Browsing by Author "Abbink, W."
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- Calcium handling in Sparus auratus: effects of water and dietary calcium levels on mineral composition, cortisol and PTHrP levelsPublication . Abbink, W.; Bevelander, G. S.; Rotllant, J.; Canario, Adelino V. M.; Flik, G.Juvenile gilthead sea bream (Sparus auratus L.; 10–40·g body mass) were acclimatized in the laboratory to full strength (34‰) or dilute (2.5‰) seawater and fed normal, calcium-sufficient or calcium-deficient diet for nine weeks. Mean growth rate, whole-body calcium and phosphorus content and accumulation rates were determined, as well as plasma levels of ionic and total calcium, cortisol and parathyroid hormone related protein (PTHrP; a hypercalcemic hormone in fish). When confronted with limited calcium access (low salinity and calcium-deficient diet), sea bream show growth arrest. Both plasma cortisol and PTHrP increase when calcium is limited in water or diet, and a positive relationship was found between plasma PTHrP and plasma ionic calcium (R2=0.29, N=18, P<0.05). Furthermore, a strong correlation was found between net calcium and phosphorus accumulation (R2=0.92, N=16, P<0.01) and between body mass and whole-body calcium (R2=0.84, N=25, P<0.01) and phosphorus (R2=0.88, N=24, P<0.01) content. Phosphorus accumulation is strongly calcium dependent, as phosphorus accumulation decreases in parallel to calcium accumulation when the diet is calcium deficient but phosphorus sufficient. We conclude that PTHrP and cortisol are involved in the regulation of the hydromineral balance of these fish, with growthrelated calcium accumulation as an important target.
- Parathyroid hormone-related protein and calcium regulation in vitamin D-deficient sea bream (Sparus auratus)Publication . Abbink, W.; Hang, X. M.; Guerreiro, P. M.; Spanings, T.; Ross, H. A.; Canario, Adelino V. M.; Flik, G.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.
- PTHrP potentiating estradiol-induced vitellogenesis in sea bream (Sparus auratus, L.)Publication . Bevelander, G. S.; Hang, X. M.; Abbink, W.; Spanings, T.; Canario, Adelino V. M.; Flik, G.n fish, vitellogenin is an important nutritional precursor protein produced solely in the liver and released into the blood where it binds calcium. In the gilthead sea bream (Sparus auratus) 17beta-Estradiol (E2) plays an important role in the synthesis of vitellogenin, but also the pituitary hormones prolactin (PRL) and growth hormone (GH) can stimulate vitellogenin induction in fish. Considering the emerging involvement of PTHrP in fish calcium metabolism and the importance of calcium regulation in reproduction, we investigated the possible role of PTHrP in vitellogenesis. E2-naïve and E2-primed sea bream hepatocytes were used in an in vitro primary hepatocyte culture and stimulated with a recombinant sea bream PTHrP (sbPTHrP) to establish the contribution of sbPTHrP alone or in combination with E2 to the regulation of hepatic vitellogenin synthesis. Hepatocytes stimulated solely with sbPTHrP were not affected in their vitellogenesis. However, in hepatocytes stimulated with E2 in combination with sbPTHrP a higher vitellogenin production was seen than with E2 alone. It is concluded that sbPTHrP has a potentiating effect on estradiol stimulation of vitellogenin production by sea bream hepatocytes. The sea bream provides a unique model where vitellogenesis regulation can be studied on E2-naïve liver cells, both in vivo and in vitro.
- PTHrP regulation and calcium balance in sea bream (Sparus auratus L.) under calcium constraintPublication . Abbink, W.; Bevelander, G. S.; Hang, X. M.; Lu, W. Q.; Guerreiro, P. M.; Spanings, T.; Canario, Adelino V. M.; Flik, G.Juvenile gilthead sea bream were exposed to diluted seawater (2.5‰ salinity; DSW) for 3·h or, in a second experiment, acclimated to DSW and fed a control or calcium-deficient diet for 30·days. Branchial Ca2+ influx, drinking rate and plasma calcium levels were assessed. Sea bream plasma parathyroid hormone related protein (sPTHrP) was measured, and mRNAs of pthrp, its main receptor, pth1r, and the calcium-sensing receptor (casr) were quantified in osmoregulatory tissues and the pituitary gland. When calcium is limited in water or diet, sea bream maintain calcium balance; however, both plasma Ca2+ and plasma sPTHrP concentrations were lower when calcium was restricted in both water and diet. Positive correlations between plasma sPTHrP and plasma Ca2+ (R2=0.30, N=39, P<0.05), and plasma sPTHrP and body mass of the fish (R2=0.37, N=148, P<0.001) were found. Immunoreactive sPTHrP was demonstrated in pituitary gland pars intermedia cells that border the pars nervosa and co-localises with somatolactin. In the pituitary gland, pthrp, pth1r and casr mRNAs were downregulated after both short- and long-term exposure to DSW. A correlation between pituitary gland pthrp mRNA expression and plasma Ca2+ (R2=0.71, N=7, P<0.01) was observed. In gill tissue, pthrp and pth1r mRNAs were significantly upregulated after 30·days exposure to DSW, whereas no effect was found for casr mRNA expression. We conclude that in water of low salinity, declining pituitary gland pthrp mRNA expression accompanied by constant plasma sPTHrP levels points to a reduced sPTHrP turnover and that sPTHrP, through paracrine interaction, is involved in the regulation of branchial calcium handling, independently of endocrine pituitary gland sPTHrP.