Programming of adult blood pressure by maternal protein restriction: Role of nephrogenesis.
Modest maternal protein restriction leads to hypertension and a reduced number of glomeruli in adult male ...but not female offspring. This study determined whether a more severe protein restriction has equivalent effects on male and female rat offspring, and examined the role of nephrogenesis in this programming.
Sprague-Dawley rats were fed a protein-restricted (5% protein) diet throughout (LLP), or during the first (LLP/NP) or second (NP/LLP) half of pregnancy. Controls ate a normal diet (NP, 19% protein). Adult offspring were chronically instrumented at 22weeks; glomerular number and volume were estimated using stereologic techniques.
Mean arterial pressures in male offspring were significantly higher in LLP (136 ± 2mm Hg) or NP/LLP (137 ± 2mm Hg) than in LLP/NP (125 ± 1mm Hg) or NP (125 ± 2mm Hg). Moreover, the hypertension was salt-sensitive (increase of 16 ± 4mm Hg in LLP on a high Na+ diet compared to 2 ± 2mm Hg in NP). Glomerular number (per kidney) was reduced (15,400 ± 2,411 in LLP vs. 27,208 ± 1,534 in NP) but average individual glomerular volume was not different (1.98 ± 0.18 106μ3 in LLP vs. 2.01 ± 0.14 106μ3 in NP). Female offspring showed qualitatively similar results.
Severe maternal dietary protein restriction reduces glomerular number and programs for salt-sensitive adult hypertension in both female and male offspring. The window of sensitivity of adult blood pressure to prenatal protein restriction falls within the period of nephrogenesis in the rat. These data are consistent with the hypothesis that maternal protein restriction causes adult hypertension in the offspring through impairment of renal development.
Ventricular arrhythmias can cause death in heart failure (HF). A trigger is the occurrence of Ca2+ waves which activate a Na+‐Ca2+ exchange (NCX) current, leading to delayed after‐depolarisations and ...triggered action potentials. Waves arise when sarcoplasmic reticulum (SR) Ca2+ content reaches a threshold and are commonly induced experimentally by raising external Ca2+, although the mechanism by which this causes waves is unclear and was the focus of this study. Intracellular Ca2+ was measured in voltage‐clamped ventricular myocytes from both control sheep and those subjected to rapid pacing to produce HF. Threshold SR Ca2+ content was determined by applying caffeine (10 mM) following a wave and integrating wave and caffeine‐induced NCX currents. Raising external Ca2+ induced waves in a greater proportion of HF cells than control. The associated increase of SR Ca2+ content was smaller in HF due to a lower threshold. Raising external Ca2+ had no effect on total influx via the L‐type Ca2+ current, ICa‐L, and increased efflux on NCX. Analysis of sarcolemmal fluxes revealed substantial background Ca2+ entry which sustains Ca2+ efflux during waves in the steady state. Wave frequency and background Ca2+ entry were decreased by Gd3+ or the TRPC6 inhibitor BI 749327. These agents also blocked Mn2+ entry. Inhibiting connexin hemi‐channels, TRPC1/4/5, L‐type channels or NCX had no effect on background entry. In conclusion, raising external Ca2+ induces waves via a background Ca2+ influx through TRPC6 channels. The greater propensity to waves in HF results from increased background entry and decreased threshold SR content.
Key points
Heart failure is a pro‐arrhythmic state and arrhythmias are a major cause of death.
At the cellular level, Ca2+ waves resulting in delayed after‐depolarisations are a key trigger of arrhythmias. Ca2+ waves arise when the sarcoplasmic reticulum (SR) becomes overloaded with Ca2+.
We investigate the mechanism by which raising external Ca2+ causes waves, and how this is modified in heart failure.
We demonstrate that a novel sarcolemmal background Ca2+ influx via the TRPC6 channel is responsible for SR Ca2+ overload and Ca2+ waves.
The increased propensity for Ca2+ waves in heart failure results from an increase of background influx, and a lower threshold SR content.
The results of the present study highlight a novel mechanism by which Ca2+ waves may arise in heart failure, providing a basis for future work and novel therapeutic targets.
figure legend Raising external Ca2+ (1) leads to a background Ca2+ influx via TRPC6 channels (2). This Ca2+ is pumped into the sarcoplasmic reticulum via SERCA leading to a rise in SR Ca2+ content (3). When SR Ca2+ content reaches a threshold, spontaneous Ca2+ release leads to propagating Ca2+ waves (4). In heart failure, the background Ca2+ influx is increased and SR threshold decreased, resulting in a greater propensity to Ca2+ waves.
