Inactive renin in infants and children: evidence for its physiological response to orthostasis in children.

The aim of this work was to investigate the presence of inactive renin (IR) in plasma of normal infants and children and nephrectomized children and to study the plasma IR response to stimulation of the renin-angiotensin system (orthostasis) in children. The study was performed in 10 normal infants (2 days to 1 yr old), 28 normal children (1-15 yr old), 8 nephrectomized children (8-14 yr old), and 7 normal adults (20-40 yr old). IR was calculated as the difference in renin activity in trypsin-treated (1500 micrograms/ml) plasma, e.g. total renin (TR), and in untreated plasma, e.g. active renin (AR). IR was not detectable in most infants in the supine position, but their AR values were high (8.8-30 ng/ml X h). Moreover, in some of these infants, trypsin appeared to degrade renin activity, since TR values were lower than AR values. IR was detectable in 3 infants and 27 children, but their AR values were in a lower range (0.3-10 ng/ml X h). Trypsin degradation of renin activity was not found in either children or adults. With increasing age (2 days to 40 yr), AR decreased while IR and the IR to TR ratio increased significantly (P less than 0.001). A significant (P less than 0.001) inverse relationship was found between the IR and AR values of subjects 2 days to 40 yr old. IR was detectable in all nephrectomized children and represented 25% of normal values, while AR was undetectable (less than 0.1 ng/ml X h). In children in the upright position, IR decreased and AR increased significantly (P less than 0.001) in a reciprocal manner. TR did not change. These data suggest 1) that trypsin degradation of renin activity and absence of trypsin-activated IR are specific to infants with high AR levels, and 2) that IR might be activated in vivo into AR, especially after changes in position in children. IR could be a prorenin playing a physiological role in children.

Comparison of plasma renin and prorenin in healthy infants and children as determined with an enzymatic method and a new direct immunoradiometric assay.

We compared plasma active and inactive renin (prorenin) concentrations and activities in infants and children, as measured with a newly available direct immunoradiometric assay kit for active renin and a widely used enzymatic renin assay (plasma renin activity). The study was performed in 57 healthy infants and children under steady-state conditions and in eight subjects after orthostatic stimulation. Our study; (i) reports concentrations for active and inactive renin determined by the immunoradiometric assay in normal infants and children; (ii) confirms, by use of the immunoradiometric assay, the previously described decrease in plasma active and inactive renin, as measured by the enzymatic assay, with increasing age; and (iii) shows close correlations between the results obtained by immunoradiometric and enzymatic assays for active and inactive renin in normal infants and children.

Nitric oxide and the renin angiotensin system: contributions to blood pressure in the young rat.

The present study was designed to investigate the effects of chronic administration of the arginine analogue L-Name (50 mg/kg body weight), the angiotensin converting enzyme inhibitor, perindopril (2 mg/kg body weight), and perindopril (2 mg/kg) plus L-Name (50 mg/kg) on blood pressure, plasma renin activity, plasma angiotensinogen, and hepatic angiotensinogen mRNA levels in young and adult rats. The drugs were given daily from birth to day 21 to puppies and for 15 days to adults. Analytical procedures were performed on day 21 for the puppies and at 10 weeks for the adults. In puppies, blood pressure did not change with L-Name, it decreased to 45% of control values (P < 0.001) with perindopril, and decreased to 77% of control values (P < 0.05) with perindopril plus L-Name. In adults, blood pressure increased to 129% of control values (P < 0.02) with L-Name, decreased to 80% of control values (P < 0.05) with perindopril, and did not change with perindopril plus L-Name. Compared with controls, plasma renin activity was unchanged in puppies and adults with L-Name, undetectable in puppies and slightly increased in adults with perindopril, undetectable in puppies and slightly decreased in adults with perindopril plus L-Name. With L-Name, angiotensinogen mRNA levels were unchanged in puppies and slightly increased in adults, while plasma angiotensinogen levels were decreased (P < 0.05) in puppies and increased (P < 0.01) in adults; with perindopril, angiotensinogen mRNA levels were unchanged in puppies and slightly decreased in adults, while plasma angiotensinogen levels were undetectable in puppies and decreased (P < 0.05) in adults; with perindopril plus L-Name, angiotensinogen mRNA levels were unchanged in puppies while plasma angiotensinogen levels were undetectable in puppies and decreased (P < 0.01) in adults. This study suggests that during the early postnatal period (1) nitric oxide does not exert a basal vasodilator tone but contributes to the hypotensive state induced by perindopril, (2) angiotensin II is essential to maintain blood pressure, (3) and angiotensinogen mRNA levels are not influenced by nitric oxide or angiotensin II.

