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These results suggest that the deletion of mtDNA associated with ageing or AF can lead to a bioenergetic deficiency due to an impaired ATP synthesis in the human atrium; however, no conclusion can be made whether mtDNA deletion were the result or the cause of an impaired ATP synthesis, ageing, hemodynamic deterioration, or AF.

PTHrP is produced in a wide variety of different cells, including cardiomyocytes. Its production is augmented by mechanical and neurohumoral stimulation, and PTHrP has positive chronotropic and vasodilatory effects. Thus, in the heart, PTHrP has the potential to serve as a mechano-sensitive regulatory molecule. We evaluated peripheral and central levels of PTHrP in patients with congestive heart failure (CHF) and tested the hypothesis that PTHrP is released from the heart in patients with CHF. Intact full-length PTHrP (i-PTHrP) and C-terminal PTHrP (c-PTHrP) levels were measured in the plasma of 64 patients with CHF and 12 controls. Plasma PTHrP concentrations in the coronary sinus and aortic root were also measured in 18 CHF patients and 10 controls. Both plasma i-PTHrP and c-PTHrP levels in CHF patients were significantly higher than control levels and increased as a function of New York Heart Association classification. There were significant correlations between c-PTHrP levels and plasma norepinephrine, brain natriuretic peptide, angiotensin II, and endothelin-1 levels. Plasma i-PTHrP was significantly correlated with left ventricular ejection fraction and end-diastolic and end-systolic dimensions. Plasma i-PTHrP levels were significantly higher in the coronary sinus than in the aortic root in CHF patients, but among controls concentrations of i-PTHrP were indistinguishable at these two sites. This is the first report demonstrating that PTHrP is produced in the myocardium and is increased in CHF; these findings suggest that PTHrPs levels might be modulated by cardiac performance in patients with CHF.

Parathyroid hormone (PTH) activates both adenylyl cyclase and phospholipase C via the PTH-1 receptor. We previously reported that PTH increased heart rate and that this effect was mediated via the pacemaker current (I f ). However, it has been reported that PTH exerts its chronotropic effect via an interaction with adrenergic receptors or via L-type calcium channels. Thus, the objective of the study was to elucidate the exact mechanism of the chronotropic effect of PTH. We tested whether its chronotropic effects could be abolished by inhibitors of the following systems in isolated perfused rat hearts: alpha-adrenergic (prazosin); beta-adrenergic (propranolol); angiotensin II (CV11974); endothelin-1 (TAK044); calcium channel (verapamil); adenylyl cyclase (miconazole); phospholipase C (U73122) or I f (CsCl). In addition, we measured the cyclic adenosine monophosphate level of the heart after PTH administration. Whereas prazosin, propranolol, CV11974, TAK044, verapamil, and U73122 did not inhibit the chronotropic effect of PTH, CsCl or miconazole suppressed it significantly. PTH increased the cyclic adenosine monophosphate level of the atrium but not the left ventricle. These results indicate that the chronotropic actions of PTH are mediated via selective activation of adenylyl cyclase to increase the I f current.