Ketone body 3-hydroxybutyrate elevates cardiac output through peripheral vasorelaxation and enhanced cardiac contractility

Abstract

The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output and myocardial perfusion without affecting blood pressure in humans, but the cardiovascular sites of action remain obscure. Here, we test the hypothesis in rats that 3-OHB acts directly on the heart to increase cardiac contractility and directly on blood vessels to lower systemic vascular resistance. We investigate effects of 3-OHB on (a) in vivo hemodynamics using echocardiography and invasive blood pressure measurements, (b) isolated perfused hearts in Langendorff systems, and (c) isolated arteries and veins in isometric myographs. We compare Na-3-OHB to equimolar NaCl added to physiological buffers or injection solutions. At plasma concentrations of 2-4 mM in vivo, 3-OHB increases cardiac output (by 28.3±7.8%), stroke volume (by 22.4±6.0%), left ventricular ejection fraction (by 13.3±4.6%), and arterial dP/dt_max (by 31.9±11.2%) and lowers systemic vascular resistance (by 30.6±11.2%) without substantially affecting heart rate or blood pressure. Applied to isolated perfused hearts at 3-10 mM, 3-OHB increases left ventricular developed pressure by up to 26.3±7.4 mmHg and coronary perfusion by up to 20.2±9.5%. Beginning at 1-3 mM, 3-OHB relaxes isolated coronary (EC₅₀=12.4 mM), cerebral, femoral, mesenteric, and renal arteries as well as brachial, femoral, and mesenteric veins by up to 60% of pre-contraction within the pathophysiological concentration range. Of the two enantiomers that constitute racemic 3-OHB, D-3-OHB dominates endogenously; but tested separately, the enantiomers induce similar vasorelaxation. We conclude that increased cardiac contractility and generalized systemic vasorelaxation can explain the elevated cardiac output during 3-OHB administration. These actions strengthen the therapeutic rationale for 3-OHB in heart failure management.

Keywords: 3-hydroxybutyrate; Contractile function; Enantiomers; Ketone bodies; Metabolism; Vasorelaxation.

Fig. 1

Hemodynamic effects of treatment with 3-OHB. A, plasma concentrations of D- and L-3-OHB combined during echocardiography (n = 7–8). B, 3-OHB-induced changes in cardiac variables measured in vivo (n = 8). In addition to the relative changes illustrated by the bars, the values at the base of the bars indicate the absolute changes. C, plasma concentrations of D- and L-3-OHB combined during invasive blood pressure measurements (n = 6–7). D, 3-OHB-induced changes in blood pressure and arterial dP/dt_max (n = 6–-7) measured in vivo. E, 3-OHB-induced change in systemic vascular resistance (n = 5) measured in vivo. In addition to the relative change in systemic vascular resistance illustrated by the bar, the value at the base of the bar indicates the absolute change. Bars represent mean±SEM. Data in panels A and C were compared by unpaired two-tailed Student’s t-tests with Welch’s correction. In panels B, D, and E, responses to Na-3-OHB and equimolar NaCl were compared by unpaired two-tailed Student’s t-tests directly or after logarithmic transformation. Abbreviations: CO cardiac output; DBP diastolic blood pressure; dP/dt_max maximal rate of rise of arterial blood pressure; HR heart rate; LVEDV left ventricular end-diastolic volume; LVEF left ventricular ejection fraction; LVESV left ventricular end-systolic volume; MAP mean arterial pressure; PP pulse pressure; SBP systolic blood pressure; SV stroke volume; SVR systemic vascular resistance

Fig. 2

Effects of 3-OHB administration on isolated perfused hearts. A, average traces from isolated hearts showing changes in left ventricular systolic pressure during perfusion with Krebs-Henseleit buffer added 3 mM Na-3-OHB or 3 mM extra NaCl (n = 10–12). Data points in panel A are also represented in panel B. B, 3-OHB-induced changes in cardiac parameters measured from isolated perfused hearts ex vivo (n = 9–12) 10 minutes after buffer change. Values after 20 minutes are reported in Supplementary Fig. S1. Bars and symbols represent mean±SEM. In addition to the relative changes illustrated by the bars, the values at the base of the bars indicate the absolute changes. In panel B, responses to Na-3-OHB and equimolar NaCl were compared by unpaired two-tailed Student’s t-tests. Abbreviations: CFR coronary flow rate; HR heart rate; LVDP left ventricular developed pressure; LVSP left ventricular systolic pressure

