Uterine motor responses to an alpha-adrenergic agonist (phenylephrine) in the ewe during oestrus and at the end of gestation

Reproduction, Nutrition, Development
M J Prud'homme

Abstract

The alpha-adrenergic activity of the myometrium was studied by recording the electromyographic activity (EMG) of the uterus in 4 conscious cyclic ewes during oestrus and in 8 conscious pregnant ewes during the last 6 days of gestation. In the cyclic ewes, changes in intra-uterine pressure were recorded at the same time as the EMG. Motor responses to perfusions of phenylephrine, a specific alpha-adrenergic agonist, were studied at three uterine sites. In the ewes in oestrus, uterine activity was stimulated at the three sites by perfusions with phenylephrine (0.6, 2.5, 5 or 10 micrograms/kg/min). The whole uterine horn was alpha-adrenergic-responsive. The effect of the drug was dose-dependent in that the uterine response increased with the dose and reached a plateau at 5 micrograms/kg/min. In the late pregnant ewes, the motor responses to the perfusion of phenylephrine at 10 micrograms/kg/min were studied at three uterine sites once a day during the last 6 days of gestation. Plasma levels of progesterone and total oestrogens were measured at the same time. Up to 48 h before parturition, the effect of phenylephrine depended on the uterine site. The drug had no or little effect at the tubal end of the horn. Phenylephrine stimulated...Continue Reading

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