Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Cortisol and parathyroid hormone-related peptide are reciprocally modulated by negative feedbackPublication . Guerreiro, P. M.; Rotllant, J.; Fuentes, J.; Power, Deborah; Canario, Adelino V. M.In previous in vitro studies, we have shown that the N-terminal region of parathyroid hormone-related protein (PTHrP) can stimulate cortisol production in sea bream, Sparus auratus, interrenal tissue, possibly through a paracrine action. In the current study, the systemic interaction between cortisol and PTHrP was studied in vivo. Sustained elevated blood cortisol levels, induced either by cortisol injection or conWnement stress, suppressed circulating PTHrP 6 and 24-fold,respectively, by comparison to control Wsh.reduced cortisol levels, prevented the decrease of plasma PTHrP observed in conWned Wsh and raised plasma PTHrPrespectively, by comparison to control fish.
- Endocrine regulation of carbonate precipitate formation in marine fish intestine by stanniocalcin and PTHrPPublication . Gregorio, Silvia F.; Carvalho, Edison S. M.; Campinho, Marco A.; Power, Deborah M.; Canario, Adelino V. M.; Fuentes, JuanIn marine fish, high epithelial bicarbonate secretion by the intestine generates luminal carbonate precipitates of divalent cations that play a key role in water and ion homeostasis. In vitro studies highlight the involvement of the calciotropic hormones PTHrP (parathyroid hormone-related protein) and stanniocalcin (STC) in the regulation of epithelial bicarbonate transport. The present study tested the hypothesis that calciotropic hormones have a regulatory role in carbonate precipitate formation in vivo. Sea bream (Sparus aurata) juveniles received single intraperitoneal injections of piscine PTHrP(1-34), the PTH/PTHrP receptor antagonist PTHrP(7-34) or purified sea bream STC, or were passively immunized with polyclonal rabbit antisera raised against sea bream STC (STC-Ab). Endocrine effects on the expression of the basolateral sodium bicarbonate cotransporter (Slc4a4.A), the apical anion exchangers Slc26a6.A and Slc26a3.B, and the V-type proton pump beta-subunit (Atp6v1b) in the anterior intestine were evaluated. In keeping with their calciotropic nature, the hypocalcaemic factors PTHrP(7-34) and STC upregulated gene expression of all transporters. In contrast, the hypercalcaemic factor PTHrP(1-34) and STC antibodies downregulated transporters involved in the bicarbonate secretion cascade. Changes in intestine luminal precipitate contents provoked by calcaemic endocrine factors validated these results: 24 h postinjection either PTHrP(1-34) or immunization with STC-Ab reduced the carbonate precipitate content in the sea bream intestine. In contrast, the PTH/PTHrP receptor antagonist PTHrP(7-34) increased not only the precipitated fraction but also the concentration of HCO3 equivalents in the intestinal fluid. These results confirm the hypothesis that calciotropic hormones have a regulatory role in carbonate precipitate formation in vivo in the intestine of marine fish. Furthermore, they illustrate for the first time in fish the counteracting effect of PTHrP and STC, and reveal an unexpected contribution of calcaemic factors to acid-base balance.
- Prolactin regulates luminal bicarbonate secretion in the intestine of the sea bream (Sparus aurata L.)Publication . Ferlazzo, A.; Carvalho, Edison Samir Mascarelhas; Gregorio, Silvia; Power, Deborah; Canario, Adelino V. M.; Tischitta, F.; Fuentes, J.The pituitary hormone prolactin is a pleiotropic endocrine factor that plays a major role in the regulation of ion balance in fish, with demonstrated actions mainly in the gills and kidney. The role of prolactin in intestinal ion transport remains little studied. In marine fish, which have high drinking rates, epithelial bicarbonate secretion in the intestine produces luminal carbonate aggregates believed to play a key role in water and ion homeostasis. The present study was designed to establish the putative role of prolactin in the regulation of intestinal bicarbonate secretion in a marine fish. Basolateral addition of prolactin to the anterior intestine of sea bream mounted in Ussing chambers caused a rapid (<20min) decrease of bicarbonate secretion measured by pH-stat. A clear inhibitory dose–response curve was obtained, with a maximal inhibition of 60–65% of basal bicarbonate secretion. The threshold concentration of prolactin for a significant effect on bicarbonate secretion was 10ngml–1, which is comparable with putative plasma levels in seawater fish. The effect of prolactin on apical bicarbonate secretion was independent of the generation route for bicarbonate, as shown in a preparation devoid of basolateral HCO3 –/CO2 buffer. Specific inhibitors of JAK2 (AG-490, 50mmoll–1), PI3K (LY-294002, 75mmoll–1) or MEK (U-012610, 10mmoll–1) caused a 50–70% reduction in the effect of prolactin on bicarbonate secretion, and demonstrated the involvement of prolactin receptors. In addition to rapid effects, prolactin has actions at the genomic level. Incubation of intestinal explants of anterior intestine of the sea bream in vitro for 3h demonstrated a specific effect of prolactin on the expression of the Slc4a4A Na+–HCO3– co-transporter, but not on the Slc26a6A or Slc26a3B Cl–/HCO3 – exchanger. We propose a new role for prolactin in the regulation of bicarbonate secretion, an essential function for ion/water homeostasis in the intestine of marine fish.
