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      Pregnancy-Induced Decrease in Evoked Excitatory Junction Potentials in Guinea Pig Uterine Artery

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          Abstract

          The effects of stimulating the intramural nerves on the membrane potential and tension in the uterine artery of virgin guinea pigs were compared with the responses during pregnancy. In all tissues the amplitude of the excitatory junction potential (EJP) increased as the stimulus voltage was increased. The rate of increase in EJP amplitude in tissues from virgin animals greatly exceeded that recorded in late pregnant tissues. EJPs were abolished by tetrodotoxin but were resistant to blockade by α-adrenoceptor antagonists. Stimulation of the nerves also evoked a slow depolarization and contraction which were abolished by both tetrodotoxin and α-adrenoceptor antagonists. The amplitudes of the depolarizations and contractions were not correlated. The role of EJPs and α-adrenoceptor activation in the control of vascular function is discussed. Fluorescence histochemistry revealed a decrease in the density of the catecholamine innervation that was correlated with a decrease in catecholamine content as pregnancy progressed. In addition, there appeared to be a difference in the arrangement of the fluorescent varicosities, with a shift from varicosities that were close to the outer layer of smooth muscle in virgin tissues to those that were more distantly dispersed in the adventitia during late pregnancy. The changes would be expected to reduce the effectiveness of vasoconstrictor drive to the uterine artery as pregnancy progresses.

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          Most cited references 6

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          ATP as a co-transmitter in rat tail artery.

          In rat tail artery the electrical response to nerve stimulation was biphasic, consisting of a fast, transient depolarisation which was resistant to alpha-adrenoceptor antagonists and a slow, prolonged depolarisation which was abolished by them. In the presence of alpha, beta-methylene-adenosine 5'-triphosphate (alpha, beta-methylene-ATP), which abolishes responses mediated via P2-purinoceptors, the fast depolarisation was abolished, whilst the slow depolarisation persisted. We propose that both adenosine 5'-triphosphate (ATP) and noradrenaline (NA) are involved in sympathetic neurotransmission in the rat tail artery.
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            Vasoactive intestinal peptide-like immunoreactivity in nerves associated with the cardiovascular system of guinea-pigs.

            The distribution of nerves with vasoactive intestinal peptide (VIP)-like immunoreactivity has been examined in the heart and vascular system of guinea-pigs. There was a very sparse supply of fibres to the heart. No immunoreactive cell bodies were found in the intrinsic cardiac ganglia; however, positive nerve cell bodies were seen along the superior vena cava near the right atrium. There were immunoreactive fibres with most arteries; these fibres were located at the media-adventitia junction. The supply to major distributing arteries, such as the aorta, subclavian, carotid and femoral arteries as well as to the pulmonary arteries, was sparse. Of the individual vascular beds, the most densely supplied arteries were the mesenteric and uterine (or in the male deferential) arteries. Arteries running to other organs or tissues, such as skeletal muscle, kidney, pancreas, spleen and heart were less densely supplied. There were clear differences in the innervation of different cerebral vessels. The greatest density was associated with the anterior and middle cerebral arteries. Fewer nerves accompanied the posterior cerebral, cerebellar and meningeal arteries. There was a sparse innervation of the rostral part of the basilar artery. Throughout the body, veins were sparsely supplied. The distribution of nerves with VIP-like immunoreactivity was not changed when noradrenergic nerves were degenerated by 6-hydroxydopamine or when substance P nerves were disrupted by capsaicin. It is concluded that VIP containing nerves innervating the heart and blood vessels form a population distinct from the substance P-containing and the noradrenergic nerves. It is suggested that the VIP fibres might be efferent vasodilator nerves to the blood vessels.
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              Noradrenaline-ATP co-transmission in the sympathetic nervous system.

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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                1998
                February 1998
                06 February 1998
                : 35
                : 1
                : 63-71
                Affiliations
                Department of Physiology, Monash University, Clayton, Vic., Australia
                Article
                25566 J Vasc Res 1998;35:63–71
                10.1159/000025566
                9482697
                © 1998 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 7, Tables: 2, References: 43, Pages: 9
                Categories
                Research Paper

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