Smooth muscle electromyography for detecting major alterations in the estrus cycle in rats.

Determining the female animal cycle is crucial in preclinical studies and animal husbandry. Changes in hormone levels during the cycle affect physiological responses, including altered contractility of the visceral smooth muscle. The study aimed to identify estrus and anestrus using smooth muscle electromyographic (SMEMG) measurements, in vivo fluorescent imaging (IVIS) and in vitro organ contractility of the uterus and cecum. The study involved sexually mature female Sprague-Dawley rats, aged 10-12 weeks. The rats received a daily injection of cetrorelix acetate solution for 7 days, while another group served as the control. The animals were subjected to gastrointestinal and myometrial SMEMG. The change in αvß3 integrin activity was measured with IVIS in the abdominal cavity. Contractility studies were performed in isolated organ baths using dissected uterus and cecum samples. Plasma samples were collected for hormone level measurements. A 3-fold increase in spontaneous contraction activity was detected in SMEMG measurements, while a significant decrease in αvß3 integrin was measured in the IVIS imaging procedure. Cetrorelix reduced the level of LH and the progesterone / estradiol ratio, increased the spontaneous activity of the cecum rings, and enhanced KCl-evoked contractions in the uterus. We found a significant change in the rate of SMEMG signals, indicating simultaneous increases in the contraction of the cecum and the non-pregnant uterus, as evidenced by isolated organ bath results. Fluorescence imaging showed high levels of uterine αvß3 integrin during the proestrus-estrus phase, but inhibiting the sexual cycle reduced fluorescence activity. Based on the results, the SMEMG and IVIS imaging methods are suitable for detecting estrus phase alterations in rats.

Non-genomic actions of steroid hormones on the contractility of non-vascular smooth muscles.

Steroid hormones play an important role in physiological processes. The classical pathway of steroid actions is mediated by nuclear receptors, which regulate genes to modify biological processes. Non-genomic pathways of steroid actions are also known, mediated by cell membrane-located seven transmembrane domain receptors. Sex steroids and glucocorticoids have several membrane receptors already identified to mediate their rapid actions. However, mineralocorticoids have no identified membrane receptors, although their rapid actions are also measurable. In non-vascular smooth muscles (bronchial, uterine, gastrointestinal, and urinary), the rapid actions of steroids are mediated through the modification of the intracellular Ca2+ level by various Ca-channels and the cAMP and IP3 system. The non-genomic action can be converted into a genomic one, suggesting that these distinct pathways may interconnect, resulting in convergence between them. Sex steroids mostly relax all the non-vascular smooth muscles, except androgens and progesterone, which contract colonic and urinary bladder smooth muscles, respectively. Corticosteroids also induce relaxation in bronchial and uterine tissues, but their actions on gastrointestinal and urinary bladder smooth muscles have not been investigated yet. Bile acids also contribute to the smooth muscle contractility. Although the therapeutic application of the rapid effects of steroid hormones and their analogues for smooth muscle contractility disorders seems remote, the actions and mechanism discovered so far are promising. Further research is needed to expand our knowledge in this field by using existing experience. One of the greatest challenges is to separate genomic and non-genomic effects, but model molecules are available to start this line of research.