Abstract
The present study was designed to investigate the role of nitric oxide (NO), guanosine 3',5'-cyclic monophosphate (cGMP), and adenosine 3',5'-cyclic monophosphate (cAMP) in the vasodilator response to beta-adrenoceptor agonists in newborn pigs equipped with a closed cranial window. Dobutamine (10(-8) and 10(-6) M), a beta 1-agonist, produced pial artery dilation that was blunted by NG-nitro-L-arginine (L-NNA; 10(-6) M), a NO synthase inhibitor (12 +/- 1 vs. 0 +/- 2% and 24 +/- 3 vs. 4 +/- 1% for 10(-8) and 10(-6) M dobutamine, respectively). Dobutamine-induced vasodilation was associated with increased cortical periarachnoid cerebrospinal fluid (CSF) cGMP, and these changes in CSF cGMP were blocked by L-NNA (391 +/- 10 and 675 +/- 36 fmol/ml vs. 307 +/- 3 and 346 +/- 37 fmol/ml for control and 10(-6) M dobutamine before and after L-NNA, respectively). In contrast, dobutamine-associated changes in CSF cAMP were unchanged by L-NNA (1,108 +/- 56 and 2,623 +/- 139 fmol/ml vs. 1,059 +/- 24 and 2,500 +/- 61 fmol/ml for control and 10(-6) M dobutamine before and after L-NNA, respectively). Salbutamol, a beta 2-agonist, and isoproterenol, a nonselective beta-agonist, elicited similar changes in pial diameter and cyclic nucleotides; vasodilation and changes in CSF cGMP also were similarly inhibited by L-NNA.(ABSTRACT TRUNCATED AT 250 WORDS)
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