Effects of long-term administration of clonidine on plasma renin activity.
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Plasma renin activity (PRA) was studied before and during long-term treatment with moderate oral doses (0.2 or 0.3 mg/d) of clonidine. Nine outpatients with essential hypertension received clonidine for 12 weeks; a significant decrease in blood pressure was evident in all patients. Except for a nonsignificant increase after 12 weeks of treatment, PRA values were not notably changed by clonidine therapy. No correlation was found between individual blood pressure changes and PRA variation during the study. The absence of a net effect on PRA in this study does not exclude more complex interactions of clonidine with the renin-angiotensin system. Nonetheless, clonidine cannot generally be classified as a "renin-inhibiting" drug. (+info)
Intrarenal site of action of calcium on renin secretion in dogs.
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We studied the effects of intrarenal calcium infusion on renin secretion in sodium-depleted dogs in an attempt to elucidate the major site of calcium-induced inhibition of renin release. Both calcium chloride and calcium gluconate reduced renal blood flow and renin secretion while renal perfusion pressure was unchanged. These data indicate that calcium inhibition of renin secretion did not occur primarily at the renal vascular receptor; decreased renal blood flow is usually associated with increased renin secretion. Calcium chloride infusion increased urinary chloride excretion without affecting sodium excretion, and calcium gluconate failed to increase either sodium or chloride excretion. Also, the filtered loads of sodium and chloride were unchanged during the calcium infusions. These results give no indication that calcium inhibited renin secretion by increasing the sodium or chloride load at the macula densa. The effects of intrarenal calcium infusion on renin release were also assessed in dogs with a nonfiltering kidney in which renal tubular mechanisms could not influence renin secretion. The observation that calcium still suppressed renin release in these dogs provides additional evidence that the the major effect of calcium involved nontubular mechanisms. Thus, it appears likely that calcium acted directly on the juxtaglomerular cells to inhibit renin secretion. (+info)
Stimulation of renin release from rabbit renal cortex by arachidonic acid and prostaglandin endoperoxides.
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The mechanism by which renal prostaglandins stimulate renin secretion in vivo is unknown. In this in vitro study we measured the effects of activation of the prostaglandin (PG) system on renin release from slices of rabbit renal cortex. The PG precursor arachidonic acid (C20:4), a natural PG endoperoxide (PGG2), two stable synthetic PG endoperoxide analogues (EPA I and II), PGE2, PGF2alpha, and two different PG synthesis inhibitors [indomethacin and 5,8,11,14-eicosatetraynoic acid (ETA)] were used to evaluate the possibility of a direct action of the cortical PG system on renin secretion. Renin release increased significantly with time after addition of C20:4, PGG2, EPA I, and EPA II to the incubation medium. Stimulation of renin release was se-related for C20:4 in concentrations of 0.6 to 4.5 X 10(-6) M, for EPA I in concentrations of 0.7 to 2.8 X 10(-6) M, and for EPA II in concentrations of 1.4 to 14.0 X 10(-6) M. Indomethacin (10(-4) M) and ETA (10(-4) M) significantly decreased basal renin release as well as the renin release stimulated by C20:4 and EPA I. PGE2(10(-12) to 10(-6) M) had no effect on renin release, whereas PGF2alpha (10(-12) to 10(-6) M) decreased renin release in a dose-dependent manner. These data raise the possibility of a direct action of the renal cortical PG system on renin secretion. The results further indicate that stimulation of renin release by C20:4 may depend more specifically on the action of PG endoperoxides than on the primary prostaglandins. (+info)
An alternative transcript of the rat renin gene can result in a truncated prorenin that is transported into adrenal mitochondria.
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Characterization of the local renin-angiotensin system in the rat adrenal zona glomerulosa indicated a dual targeting of renin both to the secretory pathway and mitochondria. To investigate the transport of renin into mitochondria, we constructed a series of amino-terminal deletion variants of preprorenin. One of these variants, lacking the complete signal sequence for the endoplasmic reticulum and 10 amino acids of the profragment, was transported efficiently into isolated mitochondria. The transport was further shown to be dependent on mitochondrial membrane potential and ATP synthesis. Analysis of adrenal RNA revealed the existence of 2 renin transcripts. While one of the transcripts corresponds to the known full-length transcript, the other one lacks exon 1; instead, exon 2 is preceded by a domain of 80 nucleotides originating from intron 1. This domain, as well as the following region of intron 1 being excised, shows all essential sequence elements defining an additional, so-far-unknown exon. The second mRNA possibly derives from an additional transcription start in intron 1 and an alternative splicing process. Translation of this mRNA could result in a truncated prorenin representing a cytosolic form of renin, which is required for transport into mitochondria. This truncated prorenin corresponds exactly to the deletion variant being imported into mitochondria in vitro. (+info)
Low calorie diet enhances renal, hemodynamic, and humoral effects of exogenous atrial natriuretic peptide in obese hypertensives.
