Regulation of myometrial phospholipase C system and uterine contraction by beta-adrenergic receptors in midpregnant rat.
We investigated whether beta-adrenergic receptors (beta-AR) regulate the phospholipase C (PLC) system in midpregnant rat myometrium. PLCbeta isoforms were characterized, and the effect of isoproterenol (beta-adrenergic agonist) was tested on myometrial inositol phosphate (InsP) production and uterine contraction. Using specific antibodies, we showed that rat myometrium expresses PLCbeta1, PLCbeta3, and PLCbeta4, and to a lesser degree PLCbeta2. Quantitative analysis revealed that PLCbeta isoforms are differentially expressed during pregnancy. Indeed, the amount of PLCbeta4 is increased at midpregnancy, whereas PLCbeta1, PLCbeta2, and PLCbeta3 are up-regulated at term. At midpregnancy, pretreatment of myometrial strips with isoproterenol significantly reduced basal and agonist-stimulated InsP production. Forskolin, a diterpene that increases cAMP accumulation by directly activating adenylyl cyclases, had no effect on InsP production. In contrast, two global potassium (K+) channel inhibitors, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), prevented attenuation of InsP production by isoproterenol. Isoproterenol also significantly decreased spontaneous and agonist-induced contraction of the longitudinal layer of midpregnant rat myometrium. Preincubation of uterine strips with TEA plus 4-AP prior to beta-AR activation blocked only partial uterine relaxation, whereas Forskolin was as potent as isoproterenol. This indicates that beta-AR operate through both K+ channels and cAMP to induce uterine relaxation. In conclusion, we show for the first time that three myometrial PLCbeta isoforms (PLCbeta1, PLCbeta2, and PLCbeta3) are down-regulated at midpregnancy. At this period, beta-AR reduce basal and agonist-stimulated InsP production through activation of K+ channels. Altogether, these mechanisms could act to decrease responsiveness of the longitudinal layer of myometrium to contractant factors.
Laboratoire de Physiologie et Physiopathologie, UMR-CNRS 7079, 75252 Paris CEDEX 05, France. smhaouty@pasteur.fr
Sakina
S
Mhaouty-Kodja
Eric
E
Houdeau
Chantal
C
Legrand
D015761:4-Aminopyridine / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D005576:Colforsin / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009215:Myometrium / Q000201:enzymology*; D054799:Phospholipase C beta; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D019789:Tetraethylammonium / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D007527:Isoenzymes; D026902:Potassium Channel Blockers; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D007545:Isoproterenol