In vivo stimulation of the beta(2)-adrenergic pathway increases expression of the Gi proteins and the alpha(2)A-adrenergic receptor genes in the pregnant rat myometrium

Abstract

Cross-regulations between G s and G i mediated pathways controlling the adenylyl cyclase activity have been clearly demonstrated in vitro. To elucidate whether activation of the -adrenergic pathway in the pregnant myometrium might affect G i proteins and 2 -adrenergic receptors (ARs), we treated late pregnant rats from day 18 to day 21 with twice-daily administration of isoproterenol (8 mg/ kg). This treatment increased myometrial cAMP levels and led after 76 h to a significant and maximal rise in the immunoreactive amount of myometrial G i 2 and G i 3 proteins (1·4-and 1·7-fold respectively) associated with a parallel increase of the steady-state levels of both G i 2 and G i 3 mRNA (1·6-and 1·9-fold respectively). Propranolol antagonized this response indicating the implication of the -adrenergic pathway. Nuclear run-on assays demonstrated that isoproterenol enhanced respectively by 1·3-and 1·2-fold the transcription rate of the G i 2 and G i 3 genes. Quantification of myometrial 2 -ARs by [3 H]rauwolscine binding revealed that the total number of receptors was also increased at 76 h by 1·7-fold when compared with controls, with no change in the affinity of the 2 -ARs for the ligand. This effect was antagonized by propranolol. Quantification of both 2A -and 2B -subtypes by Northern blotting analysis demonstrated that this elevation was due to a selective increase of the 2A -subtype mRNAs. The present results indicate that in vivo stimulation of the -adrenergic pathway by isoproterenol increases both G i 2 /G i 3 and 2A -AR expression in the pregnant rat myometrium. The possible contribution of such a mechanism in pregnancy-related changes of both entities is discussed.

β-Adrenoceptor-mediated cell signaling in the neonatal heart and liver: responses to terbutaline

“…We therefore examined the responses mediated by ␣ 2 -ARs, which ordinarily act as a negative modulators of AC activity through coupling to G i . We found that stimulation of neonatal hepatic ␣ 2 -ARs potentiated isoproterenol-stimulated cAMP production, an effect previously observed in the fetal liver (1) and in the pregnant rat myometrium (11). Neonatal terbutaline treatment did not alter this pattern.…”

“…Effects of terbutaline on the liver. Neonatal terbutaline had a much greater effect on hepatic ␤-AR binding than on cardiac ␤-ARs (treatment ϫ tissue, P Ͻ 0.0001; [11][12][13][14]. Despite the marked decline in ␤-ARs, the ability of isoproterenol to stimulate AC activity was only slightly reduced (10-15%), an effect clearly distinguishable from the robust receptor downregulation (treatment ϫ measure, P Ͻ 0.0001).…”

Molecular Mechanisms of Adenylyl Cyclase Desensitization in Pregnant Rat Myometrium following In Vivo Administration of the β-Adrenergic Agonist, Isoproterenol

“…Using immunoblotting studies, we first established that isoproterenol treatment increases Gi2␣ and Gi3␣ levels in myometrial membranes. Previous results from our laboratory demonstrated that this increase results from transcription rate activation of both genes [38]. Upregulation of Gi expression after activation of the ␤-adrenergic pathway was also reported in myocardium [12,39] as well as in in vitro models [11,13].…”

Desensitization of α2A‐adrenoceptor signalling by modest levels of adrenaline is facilitated by β2‐adrenoceptor‐dependent GRK3 up‐regulation

“…The interplay between these two ARs is important for maintaining homeostasis of various physiological mechanisms and, in some cases, causing the manifestation of pathophysiological conditions. In peripheral tissues, α 2 and β‐ARs play important roles in modulating uterine smooth muscle tone (Lécrivain et al ., 1998), insulin release from pancreatic islet cells (John et al ., 1990), cytokine release (Kalinichenko et al ., 1999) and vasomotor tone. In addition, neuronal α 2 ‐ and β 2 ‐ARs play an important role in the modulation of noradrenergic neurotransmission in the human CNS and PNS.…”