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Horm Metab Res 1990; 22(5): 278-282
DOI: 10.1055/s-2007-1004902
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© Georg Thieme Verlag, Stuttgart · New York

Production and Metabolic Clearance Rates of 1,25-Dihydroxyvitamin D3 during Maturation in Rats:

Studies Using a Rapid, Primed-Infusion TechniqueJ. Fox
  • Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana, U. S. A.
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Publication History

1989

1989

Publication Date:
14 March 2008 (online)

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Summary

I have adapted the primed-infusion technique for the rapid estimation of the metabolic clearance rate (MCR) and production rate (PR) of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in chronically catheterized conscious rats. Following a bolus injection, [3H]-1,25(OH)2D3 was infused iv at a constant rate for 7 h. Steady-state [3H]-1,25(OH)2D3 levels in plasma were achieved within 3 h. HPLC-purification of plasma [3H]-1,25(OH)2D3 was necessary. This rapid, primed-infusion technique thus eliminates the need for protracted infusions to achieve steady-state plasma [3H]-1,25(OH)2D3 levels. The MCR averaged 0.201 ± 0.003 ml·min-1·kg-1 in fed male rats weighing 200-300 g. This MCR is approximately 50% lower than that seen in other species. Overnight fasting was without effect on the MCR. The MCR increased in direct proportion to body weight in maturing rats (6-16 weeks old) weighing 150-450 g. Thus, the MCR can be normalized per kg across this age range. However, 1,25(OH)2D3 production and plasma levels both decreased by 65-67% as the rats matured. The failure of a 3-fold decrease in plasma 1,25(OH)2D3 levels to affect the MCR suggests that 1,25(OH)2D3 stimulates its own catabolism only at markedly elevated concentrations.

Key words

1,25(OH)2D3 Production - 1,25(OH)2D3 Clearance - Maturation - Rat

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