Comparison of the acute influence of neuropeptide Y and sympathetic stimulation on the composition of blood cells in the splenic vein in vivo

Abstract

The acute influence of exogenous transmitters and sympathetic nerve stimulation on the composition of blood cells in the splenic vein in relation to the splenic vascular effects was investigated in anaesthetized pigs. Intra arterial bolus injections of 720 pmol neuropeptide Y (NPY), 4.9 nmol noradrenaline (NA) and 20 nmol alpha,beta-methylene adenosine triphosphate (mATP) in the spleen were given and these doses caused arterial vasoconstriction in the same range, and increase in splenic 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 blood flow and leukocyte outflow. Sympathetic nerve stimulation caused increases in haematocrit and leukocyte outflow in control pigs as well as in pigs with reserpine-induced depletion of tissue NA, although these 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 haematocrit. It is concluded that haematocrit and leukocyte concentration in the splenic venous blood are acutely modulated in different ways by vascular changes evoked by different sympathetic mediators. Furthermore, 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.