Differential recruitment of alpha 1- and beta-adrenoceptors in inotropic control of atrial child myocardium by endogenous noradrenaline

Cardiovascular catecholamine receptors in children: their significance in cardiac disease

Adrenoceptors and dopamine receptors are grouped together under the name 'catecholamine receptors.' Catecholamines and catecholaminergic drugs act on catecholamine receptors located on or near the cardiovascular system. The physiological effects of catecholamine receptor stimulation are only partly understood. The catecholaminergic drugs used in critical care medicine today are not selective, or are, at best, in part selective for the various catecholamine receptor subtypes. Many patients, however, depend on them. A variety of animal models has been developed to unravel catecholamine distribution and function. However, the identification of species heterogeneity makes it imperative to determine catecholamine receptor distribution and function in humans. In addition, age-related alterations in catecholamine receptor distribution and function have been identified in human adults. This might have implications for our understanding of the effect of catecholamines in pediatric patients. This article will focus on the pediatric population and will review currently available in vitro data on the distribution and the function of catecholamine receptors in the cardiovascular system of fetuses and children. Also discussed are relevant young animal models and in vivo hemodynamic effects of cardiotonic drugs acting on the catecholamine receptor in children requiring major cardiac surgery. A better understanding of these topics might provide clues for new, receptor subtype-selective, therapeutic approaches in newborns and children with cardiac disease.

Assessment of myocardial triglyceride oxidation with PET and 11C-palmitate

BACKGROUND

The goal of this study was to test whether myocardial triglyceride (TG) turnover including oxidation of TG-derived fatty acids (FA) could be assessed with PET and (11)C-palmitate.

METHODS AND RESULTS

A total of 26 dogs were studied fasted (FAST), during Intralipid infusion (IL), during a hyperinsulinemic-euglycemic clamp without (HIEG), or with Intralipid infusion (HIEG + IL). (11)C-palmitate was injected, and 45 minutes were allowed for labeling of myocardial TG pool. 3D PET data were then acquired for 60 minutes, with first 15 minutes at baseline followed by 45 minutes during cardiac work stimulated with constant infusion of either phenylephrine (FAST, n = 6; IL, n = 6; HIEG + IL, n = 6) or dobutamine (FAST, n = 4; HIEG, n = 4). Myocardial (11)C washout during adrenergic stimulation (AS) was fitted to a mono-exponential function (Km(PET)). To determine the source of this (11)C clearance, Km(PET) was compared to direct coronary sinus-arterial measurements of total (11)C activity, (11)C-palmitate, and (11)CO(2). Before AS, PET curves in all groups were flat indicating absence of net clearance of (11)C activity from heart. In both FAST groups, AS resulted in negligible net (11)C activity and (11)CO(2) production higher than net (11)C-palmitate uptake. AS with phenylephrine resulted in net myocardial uptake of total (11)C activity and (11)C-palmitate in IL and HIEG + IL, and (11)CO(2) production lower than (11)C-palmitate uptake. In contrast, AS with dobutamine in HIEG resulted in net clearance of all (11)C metabolites (total (11)C activity, (11)C-palmitate and (11)CO(2)) with (11)CO(2) contributing 66% to endogenous FA oxidation. The AS resulted in significant Km(PET) in all the groups, except HIEG + IL. However, positive correlation between Km(PET) and (11)CO(2) was observed only in HIEG (R (2) = 0.83, P = .09).

CONCLUSIONS

This is the first study to demonstrate that using PET and pre-labeling of intracardiac TG pool with (11)C-palmitate, noninvasive assessment of myocardial TG use is feasible under metabolic conditions that favor endogenous TG use such as increased metabolic demand (beta-adrenergic stimulation of cardiac work) with limited availability of exogenous substrate (HIEG).

Relative cardiac expression of growth hormone receptor and insulin-like growth factor-I mRNA in congenital heart disease

GH may exert direct growth-promoting and metabolic actions on target tissues, but most of its effects are mediated by circulating (endocrine) or local (auto-/paracrine) IGF-I. The GH/IGF-I system has an important role in cardiac development and in maintaining the structure and function of the heart. A subgroup of children with pronounced heart defects will eventually need transplants, owing to congestive heart failure. Since the symptoms are often severe and may progress while waiting for surgery, it is necessary to develop supportive medical treatment. GH has been proposed as a therapeutic agent in adults with heart failure, but to date studies are lacking on children and more information is necessary. We have examined the expression of IGF-I mRNA and GH-receptor (GH-R) mRNA in children undergoing surgery for congenital heart disease. Eighteen children scheduled for open-heart surgery were included in the study. Right auricular biopsies were taken at the time of venous catheterization preceding cardiac bypass. The specimens were analysed using realtime PCR. We were able to show expression of both IGF-I mRNA and GH-R mRNA in the pediatric heart. The relative expressions were intercorrelated (r=0.75, p<0.001). GH-R mRNA correlated positively to standardized weight (r=0.65, p=0.004), body mass index (BMI) (r=0.59, p=0.01), and standardized BMI (r=0.59, p=0.01). IGF-I mRNA only correlated to BMI (r=0.50, p=0.04). This is the first study displaying cardiac expression of IGF-I mRNA and GH-R mRNA in children with congenital heart disease, although further studies are needed to define a role for GH in the treatment of these patients.