Modest maternal dietary protein restriction in the rat leads to hypertension in adult male offspring. The purpose of this study was to determine whether female rats are resistant to developing the ...increased blood pressure seen in male rats after maternal protein restriction. Pregnant rats were fed a normal protein (19%, NP) or low-protein (8.5%, LP) diet throughout gestation. Renal renin protein and ANG II levels were reduced by 50-65% in male LP compared with NP pups, but were not suppressed in female LP compared with female NP. Mean arterial pressure in conscious, chronically instrumented adult female offspring (22 wk) was not different in LP (LP: 120 +/- 3 mmHg vs. NP: 121 +/- 2 mmHg), and glomerular filtration rate was also not different in LP vs. NP. The number of glomeruli per kidney was similar in adult LP and NP female offspring (LP: 26,050 +/- 2,071 vs. NP: 26,248 +/- 1,292, NP), and individual glomerular volume was also not different (LP: 0.92 +/- 0.11 10(6) microm(3), LP vs. NP: 1.07 +/- 0.11 10(6) microm(3)); the total volume of all glomeruli per kidney was also not significantly different. Thus female rats are relatively resistant to the programming for adult hypertension by perinatal protein restriction that we have described in males. This resistance may be due to the fact that modest maternal protein restriction does not reduce the number of glomeruli with which females are endowed as it does in males. The intrarenal renin-angiotensin system during development may play a key role in this protective effect of female gender.
Ventricular arrhythmias can cause death in heart failure (HF). A trigger is the occurrence of Ca
waves which activate a Na
-Ca
exchange (NCX) current, leading to delayed after-depolarisations and ...triggered action potentials. Waves arise when sarcoplasmic reticulum (SR) Ca
content reaches a threshold and are commonly induced experimentally by raising external Ca
, although the mechanism by which this causes waves is unclear and was the focus of this study. Intracellular Ca
was measured in voltage-clamped ventricular myocytes from both control sheep and those subjected to rapid pacing to produce HF. Threshold SR Ca
content was determined by applying caffeine (10 mM) following a wave and integrating wave and caffeine-induced NCX currents. Raising external Ca
induced waves in a greater proportion of HF cells than control. The associated increase of SR Ca
content was smaller in HF due to a lower threshold. Raising external Ca
had no effect on total influx via the L-type Ca
current, I
, and increased efflux on NCX. Analysis of sarcolemmal fluxes revealed substantial background Ca
entry which sustains Ca
efflux during waves in the steady state. Wave frequency and background Ca
entry were decreased by Gd
or the TRPC6 inhibitor BI 749327. These agents also blocked Mn
entry. Inhibiting connexin hemi-channels, TRPC1/4/5, L-type channels or NCX had no effect on background entry. In conclusion, raising external Ca
induces waves via a background Ca
influx through TRPC6 channels. The greater propensity to waves in HF results from increased background entry and decreased threshold SR content. KEY POINTS: Heart failure is a pro-arrhythmic state and arrhythmias are a major cause of death. At the cellular level, Ca
waves resulting in delayed after-depolarisations are a key trigger of arrhythmias. Ca
waves arise when the sarcoplasmic reticulum (SR) becomes overloaded with Ca
. We investigate the mechanism by which raising external Ca
causes waves, and how this is modified in heart failure. We demonstrate that a novel sarcolemmal background Ca
influx via the TRPC6 channel is responsible for SR Ca
overload and Ca
waves. The increased propensity for Ca
waves in heart failure results from an increase of background influx, and a lower threshold SR content. The results of the present study highlight a novel mechanism by which Ca
waves may arise in heart failure, providing a basis for future work and novel therapeutic targets.
Both maternal glucocorticoid administration and maternal dietary protein or food restriction in pregnancy cause fewer nephrons and hypertension in the adult offspring. The purpose of these studies ...was to determine the extent to which nutritional factors contribute to programming of offspring hypertension by maternal glucocorticoids. Pregnant rats were treated with dexamethasone (100 microg x kg(-1) x d(-1) sc) on days 1-10 (ED) or days 15-20 (LD) of pregnancy. Additional groups of pregnant animals were pair fed to the early (EDPF) and late (LDPF) dexamethasone-treated groups, and another group was untreated or given vehicle (C). The dams treated with dexamethasone reduced their food intake and lost or failed to gain a normal amount of weight during treatment; body weights of ED dams caught up to normal after the treatment period, whereas those of LD dams did not. In adulthood ( approximately 21 wks), chronically instrumented male offspring of ED had normal blood pressures (125 +/- 2 mmHg vs. 126 +/- 1 mmHg in C), whereas LD offspring were hypertensive (136 +/- 3 mmHg). However, LDPF offspring were equally hypertensive (134 +/- 2 mmHg). Glomerular filtration rates normalized to body weight were not significantly different among groups. Qualitatively similar results were found in female offspring. Thus the long-term effects of maternal glucocorticoid administration at this dose on offspring's blood pressure may, in large part, be accounted for by the reduction in maternal food intake. These data suggest that maternal glucocorticoids and maternal food or protein restriction may, at least in part, share a common mechanism in programming offspring for hypertension. The window of sensitivity of future offspring blood pressure to either maternal insult coincides with nephrogenesis in the rat, suggesting that impaired renal development could play an important role in this programming.
