Endocrine Abstracts

Adult Growth Hormone Deficiency (AGHD) is associated with osteoporosis. PTH is secreted in a circadian rhythm and temporal fluctuations in PTH concentration, particularly at night, appear to be important in the regulation of bone turnover. Serum phosphate is an important determinant of PTH, with changes in phosphate preceding fluctuations in PTH concentration. We examined the difference in PTH and phosphate circadian rhythmicity in AGHD patients with normal and reduced bone mineral density (BMD).

43 AGHD patients were consented to the study. 23 patients had low BMD (femoral neck or lumbar spine T-score <−1.0). 20 patients had normal BMD. All patients were admitted to hospital for 24 h, where ½-hourly blood samples were collected for PTH and phosphate. The local ethics committee approved the study. Results are expressed as mean±SEM.

Each patient and both groups demonstrated significant PTH and phosphate circadian rhythms, as determined by cosinor analysis (P<0.001). The low BMD patients had significantly lower mean nocturnal rise in both PTH (4.9±1.9% versus 19.5±3.1%, P<0.001) and phosphate (1.9±1.3% versus 9.8±1.2%, P<0.001) concentrations, than the normal BMD patients.

Low BMD in AGHD is associated with a blunted nocturnal rise in PTH concentration, which may occur as a result of the blunted nocturnal rise in serum phosphate concentration. Therapeutic manipulation of the PTH or phosphate circadian rhythm may be of benefit in improving BMD in patients with AGHD.