Julián Rodríguez

Resistance to growth hormone and insulin-like growth factor-I in acidotic rats

Abstract Growth impairment induced by chronic metabolic acidosis is associated with an abnormal growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. To examine the potentially beneficial effects of IGF-I on acidosis-induced growth impairment and the influence of GH and IGF-I treatment on the GH/IGF-I axis, three groups of acidotic young rats (untreated, AC, n=12; treated with recombinant human GH, GH, n=8; treated with recombinant human IGF-I, IGF-I, n=8) were studied, and compared with nonacidotic rats fed ad libitum (C, n=9)) or pair-fed with the AC group (PF, n=12). After 14 days of acidosis and 7 days of treatment, growth rate, hepatic abundance of 4.7-kilobase (kb) and 1.2-kb GH receptor transcripts and 7.5-kb and 1.8- to 0.8-kb IGF-I transcripts, serum GH-binding protein (GHBP), and IGF-I concentrations (mean±SEM) were analyzed. Significant decreases of 4.7-kb GH receptor [26±2 vs. 49±6 arbitrary densitometry units (ADU)] and 7.5 kb IGF-I (41±3 vs. 104±10 ADU) transcripts and low serum GHBP (25±1 vs. 32±1 ng/ml) and IGF-I (279±50 vs. 366±6 nmol/l) levels were found in the AC compared with the C rats. The majority of these alterations were also observed in PF rats. Compared with acidotic untreated rats, GH and IGF-I therapy produced no improvement in growth rate. GH treatment normalized the levels of IGF-I mRNA, aggravated the acidosis-related inhibition of the GH receptor gene, and did not modify the serum levels of GHBP and IGF-I. In contrast, IGF-I administration depressed the hepatic expression of all GH and IGF-I transcripts and normalized serum IGF-I concentrations. Our results confirm that sustained metabolic acidosis alters the GH/IGF-I axis, in part because of associated malnutrition, and induced growth retardation that is resistant to GH therapy. Our study also shows that administration of IGF-I does not accelerate the growth of acidotic rats, suggesting a peripheral mechanism, at the level of target tissues, is responsible for the resistance to the growth-promoting actions of GH and IGF-I.

Alterations of the growth plate in chronic renal failure

Chronic renal failure modifies the morphology and dynamics of the growth plate (GP) of long bones. In young uremic rats, the height of cartilage columns of GP may vary markedly. The reasons for this variation are unknown, although the severity and duration of renal failure and the type of renal osteodystrophy have been shown to influence the height of GP cartilage. Expansion of GP cartilage is associated with that of the hypertrophic stratum. The interference of uremia with the process of chondrocyte differentiation is suggested by some morphological features. However, analysis by immunohistochemistry and/or in situ hybridization of markers of chondrocyte maturation in the GP of uremic rats has yielded conflicting results. Thus, there have been reported normal and reduced mRNA levels for collagen X, parathyroid hormone/parathyroid hormone-related peptide receptor, and matrix metalloproteinase 9, as well as normal mRNA and protein expression for vascular endothelial growth factor and chondromodulin I, peptides related to the control of angiogenesis. In addition, a decreased immunohistochemical signal for growth hormone receptor and low insulin-like growth factor I mRNA in the proliferative zone of uremic GP are supportive of reduced chondrocyte proliferation. Growth hormone treatment improves chondrocyte maturation and activates bone metabolism in the primary spongiosa.

Prophylactic vitamin D in healthy infants: assessing the need

The objective was to evaluate the need for vitamin D prophylaxis in healthy infants. This was a prospective and randomized study performed at primary care clinics. Eighty-eight full-term 1-month-old healthy infants were randomly assigned to receive (n = 41) or not (n = 47) 402 IU/d of vitamin D for 1 year. Primary outcome measures were serum 25-hydroxyvitamin D (25OHD) and parathyroid hormone (PTH) concentrations at 3, 6, and 12 months of age; secondary measures included data on feeding, habitat, season of birth, sun exposure, and physical examination. At 3 and 6 months of age, serum 25OHD levels (±SD) were significantly higher (P < .001) in the prophylaxis group. In the group without prophylaxis, serum 25OHD increased with age; and breast-fed infants aged 3 months had the lowest value (20.2 ± 9.4 ng/mL), which was significantly (P = .001) lower than that of formula-fed infants (35.0 ± 9.7 ng/mL). The PTH levels were not influenced by the prophylaxis or feeding. No influence of either the habitat or season of birth on serum 25OHD concentrations was demonstrated. No infant had clinical signs of vitamin D deficiency. Serum 25OHD and PTH concentrations were weakly but significantly correlated (r = -0.29, P = .009) at 3 months of age. Healthy infants without vitamin D prophylaxis had lower circulating concentrations of 25OHD at 3 and 6 months of age, the lowest value being found in 3-month breast-fed infants. The clinical relevance of these findings is probably negligible because serum 25OHD levels spontaneously increased with age and were not associated with high serum PTH. Clinical manifestations of rickets were not observed.

