Relaxation Of Rat Uterus Research Articles

Myometrial Calcium and Potassium Channels Play a Pivotal Role in Chromium-Induced Relaxation in Rat Uterus: an In Vitro Study.

Hexavalent chromium, a well-known environmental toxicant, adversely affects female reproduction and results in abnormal implantation, fetal resorption, and reduction in litter size. Uterine myogenic activity is under control of number of receptors and ion channels, and it regulates fetal-implantation and feto-maternal communication. Despite several known adverse effects of chromium on female reproduction, direct action of chromium on myometrial activity is yet to be understood. In the present study, the effect of in vitro exposure of hexavalent chromium (Cr-VI) on the myogenic activity of isolated myometrial strips of rats was evaluated after mounting the tissue in thermostatically (37 ± 0.5°C) controlled organ bath under a resting tension of 1g. Chromium produced concentration-dependent (0.1nM-0.1mM) inhibitory effect on myometrial activity. Following pre-treatment of the myometrial strips with glibenclamide (a KATP channel blocker) and 4-aminopyridine (a Kv channel blocker), the concentration-response curve (CRC) of chromium was significantly (P < 0.05) shifted towards right with decrease in the maximum relaxant effect. Contractile effects of CaCl2 and BAY K-8644 (a selective opener of L-type Ca2+ channel) were significantly (P < 0.05) attenuated in the presence of chromium. Chromium-induced myometrial relaxation was also significantly (P < 0.05) reduced in the presence of ICI 118,551 (a selective β2-antagonist) and SR 59230A (a selective β3-antagonist). These findings evidently suggest that chromium produced relaxant effect on rat myometrium by interfering with Ca2+ entry through voltage-dependent Ca2+ channels, and by interacting with beta-adrenoceptors (β2 and β3) and potassium channels (especially KATP and Kv channels). Graphical Abstract Proposed signaling pathway(s) of chromium (VI)-induced myometrial relaxations in rats. KATP: ATP-sensitive K+ channel; KV: voltage-dependent K+ channel; VDCC: voltage-dependent Ca2+ channel; [Ca2+]i: intracellular calcium concentration, stimulatory mechanism, inhibitory mechanism.

P69 Sodium sulphide relaxation of rat uterus is related to calcium signaling

H2S was shown as an uterine relaxant. However, the signaling pathways, including ion channels regulated by H2S mediating relaxation in uterus are still unknown. The effects on contractility in response to sodium sulphide Na2S were examined on myometrial strips from virgin Wistar rats. Our results showed that Na2S induces concentration-dependent relaxations affecting amplitude as well as frequency of contractions. Activation of potassium channels, and in particular of KATP, was one of the primary mechanisms proposed, responsible for the relaxing effects of H2S. Sodium sulphide (20–200 × 10−6 M) inhibits myometrial contractility through a K-channel-independent mechanism. An inhibitor of 4,4 – inhibitor of Cl - / HCO 3 - exchanger and/or Cl− channel, DIDS, caused a significant rightward shift of the Na2S concentration–response curve. We performed experiments aimed at different Ca2+ concentrations, using spontaneous, calcium and KCl (15 mM and 75 mM) induced contractions, as well as pharmacological inhibitors of calcium channels and modulators, showing that Na2S induced relaxation is dependent on the precontractile agent used. Taken together, our results suggests that decreased frequency induced by Na2S could be a consequence of a alterated pacemaker cells which might be related for Ca2+ events originates from sarco endoplasmatic reticulum and/or mitochondria.

Platypus Venom and Envenomation.

Curiosity and controversy have surrounded the function of the crural system of the platypus since its discovery in the late 18th century. Early work on the venom confused rather than clarified the biological significance of the crural system. Many experiments gave conflicting results, especially concerning the coagulation effects of intravenous injections of venom extracts, although consistent observations were made of general vasodilation following intravenous injection into rabbits. More recent studies have shown that crural (venom) gland activity is seasonal and in synchrony with the breeding season. Secretion from the crural glands shows proteolytic activity and contains at least three major proteins, one of which has hyaluronidase activity. Subcutaneous injection of venom produced mild toxic effects whereas intravenous doses (75-90mg protein/kg) in mice were lethal. Whole venom induced local oedema after subplantar injection in rats and a 4.2kD peptide isolated from the venom caused relaxation of rat uterus in vitro. At least 16 incidents of envenomation by the platypus have been recorded in humans but no fatalities have been reported. In most human cases, envenomation resulted in immediate and severe local pain and oedema, sometimes associated with nausea, cold sweats, dull gastric pain and vomiting, hyperaesthesia and swelling of the axillary lymph nodes. Significant functional impairment of the upper limb for some weeks or months has been observed. Various treatments have been used to alleviate the symptoms of envenomation with differing successes. Envenomation has also been recorded in platypuses and dogs. The effects of these envenomations will be discussed.

Influence of cadmium ions on contractile response of isolated aortas to stimulatory agents.

Influence of cadmium ions on contractile response of isolated aortas to stimulatory agents.

Potentiation of inhibitory and excitatory effects of catechol amines by bretylium.

Enhancement of both excitatory and inhibitory responses to adrenaline, noradrenaline and isoprenaline was demonstrated with bretylium both in vivo and in vitro. Excitatory responses studied included rise of blood pressure and contraction of the nictitating membrane in cats and the contraction of aortic strip in rabbits; the inhibitory responses studied were fall of cat blood pressure and relaxation of rat uterus and rabbit tracheal chain. Possible mechanisms of potentiation of the effects of catechol amines by bretylium are discussed. A sensitization of the peripheral effector cells is suggested as a likely mechanism of potentiation.