Prostacyclin causes splenic dilation and haematological change in dogs.

1. The effect of vasodilators on spleen volume and the blood storage function is not yet well elucidated. To this end, in the present study the effects of prostacyclin, a potent vasodilator, on splenic diameter and blood cell concentrations in arterial and splenic venous blood were evaluated in anaesthetized dogs. 2. The main splenic artery and vein were dissected for measurement of splenic arterial blood flow and intra-arterial administration and for sampling of splenic venous blood, respectively. The diameter of the spleen was measured continuously by sonomicrometry. Counts of white blood cells (WBC), red blood cells (RBC) and platelets in blood sampling from the aorta and splenic vein were estimated by an automatic blood cell counter. 3. Bolus injections of prostacyclin (1-100 ng/kg) into the splenic artery produced dose-dependent increases in splenic arterial blood flow and splenic diameter associated with significant decreases in splenic venous concentrations of WBC, RBC and platelets. When splenic blood flow was kept constant, similar changes in splenic diameter and blood cell counts were observed with prostacyclin injection. 4. Splenic dilation and haematological changes induced by prostacyclin were relatively more potent than those induced by prostaglandin E(2), acetylcholine, nitroglycerin or isoproterenol when doses producing a comparable increase in splenic blood flow were compared. 5. Infusion of prostacyclin (100 ng/kg per min) into the splenic artery caused a marked increase in splenic diameter, with immediate reductions in splenic venous concentrations of WBC, RBC and platelets, followed by significant reductions in these cell counts in the general circulation. 6. These results indicate that prostacyclin produces potent and flow-independent splenic dilation that may contribute to a decrease in circulating blood cell concentrations.

Uneven changes in circulating blood cell counts with adrenergic stimulation to the canine spleen.

1. Responses of splenic diameter measured by sonomicrometry to alpha- and beta-adrenoceptor stimulants were estimated together with simultaneously measured systemic arterial and splenic venous concentrations of red blood cells (RBC), white blood cells (WBC) and platelets (PLT) in anaesthetized dogs. 2. Intravenous and intrasplenic arterial injections of adrenaline, noradrenaline and phenylephrine all produced profound decreases in splenic diameter. Increases in systemic arterial concentrations of RBC produced by these stimulants were observed immediately following the splenic contraction and marked increases in splenic venous concentration of RBC. 3. Adrenaline and noradrenaline both caused rapid and transient decreases in WBC release from the spleen and these agonists then, in addition to phenylephrine, caused gradual and small increases in systemic arterial WBC concentrations. The increases in arterial RBC and WBC concentrations were abolished by transient isolation of the spleen from the systemic circulation. These three agents did not significantly modify differences between splenic venous and systemic arterial concentrations of PLT. 4. Intra-arterial injections of isoprenaline caused an increase in splenic diameter and a significant decrease in the splenic venous concentration of WBC, but barely influenced the veno-arterial differences in RBC and PLT concentrations across the spleen. 5. The present results indicate that contraction of the spleen through stimulation of splenic alpha1-adrenoceptors contributes to supplying RBC but not PLT into the systemic circulation, whereas splenic beta-adrenoceptor activation leads to splenic dilatation with increased sequestration of WBC to the spleen despite no changes in the release of RBC and PLT from the spleen.