Effects of porcine relaxin on contraction, membrane response and cyclic AMP content in rat myometrium in comparison with the effects of isoprenaline and forskolin

Abstract

1 The longitudinal muscle from the uterus of oestrogen-treated rats was quiescent in Mg-free Krebs solution. Electrical stimulation generated phasic contraction, which was depressed to 35% and 18% by 50 mu and 150 mu porcine relaxin, respectively. 2 The phasic contractions were more strongly depressed to 26% by 50 mu relaxin in solution containing 0.6 mm Mg, and the depression lasted for more than 4 h after the removal of relaxin. During the persisting depression, raising the external Ca to 7.5 mm did not restore the contraction, but the contraction was restored by removal of Mg. 3 The depression of the phasic contraction by relaxin, examined in Mg-free solution, was enhanced and reduced by pretreatment of the tissue with 0.6 mm Mg and 0.6 mm Mn, respectively, for about 15min. In contrast, the depression of contraction by isoprenaline or forskolin was enhanced by pretreatment with either Mg or Mn. 4 The cellular content of cyclic AMP was measured in Krebs solution containing 0.6 mm Mg. The values were 1.24 (pmolmg-' protein) in control solution, and 2.31 and 1.56 when the tissues were treated with 150 mu relaxin and 10-9 M isoprenaline, respectively. 5 The cyclic AMP production in response to 10-7M forskolin measured in Mg-free solution was enhanced when the tissue was pretreated with either 0.6mm Mg or Mn for 15min. The cyclic AMP production in response to 100mu relaxin was increased when the tissue was pretreated with 0.6mm Mg, and was unchanged by pretreatment with Mn. The cyclic AMP production in response to 10-9M isoprenaline was unchanged by pretreatment with the divalent cations. 6 The membrane potential of the muscle was -60.8mV in Krebs solution containing 0.3mm Mg, and electrical stimulation induced an action potential which consisted of spike and plateau components. Application of 150mu relaxin reduced the duration of the plateau; the contractions were progressively depressed. The resting membrane potential and membrane resistance were unchanged by application of 150 mu relaxin. The membrane was hyperpolarized by 2.8 mV, accompanied by a decrease in membrane resistance, when I0-9 M isoprenaline was applied. 7 Although there were several differences between the effects of relaxin and isoprenaline, it is probable that some process, which is cyclic AMP-dependent, accelerated by Mg and depressed by Mn, is involved in the depressant action of relaxin on contraction.

Physiological significance of hyperpolarization-activated inward currents ( I h ) in smooth muscle cells from the circular layers of pregnant rat myometrium

“…It is well known that the spontaneous electrical activities of longitudinal and circular muscle cells differ in pregnant rat uterus and that circular muscle cells show much higher spontaneous activity than longitudinal muscle cells [17,22,24]. In preliminary experiments, on mid-pregnant rat uterus, we confirmed that spontaneous contractions could be recorded only in the circular muscle, while electrical stimulation was required to generate muscle contractions in the longitudinal layer (K. Okabe, unpublished observations).…”

Relaxin Positively Regulates Matrix Metalloproteinase Expression in Human Lower Uterine Segment Fibroblasts Using a Tyrosine Kinase Signaling Pathway

“…Our previous data, which demonstrate that relaxin does not increase intracellular levels of cAMP in human lower uterine segment fibroblasts, suggest that the relaxin receptor is not a heterotrimeric G protein-associated receptor (23). Although increased intracellular cAMP concentrations in several cell types are associated with relaxin treatment (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), to date no data have been provided by any studies that demonstrate coupling of a relaxin-receptor complex to a heterotrimeric G protein-coupled receptor.…”

“…The structure of the relaxin receptor is unknown, and no complete signaling pathway has been identified. Relaxin action in several cell types is associated with the cAMP/adenylate cyclase/PKA pathway (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). However, no data that demonstrate coupling of a relaxin-receptor complex to a heterotrimeric G protein have been provided.…”

International Union of Basic and Clinical Pharmacology. XCV. Recent Advances in the Understanding of the Pharmacology and Biological Roles of Relaxin Family Peptide Receptors 1–4, the Receptors for Relaxin Family Peptides

“…4). Early studies before receptor identification, showed that treatment with relaxin increased cAMP accumulation in THP-1 cells (Parsell et al, 1996), MCF-7 cells (Bigazzi et al, 1992), the mouse pubic symphysis (Braddon, 1978), uterine strips (Sanborn et al, Relaxin Family Peptide Receptors 1980), uterine longitudinal muscle (Osa et al, 1991) from estrogen-primed rats, and in cultures of human endometrial cells (Fei et al, 1990), human endometrial glandular epithelial cells (Chen et al, 1988), newborn rhesus monkey uterine cells (Kramer et al, 1990), rat myometrial cells (Hsu et al, 1985), and rat anterior pituitary cells (Cronin et al, 1987). The importance of cAMP as a signaling pathway for relaxin was confirmed on RXFP1 deorphanization, because constitutively active mutants of RXFP1 (TM6: D637Y) increased cAMP accumulation in a ligandindependent manner (Hsu et al, 2000.…”