[Limb vasodilation provoked by stimulation of the carotid sinus. Importance of histaminergy in the dog]. / Sur la vasodilatation des membres provoquée par la stimulation du sinus carotidien. Importance de l'histaminergie chez le chien.

The vasodilator reflex induced by baroreceptor stimulation was studied on the hindlimbs of the dog. The reflex was induced by norepinephrine (1 microgram/kg) either by intravenous injection or by direct injection into the carotid sinus. In other experiences, the baroreceptor stimulation was obtained by distension of the sinus by rapid injection of 100 ml of physiological serum. The vascular response was studied by recording the hindlimbs blood flow. One of the limbs was previously pretreated by mepyramine and cimetidine (blockage of histaminergic H1 and H2 receptors). During the first minute after the baroreceptor stimulation, blood samples were collected from the venous blood of hindlimbs for histamine assay (fluorometric assay). Our results show: a much lower vasodilation on the limb pretreated by histamine antagonist, a significant increase during the reflex vasodilation of histamine blood levels measured in the efferent blood of hindlimbs. These results, obtained in experimental conditions as physiological as possible (blood perfusion of the limbs with "natural" hemodynamic parameters) permit to conclude that the vasodilation induced by baroreceptor reflex is at least partially histaminergic in the dog.

Endothelin-1 in children with chronic renal failure.

Endothelin-1 (ET-1) was measured after extraction from plasma of normal adults (5.9 +/- 1.9 pg/ml, n = 22), normal children (7.1 +/- 1.86 pg/ml, n = 29), non-haemodialysed children with chronic renal failure (CRF) (11.1 +/- 1.8 pg/ml), n = 10), renal graft recipients (9.5 +/- 3.4 pg/ml, n = 37), haemodialysed children 24 h after a haemodialysis session (20.02 +/- 10.9 pg/ml, n = 26) and haemodialysed children before and after a haemodialysis session (15.31 +/- 10.6 and 13.8 +/- 8.5 respectively, n = 14). A sensitive and specific radioimmunoassay was used. ET-1 was significantly higher in non-haemodialysed CRF children and in renal graft recipients than in normal children (P < 0.001 and P < 0.01, respectively) and significantly higher in haemodialysed children when compared with normal children, non-haemodialysed CRF children and renal graft recipients (P < 0.001). ET-1 concentrations were similar in normal children and normal adults. ET-1 was inversely correlated with glomerular filtration rate in non-haemodialysed CRF children (r = -0.39, P < 0.01) and positively correlated with extracellular volume in haemodialysed children (r = 0.435, P < 0.03). After haemodialysis, ET-1 increased in 6 and decreased in 8 of the 14 children studied before and after a haemodialysis session.

Response of nitric oxide pathway to L-arginine infusion at the altitude of 4,350 m.

