The effect of uninephrectomy on osteocalcin metabolism in sheep: a direct evaluation of renal osteocalcin clearance.

Indirect evidence has suggested that the kidney is a major organ of clearance for osteocalcin, a circulating marker of osteoblast function. The objectives of the present study were (1) to confirm the role of the kidney in osteocalcin clearance (2) to quantify the contribution of extrarenal sites and (3) to investigate the renal mechanism(s) of osteocalcin clearance. Plasma osteocalcin levels, osteocalcin plasma clearance rate (PCR) and plasma production rate (PPR) were determined in oophorectomized (OX) and uninephrectomized oophorectomized (UOX) sheep. The osteocalcin renal extraction efficiency (REE) and the effective renal plasma flow (ERPF) were measured, and the osteocalcin renal clearance rate (RCR) was calculated. The osteocalcin PCR was reduced significantly in UOX compared with OX sheep (2.0 +/- 0.1 (n = 9) vs 2.5 +/- 0.1 litres/h (n = 44); P less than 0.0005). In UOX sheep with plasma creatinine levels less than or equal to 130 mumol/l, the osteocalcin REE was 9 +/- 1.3% and the osteocalcin RCR was 50-91% of osteocalcin PCR (n = 4). In UOX sheep with plasma creatinine levels in the range 100-440 mumol/l, there was a linear relationship between osteocalcin PCR and ERPF; the osteocalcin RCR was related to the osteocalcin PCR (RCR = 0.9 x PCR - 0.50). Intravenous infusion of the synthetic glucocorticoid triamcinolone acetonide (TA) in UOX sheep led to marked decrements in plasma osteocalcin levels and the osteocalcin PPR, and a significant increase in the osteocalcin PCR. These changes were accompanied by a 44% increase in ERPF.(ABSTRACT TRUNCATED AT 250 WORDS)