The deleterious effects of cortisol implantation on reproductive function in two species of trout, Salmo trutta L. and Salmo gairdneri Richardson

The effect of cortisol administration on hepatic and plasma estradiol-binding capacity in immature female rainbow trout (Oncorhynchus mykiss)

Implantation of a cortisol-containing pellet into the peritoneal cavity of immature female rainbow trout raised plasma cortisol levels within the range commonly observed in chronically stressed fish. In cortisol-implanted fish there was a significant decline in the concentration of hepatic estradiol-binding sites relative to sham-implanted controls. This consisted of a 35% drop in cytosolic binding sites and a 29% reduction in the number of nuclear estradiol-binding sites, by 4 weeks postimplantation. Plasma estradiol-binding capacity was also influenced by cortisol treatment. After 2 weeks there was a 33% increase in plasma estradiol-binding capacity of cortisol-implanted fish. Plasma estradiol levels were unaffected by cortisol implantation, suggesting that the effects of cortisol on estradiol-binding sites were not mediated by altering the rate of estradiol secretion. The results indicate a possible mechanism by which environmental stress may suppress vitellogenesis.

The effect of stress and exogenous cortisol on receptor-like binding of cortisol in the liver of rainbow trout, Oncorhynchus mykiss

Cortisol binding has been identified in cytosols prepared from rainbow trout liver. Binding is of high affinity (kD = 5.1 +/- 0.2 nM, n = 23) low capacity (Nmax = 197 +/- 12 fmol mg-1 protein, n = 23), and high specificity, only dexamethasone, cortisol, and Ru38486 being efficient in displacing bound [3H]cortisol. Binding is not due to contamination by blood because plasma displayed no affinity for cortisol under the assay regime employed here and, although whole blood cytosol does specifically bind cortisol, the degree of contamination is demonstrably too low to account for the levels of binding detected in liver cytosol. No specific binding of [3H]cortisol could be detected in liver nuclear extracts, although the simultaneous assay for nuclear estradiol-binding sites was positive. Rainbow trout stressed by confinement displayed a significant reduction in cytosolic [3H]cortisol-binding capacity (with no concomitant detectable appearance of binding within nuclear extracts), 96-hr confinement eliciting a 40% depression in binding capacity relative to unstressed fish. The administration of cortisol via intraperitoneal implants also reduced, significantly, the number of hepatic-binding sites. The results are discussed with reference to anomalies in reported characteristics of teleost glucocorticoid receptors and the phenomenon of down-regulation observed in some mammalian systems.

The dynamics of vitellogenin sequestration into vitellogenic ovarian follicles of the rainbow trout, Salmo gairdneri

This study provides quantitative data on the dynamics of protein sequestration into vitellogenic follicles of the rainbow trout, Salmo gairdneri. The ovarian uptake of both radiolabelled vitellogenin (VTG) and bovine serum albumin (BSA) were investigated in a homogenous population of maturing vitellogenic females.Ten fish were injected with (3)H. VTG directly into the bloodstream. Concomitantly, five of these fish received an equal amount of (14)C.BSA. Twenty two hours after injection, of the tissues sampled, the greatest proportions of (3)H. VTG were present in the blood (into which the radio labels were administered) and in the ovary (up to 28% and 46% of that originally present in the blood, respectively). VTG uptake was both selective, rates of uptake far exceeding that of the (14)C.BSA, and rapid. (3)H. VTG was sequestered at rates of between 35 to 390 ng.mm(2) follicle surface(-1).h(-1) in the different fish. The rates of VTG uptake into similarly sized follicles varied both between different sites within the ovary (by up to 30%) and also between the ovaries (by up to 38%) of an individual fish.

The effect of cortisol on the secretion of sex steroids from cultured ovarian follicles of rainbow trout

In a series of experiments, the effect of cortisol on the ability of rainbow trout (Salmo gairdneri) ovarian follicles to secrete sex steroids in vitro was investigated. The basal rate of secretion of sex steroids (oestradiol and testosterone) was suppressed in a dose-dependent manner by the addition of cortisol to the incubation medium. This suppression was evident using physiological levels of cortisol (less than 100 ng ml-1). The possibility of elevated plasma cortisol levels (due to stress) reducing the reproductive ability of sexually maturing female trout through a direct effect of cortisol on the ovary is discussed.