It was hypothesized that hypoxia may inhibit nitric oxide (NO) production by reducing the availability of endothelial NO synthase (NOS III) substrate. To evaluate the effect of L-arginine on the NO release in high altitude, 11 subjects were infused with L-arginine (0.5 g x kg(-1)) during 30 min in normoxia and after 36 h at 4,350 m (hypoxia). The L-citrulline and cyclic guanosine monophosphate (cGMP) concentrations were measured to investigate NO synthesis and guanylyl cyclase activity respectively. L-citrulline concentration, arterial oxygen saturation (Sa,O2), systemic blood pressure, heart rate and acute mountain sickness (AMS) score were measured at rest and 15, 30 and 45 min after starting infusion. The results showed that baseline L-citrulline was lower in hypoxia (p<0.05). L-arginine infusion increased L-citrulline concentration in both conditions. However, in hypoxia L-citrulline concentration remained lower than in normoxia (p<0.05). The concentration of cGMP was lower in hypoxia (p<0.05). In hypoxia, Sa,O2 increased from 15 min after the start of the infusion to 45 min (p<0.05). Blood pressure and heart rate were not affected by L-arginine infusion. Subjects who experienced symptoms of AMS showed a slight decrease in AMS score with L-arginine. The decreased L-citrulline suggests a hypoxia-induced impairment of nitric oxide synthase III or a decrease in L-arginine availability. The improvement of arterial oxygen saturation by pretreatment with L-arginine could be ascribed to an enhancement of the ventilation/perfusion ratio. Collectively, these results are consistent with a decrease in nitric oxide production in hypoxia that could be antagonized by supplying nitric oxide synthase cosubstrate.

Decrease in endothelin-1 renal receptors during the 1st month of life in the rat.

Endothelin-1 (Et1), like angiotensin II, is implicated in postnatal maturation and development. The present study was designed to identify Et1 receptors and subtype Et1 receptors present in rat kidney between 1 and 30 days of postnatal life. On day 1, high-affinity and high-density Et1 binding sites were identified in rat kidney. The dissociation constant and maximum binding for ET1 to membranes from whole kidney were 0.073 +/- 0.05 nM and 1,345.9 +/- 73 fmol/mg protein, respectively. On day 30, affinity and receptor density were markedly decreased. The dissociation constant and maximum binding were 0.147 +/- 0.021 nM (P < 0.01) and 633.2 +/- 56.4 fmol/mg protein (P < 0.001), respectively. Using BQ 123 (EtA-selective antagonist) and sarafotoxin S6c (EtB-selective agonist), the two Et1 receptor subtypes EtA and EtB were identified in 1- and 30-day-old rat kidney. BQ 123 selectively recognized EtA receptors with high affinity (2.9 +/- 0.44 on day 1 and 4.0 +/- 0.5 nM on day 30) and sarafotoxin S6c bound with higher affinity EtB receptors (0.871 +/- 0.14 on day 1 and 0.717 +/- 0.12 nM on day 30). Between birth and day 30, the EtA binding capacity was decreased (304 +/- 27 vs. 752 +/- 202 fmol/mg protein, P < 0.05), whereas EtB binding was not affected (514 +/- 87 vs. 656 +/- 171 fmol/mg protein, NS). The decrease in the total number of Et1 receptors during the 1st month of life may be due to the concomitant decrease in the number of EtA receptors. Increased Et1 receptor density in early postnatal life suggests an influence of Et1 on immature kidney circulation and/or kidney growth.

Deleterious effects of inhibition of the renin-angiotensin system in neonatal rats.

The angiotensin I converting enzyme inhibitor (ACEI) perindopril (2 mg/kg body weight), the peripheral vasodilator dihydralazine (DHL) (25 mg/kg body weight) or distilled water was given daily from birth to day 14 to neonatal rats. Blood pressure, plasma creatinine, plasma renin activity (PRA), substrate (PRS) and concentration (PRC) and renin content of kidney tissue sections were evaluated on days 14 and 28. By day 14, a high mortality in the ACEI group was observed. ACEI, but not DHL, led to a significant fall (P < 0.01) in blood pressure, 57 +/- 11 versus 89 +/- 25 in the DHL group and 103 +/- 24 mmHg in controls, and to a dramatic increase in plasma creatinine. PRA and PRS were undetectable in ACEI-treated rats; in contrast, PRC and renal staining with anti-renin antibody were significantly increased in ACEI rats. On day 28, the blood pressure was normal in all groups and plasma creatinine returned to the normal range in ACEI rats. PRA, PRS and PRC were not significantly different in the ACEI group and controls. These results suggest that the renin-angiotensin system (RAS) plays a major postnatal role in the neonatal rat. Inhibition of the RAS during the first 2 weeks of life leads to high mortality, severe hypotension, reversible renal failure and a defect in circulating angiotensinogen.