Date of Award
Doctor of Philosophy
In vitro experiments were conducted to determine the extent of vitamins D(,2) and D(,3) degradation by rumen microbes. After 24 h of incubating ('3)H-vitamins D(,2) and D(,3) in rumen fluid, 10 to 25% of the added label remained as vitamims D(,2) and D(,3). Both vitamins D(,2) and D(,3) yielded three major radioactive chromatographic peaks (tabbed Q, R(,1), and R(,2)) that were more polar than the parent vitamins D(,2) and D(,3). Peak Q, the major metabolite of vitamins D(,2) and D(,3), was chosen for further characterization. Peak Q was resolved into two peaks by high-performance liquid chromatography (HPLC) (tabbed Q(,1) and Q(,2)). Ultraviolet spectra showed a (lamda)max for Q(,1) of 308 nm, a (lamda)max for Q(,2) of 310 nm, with both Q metabolites having a (lamda)min of 250 nm. Further, both Q(,1) and Q(,2) were isolated from rumen fluid of calves orally administered ('3)H-vitamin D(,2) or D(,3). Only Q(,2) could be isolated from plasma taken from ('3)H-vitamin D-treated claves. When tested in vivo, neither Q(,1) nor Q(,2) had bone mineral resorbing activity.;The concentrations of vitamin D(,2), vitamin D(,3), and their metabolites in plasma were determined after a single oral dose of ('3)H-vitamin D(,2) or D(,3) to each of six, 95-105 kg, Jersey bull calves (3 calves/group). Over a period of 3 wk after the oral doses, 14 blood samples were taken from each calf. Total plasma radioactivity peaked at 80 h in both groups (8400 dpm/ml and 4600 dpm/ml in the ('3)H-vitamin D(,3)- and ('3)H-vitamin D(,2)-treated calves, respectively). In both groups, vitamin D radioactivity peaked at 24 to 48 h and was the predominant form of ('3)H-vitamin D in plasma 10 to 15 h after dosing. After 15 h, ('3)H-25-hydroxyvitamin D (('3)H-25-OH-D) became the predominant labelled metabolite, reaching its maximal concentration between 48 and 96 h. The appearance of ('3)H-25,26-dihydroxyvitamin D (('3)H-25,26-(OH)(,2)-D) and ('3)H-1,25 dihydroxyvitamin D (('3)H-1,25-(OH)(,2)-D) paralleled the appearance of ('3)H-25-OH-D. The amount of ('3)H-25,26-(OH)(,2)-D and ('3)H-1,25-(OH)(,2)-D arising from ('3)H-vitamin D(,2) was 10- to 15-fold less than the amount of these metabolites from ('3)H-vitamin D(,3). ('3)H-24,25-Dihydroxyvitamin D steadily increased in the plasma and attained a maximum at 300 to 400 h. In addition to the known vitamin D metabolites, four unidentified ('3)H-vitamin D metabolites appeared in the plasma and reached maximal concentrations at 48 to 72 h.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Joel L. Sommerfeldt
Sommerfeldt, Joel L., "Vitamin D2 and vitamin D3 metabolism in ruminants and by rumen microbes " (1982). Retrospective Theses and Dissertations. 7543.