We have studied the vasoconstrictor potency of ornipressin in the skin of 30 volunteers. Subjects received intradermal injections (50 microliters) of five different concentrations of ornipressin (10(-4) - 10(0) u. ml-1 in 0.9% saline) and plain 0.9% saline as a control. Immediately before injection, basal cutaneous blood flow in the test field was enhanced with 1% histamine. Capillary flux was measured by laser Doppler flowmetry and the size of pallor was determined. Ornipressin was effective at 10(-4) u. ml-1 and had its largest constrictor effect at concentrations of 10(-2) and 10(-1) u. ml-1. Larger concentrations were less effective in reducing capillary flux. Interindividually, the most effective concentration varied between 10(-3) and 10(-1) u. ml-1. The size of pallor grew in a dose-dependent manner but 10(0) u. ml-1 always caused reddening in its centre. Capacitance vessels (skin colour) were more sensitive to ornipressin than resistance vessels (capillary flux). The shortest latency of vasoconstriction was obtained with concentrations of 10(-2) and 10(-1) u. ml-1. The results of this study suggest that for haemostasis of the skin a concentration of ornipressin 10(-2) u. ml-1 is useful; this low concentration would reduce total dosage and unwanted side effects.

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