E resting blood flow both with and without accompanying cardiac hypertrophy [43?5]. Furthermore, cardiac hypertrophy which is secondary to hyperthyroidism is typically associated with augmented blood 
flow and parallel or increased vascular growth due to increased crosssectional area of the vascular bed [44,46]. On the other hand, increased LV fibrosis and collagen crosslinking are associated with diastolic stiffness which contributes to LV pump dysfunction and progression to HF [31,47?9]. While previous investigations have examined the influence of THs on collagen gene expression and/or fibrotic deposition, they typically have been performed without simultaneous assessment of cardiac function or are deduced from autopsy findings [13,50?2]. For this reason, the influence of LV fibrosis on cardiac function during sustained hyperthyroidism is not well understood. THs have been implicated in the regulation of collagen dynamics, however, their influence on myocardial fibrosis has yielded conflicting results. Short-term studies have shown that THs exert anti-fibrotic 
actions, including in the setting of TH induced hypertrophy [6,53?7]. In vitro investigations by Yao Eghbali and Chen et al., suggest that THs can directly regulate and suppress collagen gene expression [53,56]. In contrast, Roy et al. found that the anti-fibrotic actions of THs were the result of regulating matrix order SMER28 metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) despite increased collagen and pro-collagen gene expression [54]. On the other hand, myocardial fibrosis caused by chronic hyperthyroidism has been reported by numerous authors [7,13,58?0]. Chronic hyperthyroidism is associated with increased cellular metabolism and increased oxidative damage [61?64]. Oxidative damage is a known stimuli for collagen deposition [65?8] and increased oxidative damage which occurs during sustained bouts of hyperthyroidism likely contributes to increased interstitial collagen deposition. Further investigation is needed to fully elucidate the mechanisms of increased interstitial collagen deposition in this setting. Although it is well established that acute hyperthyroidism is associated with augmented cardiac function and increased cardiac output [1,5,69], the importance of LV fibrosis on cardiac function during hyperthyroidism is not well characterized. Using trichrome staining, we were able to confirm in our study that prolonged hyperthyroidism was associated with increased LV fibrosis [,60 q] when compared with age matched control hamsters. The MedChemExpress JI 101 majority of fibrotic deposits were found within the perivascular space (perivascular fibrosis) and cardiac interstitium (interstitial fibrosis) without evidence of myocyte necrosis and replacement fibrosis. Moreover, we observed severe relaxation impairment (-dP/dT and Tau) and ultimately systolic dysfunction (LV EF, LV ESP, dP/dT) 1326631 in hyperthyroid hearts. Our findings further support the notion that LV fibrosis inversely affects LV function in the setting of hyperthyroidism. While increased collagen deposition certainly can impair global cardiac function, it may not similarly affect intrinsic cardiomyocyte mechanics. Accordingly, we also examined the influence of chronic hyperthyroidism on the mechanical function of individual myocytes. We hypothesized that mechanical impairment at the level of individual ventricular myocytes would strongly correlate with the decline observed in global cardiac function. Contrary to our.E resting blood flow both with and without accompanying cardiac hypertrophy [43?5]. Furthermore, cardiac hypertrophy which is secondary to hyperthyroidism is typically associated with augmented blood flow and parallel or increased vascular growth due to increased crosssectional area of the vascular bed [44,46]. On the other hand, increased LV fibrosis and collagen crosslinking are associated with diastolic stiffness which contributes to LV pump dysfunction and progression to HF [31,47?9]. While previous investigations have examined the influence of THs on collagen gene expression and/or fibrotic deposition, they typically have been performed without simultaneous assessment of cardiac function or are deduced from autopsy findings [13,50?2]. For this reason, the influence of LV fibrosis on cardiac function during sustained hyperthyroidism is not well understood. THs have been implicated in the regulation of collagen dynamics, however, their influence on myocardial fibrosis has yielded conflicting results. Short-term studies have shown that THs exert anti-fibrotic actions, including in the setting of TH induced hypertrophy [6,53?7]. In vitro investigations by Yao Eghbali and Chen et al., suggest that THs can directly regulate and suppress collagen gene expression [53,56]. In contrast, Roy et al. found that the anti-fibrotic actions of THs were the result of regulating matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) despite increased collagen and pro-collagen gene expression [54]. On the other hand, myocardial fibrosis caused by chronic hyperthyroidism has been reported by numerous authors [7,13,58?0]. Chronic hyperthyroidism is associated with increased cellular metabolism and increased oxidative damage [61?64]. Oxidative damage is a known stimuli for collagen deposition [65?8] and increased oxidative damage which occurs during sustained bouts of hyperthyroidism likely contributes to increased interstitial collagen deposition. Further investigation is needed to fully elucidate the mechanisms of increased interstitial collagen deposition in this setting. Although it is well established that acute hyperthyroidism is associated with augmented cardiac function and increased cardiac output [1,5,69], the importance of LV fibrosis on cardiac function during hyperthyroidism is not well characterized. Using trichrome staining, we were able to confirm in our study that prolonged hyperthyroidism was associated with increased LV fibrosis [,60 q] when compared with age matched control hamsters. The majority of fibrotic deposits were found within the perivascular space (perivascular fibrosis) and cardiac interstitium (interstitial fibrosis) without evidence of myocyte necrosis and replacement fibrosis. Moreover, we observed severe relaxation impairment (-dP/dT and Tau) and ultimately systolic dysfunction (LV EF, LV ESP, dP/dT) 1326631 in hyperthyroid hearts. Our findings further support the notion that LV fibrosis inversely affects LV function in the setting of hyperthyroidism. While increased collagen deposition certainly can impair global cardiac function, it may not similarly affect intrinsic cardiomyocyte mechanics. Accordingly, we also examined the influence of chronic hyperthyroidism on the mechanical function of individual myocytes. We hypothesized that mechanical impairment at the level of individual ventricular myocytes would strongly correlate with the decline observed in global cardiac function. Contrary to our.
