Parathyroid responsiveness to hypocalcemic and hypercalcemic stimuli in adult growth hormone deficiency after growth hormone replacement.
Adult growth hormone deficiency (AGHD) is associated with osteoporosis. Previous reports have suggested that alterations in parathyroid gland responsiveness to changes in calcium concentration may play a role in the genesis of osteoporosis in untreated AGHD patients. We investigated the endogenous parathyroid hormone [PTH-(1-84)] response to hypocalcemic and hypercalcemic stimuli induced by sodium EDTA and calcium gluconate infusion, respectively, and to PTH-(1-34) infusion in AGHD patients before and during GH replacement (GHR). We have demonstrated that the maximum PTH-(1-84) stimulation and suppression occurred at significantly higher calcium concentrations and in response to smaller changes in calcium concentrations after GHR. The calcemic response to the effects of PTH-(1-34) infusion significantly increased after GHR. The calcium set point (the calcium concentration at which the rate of PTH secretion is one-half of its maximal value) significantly increased in all groups after 3 mo on GHR, and it increased further at 12 mo. Our results suggest increased parathyroid gland sensitivity to smaller changes in serum calcium and increased end-organ sensitivity to the effects of PTH in AGHD patients after GHR. These findings may help us to understand the mechanisms underlying the genesis of osteoporosis in AGHD patients.
Ahmad
Aftab M
AM
Department of Diabetes & Endocrinology, Royal Liverpool University Hospital, Liverpool L7 8XP, UK. DRAAHMAD@Yahoo.com
Hopkins
Marion T
MT
Thomas
Joegi
J
Durham
Brian H
BH
Fraser
William D
WD
Vora
Jiten P
JP
D000328:Adult; D000368:Aged; D002125:Calcium Gluconate; D002614:Chelating Agents; D004492:Edetic Acid; D019382:Human Growth Hormone / Q000008:administration & dosage* / Q000172:deficiency*; D006801:Humans; D006934:Hypercalcemia / Q000139:chemically induced / Q000188:drug therapy / Q000378:metabolism*; D006996:Hypocalcemia / Q000139:chemically induced / Q000188:drug therapy / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008875:Middle Aged; D010280:Parathyroid Glands / Q000187:drug effects* / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000008:administration & dosage; D010446:Peptide Fragments / Q000008:administration & dosage; D044169:Receptors, Calcium-Sensing / Q000378:metabolism
D002614:Chelating Agents; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D044169:Receptors, Calcium-Sensing; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D004492:Edetic Acid; D002125:Calcium Gluconate