Experimental physiology
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Experimental physiology · Feb 2012
Kinetics of exercise-induced neural activation; interpretive dilemma of altered cerebral perfusion.
Neural activation decreases cerebral deoxyhaemoglobin (HHb(C)) and increases oxyhaemoglobin concentration (O(2)Hb(C)). In contrast, patients who present with restricted cerebral blood flow, such as those suffering from cerebral ischaemia or Alzheimer's disease, and during the course of ageing the converse occurs, in that HHb(C) increases and O(2)Hb(C) decreases during neural activation. In the present study, we examined the interpretive implications of altered exercise-induced cerebral blood flow for cortical oxygenation in healthy subjects. ⋯ During Cuff+, both MCA V(mean) and O(2)Hb(C) increased during exercise, whereas HHb(C) decreased. In contrast, the opposite occurred during the Cuff- manipulation. These findings highlight the inverse relationship between cerebral blood flow and cerebral oxygenation as determined by NIRS, which has interpretive implications for the kinetics underlying exercise-induced neural activation.
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Experimental physiology · Jan 2012
Endothelial dysfunction in rat mesenteric artery after regional cardiac ischaemia-reperfusion.
In most previous studies, ischaemia-reperfusion (I/R)-induced vascular injury referred to injury in the tissue or blood vessel that was directly subjected to I/R. However, less attention has been focused on remote vascular injury that might be caused by cardiac I/R. In the present study, we aimed to assess whether cardiac I/R could affect vasoconstriction and vasodilatation in mesenteric arteries from Sprague-Dawley rats. ⋯ However, L-NAME caused a similar degree of inhibition of acetylcholine-stimulated relaxation in mesenteric arteries from sham-operated and I/R rats. Electron microscopy revealed that mesenteric arterial endothelial structure was degraded in the I/R group and that N-acetyl-L-cysteine treatment prevented this structural damage. In conclusion, regional cardiac I/R caused by transient occlusion and reperfusion of the left anterior descending coronary artery results in peripheral vascular endothelial dysfunction.
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Experimental physiology · Jan 2012
Moderate cardiac-selective overexpression of angiotensin II type 2 receptor protects cardiac functions from ischaemic injury.
We hypothesized that moderate cardiac-selective overexpression of the angiotensin II type 2 receptor (AT2R) would protect the myocardium from ischaemic injury after a myocardial infarction (MI) induced by coronary artery ligation. For in vitro studies, adenoviral vector expressing genomic DNA of AT2R and enhanced green fluorescence protein (EGFP) was used to overexpress AT2R in rat neonatal cardiac myocytes. Expression of AT2R, measured by real-time PCR and immunostaining, demonstrated efficient transduction of AT2R in a dose-dependent pattern. ⋯ In the post-treatment study, the overexpression of AT2R partly reversed the MI-induced cardiac dysfunction. Myocardial infarction also induced the upregulation of angiotensin II type 1 receptor, angiotensin-converting enzyme and collagen I mRNA expression, all of which were attenuated by the overexpression of AT2R. It is concluded that moderate cardiac-selective overexpression of AT2R protects heart function from ischaemic injury, which may be mediated, at least in part, through modulation of components of the cardiac renin-angiotensin system and collagen levels in the myocardium.
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Experimental physiology · Aug 2011
Baroreflex control of renal sympathetic nerve activity and heart rate in near-term fetal sheep.
Late preterm infants, born between 34 and 36 weeks gestation, have significantly higher morbidity than neonates born at full term, which may be partly related to reduced sensitivity of the arterial baroreflex. The present study assessed baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) in near-term fetal sheep at 123 ± 1 days gestation. At this age, although fetuses are not fully mature in some respects (term is 147 days), sleep-state cycling is established [between high-voltage, low-frequency (HV) and low-voltage, high-frequency (LV) sleep], and neural myelination is similar to the term human infant. ⋯ In contrast, the fall in BP after sodium nitroprusside was associated with a significant increase in HR during LV but not HV sleep, and there was no significant effect of hypotension on RSNA. These data demonstrate that in near-term fetal sheep baroreflex activity is only partly active and is highly modulated by sleep state. Critically, there was no RSNA response to marked hypotension; this finding has implications for the ability of the late preterm fetus to adapt to low BP.
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Experimental physiology · Feb 2011
Regulation of leptin synthesis in white adipose tissue of the female fruit bat, Cynopterus sphinx: role of melatonin with or without insulin.
Factors regulating leptin synthesis during adipogenesis in wild species are not well known. Studies in the female Cynopterus sphinx bat have shown that it undergoes seasonal changes in its fat deposition and serum leptin and melatonin levels. The aim of the present study was to investigate the hormonal regulation of leptin synthesis by the white adipose tissue during the period of fat deposition in female C. sphinx. ⋯ The study showed MT(2) receptors in adipose tissue and a stimulatory effect of melatonin on leptin synthesis, which was blocked by treatment with an MT(2) receptor antagonist, suggesting that the effect of melatonin on leptin synthesis by adipose tissue is mediated through the MT(2) receptor in C. sphinx. The in vitro study showed that the synthesis of leptin is directly proportional to the amount of glucose uptake by the adipose tissue. It further showed that melatonin together with insulin synergistically enhanced the leptin synthesis by adipose tissue through phosphorylation of mitogen-activated protein kinase in C. sphinx.