Molecular mechanisms of adenylyl cyclase desensitization in pregnant rat myometrium following in vivo administration of the beta-adrenergic agonist, isoproterenol.
Beta-adrenergic agonists are widely used for preterm labor treatment, but their effectiveness may be limited by desensitization. We thus investigated the effects of a beta-agonist, isoproterenol, on the myometrial beta-adrenergic receptor (beta-AR)/adenylyl cyclase pathway after administration in vivo to late-pregnant rats (8 mg/kg, twice-daily injections). One hour after the first injection, isoproterenol-stimulated adenylyl cyclase activity was reduced by 37%. This was associated with a rapid and transient uncoupling of the beta2-ARs (53% reduction of high-affinity receptors). After prolonged isoproterenol treatment (76 h), adenylyl cyclase activity was desensitized not only to isoproterenol but also to guanosine triphosphate and forskolin. Such treatment induced 1) a selective decrease of beta2-ARs as assessed by 125I-cyanopindolol binding, which was reversed by 5'-guanylylimidodiphosphate and thus probably did not involve irreversible loss of receptors, and 2) a rapid alteration of their transcript levels. Prolonged isoproterenol treatment also led to myometrial Gi2alpha and Gi3alpha increase (44% and 70%) as assessed by Western blotting. Furthermore, pertussis toxin pretreatment of membranes abolished the decrease in isoproterenol-stimulated adenylyl cyclase activity. Thus, we demonstrated that myometrial adenylyl cyclase desensitization after beta-agonist treatment results mainly from beta2-AR uncoupling and increase in Gi activity.
Laboratoire de Physiologie de la Reproduction, CNRS URA 1449, Université P.M. Curie, Paris, France.
J L
JL
Lécrivain
J
J
Cohen-Tannoudji
M T
MT
Robin
N
N
Coudouel
C
C
Legrand
J P
JP
Maltier
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004361:Drug Tolerance; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology*; D009215:Myometrium / Q000187:drug effects / Q000201:enzymology*; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000235:genetics / Q000502:physiology
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; C047975:cyanopindolol; D006160:Guanosine Triphosphate; D010869:Pindolol; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol