Endocrine Abstracts

Background: Adult growth hormone deficient (AGHD) is associated with reduced bone turnover and reduced bone mineral density (BMD): factors improved by growth hormone replacement (GHR). Obesity is associated with reduced bone turnover but increased BMD. We investigated the impact of body mass index on parathyroid hormone (PTH), phospho-calcium metabolism and bone turnover in AGHD patients before and after GHR.

Study design: Of 31 AGHD patients (15 obese patients and 16 non-obese matched for age, sex and hormone replacement therapy types) were admitted to hospital for half-hourly blood sampling and regular urine sampling for 24 h before and after GHR.

Results: At baseline, non-obese patients had significantly lower 24 h-mean calcium (2.29±0.003 vs 2.53±0.01 mmol/l, P<0.0001) than obese patients, lower 24 h-mean urinary-calcium/createnine ratio (0.35±0.04 vs 0.39±0.02, P<0.0001) and lower 24 h-mean nephrogenous cyclic AMP (NcAMP) (10.13±0.84 nmol/LGFR versus 15.27±0.77 nmol/LGFR, P−0.007). However, non-obese AGHD patients had higher 24 h-mean PTH (4.16±0.09 vs 3.88±0.07 pmol/l, P<0.0001), type-I collagen C-telopeptide (CTX)- bone-resoption marker (0.21±0.01 μg/l versus 0.10±0.01 mmol/l, p<0.0001), procollagen type-I amino-terminal propeptide (P1NP)- bone formation marker (44.81±0.35 μg/l versus 30.01±0.40 mmol/l, P<0.0001), phosphate (1.10±0.07 versus 1.03±0.01 mmol/l, P-0.004) and urinary phosphate/Creatinine ratio (1.59±0.19 vs 0.98±0.14, P<0.0001) than obese AGHD patients.

Following GHR, PTH decreased in both groups (P<0.0001):percentage reduction was greater in non-obese AGHD patients (14.1 vs 7.5%). Significant increases in NcAMP (P<0.0001) and bone turnover markers (P<0.0001) were observed in both groups: percentage increment of bone turnover markers were greater in obese patients whereas that of NcAMP was greater in non-obese patients (84 vs 25%). Calcium increased in non-obese AGHD patients (maximum level at 3 months, p<0.001). However, reduction in calcium level was seen in obese AGHD patients (nadir at 6 months, P<0.001).

Conclusion: Following GHR, increased PTH sensitivity is seen in both groups but the magnitude and timing of response were different: improvement of renal PTH sensitivity is greater in non-obese AGHD group whereas improvement of bone PTH sensitivity seems greater in obese AGHD group.