Pregnancy reduces noradrenaline but not neuropeptide levels in the uterine artery of the guinea-pig

Abstract

Using histochemical, immunohistochemical and biochemical techniques, noradrenaline-, neuropeptide Y-, vasoactive intestinal polypeptide-, substance P- and calcitonin gene-related peptide-containing nerve fibres were studied in the uterine artery of virgin, progesterone-treated and pregnant guinea-pigs. Morphological changes following hormone treatment or in pregnancy were also evaluated in a quantitative study on semithin sections of the uterine artery. In late pregnancy, the number of noradrenaline-containing nerve fibres, which formed the densest plexus in virgin animals, was significantly decreased, a finding supported by a significant reduction in noradrenaline levels. This reduction was not mimicked by systemic progesterone treatment. In contrast, the innervation of the uterine artery by neuropeptide Y-containing nerve fibres was increased in pregnancy, while the other peptidergic nerves and peptide levels were unchanged after progesterone treatment and in pregnancy. These changes led to a predominance of innervation by neuropeptide Y- rather than noradrenaline-containing nerve fibres in late pregnancy. No morphological changes were detected following progesterone treatment, but pregnancy led to a marked increase in the cross-sectional area of the vessel accompanied by an increase in the thickness of the media.

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

“…A network of catecholamine-containing nerves was clearly visible in stretched preparations. The density was greater in tissues obtained from virgin animals, similar to the observations of Mione et al [21]. Cross sections were then treated with glyoxylic acid, and fluorescent varicosities were found to be in greater density close to the outer edge of the smooth muscle in virgin preparations, whereas they appeared to be dispersed throughout the adventitia and further from the smooth muscle in late pregnancy (fig.…”

“…Fluorescence histochemistry of stretched preparations revealed a decrease in the density of the catecholamine innervation during pregnancy and this was confirmed using HPLC to measure the content and concentration of noradrenaline in the uterine artery, similar to the observations of others [21]. Despite this, the amplitude of the slow depolarization that resulted from the activation of α-adrenoceptors appeared similar in tissues from virgin and late pregnant animals.…”

“…The content and concentration of noradrenaline in the uterine artery decline during pregnancy [21]. In this species, there are nerves supplying the uterine artery which also contain a variety of neuropeptides [2, 22] whose levels do not appear to change during pregnancy [19, 21, 23]. …”

“…During pregnancy there is a progressive reduction in the catecholamine fluorescence, associated with degeneration of the adrenergic innervation [17, 18, 19] for which progesterone may be responsible [20]. The content and concentration of noradrenaline in the uterine artery decline during pregnancy [21]. In this species, there are nerves supplying the uterine artery which also contain a variety of neuropeptides [2, 22] whose levels do not appear to change during pregnancy [19, 21, 23].…”

Molecular cloning of substance P receptor cDNA from guinea-pig uterus

“…An important target organ for SP is the uterus. lrnmunocytochemical studies have shown that numerous SP-positive neurons innervate the myometrium and uterine arteries [3][4][5]. SP, in combination with other neuropeptides, plays an essential role in the regulation of myometrial activity and, consequently, in the maintenance of pregnancy and parturition.…”