Prostaglandin E2--mediated relaxation of the ductus arteriosus: effects of gestational age on g protein-coupled receptor expression, signaling, and vasomotor control.
BACKGROUND
In the preterm newborn, a patent ductus arteriosus is in large part a result of the increased sensitivity of the immature ductus to prostaglandin E2 (PGE2). PGE2 acts through 3 G protein-coupled receptors (EP2, EP3, and EP4) that activate both adenyl cyclase and K(ATP) channels. We explored these pathways to identify the mechanisms responsible for the increased sensitivity of the immature ductus to PGE2.


RESULTS
We measured EP receptor content (mRNA and protein), receptor binding, cAMP production, and isometric tension in rings of ductus taken from immature (65% gestation) and mature (95% gestation) sheep and baboon fetuses. Ductus relaxation and cAMP generation were augmented in response to selective EP receptor agonists in the immature ductus. 8-Br-cAMP, a stable cAMP analogue, produced greater relaxation in the immature ductus. In the presence of a selective protein kinase A inhibitor, Rp-8-CPT cAMPS, the developmental differences in sensitivity to PGE2 could no longer be demonstrated. EP2, EP3, and EP4 receptor densities were higher in immature ductus, despite similar receptor mRNA and protein contents at the 2 gestational ages. In contrast, forskolin and NaF, direct activators of adenyl cyclase and Gs, respectively, elicited comparable increases in cAMP in both age groups. KATP channel inhibition also had similar effects on PGE2-induced relaxation in both age groups.


CONCLUSIONS
Two mechanisms explain the increased sensitivity of the immature ductus to PGE2: (1) increased cAMP production because of increased binding of PGE2 to the individual EP receptors and (2) increased potency of cAMP on protein kinase A-regulated pathways.
Waleh
Nahid
N
Cardiovascular Research Institute and Department of Pediatrics, University of California, San Francisco, San Francisco, Calif 94143-0544, USA.
Kajino
Hiroki
H
Marrache
Anne Marilise
AM
Ginzinger
David
D
Roman
Christine
C
Seidner
Steven R
SR
Moss
Timothy J M
TJ
Fouron
Jean-Claude
JC
Vazquez-Tello
Alejandro
A
Chemtob
Sylvain
S
Clyman
Ronald I
RI
D015064:16,16-Dimethylprostaglandin E2 / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives*; D000262:Adenylyl Cyclases / Q000378:metabolism; D000527:Alprostadil / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D015232:Dinoprostone / Q000494:pharmacology*; D004373:Ductus Arteriosus / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005865:Gestational Age; D005905:Glyburide / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007537:Isometric Contraction; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010215:Papio; D015221:Potassium Channels / Q000187:drug effects; D011247:Pregnancy; D018078:Receptors, Prostaglandin E / Q000187:drug effects* / Q000502:physiology; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058308:Receptors, Prostaglandin E, EP3 Subtype; D058309:Receptors, Prostaglandin E, EP4 Subtype; D012756:Sheep; D015398:Signal Transduction; D012969:Sodium Fluoride / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014666:Vasomotor System / Q000187:drug effects* / Q000502:physiology
D001713:Biphenyl Compounds; D015221:Potassium Channels; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058308:Receptors, Prostaglandin E, EP3 Subtype; D058309:Receptors, Prostaglandin E, EP4 Subtype; D013873:Thionucleotides; C117780:mitochondrial K(ATP) channel; D009599:Nitroprusside; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; C036038:8-bromoadenosine; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; C032405:11-deoxy-16-phenoxy-17,18,19,20-tetranorprostaglandin E1; C046926:AH 23848; D012969:Sodium Fluoride; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D000527:Alprostadil; C048491:butaprost; D000241:Adenosine; D015232:Dinoprostone; D015064:16,16-Dimethylprostaglandin E2; D005905:Glyburide; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin