Weiqun Shen

High-Resolution Quantitative Computed Tomography Demonstrating Selective Enhancement of Medium-Size Collaterals by Placental Growth Factor-1 in the Mouse Ischemic Hindlimb

Background— The process of arteriogenesis after occlusion of a major artery is poorly understood. We have used high-resolution microcomputed tomography (&mgr;-CT) imaging to define the arteriogenic response in the mouse model of hindlimb ischemia and to examine the effect of placental growth factor-1 (PlGF-1) on this process. Methods and Results— After common femoral artery ligation, &mgr;-CT imaging demonstrated formation of collateral vessels originating near the ligation site in the upper limb and connecting to the ischemic calf muscle region. Three-dimensional &mgr;-CT and quantitative image analysis revealed changes in the number of segments and the segmental volume of vessels, ranging from 8 to 160 &mgr;m in diameter. The medium-size vessels (48 to 160 &mgr;m) comprising 85% of the vascular volume were the major contributor (188%) to the change in vascular volume in response to ischemia. Intramuscular injections of Ad-PlGF-1 significantly increased Sca1+ cells in the circulation, α-actin–stained vessels, and perfusion of the ischemic hindlimb. These effects were predominantly associated with an increase in vascular volume contributed by the medium-size (96 to 144 &mgr;m) vessels as determined by &mgr;-CT. Conclusions— High-resolution &mgr;-CT delineated the formation of medium-size collaterals representing a major vascular change that contributed to the restoration of vascular volume after ischemia. This effect is selectively potentiated by PlGF-1. Such selective enhancement of arteriogenesis by therapeutically administered PlGF-1 demonstrates a desirable biological activity for promoting the growth of functionally relevant vasculature.

The Chemistry of ATP in the Failing Heart The Fundamentals

There is now compelling evidence that the [ATP] in both failed human myocardium and animal models of severe heart failure is as much as 25% lower than in normal myocardium. We also know that the tissue contents of phosphocreatine and creatine and the capacity of the creatine kinase reaction (Vmax) are also lower in the dysfunctional/failing heart. These observations increase our understanding of two important aspects of cardiac energetics: the kinetics of ATP synthesis and the thermodynamics of ATP utilization, i.e., the chemical driving force for the ATP-consuming reactions, ΔG∼P. In this chapter, we will first review the fundamentals of the chemistry of ATP synthesis in the heart and then summarize what is known about the energetics of the failing heart from the viewpoints of the kinetics of ATP synthesis and the thermodynamics of ATP utilization. We present a new model of the energetics of the failing heart and suggest that the loss of creatine from the failing heart protects the heart from an even greater loss of ATP.

Progressive loss of creatine maintains a near normal ΔG∼ATP in transgenic mouse hearts with cardiomyopathy caused by overexpressing Gsα

Myocardial [ATP] falls in the failing heart. One potential compensatory mechanism for maintaining a near normal free energy of ATP hydrolysis (DeltaG approximately (ATP)), despite a fall in [ATP], may be the reduction of myocardial creatine (Cr). To test this, we conducted a longitudinal study using transgenic mice overexpressing cardiac Gsalpha, which slowly developed cardiomyopathy. Myocardial energetics measured using (31)P NMR spectroscopy and isovolumic contractile performance were determined in perfused hearts isolated from 5-, 10-, 17-month-old Gsalpha and age-matched littermate wild type (WT) mice. In young Gsalpha hearts, contractile performance was enhanced with near normal cardiac energetics. With age, as contractile performance progressively decreased in Gsalpha hearts, [ATP] and [PCr] progressively decreased while [Pi] increased only modestly; no changes were observed in WT hearts. Myocardial (but not skeletal) [Cr] in Gsalpha mice decreased, beginning at an early age (1.5 months). Consequently, cytosolic [ADP] and the free energy available from ATP hydrolysis were maintained at normal levels in Gsalpha hearts, despite decreased [ATP]. During increased cardiac work caused by supplying isoproterenol, the relationship between the rate pressure product (RPP) and DeltaG approximately (ATP) in Gsalpha mouse hearts demonstrated an increased cost of contraction in failing hearts. Thus, our results suggest that the decrease of myocardial [Cr] and net Pi efflux play compensatory roles by maintaining a nearly normal free energy of ATP hydrolysis in the dysfunctional heart; however, it also increased the cost of contraction, which may contribute to the lower contractile reserve in the failing heart.

