SMOOTH-MUSCLE LAYER-SPECIFIC VARIATIONS IN THE AUTONOMIC INNERVATION OF BOVINE MYOMETRIUM

1. To clarify the autonomic innervation regulating longitudinal muscle (LM) and circular muscle (CM) motility in the bovine uterus, function al (nerve stimulation adrenergic drug responsiveness) and biochemical studies (catecholamine content, radioligand binding) were conducted on parous luteal phase myometrium.2. Electrical field stimulation (EFS; 60 V, 0.5-msec duration) caused tetrodotoxin (1 mu M)-sensitive contra ctions in a frequency dependent manner (0.5-20 Hz) in both LM and CM l ayers. 3. The EFS-induced LM contractions were potentiated by proprano lol and conspicuously decreased by phentolamine, yohimbine, idazoxan o r guanethidine, but were unaffected by prazosin or atropine. 4. On the other hand, CM contractions were only slightly decreased by phentolam ine, idazoxan, yohimbine and guanethidine, but were insensitive to pro pranolol, prazosin or atropine. 5. The noradrenaline content in LM was about five times higher than that in CM. 6. Noradrenaline, adrenaline , clonidine, xylazine, UK14,304 and phenylephrine caused concentration -dependent contractions of both smooth muscle layers. 7. Clonidine, UK 14,304 and xylazine were more potent contractile agents than noradrena line and phenylephrine. 8. The contractile response to noradrenaline w as competitively antagonized by yohimbine, but not by prazosin. 9. Bin ding studies using [H-3]-prazosin and [H-3]-rauwolscine revealed that the bovine myometrium contained both alpha(1)- and alpha(2)-adrenocept ors, but the alpha(2)-type receptor was dominant in both LM (94% of al pha-adrenoceptors) and CM (88%) layers. 10. The distribution of alpha- adrenoceptors was muscle layer specific; that is, the concentration of alpha(1)-receptors in LM was the same as in CM, but the concentration of alpha(2)-receptors in LM was 2.6 times higher than that in CM. 11. The results of the present study indicate that there are layer specif ic variations in the functional innervation of the parous bovine myome trium (exclusive adrenergic innervation in LM and adrenergic [minor] p lus nonadrenergic, noncholinergic innervation [major] in CM), and that alpha(2)-adrenoceptors, which were responsive to the excitatory respo nse of endogenous and exogenous noradrenaline, were dominant in both m uscle layers of the bovine myometrium. (C) 1998 Elsevier Science Inc.