Splenic contraction and optical density of blood

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Abstract
Injection of l-epinephrine into dogs shortly before the beginning of the inscription of an indocyanine dye-dilution curve resulted in a sustained elevation of the downslope of the dye-concentration curve above base line. Experiments with the spleens exteriorized or removed showed that release of red blood cells (RBC) by splenic contraction accounted for the effect. Injection of 10 ml splenic blood or an equivalent concentration of arterial RBC (hematocrit 90%) produced peak changes in optical density equivalent to the addition of 3 mg/ml of indocyanine dye to the circulating blood. The optical density tracing made after injection of the concentrated cells intersected the base line approximately at the point predicted by semilogarithmic extrapolation of the descending limb of the curve. There was little evidence of recirculation of the injected RBC in most cases. The optical density curves produced by injection of 0. 5 ml (0.25 mg) indocyanine dye and 25 ml concentrated RBC (90% hematocrit) were very similar in contour despire marked differences in injection volume and injection time.