Aims: 

Endothelium-dependent relaxation (EDR) presents multiple differences according to species, age, sex, hormonal status, vascular territory and arterial caliber, the mechanical or chemical vasodilating agent, pre-existing vascular tone and its determining factors. Regarding the latter things are surprisingly little investigated explicitly. We noticed that in rat mesenteric resistance arteries (second order branches) EDHF-mediated relaxation is increased when they are precontracted by prostaglandin F_2a (PGF) compared to phenylephrine (PHE) and we investigated the participation of K⁺ channels (K_Ca and K_ATP) in the observed effects. We extended this study upon angiotensin II and upon vascular fragments from first order branches.

Methods: 

EDR was evaluated by isometric myography in rings prepared from branches of the mesenteric artery (first and second order).

Results: 

In the case of angiotensin the phasic component of contraction is affected similarly with the PHE response, while the tonic one resembles the PGF response. The EDHF component is stronger in second order branches only when precontraction is induced by PHE and against the phasic response elicited by angiotensin II.

Conclusion: 

Others have shown that the EDHF phenomenon increases in relative importance towards periphery, but it seems that this depends upon the contracting agent used, a novel observation that may change interpretation of the physiological relevance of existing data regarding EDHF and nitric oxide as mediators of EDR in resistance arteries.

*CNCSIS grant A/ 1222, **CNCSIS grant interdisciplinary platform /68