AJP - Endocrinology and Metabolism, Vol 262, Issue 6 E840-E844, Copyright © 1992 by American Physiological Society
Intensity of lactation modulates renal 1 alpha-hydroxylase and serum 1,25(OH)2D in rats
B. Lobaugh, A. Boass, S. C. Garner and S. U. Toverud
Department of Medicine, Duke University Medical Center, Durham 27710.
Renal 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase)
activity and serum 1,25-dihydroxyvitamin D [1,25(OH)2D] concentration were
measured in lactating rats suckling litters of 3, 6, or 12 pups to
determine the effect of increasing lactational intensity on the
biosynthesis of 1,25(OH)2D. Serum Ca2+, total Ca, Pi, and immunoreactive
parathyroid hormone were also determined. The average daily litter weight
gain for each litter size was calculated from the gain over the last 4-6
days of each of three experiments and was used as an index of lactational
intensity. Highly significant correlation coefficients were found between 1
alpha-hydroxylase and average daily litter weight gain (rs = 0.63, n = 53,
P less than 0.001), serum 1,25(OH)2D and average daily litter weight gain
(rs = 0.62, n = 50, P less than 0.001), 1 alpha-hydroxylase and serum total
Ca (rs = -0.52, n = 53, P less than 0.001), and average daily litter weight
gain and total Ca (rs = -0.52, n = 53, P less than 0.001). Neither serum
phosphorus nor immunoreactive parathyroid hormone correlated significantly
with 1 alpha-hydroxylase. In addition, construction of regression models
using a stepwise forward variable selection procedure revealed serum total
Ca concentration to be a significant predictor for both serum 1,25(OH)2D
and renal 1 alpha-hydroxylase in lactating rats. These data support the
hypothesis that increasing lactational intensity leads to decreasing serum
Ca concentration, resulting in stimulation of 1 alpha-hydroxylase activity
and a rise in the serum 1,25(OH)2D level.(ABSTRACT TRUNCATED AT 250 WORDS)
