1,25-Dihydroxycholecalciferol effects on plasma calcitonin levels and calcitonin mRNA in normal or partially vitamin D-depleted rats.
The physiological effect of 1,25-(OH)2D3 on the regulation of calcitonin (CT) secretion was studied by measuring plasma CT levels and CT mRNAs extracted from thyroid glands of normal (D+) or partially vitamin D-depleted rats (D-). In both groups, acute 1,25-(OH)2D3 administration of 0.1 microgram/kg b.w. yielded an early drop in plasma calcium concentrations (around 0.6-1 mg/dl) with a maximum decrease 15 min after treatment. In spite of this hypocalcemia, a significant rise in plasma CT levels was observed within 5 min in D+ animals and within 30 min in D- animals after injection of the vitamin D metabolite. Nevertheless, the increased CT secretion was not associated with a marked and sustained rise in CT mRNA levels measured by dot-blot hybridization or CT mRNA activity evaluated by translation assay. By contrast to the observations made previously using supra-physiological doses of the vitamin D metabolites, no clear-cut effect on CT mRNA levels was found with lower doses. If we hypothesized that 1,25-(OH)2D3 plays a physiological role in CT secretion, our results suggest that this rapid control could be exerted at a post-translational level may be via an increase in the cytoplasmic ionized calcium concentration of C-cells.
Legendre
B
B
Endocrinologie Moléculaire et Métabolique, Université Pierre et Marie Curie, Paris.
Besnard
P
P
Tahri
E H
EH
Tahraoui
A
A
Segond
N
N
Jullienne
A
A
Garel
J M
JM
D000818:Animals; D001345:Autoradiography; D002116:Calcitonin / Q000097:blood* / Q000235:genetics; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D005260:Female; D010710:Phosphates / Q000097:blood; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013961:Thyroid Gland / Q000032:analysis; D014808:Vitamin D Deficiency / Q000378:metabolism*
D010710:Phosphates; D012333:RNA, Messenger; D002116:Calcitonin; D002117:Calcitriol; D002118:Calcium