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The expression of the natriuretic peptide clearance receptor is abundant in human and rat adipose tissue, where it is specifically inhibited by fasting. In obese hypertensives, plasma atrial natriuretic peptide (ANP) levels were found to be lower than in obese normotensives. Therefore, the increased adipose mass might influence ANP levels and/or its biological activity. The aim of the present study was to evaluate whether the humoral, hemodynamic, and renal effects of exogenous ANP in obese hypertensives might be enhanced by a very low calorie diet. Eight obese hypertensives received a bolus injection of ANP (0.6 mg/kg) after 2 weeks of a normal calorie/normal sodium diet, and blood pressure (BP), heart rate, ANP, cGMP, plasma renin activity, and aldosterone were evaluated for 2 hours before and after the injection. Diuresis and natriuresis were measured every 30 minutes. The patients then started a low calorie/normal sodium diet (510 kcal/150 mmol/d) for 4 days, and then the ANP injection protocol was repeated. The low calorie diet induced a slight weight loss (from 90.6+/-1.1 to 87. 7+/-1.2 kg; P<0.01), which was accompanied by increase of cGMP excretion (from 146.0+/-10.1 to 154.5+/-9.5 nmol/24 h; P<0.05) together with a reduction of BP (P<0.01 versus basal levels). ANP injection after diet was followed by an increase of ANP levels similar to that observed before diet, but plasma cGMP, diuresis, and natriuresis increased significantly only after diet. Similarly, the decrease of BP after ANP administration was significantly higher after diet (change in mean arterial pressure, -6.4+/-0.7 versus -4. 0+/-0.6 mm Hg; P<0.05) as well as that of aldosterone (P<0.01). These data show that a low calorie diet enhances the humoral, renal, and hemodynamic effects of ANP in obese hypertensives and confirm the importance of caloric intake in modulating the biological activity of ANP, suggesting that the natriuretic peptide system can play a role in the acute changes of natriuresis and diuresis associated with caloric restriction. (+info)
Recovery following relief of unilateral ureteral obstruction in the neonatal rat.
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BACKGROUND: Obstructive nephropathy is a primary cause of renal insufficiency in infants and children. This study was designed to distinguish the reversible and irreversible cellular consequences of temporary unilateral ureteral obstruction (UUO) on the developing kidney. METHODS: Rats were subjected to UUO or sham operation in the first 48 hours of life, and the obstruction was removed five days later (or was left in place). Kidneys were removed for study 14 or 28 days later. In additional groups, kidneys were removed at the end of five days of obstruction. Immunoreactive distribution of renin was determined in arterioles, and the distribution of epidermal growth factor, transforming growth factor-beta1, clusterin, vimentin, and alpha-smooth muscle actin was determined in tubules and/or interstitium. The number of glomeruli, glomerular maturation, tubular atrophy, and interstitial collagen deposition was determined by morphometry. Renal cellular proliferation and apoptosis were measured by proliferating cell nuclear antigen and the TdT uridine-nick-end-label technique, respectively. The glomerular filtration rate was measured by inulin clearance. RESULTS: Renal microvascular renin maintained a fetal distribution with persistent UUO; this was partially reversed by the relief of obstruction. Although glomerular maturation was also delayed and glomerular volume was reduced by UUO, the relief of obstruction prevented the reduction in glomerular volume. Although relief of obstruction did not reverse a 40% reduction in the number of nephrons, the glomerular filtration rate of the postobstructed kidney was normal. The relief of obstruction did not improve tubular cell proliferation and only partially reduced apoptosis induced by UUO. This was associated with a persistent reduction in the tubular epidermal growth factor. In addition, the relief of obstruction reduced but did not normalize tubular expression of transforming growth factor-beta1, clusterin, and vimentin, all of which are evidence of persistent tubular injury. The relief of obstruction significantly reduced interstitial fibrosis and expression of alpha-smooth muscle actin by interstitial fibroblasts, but not to normal levels. CONCLUSIONS: The relief of obstruction in the neonatal rat attenuates, but does not reverse, renal vascular, glomerular, tubular, and interstitial injury resulting from five days of UUO. Hyperfiltration by remaining nephrons and residual tubulointerstitial injury in the postobstructed kidney are likely to lead to deterioration of renal function later in life. (+info)
Long-term effects of growth hormone (GH) on body fluid distribution in GH deficient adults: a four months double blind placebo controlled trial.
