Differential effects of angiotensin, vasopressin and oxytocin on various smooth muscle tissues within the human uteroplacental unit

Abstract

Tissue specimens from various parts of the uteroplacental unit were obtained from women undergoing caesarean section, and placental tissue from women with normal deliveries. Strips of myometrial tissue, and segments of intramyometrial arteries were dissected together with segments of chorionic plate arteries and veins, and stem villous arteries. The preparations were mounted in organ baths, isometric tension recorded, and the responses to angiotensin II, vasopressin, and oxytocin were studied. In myometrial preparations, angiotensin caused a slight, transient increase in the frequency of spontaneous contractions, but no changes in amplitude. In all vascular preparations angiotensin produced concentration-related contractions. The responsiveness of the preparations was myometrial artery greater than villous artery greater than chorionic plate artery = chorionic plate vein. All responses were transient and tachyphylaxis was pronounced in all tissues. Tachyphylaxis was not influenced by pretreatment with indomethacin. Vasopressin increased transiently frequency and amplitude of contractions in myometrial strips. Myometrial arteries responded with a sustained contraction, as did chorionic plate arteries and veins but the latter vessels were less responsive. Villous arteries did not respond to vasopressin. Oxytocin preferentially stimulated myometrial strips, but also had a weak concentration-related contractant effect on chorionic plate arteries and veins. Villous arteries did not respond to oxytocin. At a higher concentration, causing a pronounced increase in the frequency and amplitude of contractions of myometrial strips, oxytocin abruptly caused a marked contraction of myometrial arteries. Lower concentrations of the peptide had almost no effects. The results suggest that various smooth muscle tissues of the human uterus and placenta are highly differentiated as regards responses to angiotensin II, vasopressin, and oxytocin. The physiological and possible clinical importance of the present findings deserve further investigation.

Effects of Serotonin on Vascular Tone of Isolated Human Placental Chorionic Veins

“…We selected chorionic veins instead of chorionic arteries because they transport the oxygen ated blood to the fetus. It is also accepted that small chorionic veins are representative of the placental ca pacitance vessels, and are more representative of the vil lous circulation than umbilical vessels [13,14], Our results show that 5-HT produces strong dose-dependent contractions in isolated human placental chorionic veins, which suggests that this amine has potent placen tal vascular effects at the end of pregnancy. Although fetal plasma levels of 5-HT are, to our knowledge, un known, the doses used in our experiments may be ques tioned.…”

The control of blood flow to the placenta

“…Oxytocin and vasopressin have both been detected in umbilical cord blood in relatively high concentrations, being higher in the umbilical vein than in the artery, probably due to placental metabolism by aminopeptidases (Chard, Hudson, Edwards & Boyd, 1971;Chard, 1972). However, both are weak constrictors of stem villous arteries (Maigaard, Forman & Andersson, 1986a) and are unlikely to play a major role in the control of fetoplacental vascular tone. (Kingdom, McQueen, Connell & Whittle, 1992).…”

Effect of Histamine on Human Placental Chorionic Veins: Interaction with Serotonin

“…While the contractile activity of hista mine on the human umbilical vasculature is well known [2,3,5], no study has been car ried out on the effects of histamine on hu man placental chorionic veins, which might be expected to play a greater role in placental tone, if they were taken as representative of the capacity of the placental vessels [4], The present results show that histamine produces concentration-related contractions in this venous preparation. Similar results have been obtained in human umbilical vessels [2,3,5], The H r receptor blockade with pyrilamine caused a parallel displacement to the right of the histamine concentration-re sponse curve ( fig.…”

“…As has been demon strated in previous reviews, the small blood vessels supplying the individual chorionic villi of the human placenta disclose a drug response not seen in the isolated cord vessels [3], Small chorionic veins seem to be repre sentative of the placental vessel capacity [4], Consequently, the mechanical properties of these vessels and the factors involved in the regulation of their degree of contraction will ultimately determine the placental venous tone. Also, it is important to note that, in umbilicoplacental circulation, the veins transport the oxygenated blood and nu trients to the fetus, therefore, the placental venous circulation is of obvious importance in contributing to fetal nutrition and devel opment.…”