Multiple pre- and postreceptor defects in pseudohypoparathyroidism (a multicenter study with twenty four patients).

Three different pathophysiological mechanisms are probably responsible for hereditary pseudohypoparathyroidism: 1) a defect at the prereceptor-level, 2) a defective membrane N-protein accounting for diminished second messenger production, and 3) a defect in the cytosolic response to the hormone. In a cooperative, study 24 patients (mean age, 13 yr; range, 3-23 yr, 8 girls, 16 boys) receiving vitamin D metabolites (5,000-80,000 U/day) were examined and compared to a control group of 36 normal children. Immunoreactive N-terminal PTH (N-PTH), mid-C-regional PTH (mid-C-PTH), intact PTH and bio-PTH, vitamin D metabolites, and serum calcium and phosphate, alkaline phosphatase activity, and the N-protein activity of erythrocyte membranes were measured in each subject. By clinical and biochemical criteria three groups were differentiated. Eight patients had the completely expressed features of Albright's Hereditary Osteodystrophy (AHO+), including brachydactyly and/or sc calcifications, and increased N-PTH, mid-C-PTH, and alkaline phosphatase activity. Bio-PTH, intact PTH, and N-protein were normal. Nine additional patients with complete (AHO+) had elevated levels of bio-PTH, N-PTH, and mid-C PTH, normal hydroxylation of vitamin D, but decreased N-protein activity. Seven patients with pseudohypoparathyroidism had no features of AHO (AHO-), no increase of urinary cAMP excretion after exogenous PTH, normal PTH peptide levels and N-protein activity, but elevated 25-hydroxyvitamin D and decreased 1,25-dihydroxyvitamin D concentrations. In conclusion, we identified three subpopulations of PsHP: group a had a dissociation of N-PTH and bio-PTH suggesting a defective N-PTH causing renal resistance, whereas their bones respond to PTH. Group b had defective N-protein causing generalized PTH resistance. Group c was characterized by high 25-hydroxyvitamin D and relatively low 1,25-dihydroxyvitamin D levels, thus providing evidence for a defect in the cytosolic interaction of the two different second messengers for PTH, cAMP, and calcium.

Renal adenylate cyclase assay for biologically active parathyroid hormone: clinical utility and physiological significance.

The stimulation of cyclic AMP production by human renal cortical membranes in the presence of the GTP analogue 5'-guanylimidodiphosphate and a calcium chelator represents a homologous assay system for the evaluation of biologically active parathyroid hormone (bioPTH) in human serum. Bioactive PTH was raised above normal (normal range: undetectable to 4.6 pmol human PTH(1-34) per 1) in 13/17 (76%) patients with primary hyperparathyroidism, in 5/6 (83%) patients with surgically proven hyperparathyroidism secondary to chronic renal failure, in 4/5 (80%) patients with hyperparathyroidism secondary to hypocalcaemia, in all three patients with pseudohypoparathyroidism, in 5/17 (29%) patients with osteoporosis and in 1/9 (11%) patients with renal stones and/or hypercalciuria. Bioactive PTH correlated positively with immunoreactive PTH (iPTH) measured with a radioimmunoassay predominantly recognizing the middle- and carboxyl-terminal region of the PTH molecule (r = 0.503, P less than 0.001). A positive correlation (r = 0.572, P less than 0.05) was found between values of serum calcium and bioPTH in the group with primary hyperparathyroidism. Immunoreactive PTH did not correlate significantly with calcium in this group. In the other patients except those who had chronic renal failure, a negative correlation between serum calcium and both bioPTH and iPTH was observed (P less than 0.01). When alkaline phosphatase was compared with bioPTH in all patients, the correlation was positive (r = 0.390, P less than 0.01); no significant correlation existed between iPTH and alkaline phosphatase in the patients studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of human bone cells in culture.

Cultures of human bone cells were established, maintained, and characterized with respect to several metabolic parameters. These studies were undertaken with a view to using the bone culture system as a means of studying mechanisms of bone metabolism. The donor patients' ages ranged from 1 to 90 years and their disease states included congenital limb anomalies, exostosis, and osteo- and rheumatoid arthritis. Cultures were maintained up to 5 months. The osteoblast-like character of these cells was confirmed with the use of measurements applied to bone cells from other systems. Analyses showed that (a) the cells' appearance resembled that of cultured osteoblasts from other animal sources, b) intracellular cAMP was stimulated by human parathyroid hormone, c) osteocalcin was detected in the medium of all tested bone cell cultures and its production was found to be stimulated by 1,25-dihydroxycholecalciferol, and d) newly synthesized collagen was almost exclusively type I. In contrast, cultures of human fibroblasts, established in one instance from tissue specimens of the same donor patient, grew faster, reached a higher limiting density, and produced a greater proportion of type III collagen than the corresponding bone cells. Furthermore, fibroblasts did not accumulate osteocalcin in their culture medium. The conditions described in this report to maintain human bone cells in culture should provide a suitable test system to study the regulation of human bone metabolism.