Endocrine Abstracts

BACKGROUND: Acromegaly is associated with abnormal bone metabolism, characterized by increased bone turnover. In health, PTH is secreted in a circadian rhythm, which is important in bone function. However, the effect of acromegaly on PTH secretion is unclear, with previous studies reporting increased, decreased or no change in PTH concentration. Furthermore, the presence of PTH circadian rhythmicity has not been defined in acromegaly.
OBJECTIVES: To determine the effect of acromegaly on PTH secretory pattern and phosphocalcium metabolism.
METHODS: 9 patients with active acromegaly and 9 age- and gender-matched controls were recruited. Half-hourly blood and 3-hourly urine samples were collected, over 24 hours, for PTH (picamoles per litre), calcium (millimoles per litre), phosphate (millimoles per litre) and nephrogenous cAMP (NcAMP nanomoles per litre GFR). Cosinor analysis was used to determine measurements of circadian rhythmicity (MESOR (rhythm-adjusted mean) and amplitude). Values are expressed as mean plus/minus SEM. Local Ethical Committee approval was obtained.
RESULTS: Significantly higher 24-hour mean PTH concentration (4.63plus/minus0.10 versus 3.88plus/minus0.10, p less than 0.001), NcAMP (38.6plus/minus2.9 versus 20.2plus/minus5.2, p=0.006) and serum adjusted calcium concentration (2.34plus/minus0.01 versus 2.30plus/minus0.01, p=0.036) were observed in the acromegalic group, with no significant difference in serum phosphate concentration (1.25plus/minus0.01 versus 1.24plus/minus0.01, p=0.72). Each population demonstrated significant circadian rhythms for PTH and phosphate (p less than 0.01), but not adjusted calcium. PTH MESOR was significantly higher in the acromegalic group (4.65plus/minus0.27 versus 3.88plus/minus0.27, p=0.041), and phosphate amplitude was lower (0.04plus/minus0.02 versus 0.17plus/minus0.02, p less than 0.001), without significant difference in PTH amplitude or phosphate MESOR.
CONCLUSIONS: PTH and phosphate circadian rhythms are maintained in acromegaly. The increase in bone turnover reported in active acromegaly may result from increased PTH concentration and activity. Active acromegaly appears to be associated with attenuation of phosphate circadian rhythmicity, which may be mediated by observed changes in PTH secretion.