Lack of desensitization and enhanced efficiency of calcium channel promoter in conscious dogs with heart failure

The goal of this study was to compare responses to a calcium promoter, BAY y 5959, and dobutamine (Dob) in heart failure (HF). Dogs (n = 9) were chronically instrumented and studied in the conscious state before and after pacing-induced HF. In the control state, BAY y 5959 (20 microgram. kg-1. min-1) increased the first derivative of left ventricular (LV) pressure (dP/dt) by 83 +/- 8% and mean arterial pressure (MAP) by 8 +/- 2% and decreased heart rate (HR) by 30 +/- 3%. With Dob (10 microgram. kg-1. min-1) LV dP/dt rose similarly (+80 +/- 6%), but HR also rose (+25 +/- 4%) (P < 0.05 vs. BAY y 5959). After HF developed, BAY y 5959 still increased LV dP/dt by 108 +/- 8% and MAP by 21 +/- 2% and decreased HR by 28 +/- 4%, whereas Dob increased LV dP/dt by only 50 +/- 7% (P < 0.05 vs. BAY y 5959) and MAP by 7 +/- 3%, and HR did not change (+3 +/- 3%) (P < 0.05 vs. BAY y 5959). In HF, cardiac work increased more (P < 0. 05) with BAY y 5959 (+105 +/- 13%) compared with Dob (+47 +/- 11%), yet myocardial oxygen consumption increased similarly with the two drugs. Accordingly, mechanical efficiency increased more (P < 0.05) with BAY y 5959 (+73 +/- 14%) than with Dob (+17 +/- 12%). These data indicate that 1) increases in contractility mediated directly by Ca2+ are relatively resistant to desensitization in HF; and 2) the calcium-channel promoter can produce increases in myocardial contractility and cardiac work similar to those of Dob at a significantly lower oxygen cost, thereby enhancing mechanical efficiency in HF.The goal of this study was to compare responses to a calcium promoter, BAY y 5959, and dobutamine (Dob) in heart failure (HF). Dogs ( n = 9) were chronically instrumented and studied in the conscious state before and after pacing-induced HF. In the control state, BAY y 5959 (20 μg ⋅ kg-1 ⋅ min-1) increased the first derivative of left ventricular (LV) pressure (dP/d t) by 83 ± 8% and mean arterial pressure (MAP) by 8 ± 2% and decreased heart rate (HR) by 30 ± 3%. With Dob (10 μg ⋅ kg-1 ⋅ min-1) LV dP/d t rose similarly (+80 ± 6%), but HR also rose (+25 ± 4%) ( P < 0.05 vs. BAY y 5959). After HF developed, BAY y 5959 still increased LV dP/d t by 108 ± 8% and MAP by 21 ± 2% and decreased HR by 28 ± 4%, whereas Dob increased LV dP/d t by only 50 ± 7% ( P < 0.05 vs. BAY y 5959) and MAP by 7 ± 3%, and HR did not change (+3 ± 3%) ( P < 0.05 vs. BAY y 5959). In HF, cardiac work increased more ( P < 0.05) with BAY y 5959 (+105 ± 13%) compared with Dob (+47 ± 11%), yet myocardial oxygen consumption increased similarly with the two drugs. Accordingly, mechanical efficiency increased more ( P < 0.05) with BAY y 5959 (+73 ± 14%) than with Dob (+17 ± 12%). These data indicate that 1) increases in contractility mediated directly by Ca2+ are relatively resistant to desensitization in HF; and 2) the calcium-channel promoter can produce increases in myocardial contractility and cardiac work similar to those of Dob at a significantly lower oxygen cost, thereby enhancing mechanical efficiency in HF.