[Influence of adrenergic denervation on uterine contractility of pregnant rats in vitro].

The aim of the present study was to investigate the functional changes in the sympathetic nerves in the rat myometrium during pregnancy by electric field stimulation (EFS) in vitro. In our experiments the contractility of the rat myometrium were registered at 5, 10, 15, 18, 20, 22 (term) day of pregnancy, in non pregnant rats and in 6-OH-dopamine pretreated rats. The parameters of EFS were the following: pulse width 0.6 ms, frequency range of nerve stimulation 1-70 Hz, supramaximal voltage 40 V. We concluded that low pulse width and low frequency stimulation is selective for adrenergic nerves. We found that during pregnancy a gradual drop-out of low frequency induced uterine smooth muscle contraction appears. It is surprising that very low frequency stimulation has no effect on the 5th day of pregnancy although the same frequency stimulation causes contraction on the 10th day. By the 22nd day of pregnancy the rat uterus shows the same responsiveness to nerve stimulation as it is detected in 6-OH-dopamine pretreated non pregnant rats. The adrenergic denervation of the pregnant uterus does not mean that it loses the ability to respond to cathecholamines since non-synaptic adrenergic receptors exist in the late pregnant rat uterus.