REGULATION OF GUANOSINE 3' 5'-CYCLIC MONOPHOSPHATE IN-OVINE TRACHEAL EPITHELIAL-CELLS/

1 Guanosine 3':5'-cyclic monophosphate (cyclic GMP) is an important se cond messenger mediating the effects of nitric oxide (NO) and natriure tic peptides. Cyclic GMP pathways regulate several aspects of lung pat hophysiology in a number of airway cells. The regulation of this syste m has not been extensively studied in pulmonary epithelial tissue. 2 W e have studied the production of cyclic GMP by suspensions of ovine tr acheal epithelial cells in response to activators of soluble guanylyl cyclase (sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillami ne (SNAP) and particulate guanylyl cyclase (atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (C NP) and E. coli heat stable enterotoxin (STa)). 3 Both 10(-7)-10(-3) M and 10(-7)-10(-3) M SNAP generated a concentration-dependent marked e levation in cyclic GMP production when incubated with 10(-3) M 3-isobu tyl-1-methylxanthine (IBMX) (both greater than 25 x baseline values wi th highest drug concentration). 4 The increase in production of cyclic GMP in response to 10(-6) M SNP and 10(-5) M SNAP was markedly inhibi ted by both 5 x 10(-5) M haemoglobin (102% and 92% inhibition) and 5 x 10(-5) M methylene blue (82% and 84% inhibition). 5 The increase in c yclic GMP in response to 10(-3) M SNP was measured following co-incuba tion with the phosphodiesterase inhibitors 10(-7)-10(-3) M IBMX, 10(-7 )-10(-1) M milrinone and 10(-7)-10(-4) M SKF 96231. Only 10(-4)-10(-3) M IBMX significantly increased cyclic GMP levels. 6 Cyclic GMP produc tion was also significantly elevated from baseline by 10(-5) M ANP, 10 (-5) M BNP, 10(-5) M CNP and 200 iu ml(-1) of E. coli STa toxin in the presence of 10(-3) M IBMX. Increases with these natriuretic peptides and STa toxin were smaller in magnitude (2-4 fold) than those seen wit h SNP and SNAP. CNP was the most potent of the natriuretic peptides st udied suggesting type B membrane bound guanylate cyclase is the predom inant form expressed. 7 These results suggest that ovine tracheal epit helial cells contain active guanylyl cyclases. The more marked respons e to SNP and SNAP than to natriuretic peptides suggests that soluble g uanylyl cyclase predominates.