Sunday, 15 December 2013

The Effects of Hormone Catecholamines - Epinephrine(2)

 Catecholamines, derived from the amino acid tyrosine, produced by the adrenal glands, which are found on top of the kidneys. are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. The hormone are released into the blood during times of physical or emotional stress.
A. Epinephrine
9. Catecholamine-releasing action in guinea-pig papillary muscles
In the study to  investigate wheather tetraethylammonium ion (TEA) prolongs the action potential (AP) was examined by standard microelectrode techniques in papillary muscles isolated from nonreserpinized and reserpinized guinea-pig hearts, showed that TEA modifies its intrinsic prolonging action of the AP by releasing norepinephrine from sympathetic nerve terminals; TEA prolongs the AP by reducing the time-independent outward current rather than the time-dependent outward current; and a TEA-sensitive current does not effectively contribute to the total ionic current at the time of Vmax(9).

10. The Effects of hypertension on cardiovascular responses to epinephrine
Cardiac beta-receptor responsiveness is diminished by both aging and hypertension. In the study to evaluate of14 young and 18 older normotensive men and women and in 10 young and 17 older hypertensive men and women by echocardiography cardiac responses to intravenous infusion of epinephrine and to assess the relative contribution of intrinsic cardiac and counterregulatory components to the overall respons, found that Epinephrine-induced increases in heart rate were similar in the four groups. Increases in stroke volume, ejection fraction, and cardiac index were similar in the two hypertensive and two young normotensive groups. In contrast, they were attenuated in the older normotensive group, resulting in higher left ventricular responses in older hypertensive than in normotensive subjects. Heart rate and left ventricular responses to epinephrine in the presence of ganglionic blockade did not differ between the two young groups. Increases in plasma norepinephrine due to epinephrine infusion were larger in hypertensive than in normotensive subjects(10).

11. Epinephrine, vasodilation and hemoconcentration in syncopal, healthy men and women
In the study to evaluate why healthy young people may become syncopal during standing, head up tilt (HUT) or lower body negative pressure (LBNP by measuring the hormonal indices of autonomic activity along with arterial pressure (AP), heart rate (HR), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR) and measures of plasma volume, found that the presyncopal decline in blood pressure in otherwise healthy young people resulted from declining peripheral resistance associated with plateauing norepinephrine and plasma renin activity, rising epinephrine and rising blood viscosity. The increased hemoconcentration probably reflects increased rate of venous pooling rather than rate of plasma filtration and, together with cardiovascular effects of imbalances in norepinephrine, epinephrine and plasma renin activity may provide afferent information leading to syncope(11).

12. Adrenal glands and the activation of glucogenesis during undernutrition
In adults, the adrenal glands are essential for the metabolic response to stress, but little is known about their role in fetal metabolism. In the study to investigate the effects of adrenalectomizing fetal sheep on glucose and oxygen metabolism in utero in fed conditions and after maternal fasting for 48 h near term, showed that the circulating concentrations of cortisol and total catecholamines, and the hepatic glycogen content and activities of key gluconeogenic enzymes, were also less in AX than intact fetuses in fasted animals. Insulin concentrations were also lower in AX than intact fetuses in both nutritional states. Maternal glucose utilization and its distribution between the fetal, uteroplacental, and nonuterine maternal tissues were unaffected by fetal AX in both nutritional states. Ovine fetal adrenal glands, therefore, have little effect on basal rates of fetal glucose and oxygen metabolism but are essential for activating fetal glucogenesis in response to maternal fasting. They may also be involved in regulating insulin sensitivity in utero(12).

13. Catecholamine concentrations in hyperthyroidism and hypothyroidism
In the study to measure the plasma epinephrine (E) and norepinephrine (NE) concentrations in patients with thyroid dysfunction, showed that hyperthyroidism is accompanied by normal plasma NE concentrations and that hypothyroidism is associated with significantly increased plasma NE concentrations, possible in an attempt to compensate for the lack of thyroid hormones(13).
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