COMPARISON OF THE ACUTE INFLUENCE OF NEUROPEPTIDE-Y AND SYMPATHETIC-STIMULATION ON THE COMPOSITION OF BLOOD-CELLS IN THE SPLENIC VEIN IN-VIVO

The acute influence of exogenous transmitters and sympathetic nerve st imulation on the composition of blood cells in the splenic vein in rel ation to the splenic vascular effects was investigated in anaesthetize d pigs. Intra arterial bolus injections of 720 pmol neuropeptide Y (NP Y), 4.9 nmol noradrenaline (NA) and 20 nmol alpha,beta-methylene adeno sine triphosphate (mATP) in the spleen were given and these doses caus ed arterial vasoconstriction in the same range, and increase in spleni c venous haematocrit. NPY administration evoked a decrease in splenic venous blood flow and an unchanged leukocyte outflow from the spleen. mATP and NA, on the other hand, evoked increases in splenic venous blo od flow and leukocyte outflow. Sympathetic nerve stimulation caused in creases in haematocrit and leukocyte outflow in control pigs as well a s in pigs with reserpine-induced depletion of tissue NA, although thes e effects, as well as the vascular effects, were significantly reduced after reserpine treatment. For comparison, the vasodilator calcitonin gene-related peptide increased leukocyte outflow without change in ha ematocrit. It is concluded that haematocrit and leukocyte concentratio n in the splenic venous blood are acutely modulated in different ways by vascular changes evoked by different sympathetic mediators. Further more, the capacitance function seems to be regulated by adrenergic and possibly purinergic transmission, whereas the non-adrenergic mediator NPY seems to be involved mainly in splenic arterial vasoconstriction.