Dietary calcium levels and treatment interval determine the effects of lead ingestion on plasma 1,25-dihydroxyvitamin D concentration in chicks.
The combined effects of dietary calcium level and lead level on several indices of vitamin D endocrine function were examined in young, growing chicks. Day-old animals fed a nutritionally adequate diet for 2 wk were fed diets either adequate (1.2%) or low (0.1%) in calcium, and containing 0, 0.2 or 0.8% lead for an additional 1 or 2 wk. In the calcium-adequate group, lead ingestion significantly elevated intestinal calbindin-D28k protein and mRNA levels as well as plasma 1,25-dihydroxyvitamin D concentration compared with the control animals fed a lead-free diet. The effect was apparent after 1 wk of treatment and continued through wk 2. In the calcium-deficient group, the early (1 wk) increases in plasma 1,25-dihydroxyvitamin D and calbindin-D28k protein and mRNA were significantly reversed by lead ingestion over the 2-wk trial period in a dose-dependent fashion. In these circumstances, vitamin D endocrine function is severely compromised. Therefore, lead ingestion may result in either enhanced or diminished circulating 1,25-dihydroxyvitamin D concentrations and ensuing intestinal responses, depending of dietary calcium level and the duration of lead intake. These results provide possible explanations for several apparently conflicting sets of observations regarding lead-calcium interactions.
Fullmer
C S
CS
Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
D000818:Animals; D064026:Calbindins; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000172:deficiency*; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D002645:Chickens; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D007668:Kidney / Q000378:metabolism; D007854:Lead / Q000493:pharmacokinetics / Q000633:toxicity*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D064030:S100 Calcium Binding Protein G / Q000097:blood / Q000235:genetics; D013977:Tibia / Q000378:metabolism; D013997:Time Factors
D064026:Calbindins; D002136:Calcium, Dietary; D012333:RNA, Messenger; D064030:S100 Calcium Binding Protein G; D007854:Lead; D002117:Calcitriol; D002118:Calcium