B. L Nyomba

Pancreatic secretion in man with subclinical vitamin D deficiency

SummaryThe effects of subclinical vitamin D deficiency and vitamin D supplementation on oral glucose tolerance and secretion of pancreatic hormones were studied in 10 diphenyl-hydantoin-treated epileptic patients and 15 geriatric patients. Their mean serum concentrations of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 decreased markedly, but returned to normal within 2 weeks of oral supplementation with 25-hydroxyvitamin D3. The serum concentration of ionized calcium was within the normal range before treatment, and remained unchanged. Serum parathyroid hormone was increased during vitamin D deficiency, but decreased significantly (p < 0.05) afterwards. In vitamin D-deficient epileptic and geriatric patients, the 2- and 3-h insulin levels after glucose ingestion were increased when compared with control values, and glucagon secretion was not suppressed by glucose. Oral glucose tolerance of both groups of patients did not change after 25-hydroxyvitamin D3 supplementation. Insulin secretion remained unchanged in geriatric patients, but was reduced to normal values in epileptic patients. Glucagon suppressibility by glucose was partly restored after vitamin D supplementation in epileptic patients but not in geriatric patients. In contrast to that observed in severely vitamin D-deficient rats or rabbits, correction of subclinical vitamin D deficiency failed to enhance insulin secretion or to improve glucose tolerance in man.

Vitamin D Metabolites and Their Binding Protein in Adult Diabetic Patients

Vitamin D metabolites and vitamin D—binding protein were measured in the serum of nonketotic Bantu and Caucasian insulin-requiring diabetic subjects from Zaire and Belgium, respectively. In Caucasian diabetics, whether untreated (N = 18) or insulin treated (N = 26), no abnormalities were found. The Bantu diabetics (N = 20) were more insulin-deficient and had a poorer glucose control than the Caucasians. They presented, compared with Bantu controls, a significant decrease in the serum concentrations of 25-hydroxy-vitamin D3 (26 ± 10 vs. 35 ± 14 μg/L, P < .01), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] (38 ± 15 vs. 58 ± 17 ng/L, P < .001), and vitamin D-binding protein (303 ± 55 vs. 356 ± 41 mg/L, P < .001). The decreased concentrations of vitamin D metabolites in the adult Bantu diabetic patients may be partly explained by a concomitant decrease in the concentration of vitamin D-binding protein, possibly due to insulin deficiency. The ratio between the molar concentrations of 1,25-(OH)2D3 and vitamin D-binding protein, used as an index of the free hormonal level, was also decreased, in association with a decreased serum calcium level. In conclusion, no abnormalities in vitamin D metabolism were found in Caucasian insulin-dependent diabetics, whereas low serum 1,25(OH)2D3 concentrations and hypocalcemie were found in poorly controlled Bantu diabetic subjects.

Le peptide C humain: dosage radioimmunologique et applications physiopathologiques

SummaryThe use of the C-peptide radioimmunoassay has become possible due to the availability of synthetic antigen and improvement in antisera production.Proinsulin cross-reactivity can be avoided and C-peptide specifically determined by extraction of proinsulin with sepharose-bound insulin antibodies. In insulin treated diabetics, proinsulin insulin antibody complexes can be precipitated with polyethylene glycol (PEG) or concentrated ethanol. C-peptide immunoassay is leasable even in presence of exogenous insulin.With this assay it has been shown that1) almost half of the growth-onset diabetics have a residual insulin secretion, 2) residual β-ceil activity is associated with a better diabetic control and 3) perhaps a lesser degree of degenerative complications.Finally, hypoglycemic conditions can be better documented by simultaneous determination of Cpeptide and insulin in blood.