Anti-spasmogenic activity of isoenzyme-selective phosphodiesterase inhibitors in guinea-pig trachealis

1. The anti-spasmogenic potential of SK&F 94120 (PDE3-selective), rolipram (PDE4-selective), zaprinast (PDE5-selective), zardaverine (dual PDE3/4 inhibitor) and theophylline (non-selective) was evaluated in guinea-pig trachealis. 2. SK&F 94120 or rolipram (10 and 100 μM) antagonized histamine-induced tension generation in a concentration-dependent and non-competitive manner whereas ACh-induced contractions were unaffected. Similarly, SK&F 94120 and rolipram in combination were anti-spasmogenic with respect to both contractile agonists to an extent that was greater than the effect of either drug alone. Identical results were obtained with zardaverine (1, 10 and 100 μM) and theophylline (100 μM and 1 mM). 3. Zaprinast protected guinea-pig trachealis against histamine-, but not ACh-induced contractile responses in a manner that was indistinguishable from the results obtained with SK&F 94120. However, in contrast to the interaction between SK&F 94120 and rolipram, no further antagonism was seen when zaprinast and rolipram were used in combination. 4. Pre-treatment of tissues with SNP (10 and 100 μM) antagonized histamine-induced tension generation in a concentration-dependent and non-competitive manner. However, no further antagonism was produced when SNP and rolipram were used concurrently. Likewise, the protection afforded by a combination SNP and SK&F 94120 was no greater than that produced by SNP alone. 5. These results demonstrate that an inhibitor of PDE3 enhances the anti-spasmogenic activity of rolipram but not drugs that elevate cyclic GMP mass. Moreover, the ability of SNP and zaprinast to protect guinea-pig trachealis against histamine-induced contractions apparently is not due to the inhibition of PDE3