Methods for studying drug effects on superficial human veins

Direct effects of vasoactive substances on superficial human veins in vivo can be investigated by measuring changes in the diameter of a superficial vein at a standardized congestion pressure which reflect changes in venous tone before and after local infusion of the drugs. The diameter of a superficial hand vein is measured with the aid of a linear variable differential transformer mounted directly on the back of the hand. The central core of the transformer positioned over the summit of the vein moves simultaneously with changes in venous diameter and allows continuous recording of these alterations. A series of ergot alkaloids were investigated with this technique and found to elicit a direct constrictor action when infused locally. Studies on the mode of action of the venoconstrictor effects of ergot alkaloids suggest that they are mediated by stimulation of alpha- and 5-HT-receptors. Similarly, guanfacine, a centrally-acting antihypertensive drug, reduces venous compliance after direct local administration as a result of alpha-adrenoceptor stimulation. The venodilator effect of isoprenaline can be shown in veins preconstricted with noradrenaline, whereas with nitroglycerine, venodilatation is observed by local infusions in veins not preconstricted. This method is therefore useful for studying the direct effects of venoconstrictor and venodilator drugs in man. The technique can also be used to study interactions between different agents and thus to investigate the mode of action of drugs. Drugs can be infused locally at doses which do not elicit systemic effects.