A functional and structural study of the innervation of the human uterus

We characterized the innervation of human myometrial tissues by electrical field stimulation and electron microscopy. Nerve-specific parameters (pulse duration 0.6 msec) were used for electrical field stimulation to selectively activate intrinsic nerves. In specimens from nonpregnant, nonparous women (n = 6), tetrodotoxin (10(-6) mol/L) significantly reduced the response to electrical field stimulation by 70%. Contractions to electrical field stimulation were also inhibited to 60% by atropine (10(-5) mol/L) as well as by guanethidine (10(-5) mol/L) and phentolamine (10(-5) mol/L). Propranolol (10(-5) mol/L) had no detectable effect. We obtained similar results from about 50% of the specimens from nonpregnant, parous women (n = 15). The contractile responses of specimens from the term pregnant uterus (n = 13) to electrical field stimulation were not influenced by tetrodotoxin. Ultrastructurally we found nerve profiles in close proximity to muscle cells. About 30% of nerve varicosities in tissues from nonpregnant, nonparous patients could be classified as adrenergic (small, dense-cored vesicles), 53% as cholinergic (small, agranular vesicles), and about 17% as indeterminant (sometimes large, dense-cored vesicles). However, nerve varicosities were rarely observed in term pregnant specimens. These results indicate the presence of tetrodotoxin-sensitive, excitatory innervation of human myometrium consisting of alpha-adrenergic and cholinergic components. Furthermore, denervation may be nearly complete at term and recovery of innervation occurs at a considerable length of time after delivery.