Effect of Adrenergic Nerve Stimulation on the Rabbit Oviduct: Correlation with Norepinephrine Content and Turnover Rate1

Abstract

The effects of adrenergic nerve stimulation on the motility of the oviductal isthmus of the rabbit were correlated with certain parameters of norepinephrine (NE) metabolism and with the hormonal environment of the muscle. Mature, virgin, Dutch rabbits were ovariectomized and grouped as follows: I = 12 days post-ovariectomy (p.o.); II = 12 days p.o. + 8 days 0.25 µg/kg estradiol-17β, i.,.; III = 12 days p.o. + 8 days 0.25 µg/kg estradiol-17β + 2.5 mg/kg progesterone i.m. on final 4 days. After treatment one oviductal isthmus was removed for NE determinations and the contralateral isthmus was arranged for simultaneous recording of the longitudinal and circular muscle activity during stimulation of adrenergic (perivascular) nerves. Stimulation (5–50 Hz) caused contractions of both circular and longitudinal muscles in Groups II and III but only in the circular muscles of castrates (I). Contractions were prevented by phentolamine and tetrodotoxin but unaffected by propanolol or atropine. The NE content (nmoles/isthmus) was significantly lower in castrates than in hormonally-treated animals (I = 1.03 ± 0.11; II = 1.55 ± 0.14; III = 1.42± 0.10), but the concentration of NE (nmoles/g wet weight) was not different among the three groups (I = 13.43 ± 1.6; II 15.54 ± 2.2; III = 13.85 ± 2.2). Turnover rates (nmoles/g/h) for NE were also significantly lower in the castrates (I = 0.54 ± 0.05; II = 1.29 ± 0.15; III = 1.35 ± 0.07). Turnover of NE was much higher in atria than in oviducts and not influenced by castration or hormone treatment. These findings suggest that estrogen is essential for adequate release of transmitter during adrenergic stimulation and/or for electrical communication between the muscle layers. Progesterone, in the concentration used here, has little additional effect. In vivo, tonic, nervous activity is probably quite low in castrates compared with hormonally-treated animals as suggested by the respective rates of turnover of NE. However, even in the latter animals the adrenergic tone is considerably less in oviducts than in atria.