AJP - Endocrinology and Metabolism, Vol 253, Issue 3 E246-E250, Copyright © 1987 by American Physiological Society
A primed-infusion technique for rapid estimation of the metabolic clearance rate of 1,25(OH)2D3
R. Eastell, B. L. Riggs and R. Kumar
We have developed a rapid primed-infusion technique for the measurement of
the metabolic clearance and production rate of 1,25-dihydroxyvitamin D3 in
normal human subjects and experimental animals. With this method, an
estimate of the metabolic clearance rate of 1,25-dihydroxyvitamin D3 can
generally be made within 3 to 4 h. Initial studies in five dogs using
1,25-[3H]-dihydroxyvitamin D3 (180 Ci/mmol) allowed us to determine the
optimal ratio of loading dose to infusion rate that resulted in the most
rapid attainment of steady-state levels of plasma radioactivity. By use of
this technique we found that the metabolic clearance rate of
1,25-dihydroxyvitamin D3 in dogs was 6.3 +/- 1.2 ml/min (mean +/- SD); the
production rate of the hormone was 0.40 +/- 0.25 microgram/day (20.4 +/-
14.4 ng . kg-1 . day-1). In eight normal women, aged 28-51 yr, the
metabolic clearance rate for 1,25-dihydroxyvitamin D3 was 25.9 +/- 4.7
ml/min; the production rate was 1.38 +/- 0.45 microgram/day (20.7 ng . kg-1
. day-1). The advantages of this method relative to ones used in the past
are that it can be performed quickly (generally within 3-4 h) with the use
of only tracer amounts of this hormone (equivalent to 1.1% of the
production rate). With this method, no assumptions about the most
appropriate model to which to fit the data need to be made. Because of its
rapidity, no metabolites of the injected 1,25-dihydroxyvitamin D3 are
formed during the study interval.
