Actions of prostaglandin F2-alpha on the splenic vascular and capsular smooth muscle in the dog.

1. The actions of prostaglandin F(2alpha), which is known to be released by the spleen on sympathetic nerve stimulation, have been investigated in the isolated blood perfused spleen of the dog.2. Low arterial concentrations of F(2alpha) (less than 10 mug/100 ml) caused marked reductions in splenic vascular resistance.3. High arterial concentrations of F(2alpha) (above 10 mug/100 ml) caused increases in splenic vascular resistance.4. Little action on splenic volume was observed by any arterial concentration of F(2alpha).5. The reductions in splenic vascular resistance caused by low arterial concentrations of F(2alpha) were reversed by blocking doses of phenoxybenzamine.6. No appreciable interaction between F(2alpha) and the splenic responses to sympathetic nerve stimulation, adrenaline and noradrenaline was observed.7. The role of the prostaglandins released by the spleen is discussed.