Diane C. Tucker - US grants

The proposed studies will examine the influence of sympathetic and parasympathetic innervation and circulating catecholamine stimulation on the growth, differentiation and intrinsic beating rate of the fetal rat heart. Neural and cardiac controls of cardiac development will be isolated by studying hearts maturing in an in vivo organ culture system, the anterior chamber of the eye of host rat. The following hypotheses will be tested: 1. By morphological and electrophysiological criteria, myocardial tissue cultured in oculo develops to an adult-like stage from the fetal stage at which it is implanted. 2. Circulating catecholamines contribute to the growth, differentiation, and determination of intrinsic beating rate of heart tissue maturing in oculo. 3. Both the sympathetic and parasympathetic nervous systems regulate growth, differentiation, and intrinsic beating rate of heart tissue developing in oculo. 4. Autonomic innervation ceases to influence cardiac growth, differentiation, and intrinsic beating rate after 30 days in oculo. Cardiac growth will be measured by increases in size of the transplanted hearts. The sizes of myocytes from implanted heart tissue will be measured to distinguish between growth by hypertrophy vs hyperplasia. Differentiation from fetal to adult-like heart tissue will be confirmed by ultrastructural criteria (electron microscopy). Intrinsic heart rate will be measured in cultured tissue after combined beta-adrenergic and muscarinic receptor blockade. With the in oculo culture system, development of the heart can be studied under conditions where neural influences can be selectively controlled. This model provides a method for studying interactions between developing cardiovascular target organs and their autonomic innervation. These early developmental influences may modulate genetically programmed maturation, contributing to subsequent individual differences in cardiovascular regulation and in the predisposition to cardiovascular diseases such as hypertension.

The proposed studies will investigate regulation of growth, differentiation, and intrinsic beating rate of fetal rat heart by autonomic nerves, circulating factors and mechanisms intrinsic to the heart. Neural, hormonal and cardiac controls of cardiac development will be isolated by studying hearts maturing in an in vivo culture system, the anterior chamber of the eye of a host rat (i.e., in oculo). The following hypotheses will be tested: 1. Sympathetic innervation of heart tissue maturing in oculo causes myocyte hypertrophy and promotes differentiation into adult-like heart tissue. 2. Circulating catecholamines contribute to the growth, differentiation and determination of intrinsic beating rat of heart tissue maturing in oculo. 3. Growth, differentiation, and intrinsic beating rate of heart tissue developing in oculo are regulated by both sympathetic and parasympathetic innervation. 4. Autonomic innervation ceases to influence cardiac growth, differentiation, and intrinsic beating rate by 2 months in oculo. 5. Thyroid hormone promotes growth, differentiation and intrinsic beating rate of fetal heart cultured in oculo both by direct action and by increasing sensitivity to sympathetic stimulation. Cardiac growth will be measured by increases in size of transplanted atria and ventricles. The sizes of myocytes from implanted heart tissue will be measured to identify growth by hypertrophy. Differentiation from fetal to adult-like heart tissue will be examined by ultrastructural and biochemical criteria (i.e. electron microscopy and myosin isoenzyme composition). Intrinsic heart rate will be measured from in oculo atria after combined beta-adrenergic and muscarinic receptor blockade. With the in oculo culture system, heart development can be studied under conditions where neural and hormonal influences can be selectively controlled without changing hemodynamic load. This model provides a method for studying interactions among developing cardiovascular target organs, their autonomic innervation and their hormonal milieu. Early developmental influences may modulate genetically programmed maturation and contribute to subsequent individual differences in cardiovascular regulation and in the predisposition to cardiovascular diseases such as hypertension.

biomedical equipment purchase;

The primary objective of this clinical research program is to assess the importance of vascular nitric oxide (NO) production in the regulation of cardiovascular responses to stress (reactivity), with special attention given to NO effects on gender and racial differences in reactivity. NO plays an important role in blood pressure (BP) regulation, and potentially influences the development of hypertension. Studies by ourselves and others indicate that BP reactivity is strongly inversely related to NO production during stress. However, the contribution of NO in the regulation of reactivity has not been fully explored in human studies. In particular, estrogen-induced endothelial NO production may contribute to differences in reactivity between men and premenopausal women, and there may be differences in NO production among blacks and those with a family history of hypertension (FH) that may affect reactivity. Our preliminary studies support these ideas. In our proposed studies, normotensive subjects will be put on a low nitrate/nitrite diet for two days, and then have psychophysiologic testing with measures of BP, forearm blood flow, and plasma levels of NO metabolites (nitrates/nitrites) and catecholamines taken before and after two stressors (speech task and cold pressor). Two separate studies using the above protocol will employ a within-subjects design to determine the effects of two factors (menstrual cycle variation of estrogen and L-arginine loading to induce NO production) on the relationship of NO and reactivity. Our major hypotheses are: 1) NO production contributes significantly to the regulation of reactivity, and is inversely related to reactivity measures, particularly those related to vasoconstriction; 2) Among women, higher levels of estrogen in the late luteal phase induce greater vascular NO production and lower reactivity than in the low-estrogen menstrual phase; 3) individuals at risk for hypertension (blacks, those with FH) have less NO change with stress than low risk individuals, and this difference contributes to differences in reactivity; 4) dietary supplementation with the NO precursor L-arginine increases NO production and diminishes reactivity, with the greatest effects occurring among blacks and those with FH; and 5) NO is inversely related to measures of adrenergic activity, and both systems contribute to the regulation of reactivity.