Subterranean mole-rats naturally have an impoverished calciol status, yet synthesize calciol metabolites and calbindins

Abstract

Buffenstein R, Jarvis JUM, Opperman LA, Cavaleros M, Ross FP, Pettifor JM. Subterranean mole-rats naturally have an impoverished calciol status, yet synthesize calciol metabolites and calbindins. Eur J Endocrinol 1994;130:402–9. ISSN 0804–4643 Mole-rats (Family Bathyergidae) have no obvious source of calciol. They live in an environment devoid of sunlight and consume a herbivorous diet. Calciol status, metabolism and expression were examined in six species of Bathyergids. Serum levels of calcidiol in all species were < 5μg/l and those of calcitriol were low (18.0 ± 11.0 ( sd ) ng/l, N = 57) when compared to other rodents. Within 72 h of injecting animals with tritium-labelled calciol, most of the labelled prohormone had been metabolized to more polar metabolites. Three times more tritium-labelled calcitriol (19.3 ± 2.9%) was present than (24 R )-hydroxycalcidiol (6.2 ± 10%). The natural absence of detectable circulating concentrations of calcidiol and the threefold greater amount of calcitriol to (24 R )-hydroxycalcidiol produced indicate that calciol naturally is in short supply. Calciol-dependent calbindins were absent in the duodenum. Calbindin-D 28k was present in the Purkinje cells of the cerebellum and in some collecting ducts and proximal and distal convoluted tubules of the kidney. Calbindin-D 9k also was present but was localized uniquely in the juxtaglomerular cells of the five southern African species. These data confirm that Bathyergid mole-rats naturally have an impoverished calciol status. Despite the presence of calbindins in renal tissues, the functional importance of this hormone in calbindin synthesis and other normal mole-rat physiology is not known. R Buffenstein, Department of Physiology, University of the Witwatersrand, Medical School, 7 York Road, Parktown 2193, South Africa