Endocrine Abstracts

BACKGROUND: Untreated Adult Growth Hormone Deficiency (AGHD) is associated with reduced bone mineral density (BMD). PTH plays an important role in bone metabolism and reports suggest that bone and renal target cell insensitivity to PTH may contribute to changes in bone turnover in AGHD.

OBJECTIVES: To determine the difference in PTH and phosphocalcium metabolism in untreated AGHD patients who have normal and reduced BMD.

METHODS: 13 patients with AGHD (7 with normal BMD (t-score range minus0.5 to 1.9 SD), 6 with reduced BMD (t-score range minu2.7 to minus1.0 SD)) were consented to the study, prior to the initiation of GH replacement. Patients were admitted to hospital for 24 hours where half-hourly blood and 3-hourly urine samples were collected for PTH, calcium, phosphate and nephrogenous cAMP (NcAMP, marker of PTH circulating activity). Local Ethical Committee approval was obtained.

RESULTS: There was no significant difference in age, gender or duration of disease between the 2 groups. Mean spine BMD (plus/minus SEM) was 1.27 plus/minus 0.05g/cm² compared with 1.02 plus/minus 0.05g/cm² in the normal and osteopaenic groups respectively (p=0.003, mean t-score (plus/minus SEM) 0.52 plus/minus 0.30 SD compared with minus1.60 plus/minus 0.30 SD (p=0.001)). Mean femoral BMD (plus/minus SEM) was 1.24 plus/minus 0.04g/cm² and 0.89 plus/minus 0.04g/cm² respectively (p<0.001, mean t-score (plus/minus SEM)1.05 plus/minus 0.34 SD compared with minus1.52 plus/minus 0.34 SD (p<0.001)). 24-hour mean PTH, serum and urinary phosphate were significantly higher (p<0.001) and NcAMP (p<0.001) and serum calcium (p=0.002) significantly lower in the osteopaenic group.

CONCLUSIONS: The significantly higher concentrations of PTH, in the presence of higher serum phosphate and lower NcAMP and serum calcium, demonstrated in the osteopaenic group of patients, suggest that reduced BMD in patients with AGHD may be due to a relative decrease in the renal and skeletal sensitivity to PTH.