Prostaglandins release plasma 'reciprocal coupling factor' in anaesthetized rats.

1. Prostaglandins E1, E2, I2 and endoperoxide analogue U46619 injected intra-arterially (i.a.) into anaesthetized rats at 2 micrograms/kg caused a substantial increase within 60 min of the plasma activity of prostaglandin 'reciprocal coupling factor' (RCF). RCF is the provisional name for the component(s) of plasma which inhibit microsomal prostaglandin synthesis and enhance cytosolic prostaglandin breakdown. 2. RCF is not released by inactive metabolite 13,14-dihydro-15-keto prostaglandin E2 (10 micrograms/kg, i.a.) or acetylcholine or histamine (2 micrograms/kg, i.a.). 3. We suggest that release by prostaglandins of RCF would provide the basis in vivo for a negative feedback mechanism controlling the activity of the prostaglandin system.