Abstract
Background and PurposeWe investigated whether pregnancy was associated with changed function in components of perivascular mesenteric innervation and the mechanism/s involved.Experimental ApproachWe used superior mesenteric arteries from female Sprague-Dawley rats divided into two groups: control rats (in oestrous phase) and pregnant rats (20 days of pregnancy). Modifications in the vasoconstrictor response to electrical field stimulation (EFS) were analysed in the presence/absence of phentolamine (alpha-adrenoceptor antagonist) or L-NAME (nitric oxide synthase-NOS- non-specific inhibitor). Vasomotor responses to noradrenaline (NA), and to NO donor DEA-NO were studied, NA and NO release measured and neuronal NOS (nNOS) expression/activation analysed.Key ResultsEFS induced a lower frequency-dependent contraction in pregnant than in control rats. Phentolamine decreased EFS-induced vasoconstriction in segments from both experimental groups, but to a greater extent in control rats. EFS-induced vasoconstriction was increased by L-NAME in arteries from both experimental groups. This increase was greater in segments from pregnant rats. Pregnancy decreased NA release while increasing NO release. nNOS expression was not modified but nNOS activation was increased by pregnancy. Pregnancy decreased NA-induced vasoconstriction response and did not modify DEA-NO-induced vasodilation response.Conclusions and ImplicationsNeural control of mesenteric vasomotor tone was altered by pregnancy. Diminished sympathetic and enhanced nitrergic components both contributed to the decreased vasoconstriction response to EFS during pregnancy. All these changes indicate the selective participation of sympathetic and nitrergic innervations in vascular adaptations produced during pregnancy.
Highlights
Pregnancy is associated with a decrease in systemic vascular resistance that, despite the marked increase in blood volume and cardiac output, maintains or reduces maternal blood pressure, in both experimental animals and humans
To the best of our knowledge, the possible role of nitrergic innervation in vascular adaptations to pregnancy remains unexplored. Taking these data into account, we considered it relevant to study possible simultaneous changes in the different kinds of perivascular innervation during pregnancy, the aim of this work is to analyze whether the possible functional changes in sympathetic, nitrergic and sensory innervations in late pregnancy could be associated with the decreased vascular resistance observed in the mesenteric artery, as well as the mechanisms that may be implicated
In endothelium-intact mesenteric segments, the vasoconstrictor response to 75 mmol/L KCl was similar in mesenteric segments from control and pregnant rats (Control: 1421 ± 114 mg; pregnant; 1538 ± 67.3 mg; P>0.05)
Summary
Pregnancy is associated with a decrease in systemic vascular resistance that, despite the marked increase in blood volume and cardiac output, maintains or reduces maternal blood pressure, in both experimental animals and humans. The mesenteric artery plays a pivotal role in global peripheral resistance in rats, especially in pregnancy; during this physiological process, mesenteric perfusion is strongly increased. These arteries are innervated by sympathetic nerves, which mediate vasoconstriction mainly via noradrenaline (NA) release, and by nitrergic innervation, which induces vasodilatation by nitric oxide (NO) release, and sensory innervation through release of the vasodilator calcitonin gene-related peptide neuropeptide (CGRP) [8,9,10]. The alterations in the functional roles of these components have been associated with changes in synthesis, release, response and/or metabolism of the different neurotransmitters in several physiological and pathological circumstances [11,12,13,14]. Vasomotor responses to noradrenaline (NA), and to NO donor DEA-NO were studied, NA and NO release measured and neuronal NOS (nNOS) expression/activation analysed
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