Myocardial glucose and lactate metabolism during rest and atrial pacing in humans

Abstract

There is minimal in vivo data in humans evaluating myocardial substrate utilization during increased heart work. This study was performed to determine the balance of myocardial glucose and lactate metabolism during rest and increased heart work induced by atrial pacing in seven healthy men and women (age, 49.7 +/- 3.9 years; body mass index, 23.4 +/- 1.1 kg m(-2), maximum oxygen consumption, 35.5 +/- 3.0 ml kg(-1) min(-1), ejection fraction, 68 +/- 3%). After 3 days of dietary control, catheters were placed in coronary sinus, femoral arterial and venous, and peripheral venous blood vessels. Subjects received a primed continuous infusion of [3,3,3-(2)H]lactate and [6,6-(2)H]glucose throughout the study. Arterial and coronary sinus blood sampling and measurements of coronary sinus blood flow were made during rest and atrial pacing at approximately 111 beats min(-1). Myocardial oxygen consumption increased (P = 0.04) from rest to atrial pacing. Net glucose uptake increased (P = 0.04) from rest to atrial pacing with unchanged fractional extraction (rest: 9.1 +/- 2.7%, atrial pacing 9.8 +/- 2.9%). The percentage of whole body glucose disposal from myocardial uptake also increased from rest to atrial pacing. Isotopically measured lactate uptake also increased significantly from rest to atrial pacing with no significant differences in fractional extraction. The myocardium released lactate throughout the experiment, which increased significantly from rest and atrial pacing (P < 0.05). The heart accounted for a significantly greater percentage of whole body lactate disposal during atrial pacing (15.0 +/- 4.4%) compared to rest (4.9 +/- 0.9%, P = 0.03). These data suggest: (1) in the absence of ischaemia the myocardium is constantly taking up and releasing lactate at rest which increases during atrial pacing, and (2) when arterial substrate delivery is unchanged, increased myocardial work is accomplished with similar proportions of glucose and lactate utilization in healthy humans in vivo.

Figure 1

Coronary sinus blood flow (A) and myocardial (B) during rest and atrial pacing in men and women. Values are means ±s.e.m. § Significantly different from rest, P < 0.05.

Figure 2

Glucose and lactate arterial and coronary sinus enrichment in lean men and women during 90 min of rest and 50 min of atrial pacing. Values are means ±s.e.m. ¥ Significantly different from arterial, P < 0.05.

Figure 3

Arterial and coronary sinus glucose concentration (A), arterial–coronary sinus glucose difference (B), and myocardial net glucose uptake (C), myocardial glucose fractional extraction (D), and percentage of glucose disappearance (R_d) from myocardial glucose uptake (E) during rest and atrial pacing in men and women. Values are means ±s.e.m. § Significantly different from rest, P < 0.05. ¥ Significantly different from arterial, P < 0.05.

Figure 4

Arterial and coronary sinus lactate concentration (A), arterial–coronary sinus lactate difference (B), and myocardial net lactate uptake (C), myocardial lactate release (D), myocardial lactate fractional extraction (E), and percentage of lactate R_d from myocardial lactate uptake (F) during rest and atrial pacing in men and women. Values are means ±s.e.m. § Significantly different from rest, P < 0.05. ¥ Significantly different from arterial, P < 0.05.