Introduction to 'electrical propagation in smooth muscle organs'

Characteristics of bioelectrical activity of oviducts and uterus during early pregnancy in sows recorded by telemetry method

NEW FINDINGS

What is the central question of this study? The aim of present study was to record and analyse the myoelectrical activity in the female pig reproductive tract (uterus and oviduct) during early pregnancy. What is the main finding and its importance? Understanding the contractile activity of the uterus and oviducts is indispensable for understanding the physiological mechanisms as well as all irregularities associated with the period of conception and early pregnancy. The aim of the present study was to record the myoelectrical activity of the reproductive tract in sows during the oestrous phase and early pregnancy via a telemetry recording system. In a total of eight non-pregnant pigs, the bioelectrical activity was recorded through three silicone electrodes sutured on the oviduct (isthmus and ampulla) and the uterine horn. Blood samples were collected to monitor the concentrations of progesterone (P4) and luteinizing hormone (LH). The oestrous cycle was synchronized with equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG), and the animals were subjected to artificial insemination. Analysis of the EMG activity of the oviduct and uterus in the oestrous phase and in early stages of pregnancy suggests explicitly that telemetry could enable in vivo assessment of myoelectrical activity of parts of the reproductive system in sows. Off-line analysis of the duration of EMG activity bursts in the uterus, isthmus and ampulla were significantly higher during early pregnancy (phases II and III) than in the oestrous phase. The EMG signals demonstrated low mean amplitudes of activity in the oviduct and uterus during early pregnancy (phases I-III). Significant differences between the root mean square signals were observed in the isthmus and ampulla both during oestrus and in early pregnancy (phase I; P < 0.01). During the oestrous phase, the P4 concentration was estimated at <1 ng ml^-1 , whereas the LH concentration was >4 ng ml^-1 . In contrast, during early pregnancy, the P4 and LH concentrations were estimated at >4 and <1 ng ml^-1 , respectively.

Bioelectrical activity of porcine oviduct and uterus during spontaneous and induced estrus associated with cyclic hormone changes

It is widely accepted that uterine contraction is initiated by spontaneous generation of electrical activity at a cellular level in the form of action potentials. Such action potential events, when they involve many myometrial cells and occur in immediate succession, are described by their amplitude and duration. In an effort to improve clinical management of uterine contractions, research has focused on determination of the properties of the reproductive tract's electrical activity under hormonal stimulation. The aim of this study was to evaluate the myoelectric activity (amplitude and duration) of the oviduct and the uterus in relation to plasma concentration of LH, estradiol (E2), and progesterone (P4) during spontaneous and induced estrus in gilts. The course of the experiment was divided into eight periods defined by hormone concentrations (LH, P4, and E2) and time intervals before and after the start of the LH surge. Myoelectric signals were recorded, and the hormone levels were measured during proestrus and estrus in natural and hormone-induced estrus cycle. During the natural estrus, the LH surge was longer than after hormonal stimulation (28 vs. 20 hours) and suggested an inverse relationship between the LH concentration and the duration of myoelectric activity (S_R = -0.68). Analyses of the records of the amplitudes and durations of the electromyography activity in uterine horns and oviducts showed significant differences between spontaneous and induced estrus (P < 0.05). During induced estrus, the LH surge began earlier (T1 vs. T2) and increased more (7.46 vs. 6.50 ng/mL) than during spontaneous estrus. This observation suggests a direct relationship between the LH concentration and the amplitude of the myoelectric activity (Spearman rank correlation = 0.71). The significantly higher duration and amplitude of the activity in the isthmus of the oviduct and the uterus during induced estrus shortly after the onset of standing heat (4-8 hours after the LH surge) suggested more favorable conditions for effective artificial insemination.

The location of pacemakers in the uteri of pregnant guinea pigs and rats

The pregnant uterus is a smooth muscle organ whose pattern of contraction is dictated by the propagation of electrical impulses. Such electrical activity may originate from one or more pacemakers, but the location of these sites has not yet been determined. To detect the location of the pacemaker in the gravid uterus, two approaches were used: 1) determine the site from where the contraction started using isolated uteri from the pregnant guinea pig, and videotape their contractions; and 2) record, in isolated uteri from pregnant term rats, with 240 extracellular electrodes simultaneously, and determine where the electrical bursts started. In both the contractile and electrophysiological experiments, there was not a single, specific pacemaker area. However, most contractions (guinea pig 87%) and bursts (rat 76%) started close to the mesometrial border (mean 2.7 ± 4.0 mm SD in guinea pigs and 1.3 ± 1.4 mm in rats). In addition, in the rat, most sites of initiations were located closer to the ovarial end of the horn (mean distance from the ovarial end 6.0 ± 6.2 mm SD), whereas such an orientation was not seen in the guinea pig. In both guinea pig and rat uteri at term, there is not one specific pacemaker area. Rather, contractile and electrical activity may arise from any site, with the majority starting close to the mesometrial border. Furthermore, in the rat, most activities started at the ovarial end of the horn. This may suggest a slightly different pattern of contraction in both species.