Effect of PPADS on P2X receptor-mediated responses of human blood vessels

Participation of Purinergic P2X Receptors in the Thermoregulatory Response to Cooling

We studied the role of purinergic P₂X receptors in the body response to cooling. In experiments on rats, P₂X receptor antagonist PPADS was administered in different modes, which resulted in changes of different characteristics of the thermoregulatory response to cold. Iontophoresis of P₂X antagonist into the skin decreased the thermal thresholds of all thermoregulatory responses to cooling, which can attest to a modulating effect of P₂X receptors on peripheral thermosensitive afferents. Intraperitoneal administration of P₂X antagonist suppressed thermoregulatory activity of skeletal muscles (shivering) developing during cooling without changing the thresholds of thermoregulatory responses. The findings suggest that ATP and P₂X receptors play an important role in the formation of the response to cooling.

Functional activity of varicose human great saphenous vein at different sites

Experiments on isolated preparations of varicose human great saphenous vein revealed different sensitivity of the distal and proximal portions to P2X receptor agonist α,β-methylene-ATP, but not to norepinephrine and histamine. It is suggested that restructuring of the P2 receptor system plays an important role in the pathogenesis of varicose veins, which affects the trunk of the great saphenous vein in varying degrees.

Diadenosine polyphosphates are selective vasoconstrictors in human coronary artery bypass grafts

Diadenosine polyphosphates (Ap(n)A) are released by degranulating platelets and high, local concentrations may form at sites of platelet activation. Radial artery grafts, now often used alongside the internal mammary artery in coronary artery bypass surgery, are particularly reactive to several vasoconstrictors but the response to Ap(n)A has not been investigated. This study compared the vasoconstrictor activity of Ap(n)A in human radial artery with other vessels commonly used as bypass grafts. Radial artery demonstrated robust concentration-dependent vasoconstriction to Ap(n)A (n=4-6) at concentrations in the micromolar range. In contrast, average responses in internal mammary artery were negligible. Cross-desensitization revealed that Ap(n)A-mediated vasoconstriction occurred via an alphabetamethyleneATP-sensitive receptor. Responses to both Ap(5)A and alphabetamethyleneATP were inhibited by suramin but were insensitive to the P2X(1) receptor antagonist 8,8'-[Carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)]bis-1,3,5-naphthalenetrisulfonic acid (NF279). Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) enhanced responses to Ap(5)A. Similar responses were obtained in saphenous vein. In conclusion, diadenosine polyphosphates contract radial artery and saphenous vein by an as yet uncharacterized P2X receptor but have only limited activity in internal mammary artery. The selective activity of diadenosine polyphosphates in radial artery would implicate them as potential mediators of post-operative contraction in this graft.