Open AccessThe effects of α‐methyldopa on myometrial noradrenaline release and myometrial contractility in rat
Author(s) -
CSONKA DÉNES,
ZUPKÓ ISTVÁN,
MINORICS RENÁTA,
MÁRKI ÁRPÁD,
CSÍK GÁBOR,
FALKAY GEORGE
Publication year - 2007
Publication title -
acta obstetricia et gynecologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.401
H-Index - 102
eISSN - 1600-0412
pISSN - 0001-6349
DOI - 10.1080/00016340701463830
Subject(s) - contractility , medicine , myometrium , methyldopa , endocrinology , uterus , blood pressure
Background. α‐Methyldopa is a classic antihypertensive agent, used routinely in the treatment of pregnancy‐induced hypertension. However, only a few data are available about its direct uterotropic effect. Accordingly, the aim of the present study was to investigate the direct effects of α‐methyldopa on the myometrial adrenergic functions in rat. Methods. The effects of α‐methyldopa on the sympathetic transmission in the non‐pregnant, early pregnant and late‐pregnant myometrium were investigated by a superfusion technique. Myometrial samples from control and α‐methyldopa‐treated (200 mg/kg i.p. for 7 days) non‐pregnant, 7‐day and 21‐day pregnant rats were saturated with [ 3 H]noradrenaline, and the liberation evoked by electric field stimulation was determined. The contractility responses to α‐ and β‐adrenergic stimulation were additionally characterised by generating concentration–response curves of myometrial rings to noradrenaline and terbutaline in the same arrangement. The changes in the density and affinity of the adrenergic receptors (α 2 and β 2 ) were investigated by a radioligand binding technique. Results. The treatment with α‐methyldopa substantially decreased both the [ 3 H]noradrenaline uptake and release in both the non‐pregnant and early pregnant uterus, while treatment‐dependent changes were observed at term only in the uptake capacity. The contractility response to exogenous α‐sympathomimetics was higher in the group treated in early pregnancy, and a decreased terbutaline‐induced relaxation was observed in the non‐pregnant state and at term. The treatment resulted in increased affinity for α 2 receptors in early pregnancy, while K d for β 2 was increased at term. Conclusions. Our experimental data suggest that besides its antihypertensive effect, α‐methyldopa may influence the adrenergic transmission of the pregnant uterus. Our results indicate that the agent decreases the efficacy of β 2 ‐adrenergic agonists at term pregnancy and increases the response to α‐sympathomimetics in early pregnancy.