Yoshiki Seino

Intrarenal localization of degradation of atrial natriuretic peptide in isolated glomeruli and cortical nephron segments

Using isolated glomeruli and nephron segments obtained from collagenase treated rabbit kidneys, we examined the in vitro degradation of alpha-human atrial natriuretic polypeptide (alpha-hANP). The ANP-degrading activity was measured by the amount of immunoreactive ANP remaining after incubation of about 50 fmoles alpha-hANP with each tissue preparation for 7.5 min. The sequence of degrading activity among isolated nephron segments was as follows: proximal straight tubule greater than proximal convoluted tubule greater than cortical collecting tubule greater than distal convoluted tubule greater than cortical thick ascending limb. A single glomerulus exhibited the degrading activity which was comparable to approximately 50% of the activity of 1 mm proximal convoluted tubule. Phosphoramidon, an inhibitor of endopeptidase, prevented the degradation of ANP in proximal convoluted tubule and glomerulus by 68% and 89%, respectively, but not in cortical thick ascending limb and cortical collecting tubule. From these results, we conclude that the degradation of ANP by endopeptidase occurs mainly in the proximal tubule and glomerulus.

[55] Competitive protein binding assay for plasma 25-hydroxycholecalciferol

Publisher Summary This chapter discusses competitive protein binding assay for plasma 25-hydroxycholecalciferol. The present method was developed in authors laboratory, using a specific 25-hydroxycholecalciferol (25-OH-D 3 ) binding protein from the plasma or kidney cytosol of vitamin D-deficient rat. It has been shown that 25-hydroxycholecalciferol and 25-hydroxyergocalciferol react identically in this assay, such that it can be used for the measurement of 25-hydroxy derivatives of vitamin D2 and vitamin D3. Crystalline 25-OH-D 3 is dissolved in ethanol to give a concentration of 280 μg/ml and stored at –20°. Before using in an assay, an aliquot is serially diluted with ethanol to give several standard solutions with a concentration range of 25-OH-D 3 from 10 ng/50μl to 0.5 ng/50 μl. The intra-assay variation was assessed by extracting five 0.5-ml aliquots of the same plasma sample from a healthy subject and assaying each concentrations of 25-OH-D 3 in one assay. A coefficient of intra-assay variation was 7.7%. The inter-assay variation was estimated by extracting and assaying samples from a healthy subject on six different occasions. A coefficient of inter-assay variation was 11.8%.

Serum calcium regulating hormones in the perinatal period.

SummaryTo clarify perinatal vitamin D metabolism, we measured 25-hydroxyvitamin D (25OHD), 24,25-dihydroxyvitamin D [24,25(OH)2D], 1,25-dihydroxyvitamin D [1,25(OH)2D], calcium (Ca), phosphorus (P), parathyroid hormone (PTH), and human calcitonin (CT) in paired maternal, cord, and infant serum. Cord serum 25OHD was significantly lower than the maternal level, and cord serum 24,25(OH)2D was also significantly below the maternal concentrations. Maternal, cord, and infant serum 1,25(OH)2D, on the other hand, was significantly higher than the normal adult level. The serum PTH was low, but the CT concentration was high in the cord. Cord serum Ca and P levels were significantly higher than maternal. The reason for the elevated circulating 1,25(OH)2D level in the perinatal period is uncertain, and we speculate that the possible factors are gonadal steroids, placental lactogen, prolactin, and CT. In addition, serum 24,25(OH)2D and 1,25(OH)2D concentrations are under some control by the fetus.

Intranasal absorption of salmon calcitonin

SummaryEight normal subjects and 4 children with osteogenesis imperfecta were administered salmon calcitonin (S-CT) intranasally, and the phamacokinetics of S-CT were studied. In the normal subjects, the plasma S-CT concentration showed a dose-dependent increase over a dosage range of 200–400 IU. Maximal plasma concentrations were reached 20–60 min after intranasal administration of S-CT. The plasma calcium concentration was significantly decreased 60 min after the administration. In the children. S-CT was also absorbed through the nasal mucosa. This suggests that nasal spraying may be an efficient method for administration of S-CT.

Plasma 1,25-dihydroxyvitamin D concentrations in cords, newborns, infants, and children

SummaryPlasma 1,25-dihydroxyvitamin D [1,25-(OH)2-D] was measured in cord serum, newborns, infants, and children. The mean for the values obtained from the six cords was significantly higher than the mean for the older children (6–15 years). The mean for the six newborns (0–1 week) was significantly higher than that for the older children. The mean for the nine infants (1 week-6 months) and the 14 younger children (6 months-6 years) was significantly higher than that for older children. The present study suggests that the perinatal period is associated with a marked increase in 1,25-(OH)2-D.