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OBJECTIVE: Short-term growth hormone (GH) treatment normalises body fluid distribution in adult GH deficient patients, but the impact of long-term treatment on body fluid homeostasis has hitherto not been thoroughly examined in placebo controlled trials. To investigate if the water retaining effect of GH persists for a longer time we examined the impact of 4 months GH treatment on extracellular volume (ECV) and plasma volume (PV) in GH deficient adults. DESIGN: Twenty-four (18 male, 6 female) adult GH deficient patients aged 25-64 years were included and received either GH (n=11) or placebo (n=13) in a double blind parallel design. METHODS: Before and at the end of each 4 month period ECV and PV were assessed directly using 82Br- and 125I-albumin respectively, and blood samples were obtained. RESULTS: During GH treatment ECV increased significantly (before: 20.48+/-0.99 l, 4 months: 23.77+/-1.38 l (P<0.01)), but remained unchanged during placebo administration (before: 16.92+/-1.01 l, 4 months: 17.60+/-1.24 l (P=0.37)). The difference between the groups was significant (P<0.05). GH treatment also increased PV (before: 3.39+/-0.27 l. 4 months: 3.71+/-0.261 (P=0.01)), although an insignificant increase in the placebo treated patients (before: 2.81+/-0.18 l, 4 months: 2.89+/-0.20 l (P=0.37)) resulted in an insignificant treatment effect (P=0.07). Serum insulin-like growth factor-I increased significantly during GH treatment and was not affected by placebo treatment. Plasma renin (mIU/l) increased during GH administration (before: 14.73+/-2.16, 4 months: 26.00+/-6.22 (P=0.03)) and remained unchanged following placebo (before: 20.77+/-5.13, 4 months: 20.69+/-6.67 (P=0.99)) leaving no significant treatment effect (P=0.08). CONCLUSION: The long-term impact of GH treatment on body fluid distribution in adult GH deficient patients involves expansion of ECV and probably also PV. These data substantiate the role of GH as a regulator of fluid homeostasis in adult GH deficiency. (+info)
Tranilast suppresses vascular chymase expression and neointima formation in balloon-injured dog carotid artery.
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BACKGROUND: Activation of vascular chymase plays a major role in myointimal hypertrophy after vascular injury by augmenting the production of angiotensin (ANG) II. Because chymase is synthesized mainly in mast cells, we assumed that the chymase-dependent ANG II formation could be downregulated by tranilast, a mast cell-stabilizing antiallergic agent. We have assessed inhibitory effects of tranilast on neointima formation after balloon injury in the carotid artery of dogs, which share a similar ANG II-forming chymase with humans, and further explored the pathophysiological significance of vascular chymase. METHODS AND RESULTS: Either tranilast (50 mg/kg BID) or vehicle was orally administered to beagles for 2 weeks before and 4 weeks after balloon injury. Four weeks after the injury, remarkable neointima was formed in the carotid arteries of vehicle-treated dogs. Chymase mRNA levels and chymaselike activity of vehicle-treated injured arteries were increased 10.2- and 4.8-fold, respectively, those of uninjured arteries. Angiotensin-converting enzyme (ACE) activity was slightly increased in the injured arteries, whereas ACE mRNA levels were not. Tranilast treatment completely prevented the increase in chymaselike activity, reduced the chymase mRNA levels by 43%, and decreased the carotid intima/media ratio by 63%. In vehicle-treated injured arteries, mast cell count in the adventitia showed a great increase, which was completely prevented by the tranilast treatment. Vascular ACE activity and mRNA levels were unaffected by tranilast. CONCLUSIONS: Tranilast suppressed chymase gene expression, which was specifically activated in the injured arteries, and prevented neointima formation. Suppression of the chymase-dependent ANG II-forming pathway may contribute to the beneficial effects of tranilast. (+info)