Comparison of effects of tolmesoxide (RX71107), diazoxide, hydrallazine, prazosin, glyceryl trinitrate and sodium nitroprusside on forearm arteries and dorsal hand veins of man

1 Dilator drugs used in treatment of hypertension and angina pectoris vary greatly in their clinical effects. The action of selected drugs of this group on the human forearm arterial bed and dorsal hand veins has been studied in an attempt to account for these differences.

2 Arterial responses were studied by infusing the drug into the brachial artery and measuring changes in forearm blood flow by plethysmography. Venous responses were studied by local infusion of the drug into a dorsal hand vein preconstricted by infusion of noradrenaline or other constrictor agent and measuring changes in vein size at a standard congesting pressure.

3 Tolmesoxide (RX71107), diazoxide, prazosin, glyceryl trinitrate and sodium nitroprusside produced dose dependent increases in forearm flow which had a rapid onset and waned quickly when the drug was discontinued. The response to hydrallazine was delayed and reached a maximum about 30 min after completion of short infusions.

4 Tolmesoxide, diazoxide, prazosin, glyceryl trinitrate and sodium nitroprusside all produced dilatation of the constricted hand vein. Hydrallazine had a weak dilator effect in some subjects but the responses were inconsistent.

5 Tolmesoxide was approximately equipotent in dilating arteries and veins, and diazoxide behaved similarly. Prazosin, glyceryl trinitrate and sodium nitroprusside were relatively more effective in the veins than the arteries. Hydrallazine was much more effective in arteries than veins.

6 The relative effectiveness of these drugs on peripheral arteries and veins can be correlated with their action on the circulation as a whole and with their clinical effectiveness.