MUSCLE LAYER AND REGIONAL DIFFERENCES IN AUTONOMIC INNERVATION AND RESPONSIVENESS TO TRANSMITTER AGENTS IN SWINE MYOMETRIUM

1 To clarify possible regional and muscle layer differences in adrener gic innervation of swine myometrium, functional, biochemical and histo chemical experiments were performed on longitudinal (LM) and circular (CM) muscle isolated from non-pregnant uteri of 84 gilts. 2 Transmural stimulation (TMS) in the presence of propranolol evoked tetrodotoxin- sensitive contractions in a frequency-dependent manner (2-20 Hz) in LM and CM. The cornual LM contractions were attenuated by phentolamine ( 1 mu M) and by guanethidine (10 mu M) though unaffected by atropine (1 mu M). Contractions in cervical LM were diminished by atropine but no t by phentolamine, and the corpus LM contractions were reduced increme ntally by atropine and phentolamine when added sequentially. In CM, th e TMS-induced contractions were abolished by tetrodotoxin and atropine in all three regions. 3 In response to noradrenaline (NA) and acetylc holine (ACh), LM contractile intensity was the most potent in cornua, slightly weaker in the corpus and weakest in the cervix. CM was insens itive to NA, and contractile responses elicited by ACh indicated no re gional variation. 4 NA content, significantly greater in LM than in CM , was most highly concentrated in cornual LM. Nerves exhibiting glyoxy lic acid-induced histofluorescence occurred in both LM and CM, though more abundantly in LM and with notable density in the cornual LM. Chol inesterase activity, distributed evenly throughout the three myometria l regions studied, was more intense in LM than in CM. 5 These results show that, in swine myometrium, innervation in cornual LM is predomina ntly noradrenergic, cervical LM is mostly cholinergic, and throughout the myometrium the CM layers are principally cholinergic.