Tubal muscles determine embryo implantation site; prognosis of ectopic pregnancy at chronic functional disorders

Abstract

Mammalian oviducts contain smooth muscles and inward-facing ciliated epithelium. Muscular contractions, not ciliary beating, propel oocytes through the oviduct towards the uterus. In crawling gastropods (unique models for studying the functioning of phasic smooth muscles), muscular contractions, propagating along the foot sole, play a principal role in determining the crawling rate. We have described the muscular mechanisms controlling the crawling rate and hypothesize here that the same mechanisms provide embryo transportation through the human fallopian tube. The data collected for gastropods were transferred to the human fallopian tube, using embryo speed and tube length (tonus) instead of crawling speed and sole length. Smooth muscle active states: tonic contraction/relaxation and rhythmic contractions (peristalsis) are involved in ovum transport. The ovum/embryo speed is linearly correlated with the tonus of the longitudinal and/or the circular muscles of the tube. Some known bioactive substances control muscular tonus and we suppose embryo speed through the contraction force of muscle cells involved in peristaltic waves. Other known substances facilitate peristalsis and we suppose that they have no effect on muscular tonus and increase dose-dependently embryo speed through the number of muscle cells recruited in peristaltic waves (at a constant wave frequency). This number depends on the physiological state of the woman. The combination of all possible effects and the ability of muscles to contract rhythmically determine the embryo speed and its implantation site. This hypothesis is the first description of the tubal muscular mechanisms that determine normal and any type of ectopic pregnancy at chronic disorders of tubal contractility. How to predict ectopic pregnancy? We have reason to assume that the intensity of rhythmic uterine contractions reflects that in the fallopian tube. It is known that uterine contractility significantly increases during the preovulatory phase and decreases during the mid-luteal phase. The hypothesis supposes that in women with increased risk of ectopic pregnancy, decreased uterine contractility during the preovulatory phase in comparison with the norm indicates a future tubal/abdominal gestation; increased uterine contractility during this phase and/or the mid-luteal phase as compared to the norm points to a future cervical pregnancy. The optimal methods for recording uterine activity are up to clinicians.