However, we found a lack of effect of metformin on hypertension development, ENaC activity, and heart rate changes in this animal model. Similarly, earlier studies by Zhang and colleagues have shown that metformin did not affect development of hypertension in Dahl SS rats fed a 3% NaCl diet (Zhang et al., 1994). On the other hand, Yu et al. recently reported that chronic treatment with caffeine, which activated AMPK, increased natriuresis and precluded 8% NaCl salt-induced hypertension. Also, these authors suggested that in cell culture studies this effect of caffeine might be mediated by downregulation of ENaC via AMPK activation, as the caffeine effect was blocked by the putative AMPK inhibitor compound C (Yu et al., 2016). However, these results should be interpreted with caution because compound C is known to have significant off-target effects on a number of other kinases and signaling pathways (Bain et al., 2007). We studied the effect of chronic metformin administration on ENaC activity in the freshly isolated CCD segments of these high-sodium fed animals and did not detect any significant difference in ENaC function as compared to vehicle-treated animals. The lack of effect in our experiments may well be due to our finding that AMPK was already strongly activated following the institution of a high-salt (8% NaCl) diet (Figure 1), a finding that is consistent with earlier work in rats fed a high-salt diet (Fraser et al., 2005). Similarly, no further AMPK activation by AICAR infusion, as compared to vehicle, was found in our studies using Dahl SS rats fed a high-salt diet (Figure 6). It is therefore conceivable that any potential effect of AMPK activation on the hemodynamic parameters we measured was already maximized even in vehicle-treated animals during this exposure period. It would thus be interesting to examine the potential role of AMPK modulation in other hypertension models where AMPK may not be already activated.