Comparative effects of 6-hydroxydopamine and -adrenoceptor antagonists on intrauterine migration and spacing of blastocysts in the rat

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Abstract
Sympathetic nerve terminals were destroyed by administration of 6-hydroxydopamine (2 .times. 50 mg/kg) at 10:00 h on Days 4 and 5 of pregnancy in the rat. In the myometrium, this treatment markedly decreased noradrenaline concentrations (by 99%, p < 0.001), demonstrating that myometrial noradrenaline is mainly originated from sympathetic nerves; therefore after 6-hydroxydopamine, the distribution and spacing of blastocysts remain unaffected throughout the uterus. Administration of phenoxybenzamine (2 .times. 6 mg/kg) in the morning of Days 4 and 5, or prazosin (4 .times. 3 mg/kg) from 12:00 h on Day 4 until 12:00 h on Day 5 disorganized the even distribution of blastocysts from the tubal end to the cervical end of the uterine horns. These results provide evidence that a noradrenergic transmission via action on myometrial post-synaptic .alpha.1-adrenoceptors is involved as a regulatory mechanism of uterine motility for distribution and spacing of blastocysts in the rat uterus.