Restriction of maternal protein intake during rat pregnancy produces offspring that are hypertensive in adulthood, but the mechanisms are not well understood. Our purpose was to determine whether ...this adult hypertension could be programmed during development by suppression of the fetal/newborn renin-angiotensin system (RAS) and a consequent reduction in nephron number. Pregnant rats were fed a normal protein (19%, NP) or low-protein (8.5%, LP) diet throughout gestation. Birth weight was reduced by 13% (p < 0.0005), and the kidney/body weight ratio was reduced in LP pups. Renal renin mRNA levels were significantly reduced in newborn LP pups; renal renin concentration and renin immunostaining were suppressed. Renal tissue angiotensin II levels were also suppressed in newborn LP (0.079 +/- 0.002 ng/mg, LP versus 0.146 +/- 0.016 ng/mg, NP, p < 0.01). Mean arterial pressure in conscious, chronically instrumented adult offspring (21 wk) was higher in LP (135 +/- 1 mm Hg, LP versus 126 +/- 1 mm Hg, NP, p < 0.00007), and GFR normalized to kidney weight was reduced in LP (p < 0.04). The number of glomeruli per kidney was lower in adult LP offspring (21,567 +/- 1,694, LP versus 28,917 +/- 2,342, NP, p < 0.03), and individual glomerular volume was higher (1.81 +/- 0.16 10(6) microm(3), LP versus 1.11 +/- 0.10 10(6) microm(3), NP, p < 0.005); the total volume of all glomeruli per kidney was not significantly different. Thus, perinatal protein restriction in the rat suppresses the newborn intrarenal RAS and leads to a reduced number of glomeruli, glomerular enlargement, and hypertension in the adult.
Heart failure (HF) is characterized by poor survival, a loss of catecholamine reserve and cellular structural remodeling in the form of disorganization and loss of the transverse tubule network. ...Indeed, survival rates for HF are worse than many common cancers and have not improved over time. Tadalafil is a clinically relevant drug that blocks phosphodiesterase 5 with high specificity and is used to treat erectile dysfunction. Using a sheep model of advanced HF, we show that tadalafil treatment improves contractile function, reverses transverse tubule loss, restores calcium transient amplitude and the heart's response to catecholamines. Accompanying these effects, tadalafil treatment normalized BNP mRNA and prevented development of subjective signs of HF. These effects were independent of changes in myocardial cGMP content and were associated with upregulation of both monomeric and dimerized forms of protein kinase G and of the cGMP hydrolyzing phosphodiesterases 2 and 3. We propose that the molecular switch for the loss of transverse tubules in HF and their restoration following tadalafil treatment involves the BAR domain protein Amphiphysin II (BIN1) and the restoration of catecholamine sensitivity is through reductions in G-protein receptor kinase 2, protein phosphatase 1 and protein phosphatase 2 A abundance following phosphodiesterase 5 inhibition.
Maternal glucocorticoids have been postulated to play an important role in prenatal programming for adult hypertension in the offspring. However, we have shown previously that offspring hypertension ...caused by maternal dexamethasone subcutaneous administration at 100 microg x kg(-1) x day(-1) can be accounted for by the corresponding reduction in food intake that these mothers experience. The present studies were designed to determine whether there is a lower dose of dexamethasone that does not reduce maternal food intake yet still causes hypertension in the adult offspring. Pregnant rats were treated with subcutaneous dexamethasone at 50 (D50) or 25 (D25) microg x kg(-1) x day(-1) on days 15-20 of pregnancy. An additional group was untreated or received vehicle injections (control). D25 and D50 dams reduced their food intake by 17% during and after treatment and gained 31% less weight than control over the course of gestation. In adulthood ( approximately 21 wk), chronically instrumented male offspring of D50 and D25 had normal blood pressures (D50: 131 +/- 2 mmHg and D25: 127 +/- 3 mmHg vs. 127 +/- 2 mmHg in control). Qualitatively similar results were found in female offspring. Thus neither dexamethasone per se at these doses nor the accompanying modest reductions in maternal food intake and weight gain have blood pressure programming effects. As far as has been tested, there does not appear to be a dose of dexamethasone that, given over this time period in the rat, programs offspring hypertension without reducing maternal food intake and weight gain. These data do not support the hypothesis that maternal glucocorticoids program offspring hypertension directly.
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