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Department of Animal Physiology, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
¹ Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
² CCMAR, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
³ Department of Chemical Endocrinology, University Medical Centre, 6500 HB Nijmegen, The Netherlands

(Requests for offprints should be addressed to G Flik; Email: g.flik{at}science.ru.nl)

Gilthead sea bream (Sparus auratus L.) were fed a vitamin D-deficient diet for 22 weeks. Growth rate, whole body mineral pools and calcium balance were determined. Plasma parathyroid hormone-related protein (PTHrP) and calcitriol levels were assessed. Expression of mRNA for pthrp and pth1r was quantified in gills and hypophysis. Fish on vitamin D-deficient diet (D– fish) showed reduced growth and lower calcium turnover (calcium influx, efflux and accumulation rates decreased) and unaltered plasma calcium levels. Plasma calcitriol levels became undetectable, PTHrP levels decreased in the D– fish. In controls, a significant increase in plasma PTHrP level over time was seen, i.e. it increased with body mass. Relationships were found between plasma PTHrP and the whole body pools of calcium, phosphorus and magnesium, indicative of a role for PTHrP in bone development. Expression of pthrp and pth1r mRNA was down-regulated in the hypophysis of D–fish, whereas in gill tissue, pthrp and pth1r mRNA were up-regulated. We conclude that lower pthrp mRNA expression and plasma values in D– fish reflect lower turnover of PTHrP under conditions of hampered growth; up-regulation of pthrp mRNA in gills indicate compensatory paracrine activity of PTHrP during calcitriol deficiency to guarantee well-regulated branchial calcium uptake. This is the first report to document a relation between PTHrP and calcitriol in fish.

This article has been cited by other articles:

				R Ornsrud, E J Lock, C N Glover, and G Flik Retinoic acid cross-talk with calcitriol activity in Atlantic salmon (Salmo salar) J. Endocrinol., September 1, 2009; 202(3): 473 - 482. [Abstract] [Full Text] [PDF]

				G. S Bevelander, E. S L C Pinto, A. V M Canario, T. Spanings, and G. Flik CYP27A1 expression in gilthead sea bream (Sparus auratus, L.): effects of calcitriol and parathyroid hormone-related protein J. Endocrinol., March 1, 2008; 196(3): 625 - 635. [Abstract] [Full Text] [PDF]