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Evidence supporting a dual glucocorticoid and mineralocorticoid role for the elasmobranch steroid 1[alpha]-hydroxycorticosterone

In mammals distinct steroid hormones termed mineralocorticoids (MCs) and glucocorticoids (GCs) regulate hydromineral balance and the stress response, respectively. In contrast, it is thought that a single corticosteroid, 1[alpha]-hydroxycorticosterone (1[alpha]-B) serves as both a GC and MC in elasmobranchs. I investigated the putative dual MC and GC roles of 1[alpha]-B by examining ex vivo regulation of interrenal 1[alpha]-B synthesis by osmoregulatory and stress hormones in the euryhaline stingray Dasyatis sabina. A commercial enzyme-linked immunoassay was adapted for the quantification of 1[alpha]-B. I also isolated cDNA sequences encoding two rate-limiting steroidogenic enzymes, the steroidogenic acute regulatory protein (StAR) and P450 cholesterol side-chain cleavage (P450scc), and characterized the steroidogenic activity of the encoded proteins using a heterologous expression system. Both the stress hormone adrenocorticotropic hormone (ACTH) and the antinatriuretic peptide angiotensin II (ANG II) were potently steroidogenic in ex vivo interrenal cultures, whereas C-type natriuretic peptide (CNP) inhibited 1[alpha]-B synthesis. StAR and P450scc mRNA levels were increased by 24 h incubation with ACTH and decreased by both ANG II and CNP. To examine changes in osmoregulatory hormone systems that impinge upon 1[alpha]-B synthesis, I also isolated the cDNA sequences of the ANG II and CNP receptors, AT and NPR-B. Both AT and NPR-B mRNA levels were significantly elevated in osmoregulatory tissues of freshwater (FW; Lake Monroe, FL) versus saltwater (SW; Corpus Christi Bay, TX) populations of D. sabina. Interrenal StAR and NPR-B mRNA levels were also significantly higher in FW individuals. The physiological roles of 1[alpha]-B were further investigated in vivo by examining the effects of stress and FW transfer on interrenal synthesis of 1[alpha]-B. Plasma 1[alpha]-B and glucose were significantly elevated by hook-and-line capture stress, indicating that 1[alpha]-B acts in classical GC fashion to facilitate the stress response. In contrast, 1[alpha]-B was significantly decreased 24 h after SW-FW transfer. In light of the osmotic strategy of euryhaline elasmobranchs, this result is consistent with a MC role for 1[alpha]-B. Taken together, the results of this research strongly support a dual role for 1[alpha]-B in facilitating both hydromineral balance and the stress response in elasmobranchs. / text

Identiferoai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/17849
Date10 September 2012
CreatorsEvans, Andrew Neil, 1979-
Source SetsUniversity of Texas
LanguageEnglish
Detected LanguageEnglish
Formatelectronic
RightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.

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