ptxsensitive g proteins and permissive action of prostacyclin in newborn pig cerebral circulation the present study of newborn pig cerebral circulation investigated the role of pertussis toxin ptxsensitive gtp binding proteins in the permissive action of prostacyclin in specific dilator responses pial arterioles of anesthetized piglets were observed through closed cranial windows the piglets were treated topically with ptx and intravenously with indomethacin the effects of hypercapnia 10 co2 ventilation and topical 56epoxyeicosatrienoic acid 56eet on pial arteriolar diameter were noted before and after the intervention samples of the artificial cerebrospinal fluid acsf were collected from beneath the cranial windows for determination of the camp concentration after administration of ptx indomethacin still abolished pial arteriolar dilation to both hypercapnia and 5 6eet and also inhibited the camp elevation caused by hypercapnia the addition of phorbol 12myristate 13acetate pma but not iloprost restored the increase in camp and vascular responses to hypercapnia and 56eet therefore in the newborn pig cerebral microvasculature ptx appears to inhibit a g protein involved in the permissive action of prostacyclin however the protein kinase c pkc activator pma appears to act downstream from the block and therefore the permissive action of pma is not affected by ptx we suggest that the prostacyclin ip receptor may be coupled to phospholipase c via a ptxsensitive g protein that normally permits vasodilation to specific stimuli via activation of a pkc resulting in phosphorylation of a component of the adenylyl cyclase pathway