Fig. 3

Effects of 3-OHB on isolated coronary resistance arteries. The vasorelaxant responses in panel A through G are shown relative to a stable U46619-induced pre-contraction. A, 3-OHB-induced changes in coronary artery tone (n = 6). B, concentration-dependent vasorelaxant responses of coronary arteries to 3-OHB (n = 8). Na-3-OHB was substituted for NaCl and tested by successive full exchanges of the bath solution. The relaxant response was calculated relative to time control experiments where arteries were repeatedly washed to PSS without 3-OHB. In both cases, the concentration of U46619 was kept constant at the pre-contraction level. C+D, effects of D-3-OHB (C, n = 5–8) and L-3-OHB (D, n = 4–7) on coronary artery tone. In both cases, Na-3-OHB was compared to equimolar extra NaCl. E, assessment of vasorelaxation induced by 5 µM acetylcholine under control conditions (n = 8) and following endothelial denudation of coronary septal arteries (n = 6). F+G, 3-OHB-induced vasorelaxation in coronary arteries without functional endothelium (F, n = 6) and in intact arteries treated with 3 µM of the non-selective cyclooxygenase inhibitor indomethacin (G, n = 5). Na-3-OHB was compared to equimolar extra NaCl. H. U46619-induced contractions of coronary arteries in presence of Na-3-OHB or equimolar extra NaCl. Vessels were exposed to cumulative stepwise increases in U46619 concentration, and contractions—relative to the initial maximal contraction to 120 mM extracellular K⁺ and 0.1 μM U46619—were fitted to sigmoidal functions (n = 6). Bars and symbols represent mean±SEM. Data in panels A, C, D, F, and G were compared by repeated-measures two-way ANOVA (interaction) or, in case of missing values, by mixed-effects analysis. In panel B and H, data were fitted to sigmoidal functions. In panel E, data were compared by unpaired two-tailed Student’s t-test; in panel H, by extra sum-of-squares F-test

Fig. 4

3-OHB-induced changes in vascular tone in different arterial beds. The vasorelaxant responses are shown relative to a stable U46619-induced pre-contraction. A + C + E + G + I, 3-OHB-induced changes in coronary septal (A, n = 13), caudal femoral (C, n = 6–7), middle cerebral (E, n = 5), mesenteric (G, n = 7), and renal interlobar (I, n = 7) artery tone. B + D + F + H, concentration-dependent vasorelaxant responses of coronary septal (B, n = 7), caudal femoral (D, n = 8), middle cerebral (F, n = 5), and mesenteric (H, n = 7) arteries to 3-OHB. Bars and symbols represent mean±SEM. In all cases, Na-3-OHB was compared to equimolar extra NaCl. Data in panels A, C, E, G, and I were compared by repeated-measures two-way ANOVA (interaction) or, in case of missing values, mixed-effects analysis. Data in panels B, D, F and H were compared by repeated-measures two-way ANOVA followed by Šídák's multiple comparisons tests

Fig. 5

3-OHB-induced changes in peripheral venous tone. The venorelaxant responses are shown relative to a stable U46619-induced pre-contraction. A, 3-OHB-induced changes in femoral venous tone (n = 6–7). B–D, concentration-dependent relaxant responses of caudal femoral (B, n = 10), profound brachial (C, n = 10), and mesenteric (D, n = 8) veins to 3-OHB. Bars and symbols represent mean±SEM. In all cases, Na-3-OHB was compared to equimolar extra NaCl. Data in panel A were compared by mixed-effects analysis; data in panels B, C, and D were compared by repeated-measures two-way ANOVA followed by Šídák's multiple comparisons tests