Description (Adapted from Application): The long-term goal is to better understand the homeostatic responsiveness of vertebrates to stress. It is proposed to use a rat model of human pathophysiology, specifically obesity, to investigate how systemic and cellular responsiveness is altered during stress. Sleep deprivation will be employed as the stress paradigm on the genetically obese (fa/fa) and lean (Fa/?) Zucker rat. With this model, the PI will examine neuroendocrine and cardiovascular indices of stress involving four homeostatic systems: (1) the hypothalamic-pituitary-thyroid (HPT) axis; (3) the sympathoadrenal (SA) system, including endocrine pancreas; and (4) hemodynamic parameters of the cardiovascular (CV) system. The specific aims are: (1) to characterize and compare neuroendocrine responsiveness by determining tissue and plasma levels of HPA axis hormones (CRF, ACTH, prolactin, and corticosterone); HPT axis (TRF, TSH, and thyroid hormones, including both total and free components); and SA system hormones (NE, E, DA; and catecholamine synthesizing enzymes); (2) to determine the hemodynamic responsiveness of the CV system by measuring mean arterial pressure, heart rate, respiratory rate, and electrocardiogram waveforms; (3) to measure cellular responsiveness to stress by determining changes in expression of stress-related genes (heat-shock genes); and (4) to measure changes in activities of rate-limiting enzymes of key metabolic of key metabolic pathways as an index of change in cellular carbon flow and energy utilization. Experimental approaches for aims 1 and 3 will be to use immunoassay, Western blots, Northern blots, immunocytochemistry, in situ hybridization, and HPLC for specific localization and quantitative determination of the designated analyses. Aim 2 will be accomplished by implantation of radiotelemetry devices to measure cardiovascular parameters. Little is known about how stress affects a rat model with a disorder characteristic of many humans, obesity. The working hypotheses is as follows: Given the morbidity observed when a potent stressor is applied chronically to normal lean animals, it is hypothesized that obesity, with its own underlying pathologies that also lead to morbidity, will result in a significantly shorter time course of homeostatic responsiveness compared to lean animals and that the responsiveness will be greater in magnitude compared to lean animals. These predicted observations will be consistent with the overall decline of the health of stressed animals, indicating that homeostatically, the obese phenotype is in markedly greater physiological distress.