Role of bradykinin in the antihypertrophic effects of enalapril in the newborn pig heart

Understanding developmental pharmacodynamics: importance for drug development and clinical practice

Developmental pharmacodynamics is the study of age-related maturation of the structure and function of biologic systems and how this affects response to pharmacotherapy. This may manifest as a change in the potency, efficacy, or therapeutic range of a drug. The paucity of studies exploring developmental pharmacodynamics reflects the lack of suitable juvenile animal models and the ethical and practical constraints of conducting studies in children. However, where data from animal models are available, valuable insight has been gained into how response to therapy can change through the course of development. For example, animal neurodevelopmental models have revealed that temporal differences in the maturation of norepinephrine and serotonin neurotransmitter systems may explain the lack of efficacy of some antidepressants in children. GABA(A) receptors that switch from an excitatory to inhibitory mode during early development help to explain paradoxical seizures experienced by infants after exposure to benzodiazepines. The increased sensitivity of neonates to morphine may be due to increased postnatal expression of the mu opioid receptor. An age dependency to the pharmacokinetic-pharmacodynamic relationship has also been found in some clinical studies. For example, immunosuppressive effects of ciclosporin (cyclosporine) revealed markedly enhanced sensitivity in infants compared with older children and adults. A study of sotalol in the treatment of children with supraventricular tachycardia showed that neonates exhibited a higher sensitivity towards QTc interval prolongation compared with older children. However, the data are limited and efforts to increase and establish data on developmental pharmacodynamics are necessary to achieve optimal drug therapy in children and to ensure long-term success of pediatric drug development. This requires a dual 'bottom up' (ontogeny knowledge driven) and 'top down' (pediatric pharmacokinetic-pharmacodynamic studies) approach.

Angiotensin-converting enzyme inhibitor therapy for ventricular dysfunction in infants, children and adolescents: a review

Angiotensin-converting enzyme (ACE) inhibitors have become an important part of the pharmacologic armamentarium in the battle against treatment of ventricular dysfunction. There have been a number of large controlled, randomized trials in adults with both asymptomatic and symptomatic ventricular dysfunction, which confirm the safety and efficacy of this category of drugs for the treatment of this potentially lethal condition. ACE inhibitors may be used to treat infants, children and adolescents with asymptomatic and symptomatic ventricular dysfunction as well. The data supporting their use in children is less complete than that concerning the treatment of adults. We review here the various causes of ventricular dysfunction and congestive heart failure (CHF) in infants, children, and adolescents; the data available regarding treatment of these conditions with ACE inhibitors, and the safety and efficacy of these drugs for the various conditions. The pharmacokinetics and proposed mechanisms of action of ACE inhibitors in children are reviewed, as are speculated long-term results of ACE inhibitor use in cohorts of growing children. Recommendations are made for future studies.

Rapid cardiac growth--mechanical, neural and endocrine dependence

Rapid growth of the cardiac left ventricle is a hallmark of the neonatal period. During the first 2 weeks of life in the piglet, weight of the left ventricle increases 4 fold. The increase in weight is accompanied by approximately a 4 fold increase in myocyte volume indicating hypertrophic growth. Total RNA also increases approximately 4 fold indicating that the mechanism of growth involves greater ribosome content and greater capacity for protein synthesis. The rapid rate of ribosome formation and protein synthesis cannot be further accelerated in isolated perfused hearts by insulin, agents that increase 3',5'-cyclic monophosphate, alpha 1-adrenergic agonists or angiotensin II. In an attempt to slow cardiac growth and make it responsive to growth-promoting agonists, piglets are treated with an angiotensin converting enzyme inhibitor, enalapril maleate. Enalapril decreases left ventricular growth by 19% and total RNA content by 36%. When enalapril-treated hearts are perfused in vitro for 1 h, alpha 1-adrenergic agents restore rates of ribosome formation to control values but angiotensin II has no effect. In left ventricular myocytes that are cultured for 3 days, an alpha 1-adrenergic agonist and endothelin increases the rate of protein synthesis by 20 to 75% but angiotensin II has only a marginal effect (8%). These findings indicate that inhibition of growth by enalapril most likely is due to decreased ventricular pressure development that is secondary to peripheral vasodilation and a fall in mean arterial pressure.