Cardiovascular disease is responsible for the loss of one life every 38 seconds and accounts for 26.6 percent of all infants that die of congenital birth defects. Adrenergic hormones are critically important regulators of cardiovascular physiology in embryos and adults. They are key mediators of stress responses and have profound stimulatory effects on cardiovascular function, and dysregulation of adrenergic function has been associated with many adverse cardiac conditions, including congenital malformations, arrhythmias, ischemic heart disease, heart failure, and sudden cardiac death. Despite intensive study, the specific roles these hormones play in the developing heart is not well-understood. Further, there is little information available regarding how these important hormones mediate stress responses in adult females (before and after menopause) in comparison to males. My thesis thus has two major foci: (1) What role(s) do catecholamines play in the embryonic heart?, and (2) Do catecholamines differentially influence cardiac function in aging male and female hearts? Initially, we sought to uncover the roles of adrenergic hormones in the embryonic heart by utilizing an adrenergic-deficient (Dbh-/-) mouse model. We found that adrenergic hormones influence heart development by stimulating expression of the gap junction protein, connexin 43, facilitating atrioventricular conduction, and helping to maintain cardiac rhythm. As development progresses, cardiac energy demands increase substantially, and oxidative phosphorylation becomes vital. Adrenergic hormones regulate metabolism in adults, thus we hypothesized they may stimulate energy metabolism during the embryonic/fetal transition period. We examined ATP, ADP, oxygen consumption rate, and extracellular acidification rates and found these metabolic indices were significantly decreased in Dbh-/- hearts compared to Dbh+/+ controls. We employed transmission electron microscopy of embryonic cardiomyocytes and found the mitochondria were significantly larger in Dbh-/- hearts compared to controls, and had more branch points. Taken together, these results suggest adrenergic hormones play a major role mediating the shift from predominantly anaerobic to aerobic metabolism during the embryonic/fetal transition period. Since there are known differential cardiac responses due to sex, age, and menopause to stress, we used echocardiography to measure left ventricular (LV) function in adult (9, 18 and 21 month) male and female mice (pre and postmenopausal) in response to epinephrine, and immobilization stress to investigate the roles of these factors. My results show 9-month premenopausal female mice display significantly decreased LV responsiveness to epinephrine compared to males, and an increased response to epinephrine due to age, especially in the premenopausal females. Similar LV function was also observed between postmenopausal females and males, and this pattern persisted after immobilization stress. I also investigated anatomical differences in the distribution of adrenergic cells within the heart comparing age, sex, and menopausal status. Notably, the density of cells derived from an adrenergic lineage in the heart was significantly increased in postmenopausal mice compared to age-matched males and cycling females. The selective re-appearance of adrenergic cells in the heart following menopause may provide an explanation for the differential stress responses observed in our system, and could have important clinical ramifications for stress-induced cardiomyopathies.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd-5833 |
| Date | 01 January 2014 |
| Creators | Baker, Candice |
| Publisher | University of Central Florida |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations |
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