Relaxant effect of dopamine on the isolated rat uterus

Abstract

The effect of dopamine was studied on the isolated uterus of diethylstilboestrol-treated rats. Dopamine, at concentrations (10(7)-10(-4) M) produced a concentration-dependent relaxation in the K+-depolarized rat uterus. On a molar basis, dopamine was about 500 times less potent than adrenaline in relaxing the uterus, the maximum degree of relaxation obtained with both drugs was the same. Pretreatment of the rats with reserpine (5 mg/kg) did not produce any modification of the dose-response curve to dopamine. Similarly, cocaine (3 x 10(-6) M) failed to modify the relaxant effect of dopamine. The dopamine induced relaxation was inhibited by propranolol (10(-9)-10(-7) M) in a dose-dependent manner. Prazosin (10(-7) M), SCH 23390 (10(-7) M) and sulpiride (10(-7) M) did not affect the dopamine dose-response curve. In the isolated rat uterus which was not preconstricted by KCl neither dopamine nor adrenaline produced any effect when added to the organ bath. This lack of response to both catecholamines was present even in tissues pretreated with propranolol or sulpiride. It is concluded that dopamine produced a concentration-dependent relaxation of the uterus from diethylstilboestrol-treated rats by direct activation of beta-adrenoceptors. There was no evidence for indirect action (catecholamine release and neuronal uptake mechanisms) and specific dopamine receptor mediated relaxation and alpha-adrenoceptor mediated contractions have not been found in this preparation.

Influence of Dopamine on Rat Uterine Motility in vitro

“…The uterine strips placed in the automatic bath organ exhibited periodical contractility as confirmed by earlier experiments carried out by and other authors (Estan et al 1988;Parija et al 2001). The addition of dopamine to the incubation bath organ at a concentration of 2.6·10 -4 mol/L resulted in atony of the isolated strip.…”

“…The addition of dopamine to the incubation bath organ at a concentration of 2.6·10 -4 mol/L resulted in atony of the isolated strip. Similarly, Estan et al (1988) obtained atony of the isolated strips in rats after the addition of dopamine at a concentration of 10 -7 to 10 -4 mol/L. The decrease in uterine contractility was in direct proportion to the concentration of dopamine in the bath organ.…”

“…Blocking dopaminergic receptors with metoclopramide, domperidone and clozapine did not prevent from atony after the addition of dopamine. The obtained results indicated that the blocking effect of dopamine on uterus contractility was not carried out through dopaminergic receptors (Estan et al 1988).…”

“…Dopamine could cause uterine atony through stimulating adrenergic receptors. Similarly, Estan et al (1988) also obtained a blocking effect of dopamine on uterus contractility carried out through β-adrenergic receptors. However, blocking β-adrenergic receptors with propranolol or blocking α 1 -adrenergic ones with prazosine did not counteract uterine atony after the addition of dopamine.…”

Effects of Methoxamine on Spontaneous Uterine Activity and Blood Flow of the Rat Uterus ‘in vivo’

“…Moreover, similar to Borda et al [9], we show an increase in uterine activity mainly due to an increase in isometric tension, although the increase in frequency of contraction with 1 mg/kg of intravenous methoxamine also contributed to the maxi mal effect. Our results do not agree with previous findings from this laboratory with dopamine and noradrenaline [11]. although the drugs used and the experimental condi tions are different.…”