No abstract

The ultrastructure of the porcine myometrium was studied at well-defined stages of the oestrous cycle by transmission electron microscopy. The fine structure of the myometrium in the pig was found to be similar to that observed in other genital organs and species and did not show obvious variations through the oestrous cycle.The cell-to-cell contacts between smooth-muscle cells most consistently found were intermediate junctions and simple appositions, whereas interdigitations of muscle cell processes were more sparse. Gap junctions were few and small. Nerve terminals possessing presynaptic vesicles typical of the adrenergic and cholinergic type were found, though sparsely, both within and close to muscle bundles.

Earlier, it was questioned whether gap junctions (GJs) were necessary for cell-cell communication in smooth muscle, and GJs were not seen in some smooth muscles. We reexamined this question in the myometrium and in intestinal smooth muscle, in light of current knowledge of the presence and function of GJs. In the uterus, numerous studies show that an increase in GJ number is associated with the onset of delivery and is required for effective parturition. In all cases, this increase in GJ number and the changes in uterine contractility were correlated with increased electrical and metabolic coupling. Evidence for the much smaller, but detectable, degree of electrical coupling in the preterm uterus is explained by the small (but again detectable) number of GJs present. In the intestine, GJs are readily detected in the circular muscle layer but have not been described in the adjacent longitudinal layer. While our immunohistochemical studies failed to detect GJs in the longitudinal layer, this may not be adequate to prove their absence. Therefore, current knowledge of GJ number and function is adequate to explain cell-cell coupling in the uterus. Although it remains uncertain whether GJs are absent from the longitudinal muscle of the intestine, there is no definitive evidence that cell-cell coupling can occur by means other than GJs.

The fine structure of myometrium from pigs collected at well-defined stages during pregnancy was investigated by transmission electron microscopy. The morphology of the pregnant myometrium resembled that in non-pregnant pigs. Thick myofilaments were conspicuous during early pregnancy, inapparent during mid-pregnancy and visible again by days 80–84 and towards parturition. Gap junctions were extremely rare throughout pregnancy. Only occasionally were nerve axons observed.

Summary The presence and distribution of adrenergic and cholinergic (acetylcholine esterase‐containing) nerves within the porcine myometrium and cervix were investigated by histochemical methods. The pig myometrium showed a scanty intrinsic innervation. The acetylcholine esterase‐containing nerve fibres were mostly vasomotor, while the adrenergic ones were also seen among non‐vascular smooth muscle cells. The adrenergic nerves were distributed in both muscle layers, and they were more numerous adcervically. The cholinergic nerves were more numerous in the adtubal part of the cornua and the cervix than in the rest of the uterus, and they predominated in the circularly oriented muscle. The scantiness of the intrinsic innervation of the myometrium, compared to other areas of the pig genitalia, might reflect differences in the neurogenic modulation of the contractility. Zusammenfassung Verteilung der adrenergenen und cholinergenen Nerven im Schweine‐Myometrium während des Brunstzyklus. Eine histochemische Untersuchung Es wurden histochemische Untersuchungen über das Vorhandensein und die Verteilung adrenerger und cholinerger (Azetylcholinesterase‐haltiger) Nerven im Myometrium und in der Cervix des Schweines durchgeführt. Das Schweine‐Myometrium zeigte eine spärliche intrinsische Innervation. Die Azetylcholinesterase‐haltigen Nerven waren meist vasomotorische Nerven, während die adrenergenen Nerven auch zwischen den nicht‐vaskulären glatten Muskelzellen nachweisbar waren. Die adrenergen Nerven waren in beiden Muskelschichten verteilt. Sie nahmen zur Cervix hin zu. Die cholinergen Nerven waren im oviduktnahen Abschnitt der Uterushörner und in der Cervix häufiger als im übrigen Uterus. Sie überwogen in der zirkulär orientierten Muskulatur gegenüber der Längsmuskulatur. Die im Vergleich zu anderen Abschnitten des Geschlechtstrakts spärliche intrinsische Innervation des Myometriums beim Schwein dürfte Unterschiede in der neurogenen Modulation der Kontraktilität widerspiegeln.