Rat models of normocalcemic hypercalciuria of different pathogenic mechanisms

Abstract. Hypercalciuria was induced in female Sprague-Dawley rats, aged 40±2 days, by 7-day administration (mean±SEM) of calcitriol (5.4±0.1 ng/100 g per day, intraperitoneal), furosemide (14.9±1.9 mg/100 g per day, oral), or ammonium chloride (3.8±0.1 mEq/100 g per day, oral). Calciuria increased from 1.9±0.2, 1.6±0.2, and 1.9±0.3 to 5.4±0.5, 4.0±0.9, and 5.4±0.5 mg/100 g per day in the calcitriol (VD, n = 9), furosemide (F, n = 6), and ammonium chloride (AC, n = 10) groups, respectively. Calciuria did not change (1.9±0.3 vs. 1.6±0.1 mg/100 g per day) in control rats (n = 8). Ninety-six percent of treated rats became hypercalciuric as assessed by urine calcium excretion above the 90th percentile of normal values. Hypercalciuria was of similar degree in the three groups of rats and was not associated with hypercalcemia, metabolic acidosis, severe serum electrolyte imbalance, or growth impairment. VD rats had low serum parathyroid hormone (PTH) concentrations (3.0±0.5 pg/ml vs. 15.8±1.3 pg/ml in controls, P <0.05), whereas serum PTH was not significantly elevated in F rats (16.2±1.8 pg/ml). Thus, the protocol caused three forms of hypercalciuria that mimicked the clinical conditions of idiopathic hypercalciuria in humans and may clearly be differentiated according to their mechanism of production. This experimental model of normocalcemic hypercalciuria may be useful to clarify unknown aspects of pathogenesis and pathophysiology of idiopathic hypercalciuria in children.

Gitelman syndrome in Gypsy paediatric patients carrying the same intron 9 + 1 G>T mutation. Clinical features and impact on quality of life

BACKGROUND Gitelman syndrome is a primary tubular disorder causing hypokalaemic metabolic alkalosis with hypocalciuria. Its prevalence is high in Gypsies, who harbour an identical mutation, intron 9 + 1 G>T, in the SLC12A3 gene. METHODS To better define the Gitelman syndrome in Gypsies, the clinical and biochemical features of 34 Spanish paediatric Gypsy patients were analysed. At diagnosis, symptoms, height and weight as well as serum and urinary biochemical data were collected. During a follow-up of 4.5 ± 2.4 years [X ± standard deviation (SD)], therapy, treatment compliance, symptoms, frequency of hospital admissions and, at the last visit, growth and biochemical work-up of 29 patients followed for at least 6 months were analysed. Quality of life items were also assessed by a questionnaire. RESULTS Muscle cramps (41%) and asthenia (35%) were the most frequent presenting symptoms. Biochemical data at diagnosis were serum K 2.76 ± 0.46 mEq/L, serum Mg 1.32 ± 0.28 mg/dL, blood pH 7.45 ± 0.06, serum bicarbonate 28.2 ± 2.9 mEq/L, urinary calcium/creatinine ratio 0.03 ± 0.04 mg/mg, fractional K excretion 24.4 ± 17.1% and fractional Mg excretion 8.9 ± 8.3%. During follow-up, Mg and K supplements were prescribed to 79 and 86% of patients, respectively; compliance with treatment was good in 35%. Hospital admission rate was 0.03/patient/month. Muscle cramps were the symptom most often referred by the patients (45%) during the follow-up, and 71% of patients considered their health status as excellent or good. Twenty-one patients stated that their disease did not adversely interfere with their mood or social relationships. Height and weight of patients at diagnosis were -0.60 ± 1.17 and -0.49 ± 1.32 SD, respectively, and improved to -0.44 ± 1.28 (P < 0.05) and 0.18 ± 1.79 SD (P < 0.01) at the last visit. CONCLUSIONS Gypsy children with Gitelman syndrome mostly exhibit muscle symptoms and asthenia although the disease is not particularly severe in this ethnic group. Body growth improves with treatment and close follow-up.

Prepubertal Rats Are More Resistant to Ischemic Renal Injury and Recover More Rapidly than Adult Rats

Bilateral clamping of renal pedicles during 60, 75 or 90 min was used to characterize the evolution of ischemic acute renal failure (ARF) in prepubertal rats. To verify the existence of age-conditioned differences in the evolution of ARF, adult rats were exposed to 40, 60 or 75 min of clamping. After 7 days, survival rate was significantly better in young than adult rats for identical times of clamping (89 vs. 35% for 60 min and 69 vs. 35% for 75 min). Young rats largely died within the first 24 h following ischemia while the risk of death extended until the 4th day after ischemia in adult rats. Peak values of serum urea nitrogen and creatinine were observed on the 1st and 3rd day after ischemia in young and adult rats, respectively. In young rats, these markers of renal function returned to normal on days 5 and 6 whereas they remained elevated at the end of the study in adult animals. Growth curves of young rats paralleled those of sham-operated animals from the 3rd day of clamping whereas adult rats did not even reach the initial weight at the end of the study. Analysis of kidneys obtained 7 days after clamping revealed more severe histopathological lesions in adult rats as well as a higher proliferative activity (10–40 times the value of sham-operated animals versus 2–4 times the control value in young rats). Our findings indicate that kidneys from young rats are more resistant to ischemia and recover more quickly from the ischemic insult. Therefore, the experimental model of ischemic ARF is clearly different in young and adult rats.