EFFECT OF AGE ON DUODENAL 1,25-DIHYDROXYVITAMIN D-3 RECEPTORS IN WISTAR RATS

We confirmed our previous observation that duodenal Ca2+ absorption and serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels declined concurrently in old (24 months old) rats as compared to young (6 months old) rats. It is well known that 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) expresses its action after binding to specific receptor molecules. In this paper, we compared certain properties of rat duodenal 1,25-(OH)2D3 receptors from old and young animals. Receptor preparations were incubated with [3H]1,25-(OH)2D3 to quantitate the number of unoccupied and total receptor sites and showed that total and unoccupied receptor sites decreased by 22 and 16%, respectively in old rats. Endogenously occupied sites were reduced by 43% in duodenum of the old rat and, consequently, the percentage of receptor occupancy also declined. Age did not affect the dissociation constant (KD) of 1,25-(OH)2D3 from the receptor; the sedimentation coefficient (3.3 S) of the tritiated 1,25-(OH)2D3-receptor complex in sucrose density centrifugation; or its affinity for DNA. The data are consistent with the hypothesis that the age-related decline in Ca2+ absorption in the intestine may be due, in part, to the decrement in the circulating level of 1,25-(OH)2D and a reduction of intestinal 1,25-(OH)2D3 receptor occupancy status.

Multiple associated endocrine abnormalities in a patient with pseudohypoparathyroidism type 1a

A girl with type 1a pseudohypoparathyroidism (PHP) presented several hormonal abnormalities. Although she had eluded neonatal thyroid screening, she was diagnosed as having hypothyroidism at the age of 5 months. Thereafter, a diagnosis of PHP was made on the basis of skeletal features of Albright osteodystrophy and lack of both cyclic adenosine monophosphate (c-AMP) and phosphaturic responses after parathyroid hormone (PTH) infusion. The basal levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were higher than normal and showed exaggerated responses to luteinizing hormone-releasing hormone (LH-RH). There was no growth hormone (GH) response to arginine infusion, and the prolactin (PRL) response after thyrotropin-releasing hormone (TRH) infusion was also impaired. The stimulating guanine nucleotide-binding protein (Ns) activity of the erythrocytes was reduced to 66.9%. The skeletal age was not delayed at the age of 5 months in spite of the hypothyroid state, and it advanced following thyroxine and vitamin D treatments.

Increased circulating levels of γ-carboxyglutamic acid-containing protein and decreased bone mass in children on anticonvulsant therapy

SummaryIn order to investigate the pathophysiology of anticonvulsant-induced osteopenia, circulating levels of bone γ-carboxyglutamic acid-containing protein (Bone Gla Protein: BGP) and urinary excretion of BGP were measured in 16 chidren on chronic anticonvulsant therapy and in 12 control children. Using microdensitometry analysis, osteopenia was found in 25% of the anticonvulsant therapy group, but it was not observed in the control group. Serum BGP and A1-P levels were significantly increased in the anticonvulsant group compared with the control group (P<0.05 andP<0.01, respectively), and a positive correlation was found between serum BGP and A1-P levels (P<0.05). Urinary excretion of BGP and hydroxyproline showed an increase in the anticonvulsant group, but it was not statistically significant. On the other hand, there was no significant difference between the two groups in serum levels of vitamin D metabolites, PTH, calcitonin, Ca, or P or in urinary excretion of Ca or P. It is suggested, therefore, that the increased BGP level in children receiving anticonvulsant therapy is a reflection of high bone turnover due to anticonvulsant drug complications.

Effect of 1α-hydroxycholecalciferol on psoriasis vulgaris: a pilot study

SummaryWe carried out a clinical trial of 1α-hydroxycholecalciferol [1α(OH)D3] at a dose of 1.0 μg a day on 7 patients with psoriasis vulgaris. These patients had been treated by topical applications of corticosteroids before this study without improvement, and during the clinical trial, treatment of topical corticosteroids was continued on 6 of the 7 patients. Four of 7 patients showed complete remission and marked improvement and 2 additional patients showed minimal improvement of their skin lesions during and after the treatment with 1α(OH)D3. No adverse reactions were noted during the treatment period. The mechanism of the phenomenon we observed has yet to be elucidated. Controlled trials of large numbers of patients with psoriasis vulgaris treated with 1α(OH)D3 are under way.

A specific competitive protein binding assay for serum 24,25-dihydroxyvitamin d in normal children and patients with nephrotic syndrome

A specific competitive protein binding assay for 24,25-dihydroxyvitamin D by Sephadex LH-20 column chromatography, followed by high pressure liquid chromatography with normal rat kidney cytosol as the binding protein, was developed. The mean concentrations of serum 24,25-dihydroxyvitamin D of the cord, in newborn infants and in infants under 12 months of age were 0.90 +/- 0.40 (S.D.) ng/ml, 0.52 +/- 0.21 (S.D.) ng/ml and 1.20 +/- 0.38 (S.D.) ng/ml, respectively. These concentrations were significantly lower than those in children aged 1-15 years (1.96 +/- 0.83 (S.D.) ng/ml). The serum levels in the acute stage of the nephrotic syndrome were significantly reduced, and they increased in remission. These results show that patients wioth nephrotic syndrome have low levels of serum 24,25-dihydroxyvitamin D. This is probably due to its loss in the urine.