The sympathetic control of blood supply is different in the spleen and lymph nodes.

OBJECTIVES: The noradrenergic innervation of lymphoid organs controls several immune cell functions and local blood perfusion. Considering that cell and antigen uptake depend on the blood supply to lymphoid organs, the hypothesis was tested that feedback signals from activated immune cells control sympathetic vasomotor activity. METHODS: We determined the blood flow in spleen and mesenteric lymph nodes (mLN) of Wistar Kyoto rats during immune stimulation with endotoxin (LPS; 10 microg/kg) and following disruption of the noradrenergic transmission. RESULTS: Our data indicate that (a) the splenic noradrenaline content, which reflects the density of the sympathetic innervation, is 5 times higher in the spleen than in other peripheral organs and the spleen receives stronger tonic sympathetic input than mLN; (b) immune stimulation with LPS causes a 4-fold increase in the IL-1beta production in the spleen, but only 2-fold in mLN; (c) IL-1beta causes an inhibition of the sympathetic vasoconstrictor tonus in the spleen, but has no significant effect on the noradrenergic vascular tonus in mLN, and (d) in mLN, the local hyperemia induced by LPS is attenuated by the degranulation of vesicular stores of histamine and serotonin, indicating that these monoamines participate in the vasodilator effect of LPS in mLN. CONCLUSIONS: The present experiments, taken together with our previous studies, indicate that the control of blood supply to the spleen and mLN involves different mechanisms. While blood perfusion in the spleen depends on the inhibition of the noradrenergic vasoconstriction by endogenously produced IL-1beta, other vasoactive mediators such as serotonin and histamine play a role in the control of mLN perfusion.

Local and systemic autonomic nervous effects on cell migration to the spleen.

This work is based on the hypothesis that sympathetic nerves regulate the uptake of circulating cells by the spleen by affecting splenic blood flow and that the quantity of cells sequestered depends on whether changes in noradrenergic transmission occur at local or systemic levels. Fluorescently labeled lymphoid cells were injected into rats, and organ blood flow was measured by the microsphere method. Increased retention of cells in the spleen paralleled by increased blood flow was detected after local denervation of this organ or administration of bacterial endotoxin. A comparable enhanced splenic blood flow was observed after general sympathectomy. However, the redistribution of blood perfusion during general vasodilatation resulted in deviation of leukocyte flow from the spleen, thus resulting in reduced uptake of cells by this organ. These results indicate that, although the uptake of cells by the spleen depends on arterial blood supply, enhanced perfusion does not always result in increased cell sequestration because general vasodilatation reduces cell uptake by this organ and even overrides stimulatory effects of endotoxin.