Mechanisms of prostaglandin F2 alpha and histamine-induced contractions in human chorionic vasculature

Pharmacological profile of vascular activity of human stem villous arteries

INTRODUCTION

The function of the placental vasculature differs considerably from other systemic vascular beds of the human body. A detailed understanding of the normal placental vascular physiology is the foundation to understand perturbed conditions potentially leading to placental dysfunction.

METHODS

Behaviour of human stem villous arteries isolated from placentae at term pregnancy was assessed using wire myography. Effects of a selection of known vasoconstrictors and vasodilators of the systemic vasculature were assessed. The morphology of stem villous arteries was examined using IHC and TEM.

RESULTS

Contractile effects in stem villous arteries were caused by U46619, 5-HT, angiotensin II and endothelin-1 (p ≤ 0.05), whereas noradrenaline and AVP failed to result in a contraction. Dilating effects were seen for histamine, riluzole, nifedipine, papaverine, SNP and SQ29548 (p ≤ 0.05) but not for acetylcholine, bradykinin and substance P.

DISCUSSION

Stem villous arteries behave differently to vessels of the systemic vasculature and results indicate that the placenta is cut off from the systemic maternal vascular regulation. Particularly, endothelium-dependent processes were attenuated in the placental vasculature, creating a need to determine the role of the endothelium in the placenta in future studies.

The effect of a mast cell degranulating agent on vascular resistance in the human placental vascular bed and on the tone of isolated placental vessels

The objective of this study is to investigate the effect of a mast cell degranulating agent, compound 48/80, on vascular resistance in the perfused human placenta and on the tone of isolated human chorionic vessels. Human placenta was obtained from term nonlaboring women undergoing cesarean delivery. Placental vascular bed perfusion pressure and isometric tension for segments of chorionic plate artery and vein were obtained in response to potassium chloride, compound 48/80, a mast cell stabilizer (cromolyn), and thromboxane A2 mimetic (U46619). Compound 48/80 significantly increased perfusion pressure in isolated human placental cotyledons. This effect was significantly potentiated further after induction of active vascular tone by thromboxane A2 mimetic U46619. Cromolyn significantly attenuated responses to compound 48/80 in these preparations. Compound 48/80 also significantly increased tone in isolated human chorionic artery and vein rings, and responses were abolished by cromolyn. In conclusion, degranulation of placental and intravascular mast cells by compound 48/80 leads to the release of vasoconstrictive substances. This could impair placental blood flow and result in growth restriction in fetuses of women with type l hypersensitivity reactions.

Potentiation by neuropeptide Y of histamine H1 receptor-mediated contraction in rat blood vessels

Histamine-induced contraction and its potentiation by neuropeptide Y were investigated in rat blood vessels. Rat arteries and veins constricted with single concentrations of histamine dose-dependently (0.1-100 microM). This histamine-induced contraction immediately desensitized. Histamine H1 receptor antagonists, 1 microM mepyramine and 1 microM diphenhydramine, abolished this transient contraction completely, whereas cimetidine, phentolamine, reserpine and tetrodotoxin failed to inhibit the contraction. Histamine H1 receptor mRNA level by reverse transcription-polymerase chain reaction was quite parallel to histamine H1 receptor-mediated contraction, indicating that the contraction is mediated through histamine H1 receptors in the smooth muscle. Neuropeptide Y (10 nM in arteries and 3 nM in veins, respectively) significantly potentiated histamine H1 receptor-mediated contraction via neuropeptide Y1 receptors in most of rat blood vessels. Since the phospholipase C inhibitors, neomycin (1 mM) and 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate (NCDC, 10 microM), respectively, specifically abolished the potentiation, the potentiation by neuropeptide Y may depend on activation of phospholipase C.