AJP - Heart and Circulatory Physiology, Vol 240, Issue 4 498-H504, Copyright © 1981 by American Physiological Society
Relaxation of bovine mesenteric lymphatics in response to transmural stimulation
T. Ohhashi and I. C. Roddie
The responses of isolated quiescent segments of bovine mesenteric
lymphatics to 10-s trains of pulses (50 V for 0.3 ms at 2 Hz) administered
transmurally have been studied using various drugs. Each train of pulses
consistently produced a brief contraction that was completely blocked by
tetrodotoxin, alpha-adrenoceptor antagonists, bretylium, and guanethidine.
Cocaine potentiated the contractions. Tyramine caused an increase in the
basal tone, some spontaneous contractions, and an inhibition of
contraction. The contraction was sometimes followed by a relaxation that
could be of short duration or long lasting. Both types of relaxation were
abolished by tetrodotoxin. Propranolol reduced both types of relaxation,
causing more suppression of the short type. Bretylium completely blocked
the short type of relaxation and slightly reduced the long-lasting type.
Hexamethonium and atropine had no effect on any of the responses. These
findings suggest that the contraction resulting from transmural stimulation
is due to the action of excitatory postganglionic sympathetic nerves. It is
concluded that both types of relaxation occur mainly in response to
beta-adrenergic inhibitory stimulation. The possibility of nonadrenergic
inhibitory innervation in bovine mesenteric lymphatics is also discussed.
