The effects of some phosphodiesterase inhibitors on the conductance of the perfused vascular beds of the chloralosed cat.

1. The vasoactivity of a number of phosphodiesterase inhibitors in the auto-perfused splanchnic region and hindquarters of the cat have been investigated.2. Theophylline, dipyridamole and 4-(3,4-dimethoxybenzyl)-2-imidazolidinone (Ro 7-2956) and its analogues were more potent vasodilators in the splanchnic region than in the hindquarters, whereas papaverine was a potent vasodilator in both these vascular beds.3. The vasodilator response to the phosphodiesterase inhibitors in the splanchnic region and hindquarters was not susceptible to beta-adrenoceptor blockade.4. Infusion of dibutyryl cyclic AMP into the superior mesenteric artery increased vascular conductance of the splanchnic region. This effect was enhanced by Ro 20-1724 in doses below those in which this compound affected conductance.5. These results are consistent with the hypothesis that accumulation of cyclic AMP in vascular smooth muscle mediates the vasodilator response to phosphodiesterase inhibitors.