Characteristics of ovarian follicle steroidogenesis during vitellogenesis in an asynchronously ovulating stock of rainbow trout Oncorhynchus mykiss.

This study explored several physiological criteria that could be used to assess the steroidogenic condition of the ovarian follicles of individual fish of an asynchronously ovulating captive rainbow trout Oncorhynchus mykiss stock. In these fish, the date of sampling, morphological variables such as gonado-somatic index or ovarian follicle mass and visual assessment of the ovary provided accurate indications of the maturational condition of an individual. The physiological variables measured included the in vitro basal and cyclic adenosine monophosphate (cAMP)-stimulated synthesis by ovarian follicles of 17ß-oestradiol (E(2)) and testosterone (T); in addition, quantitative reverse-transcription (RT)-PCR was used to measure the relative expression of star and p450scc genes by ovarian follicles. The ratios of cAMP-stimulated E(2) and T synthesis to basal E(2) and T synthesis provided a reliable indication of differences in the steroidogenic status of the follicles of individual animals. On the basis of these criteria, together with the use of gene expression profiles, it was possible to classify individual fish as being at an early, mid or late-vitellogenic stage.

Stressors, glucocorticoids and ovarian function in teleosts.

The purpose of this overview is to re-examine the postulated direct and indirect actions of glucocorticoids on ovarian function in teleosts. The re-examination is undertaken in light of recent advances in the understanding of the stress response itself, the mode of action of the hypothalamus-pituitary gland-ovarian (HPO) axis, the mechanisms of control of oestrogen-dependent hepatic vitellogenin (VtG) secretion and the apparent roles of corticotrophin-releasing hormone (CRH) and CRH-related factors in the regulation of feeding activity. Many of the results of different studies, particularly whole-animal studies, are conflicting, and little is known as to whether the hormone acts directly on various components of the HPO axis or indirectly by virtue of redirection of energy resources away from ovarian growth to provide a source of metabolic resources for other organ systems involved in the physiological stress response. In vitro studies provide some new insights into the direct actions of glucocorticoid on hepatic VtG synthesis and ovarian follicle steroidogenesis, but even here, in some studies the cellular sites of action of these hormones is not altogether clear. The overview emphasizes the complexity of the stress response, the complexity of the regulation of glucocorticoid-dependent gene expression and the extensive interactive nature of the HPO with other hypothalamus-pituitary gland-peripheral endocrine gland axes, such as the thyroid (HPT), 'somatic' (GH-IGF) and interrenal tissue (HPI) axes.