OBJECTIVE Bovine lactoferrin (LF) hydrolysates and peptides identified thereof have shown antihypertensive effects in rat models, mainly but not exclusively by angiotensin-converting enzyme inhibition. In this study we aimed to assess the vasoactive effects and mechanisms of an ultrafiltered (<3kDa) pepsin LF hydrolysate (LFH) and a heptapeptide identified in a LF hydrolysate produced by yeast proteolysis (DPYKLRP) in peripheral resistance arteries from spontaneously hypertensive rats (SHRs). METHODS We used a myograph system for isometric tension recording in isolated small mesenteric arteries from SHRs. Direct vasoactive effects of LFH (30-100μg/mL) and DPYKLRP (30-100μM) were assessed in arteries precontracted with phenylephrine (PE, 10μM) or KCl (120mM), and in PE-precontracted arteries preincubated (10min) with the NO synthase inhibitor L-NAME (0.1mM) or the cyclooxygenase inhibitor indomethacin (10μM). Indirect vasoactive effects of LFH (30-100μg/mL) or DPYKLRP (30-100μM) preincubation (10min) on the relaxant responses to the NO donor sodium nitroprusside (SNP, 0.01-10μM) or acetylcholine (Ach, 1-100μM) were also studied in PE-precontracted arteries. RESULTS Both LHF and DPYKLRP elicited direct relaxation of mesenteric arteries, by a mechanism involving NO release, counteracting modulation by prostanoids and K+ efflux. Moreover, LF-derived peptides also showed indirect vasoactive effects by enhancing endothelium-dependent relaxation to Ach and endothelium-independent relaxation to SNP. CONCLUSIONS In conclusion, LF-derived peptides show ex vivodirect and indirect relaxing effects in small mesenteric arteries from SHRs. These vasoactive effects would reduce vascular peripheral resistance in vivo, and thus contribute to their antihypertensive effects.