Experimental physiology
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Experimental physiology · Sep 2014
ReviewIntestinal regulation of urinary sodium excretion and the pathophysiology of diabetic kidney disease: a focus on glucagon-like peptide 1 and dipeptidyl peptidase 4.
The tubular hypothesis of glomerular filtration and nephropathy in diabetes is a pathophysiological concept that assigns a critical role to the tubular system, including proximal tubular hyper-reabsorption and growth, which is relevant for early glomerular hyperfiltration and later chronic kidney disease. Here we focus on how harnessing the bioactivity of hormones released from the gut may ameliorate the early effects of diabetes on the kidney in part by attenuating proximal tubular hyper-reabsorption and growth. The endogenous tone of the glucagon-like peptide 1 (GLP-1)/GLP-1 receptor (GLP-1R) system and its pharmacological activation are nephroprotective in diabetes independent of changes in blood glucose. ⋯ The GLP-1R agonist exendin-4 induces natriuresis via activation of the GLP-1R. In contrast, DPP4 inhibition increases circulating GLP-1, but drives a GLP-1R-independent natriuretic response, implying a role for other DPP-4 substrates. The extent to which the intrarenal DPP-4/GLP-1 receptor system contributes to all these changes remains to be established, as does the direct impact of the system on renal inflammation.
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Experimental physiology · Apr 2014
Comparative StudyAlterations in Notch signalling in skeletal muscles from mdx and dko dystrophic mice and patients with Duchenne muscular dystrophy.
New Findings What is the central question of this study? The Notch signalling pathway plays an important role in muscle regeneration, and activation of the pathway has been shown to enhance muscle regeneration in aged mice. It is unknown whether Notch activation will have a similarly beneficial effect on muscle regeneration in the context of Duchenne muscular dystrophy (DMD). What is the main finding and its importance? Although expression of Notch signalling components is altered in both mouse models of DMD and in human DMD patients, activation of the Notch signalling pathway does not confer any functional benefit on muscles from dystrophic mice, suggesting that other signalling pathways may be more fruitful targets for manipulation in treating DMD. ⋯ Notch inhibition significantly depressed the frequency-force relationship in regenerating muscles of C57BL/10 and mdx mice after injury, indicating reduced force at each stimulation frequency, but enhanced the frequency-force relationship in muscles from dko mice. We conclude that while Notch inhibition produces slight functional defects in dystrophic muscle, Notch activation does not significantly improve muscle regeneration in murine models of muscular dystrophy. Furthermore, the inconsistent expression of Notch targets between murine models and DMD patients suggests caution when making interspecies comparisons.
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Experimental physiology · Mar 2014
Assessment of dynamic cerebral autoregulation and cerebrovascular CO2 reactivity in ageing by measurements of cerebral blood flow and cortical oxygenation.
With ageing, cerebral blood flow velocity (CBFV) decreases; however, to what extent dynamic cerebral autoregulation and cerebrovascular CO2 reactivity are influenced by ageing is unknown. The aim was to examine the dynamic responses of CBFV and cortical oxygenation to changes in blood pressure (BP) and arterial CO2 across different ages. Fifty-eight participants in three age groups were included, as follows: young (n = 20, 24 ± 2 years old), elderly (n = 20, 66 ± 1 years old), and older elderly (n = 18, 78 ± 3 years old). ⋯ Even though the absolute changes in CBFV and cerebrovascular resistance index during the cerebrovascular CO2 reactivity were higher in the young group, the percentage changes in CBFV, cerebrovascular resistance index and O2Hb were similar in all age groups. In conclusion, there was no decline in dynamic cerebral autoregulation and cerebrovascular CO2 reactivity with increasing age up to 86 years. Despite the decrease in cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age, CBFV and cortical oxygenation were not compromised in these elderly humans during manoeuvres that mimic daily life activities.
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Experimental physiology · Mar 2014
Phox2b-expressing retrotrapezoid neurons and the integration of central and peripheral chemosensory control of breathing in conscious rats.
Chemoreception is the classic mechanism by which the brain regulates breathing in response to changes in tissue CO2/H(+). A brainstem region called the retrotrapezoid nucleus (RTN) contains a population of Phox2b-expressing glutamatergic neurons that appear to function as important chemoreceptors. In the present study, we ask whether the destruction of a type of pH-sensitive interneuron that expresses the transcription factor Phox2b and is non-catecholaminergic (Phox2b(+)TH(-)) could affect breathing in conscious adult rats. ⋯ In anaesthetized rats with bilateral lesions of around 90% of the Phox2b(+)TH(-) neurons, acute activation of the Bötzinger complex, the pre-Bötzinger complex or the rostral ventral respiratory group with NMDA (5 pmol in 50 nl) elicited normal cardiorespiratory output. In conclusion, the destruction of the Phox2b(+)TH(-) neurons is a plausible cause of the respiratory deficits observed after injection of SSP-SAP into the RTN. Our results also suggest that RTN neurons activate facilitatory mechanisms important to the control of breathing in resting or hypercapnic conditions in conscious adult rats.
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Experimental physiology · Feb 2014
Differential visceral pain sensitivity and colonic morphology in four common laboratory rat strains.
What is the central question of this study? Does stress sensitivity and susceptibility to inflammation innate to certain rat strains make them vulnerable to bowel dysfunction? What is the main finding and its importance? Of four different rat strains, the Lewis rat, which displays both susceptibility to gastrointestinal inflammation and sensitivity to stress, exhibits the most aberrant gastrointestinal morphology and visceral pain sensitivity. Given the similarities to human functional bowel disorders, such as irritable bowel syndrome, this may make it a good model of this disease. Irritable bowel syndrome is a common, debilitating gastrointestinal (GI) disorder characterized by episodic exacerbations of symptoms such as abdominal pain, bloating and altered bowel habit. ⋯ At a morphological level, the gastrointestinal tract from these rats displayed mucosal goblet cell hyperplasia and alterations in muscle layer thickness. The Lewis rat strain, which is reported to have increased susceptibility to GI inflammation in addition to stress sensitivity, had the most prominent features of physiological and morphological GI dysfunction. These data support the hypothesis that background strain is a key factor in the development and exacerbation of bowel dysfunction in rodent models.