Ethnic differences in parathyroid hormone secretion and mineral metabolism in response to oral phosphate administration

Ethnic differences in bone metabolism have been reported and it has been suggested that these may be partly due to prolonged exposure to an elevated plasma parathyroid hormone (PTH) concentration or a decreased sensitivity to PTH. We explored ethnic differences in bone and mineral metabolism by 5 days of oral phosphate (P) loading to stimulate PTH secretion. Healthy older people from UK (B), The Gambia (G) and China (C), 15 individuals from each sex and ethnic group, were studied. Blood and urine samples were collected before and 2 h after P dose on days 1, 4 and 5 and on a control day. The induced changes (%) in PTH and markers of mineral and bone metabolism after 2 h and over 5 days were examined. At baseline, PTH, 1,25(OH)(2)D and bone turnover markers were higher in Gambian subjects than in British and Chinese subjects (P ≤ 0.01). 2 h after P loading, ionized calcium (iCa) decreased and PTH and plasma P (P) increased in all groups (P ≤ 0.01, n.s. between groups). Urinary P to creatinine ratio (uP/Cr) increased, the increase being greater in Chinese subjects than in British and Gambian subjects on days 4 and 5 (P ≤ 0.01). By day 5, fasting iCa was decreased and P increased in British and Gambian (P ≤ 0.01) but not in Chinese subjects. Fasting PTH and uP/Cr increased in all groups. There were ethnic differences in changes in bone markers, but the relationship with changes in PTH was comparable between groups. In conclusion, ethnic differences in mineral metabolism in response to 5-day P loading were found. Chinese subjects showed a more rapid renal clearance of P than British and Gambian counterparts and there were differences between the groups in the skeletal response to P loading, but no evidence was found for resistance to the resorbing effects of PTH.