Chronic oxytocin pretreatment inhibits adenylyl cyclase activity in cultured rat myometrial cells.
To determine whether chronic oxytocin pretreatment inhibits adenylyl cyclase, we compared adenylyl cyclase activity in membranes prepared from cultured, immortalized rat myometrial cells that were untreated or pretreated for 24 h with oxytocin. Chronic oxytocin pretreatment (1 x 10(-5) M for 24 h) attenuated basal, guanosine triphosphate (1 x 10(-5) M)-, isoproterenol (1 x 10(-4) M)-, forskolin (1 x 10(-5) M)-, MnCl2 (20 mM)- or NaF (1 x 10(-2) M)-stimulated adenylyl cyclase activity by 27 +/- 5% to 39 +/- 11% (n = 6, p < 0.05). Oxytocin pretreatment for 2 h (n = 5) did not produce a significant effect. To understand the mechanism by which oxytocin pretreatment decreased activity of the adenylyl cyclase pathway, we compared effects of pretreatment with either oxytocin or phenylephrine on adenylyl cyclase activity and determined the effects of Gi inhibition and protein kinase C (PKC) depletion. Chronic (24 h) phenylephrine pretreatment (1 x 10(-4) M) had effects similar to those of oxytocin pretreatment (1 x 10(-5) M). PKC depletion with phorbol 12-myristate 13-acetate (1 x 10(-6) M, 41 h) prevented attenuation of adenylyl cyclase activity by oxytocin pretreatment (1 x 10(-5) M for 24 h). Inhibition of Gi by pertussis toxin pretreatment (1.25 microg/ml, 41 h) had no significant effect. These findings suggest that chronic oxytocin pretreatment desensitizes the adenylyl cyclase pathway by a cross-regulatory mechanism that involves activation of Gq and PKC.
Lindeman
K S
KS
Department of Anesthesiology/Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA. klindema@welchlink.welch.jhu.edu
Hirshman
C A
CA
Kuhl
J S
JS
Levitsky
H I
HI
Emala
C W
CW
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D017895:Manganese Compounds / Q000494:pharmacology; D009215:Myometrium / Q000201:enzymology*; D010121:Oxytocin / Q000494:pharmacology*; D037342:Pertussis Toxin; D010656:Phenylephrine / Q000494:pharmacology; D011247:Pregnancy; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012969:Sodium Fluoride / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D002712:Chlorides; D004791:Enzyme Inhibitors; D017895:Manganese Compounds; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D010656:Phenylephrine; D010121:Oxytocin; D006160:Guanosine Triphosphate; D012969:Sodium Fluoride; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate; C025340:manganese chloride