence of alpha-adrenoceptors on lymphatic smooth muscle. It is concluded that conditions characterized by increased sympathetic outflow may augment lymphatic function through alpha 1- but not alpha 2-adrenoceptors.

This article has been cited by other articles:

				P. J. Dougherty, M. J. Davis, D. C. Zawieja, and M. Muthuchamy Calcium sensitivity and cooperativity of permeabilized rat mesenteric lymphatics Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2008; 294(5): R1524 - R1532. [Abstract] [Full Text] [PDF]

				J. K. Meisner, R. H. Stewart, G. A. Laine, and C. M. Quick Lymphatic vessels transition to state of summation above a critical contraction frequency Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R200 - R208. [Abstract] [Full Text] [PDF]

				Y. Shirasawa, F. Ikomi, and T. Ohhashi Physiological roles of endogenous nitric oxide in lymphatic pump activity of rat mesentery in vivo Am J Physiol Gastrointest Liver Physiol, April 1, 2000; 278(4): G551 - G556. [Abstract] [Full Text] [PDF]