- Parathyroid hormone-related protein-stanniocalcin antagonism in regulation of bicarbonate secretion and calcium precipitation in a marine fish intestinePublication . Fuentes, J.; Power, Deborah; Canario, Adelino V. M.Parathyroid hormone-related protein-stanniocalcin antagonism in regulation of bicarbonate secretion and calcium precipitation in a marine fish intestine. Am J Physiol Regul Integr Comp Physiol 299: R150–R158, 2010. First published April 21, 2010; doi:10.1152/ajpregu.00378.2009.—Bicarbonate secretion in the intestine (duodenum) of marine fish has been suggested to play a major role in regulation of calcium availability for uptake. However, while the end process may lead to carbonate precipitation, regulation of transport of calcium and/or bicarbonate may actually result in fine-tuning of calcium availability for transport. To test this hypothesis, sea bream (Sparus auratus) duodenal preparations were mounted in Ussing-type chambers and the effect of parathyroid hormone-related protein (PTHrP) and stanniocalcin 1 (STC 1) on the control of intestinal bicarbonate secretion and calcium transport was analyzed. As expected, PTHrP increased net calcium uptake, as a result of an increase of calcium uptake without changes in calcium efflux. In contrast, purified sea bream STC 1 caused a minor decrease of calcium uptake and a two- to threefold increase in calcium efflux. As a result, STC 1 was able to invert the calcium flux from net calcium uptake to net calcium loss, which is in keeping with its known actions as a hypocalcemic factor. Furthermore, both PTHrP and STC 1 regulate intestinal bicarbonate secretion. PTHrP increased calcium uptake and simultaneously reduced the single factor that induces calcium precipitation, bicarbonate secretion. In contrast, STC 1, while reversing the calcium net flux to make it secretory, promoted intestinal bicarbonate secretion, both actions directed to decrease the calcium gradient across the epithelium and promote immobilization in the form of bicarbonate in the intestinal lumen. Together our results provide robust evidence to support an antagonistic action of PTHrP and STC 1 in the fine control of movements of both calcium and bicarbonate in the intestine of seawater fish.
- AVT is involved in the regulation of ion transport in the intestine of the sea bream (Sparus aurata)Publication . Martos-Sitcha, J. A.; Gregorio, Silvia; Carvalho, Edison Samir Mascarelhas; Canario, Adelino V. M.; Power, Deborah; Mancera, J. M.; Martínez-Rodriguez, G.; Fuentes, J.The intestine of marine fish plays a crucial role in ion homeostasis by selective processing of ingested fluid. Although arginine vasotocin (AVT) is suggested to play a role in ion regulation in fish, its action in the intestine has not been demonstrated. Thus, the present study investigated in vitro the putative role of AVT in intestinal ion transport in the sea bream (Sparus aurata). A cDNA encoding part of an AVT receptor was isolated and phylogenetic analysis revealed it clustered with the V1a2-type receptor clade. V1a2 transcripts were expressed throughout the gastrointestinal tract, from esophagus to rectum, and were most abundant in the rectum regardless of long-term exposure to external salinities of 12, 35 or 55 p.p.t. Basolateral addition of AVT (10 6 M) to the anterior intestine and rectum of sea bream adapted to 12, 35 or 55 p.p.t. mounted in Ussing chambers produced rapid salinity and region dependent responses in short circuit current (Isc), always in the absorptive direction. In addition, AVT stimulation of absorptive Isc conformed to a dose–response curve, with significant effects achieved at 10 8 M, which corresponds to physiological values of plasma AVT for this species. The effect of AVT on intestinal Isc was insensitive to the CFTR selective inhibitor NPPB (200 lM) applied apically, but was completely abolished in the presence of apical bumetanide (200 lM). We propose a role for AVT in the regulation of ion absorption in the intestine of the sea bream mediated by an absorptive bumetanide-sensitive mechanism, likely NKCC2.