β‐Hydroxybutyrate (βHOB) Increases Nitric Oxide Synthase Activity in Resistance Arteries from Dahl Salt‐sensitive Rats

The deleterious link between overconsumption of dietary salt and hypertension is unequivocal. This dogma has recently expanded with the report that a high salt diet lowers the circulating levels of the ketone metabolite, beta‐hydroxybutyrate (βHOB), in Dahl salt‐sensitive rats (Dahl S‐HS). While stimulators of ketogenesis are well known for improving cardiovascular health (e.g., exercise and caloric restriction), less is known about negative‐regulation of ketone body metabolism and how it may impact hypertension and vascular aging. Therefore, we hypothesized that raising the circulating levels of βHOB would improve endothelium‐dependent relaxation in mesenteric resistance arteries (MRA) of Dahl S‐HS. To test this hypothesis, 1,3‐butanediol (20% v/v), which is a precursor of βHOB, was supplemented in the drinking water of 5 week old, male Dahl S‐HS for 8 weeks. Subsequently MRA function was analyzed using wire myographs. Although relaxation to endothelium‐dependent vasodilator acetylcholine (ACh) was not different [%Relaxation, Dahl S‐low salt (LS): 40±11 vs. Dahl S‐HS: 52±11 vs. Dahl S‐HS+βHOB: 44±11, p>0.05], the mechanism of relaxation was different between the groups. Specifically, while nitric oxide synthase inhibitor (L‐NAME; 100 μM) completely prevented relaxation in Dahl S‐LS and Dahl S‐HS+βHOB groups, MRA from Dahl S‐HS still partially relaxed in the presence of L‐NAME (%Relaxation, Dahl S‐LS: 1±4 vs. Dahl S‐HS: 33±5 vs. Dahl S‐HS+βHOB: 6±4, p<0.05; Figure 1A–C). These data suggest that MRA from Dahl S‐HS relax through nitric oxide‐independent mechanisms and that βHOB treatment restores nitric oxide synthase activity, despite consumption of a high salt diet. To test whether 1,3‐butanediol treatment had direct effects on arterial function, concentrations‐response curves were performed to βHOB and 1,3‐butanediol in MRA from naïve 5 week old, male Dahl S‐LS rats. We observed that βHOB and 1,3‐butanediol caused triphasic‐quadriphasic responses after pre‐contraction to phenylephrine (PE; Figure 2A–B). Specifically, we observed that low concentrations (<3 nM) of βHOB caused pronounced vasodilation and this was inhibited by both L‐NAME and tetraethylammonium (TEA; potassium channel inhibitor; both, p<0.05; Figure 3A–B). Intermediate concentrations of βHOB (3 nM–100 nM) caused contraction and this tended to be inhibited by indomethacin (cyclooxygenase inhibitor; p=0.08; Figure 3C). Finally, high concentrations (100 nM–30 μM) of βHOB caused relaxation again and this was predominately mediated by nitric oxide (p<0.05; Figure 3A). Overall, these data suggest that βHOB stimulates the production of endothelium‐derived factors and low concentrations of βHOB could be a novel therapy against hypertension‐associated vascular aging by increasing nitric oxide synthesis. Support or Funding Information American Heart Association (18POST34060003) and National Institutes of Health (K99GM118885 and R01HL143082). This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .