Endocrine Abstracts

PTH plays an important role in bone metabolism. Active acromegaly is associated with increased bone turnover. Reduction in bone turnover markers occurs following biochemical cure/control of acromegaly. We examined the effect of active acromegaly and its treatment on PTH concentration and PTH target-organ sensitivity.

10 patients with active acromegaly (defined as GH nadir greater than 1mU/L following 75g oral glucose load and IGF1 above reference range) and 10 age- and gender-matched controls were consented to the study. Patients were hospitalised for 24h. 1/2-hourly blood and 3-hourly urine samples were collected for PTH, calcium, phosphate and nephrogenous cyclic AMP (NcAMP, marker of renal PTH activity). Serum calcium was adjusted for albumin (ACa). Acromegalic patients received standard surgical and/or medical treatment. Sampling was repeated in 8 patients who achieved biochemical cure/control (GH nadir less than 1mU/L following 75g oral glucose load and IGF1 within reference range). Results are expressed as mean(SEM).

Active acromegalics had significantly higher 24-hour mean PTH (4.63(0.10)pmol/L versus 3.88(0.10)pmol/L, p<0.001), NcAMP (38.6(2.9)nmol/LGFR versus 20.2(5.2)nmol/LGFR, p=0.006) and ACa concentrations (2.34(0.001)mmol/L versus 2.30(0.001)mmol/L, p<0.001), with significantly lower 24-hour urine calcium excretion (1.93(0.37)mmol/24h versus 2.67(0.32)mmol/24h, p=0.03), compared to matched controls. Post-treatment, 24-hour mean PTH increased significantly (4.89(0.12)pmol/L, p=0.01), while NcAMP and ACa concentrations decreased significantly (15.2(2.1)nmol/LGFR and 2.28(0.001)mmol/L, respectively, both p<0.001) in the acromegalic patients compared with pre-treatment concentrations.

Increased bone turnover associated with active acromegaly may result from increased PTH concentration and activity. Biochemical cure/control of acromegaly results in a reduction in PTH target-organ sensitivity (as indicated by a significant increase in PTH and decrease in NcAMP and ACa concentrations), and may lead to the previously reported reduction in bone turnover. PTH target-organ sensitivity and phosphocalcium metabolism do not appear in the short term to return to normal following successful treatment of acromegaly.