Role of cAMP and K(+) channel-dependent mechanisms in piglet hypoxic/ischemic impaired nociceptin/orphanin FQ-induced cerebrovasodilation.
This study was designed to determine the role of altered cAMP and K(+) channel-dependent mechanisms in impaired pial artery dilation to the newly described opioid, nociceptin/orphanin FQ (NOC/oFQ) following hypoxia/ischemia in newborn pigs equipped with a closed cranial window. Recent studies have observed that NOC/oFQ elicits pial dilation via release of cAMP, which, in turn, activates the calcium sensitive (K(ca)) and the ATP-dependent K(+) (K(ATP)) channel. Global cerebral ischemia (20 min) was induced via elevation of intracranial pressure, while hypoxia (10 min) decreased pO(2) to 35+/-3 mm Hg with unchanged pCO(2). Topical NOC/oFQ (10(-8), 10(-6) M) induced vasodilation was attenuated by ischemia/reperfusion (I+R) and reversed to vasoconstriction by hypoxia/ischemia/reperfusion (H+I+R) at 1 h of reperfusion (control, 9+/-1 and 16+/-1%; I+R, 3+/-1 and 6+/-1%; H+I+R, -7+/-1 and -12+/-1%). Such altered dilation returned to control values within 4 h in I+R animals and within 12 h in H+I+R animals. NOC/oFQ dilation was associated with elevated CSF cAMP in control animals but such biochemical changes were attenuated in I+R animals and reversed to decreases in cAMP concentration in H+I+R animals (control, 1037+/-58 and 1919+/-209 fmol/ml; I+R, 1068+/-33 and 1289+/-30 fmol/ml; H+I+R, 976+/-36 and 772+/-27 fmol/ml for absence and presence of NOC/oFQ 10(-6) M, respectively). Topical 8-Bromo cAMP (10(-8), 10(-6) M) pial dilation was unchanged by I+R but blunted by H+I+R (control, 10+/-1 and 20+/-1%; I+R, 11+/-1 and 20+/-2%; H+I+R, 0+/-1 and 0+/-2%). Pituitary adenylate cyclase activating polypeptide and cromakalim, adenylate cyclase and K(ATP) channel activators, respectively, elicited dilation that was blunted by both I+R and H+I+R while NS1619, a K(ca) channel activator, elicited dilation that was unchanged by I+R but blunted by H+I+R. These data indicate that impaired NOC/oFQ dilation following I+R results form altered adenylate cyclase and K(ATP) channel-dependent mechanisms. These data further indicate that impaired NOC/oFQ dilation following H+I+R results not only from altered adenylate cyclase and K(ATP) channel but also from altered cAMP and K(ca) channel-dependent mechanisms.
Ben-Haim
G
G
Departments of Anesthesia and Pharmacology, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA.
Armstead
W M
WM
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D001238:Asphyxia Neonatorum / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D002536:Cerebral Arteries / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D019806:Cromakalim / Q000494:pharmacology; D000242:Cyclic AMP / Q000134:cerebrospinal fluid*; D006801:Humans; D020925:Hypoxia-Ischemia, Brain / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D007231:Infant, Newborn; D009479:Neuropeptides / Q000494:pharmacology; D018696:Neuroprotective Agents / Q000494:pharmacology; D018847:Opioid Peptides / Q000494:pharmacology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D015427:Reperfusion Injury / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D013552:Swine; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology*; D000097629:Nociceptin
D015124:8-Bromo Cyclic Adenosine Monophosphate; D019806:Cromakalim; D000242:Cyclic AMP; D009479:Neuropeptides; D018696:Neuroprotective Agents; D018847:Opioid Peptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015221:Potassium Channels; D014665:Vasodilator Agents; D000097629:Nociceptin; C495401:ADCYAP1 protein, human