Modulation of autonomic neurotransmission by PGD2: Comparison with effects of other prostaglandins in anesthetized cats

Experiments with anesthetized cats were done to study possible roles of different prostaglandins (PGs) in modulating sympathetic neuroeffector transmission. We recorded contractions of the nictitating membrane (n.m.), blood flow in the carotid artery, heart rate and blood pressure, both under control conditions and while stimulating the cut cervical sympathetic nerve. Intra-carotid arterial injection (i.a.) of PGD₂ depressed sympathetic transmission to the n.m. without depressing the effects of exogenous norepinephrine (NE). In contrast, PGE₂ enhanced the effects of nerve transmission or exogenous NE on the stimulated n.m. PGI₂ had similar but shorter effects to PGE₂. PGF_2α or a stable PGH₂ analog, contracted the n.m. smooth muscle with no detected effect on nerve transmission. Carotid blood flow was increased by PGD₂, PGE₂ and PGI₂. PGD₂ and PGI₂ caused bradycardia that could be blocked by atropine. This ability of PGD₂ to modulate autonomic nerve activity is of particular interest because of recent reports that nerve tissue synthesizes PGD₂.