Effects of increased white blood cell count on endothelin-induced vasoconstriction in healthy subjects

It is known that administration of granulocyte-colony stimulating factor is followed by an increase of white blood cell count. There is evidence from other vascular beds that an increase in white blood cell count impairs blood flow regulation especially in the microcirculation. Whether this also holds true for the ocular circulation is unknown. In the following study we investigated whether an increase in white blood cell count alters the endothelin-1 induced vasoconstriction in humans. Neither granulocyte-colony stimulating factor nor endothelin-1 had any consistent effect on blood pressure, pulse rate or intraocular pressure. Administration of granulocyte-colony stimulating factor induced a pronounced increase in retinal white blood cell density (p < 0.01). Administration of endothelin-1 decreased choroidal (p < 0.01) and retinal blood flow (p < 0.01). The change in choroidal blood flow in response to endothelin-1 was not altered by pre-treatment with granulocyte-colony stimulating factor. By contrast, the decrease in retinal blood flow was more pronounced during an increase in white blood cell count (p = 0.02) when compared to placebo. Our data indicates that during pronounced vasoconstriction, as induced by administration of endothelin-1, vascular regulation can be altered by the number of circulating white blood cells. Whether this effect is caused by an interaction of red and white blood cells in the microcirculation or a yet unknown mechanism needs further investigation.