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The role of cortisol on the osmoregulation of pejerrey Odontesthes bonariensis at different salinities was investigated in adult fish injected with 0.7mg hydrocortisone per 100g body weight of fish, and transferred to 0, 5 and 20ppt of NaCl. Blood cortisol was 566ng/ml at the beginning of the experiment (0h) but surged to 1250ng/ml within 3h in cortisol-injected fish. Cortisol levels were influenced not only by treatment but also by time, being higher at 3h compared to 24h. Salinity level, time of exposure and their interaction, but not cortisol treatment, significantly affected plasma osmolality and the concentration of ions Cl -and Na + . This study showed that exogenous cortisol does not seem to play a significant role on the regulation of plasma osmolality and concentration of individual ions in pejerrey.Keywords: pejerrey, Odontesthes bonariensis, cortisol, osmoregulation, salinity RESUMO Investigou-se a participação do cortisol na osmoregulação de peixe-rei

Renal resistance to antidiuretic hormone (ADH) has been speculated to be a mechanism of transient nephrogenic diabetes insipidus occurring during late pregnancy. In order to study possible involvement of ovarian steroids in this mechanism, their effect on cyclic adenosine 3':5'-monophosphate (cAMP) response to arginine vasopressin (AVP) was examined utilizing rat and human renal medullary cells in monolayer culture. In both rat and human cells, estradiol significantly reduced cAMP response to AVP; estradiol at 1.84 x 10(-8) M, 1.84 x 10(-7) M and 1.84 x 10(-6) M decreased cAMP production stimulated by 10(-8) M AVP to 78 +/- 5%, 67 +/- 2% (P less than 0.05) and 52 +/- 1% (P less than 0.001) of the control in rat renal cells, respectively, and in human renal cells the effect of estradiol was comparable to that in rat cells. In rat renal cells, progesterone also reduced cAMP response to AVP dose-dependently; progesterone at 1.59 x 10(-7) M, 1.59 x 10(-6) M and 1.59 x 10(-5) M decreased cAMP production stimulated by 10(-8) M AVP to 87 +/- 1%, 72 +/- 5% (P less than 0.001) and 37 +/- 5% (P less than 0.001) of the control, respectively. On the other hand, corticosterone and dexamethasone at concentrations ranging from 10(-8) M to 10(-5) M and aldosterone at concentrations ranging from 10(-9) M to 10(-5) M did not alter cAMP response to AVP significantly. The suppressive effect of estradiol increased with time until six hours and thereafter it reached a plateau.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of transcortin on [3H]thymidine incorporation into phytohemagglutinin-stimulated human peripheral blood mononuclear cells and its influence on the well known suppressive effect of cortisol were investigated. Human transcortin by itself had no effect on thymidine incorporation between the concentrations of 0.25-1 X 10(-6) M. When transcortin was added to cortisol, the suppressive effect of cortisol decreased in proportion to the decrease in the protein-unbound cortisol concentration. We also investigated the influence of progesterone on transcortin-bound cortisol. When 0.5 and 1 X 10(-6) M transcortin, which contained 1 and 2 X 10(-7) M cortisol as a transcortin-bound form, were added to 5 X 10(-6) M progesterone, greater suppression of thymidine incorporation was observed that than produced by progesterone alone (86.1% and 81.3 for 0.5 and 1 X 10(-6) M transcortin, respectively). Moreover, when 5 X 10(-7) M transcortin containing the same amount of cortisol was added with 1, 2, and 5 X 10(-6) M progesterone, a greater suppression (92.6%, 74.1%, and 32.4% of control for 1, 2, and 5 x 10(-6) M progesterone) was demonstrated than that caused by progesterone alone (95.1%, 75.8%, and 49.5% of control for the corresponding concentrations of progesterone). This increased suppression was accompanied by an increase in the percentage of protein-unbound cortisol. These results indicate that unbound cortisol, whose concentration increases in the presence of progesterone, may be biologically active. The interaction between progesterone and cortisol may be modulated in part by the transcortin concentration.

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