Placental Distribution and the Effect of Antihypertensive Drugs on Monoamine Oxidase and Cathechol-o-Methyl Transferase Activity at Term
Pregnancy associated with hypertension frequently requires antihypertensive medications, which among other effects should improve the uteroplacental circulation. The mechanism and site of action of the commonly used antihypertensive drugs (AHD) used in pregnancy in the circulation has been previously investigated (Lunell et al., 1981; Johanson et al., 1980, Freed et al., 1978; Moskowitz and Cohn, 1980). Unfortunately, knowledge concerning mechanism of action of this group of AHD on the placenta and the uterus is limited. It has been suggested that their effect among others may be mediated via a direct action on the placental blood vessel wall. Moreover, beta adrenergic receptors were found in the brush border membrane of the placenta where some AHD could exert their action (Moore and Whitsett, 1981; Karlsson et al., 1984; Maigaard et al., 1984). Other effects might be exerted on metabolizing enzymes for placental catecholamine and serotonin, monoamine oxidase (MAO) and catechol-o-methyl transferase (COMT). The activities of these metabolizing enzymes have been shown previously to be lower in placentae of patients with hypertension (Barnea et al., 1983, 1986) where a high concentration of norepinephrine was found (DeMaria, 1966). In addition, alpha methyl DOPA and hydralazine can interact with COMT and MAO, respectively in other tissues (Gordonsmith et al., 1982; Lyles et al., 1983).
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