in the current issue of critical care , friesenecker and colleagues   present a well - designed comparative study on the microvascular effects of arginine vasopressin ( avp ) and norepinephrine ( ne ) in awake hamsters under physiological conditions . the authors used the dorsal skinfold window chamber technique to measure vascular diameter , cross - sectional area and blood flow of five different sizes ( a0 to a4 ) of subcutaneous arterioles . whereas continuous infusion of both drugs resulted in similar macrohemodynamic changes , avp led to a more pronounced reduction in vessel diameter and blood flow of the proximal , large ( a0 ) arterioles than ne . interestingly , both vasopressors had similar effects on the skin microvasculature in more distal , smaller ( a1 to a4 ) arterioles . from these results the authors conclude that the strong vasoconstrictive effect of avp on large arterioles accounts for its strong vasopressive potency and may explain its efficacy in catecholamine - refractory vasodilatory shock . to the best of our knowledge , friesenecker and colleagues are the first to have compared the effects of avp and ne on different subcutaneous vessel calibers . first of all , the conclusion that especially the vasoconstrictive effect of avp on large ( a0 ) arterioles accounts for its strong vasopressor effect can not be drawn from the presented data . in this context it is especially noteworthy that the authors observed differences in neither macrohemodynamics ( i.e. mean arterial pressure ( map ) ) nor microcirculatory effects on a1 to a4 arterioles between both study groups . the fact that the stronger vasoconstrictive effect of avp on a0 arterioles was the only difference between groups suggests that the constriction of large arterioles had ( almost ) no impact on total peripheral resistance . this thesis is supported by poiseuille 's law implying that resistance is inversely correlated to the fourth power of the vessel radius . accordingly , the small vessels primarily account for changes in vascular resistance rather than the large ones . using the same animal model , gerstberger and colleagues   compared the effects of either 10 pmoles / kg of avp orthe same dose of angiotensin ( ang ) ii on the hamster subcutaneous microcirculation . these authors reported that the vasoconstrictive effects of both drugs on small ( a3 ) arterioles were comparable , whereas ang ii , but not avp , contributed to a marked constriction of greater ( a1 ) arterioles . this vasoconstriction of a1 arterioles by ang ii was associated with a much greater vasopressor effect ( i.e. change in map ) than avp . notably , the avp plasma levels measured in the study by gerstberger and colleagues were about 100 pg / ml , thus representing the upper therapeutic range during avp infusion in patients with hyperdynamic septic shock . the contradictory results of friesenecker and colleagues   and gerstberger and colleagues   emphasize that the effects of vasoactive agents on the microcirculation are still not fully understood . therefore , the study of friesenecker and colleagues   gives another important and interesting insight into the diversity of the microvascular response to vasoconstrictor agents . with respect to the second conclusion , the study by friesenecker and colleagues would have certainly profited from studying groups suffering from vasodilatory shock secondary to systemic inflammation . this holds especially true , since clinical and experimental research has clearly shown that distribution abnormalities in vasodilatory shock states contribute to significant changes in microvascular hemodynamics . therefore , interventions in the physiological state may not necessarily be suitable to predict the response of the same intervention under pathological conditions , such as sepsis . finally , although redistribution of blood flow away from non - vital organs ( e.g. the skin ) to vital organs represents one of the primary therapeutic aims of vasopressor therapy ( especially in septic shock patients ) , it should be kept in mind that this approach may result in severe hypoperfusion of non - vital organs . whereas it is well known that avp infusion ( especially when applied in higher doses ) increases the risk of gut mucosal ischemia , skin hypoperfusion appears to be another clinically relevant complication . in this regard , the study group of friesenecker and dunser recently reported on the incidence and risk factors of ischemic skin lesions in patients with catecholamine - resistant vasodilatory shock . importantly , the authors found that ischemic skin lesions are common among patients with vasodilatory shock treated with avp and that the combination of sepsis and treatment with avp may especially be a risk factor for the development of ischemic skin lesions . in conclusion , friesenecker and colleagues   correctly state that avp has a stronger vasoconstrictive effect on large arterioles of the subcutaneous vasculature in healthy hamsters compared to ne . unfortunately , the very interesting question of whether or not the stronger vasoconstrictive effect on large vessels is also maintained in vasodilatory shock remains unresolved . the fact that avp infusion may impair gut mucosal microcirculation   and skin perfusion   suggests that the stronger one may not necessarily be the better one . ang = angiotensin ; avp = arginine vasopressin ; map = mean arterial pressure ; ne = norepinephrine .
in the current issue of critical care , friesenecker and colleagues present a well - designed comparative study on the microvascular effects of arginine vasopressin ( avp ) and norepinephrine ( ne ) in a physiological , unanesthetized hamster model . 
 the authors clearly demonstrate that avp , but not ne , has marked vasoconstrictive effects on large arterioles , whereas the impact on small arterioles is comparable for both vasopressors . 
 however , it remains unclear if these results , per se , reflect a stronger vasopressive potential of avp versus ne , as macrohemodynamic variables were not different between study groups . 
 since the authors did not investigate the effects of avp and ne in vasodilatory shock states , the microcirculatory response in sepsis or systemic inflammatory response syndrome remains inconclusive . 
 the same authors previously reported that avp infusion in patients suffering from vasodilatory shock carries the risk for ischemic skin lesions . 
 this in turn raises the question whether the quality of vasopressors should be judged by their potency .