Egg Cortisol Research Articles

Ontogeny of the thyroid hormones and cortisol in the gilthead sea bream, Sparus aurata

The aim of the study was to elucidate the pattern of changes in the whole body concentrations of thyroid hormones (TH) and cortisol in eggs, pre-larvae, and larvae in the gilthead sea bream, Sparus aurata. The ontogeny of these hormones was related to specific morphological characteristics that characterize early development. TH and cortisol were detected in substantial amounts in the eggs of sea bream. T 3 concentration in eggs was found to be higher than that of T 4 (T 3, 4.02 ± 0.38 ng g −1; T 4, 1.63 ± 0.28 ng g −1), as it is often observed in marine teleosts. T 4 decreased until hatching (T 4, 1.01 ± 0.58 ng g −1), while T 3 reached a minimum at the time of first feeding (T 3, 0.19 ± 0.02 ng g −1). As development proceeded, both hormones displayed a similar pattern of changes with increasing concentrations until the completion of metamorphosis (T 3, 15.84 ± 2.92 ng g −1; T 4, 9.78 ± 2.39 ng g −1), indicating that the hypothalamo–adenohypophysial–thyroid axis begins to function soon after first feeding. The pattern of changes of cortisol (F) concentration was almost parallel to that of T 4, starting from 0.83 ng g −1 in eggs. Minimum F concentration was observed at hatching (0.39 ± 0.03 ng g −1) and maximum at melanophores and scale formation (14.82 ± 2.71 and 14.82 ± 3.12 ng g −1, respectively). Results provide data for the first time on the ontogeny of thyroid hormones and cortisol during the early development in sea bream and are in agreement with results in other fish species for an important action of TH during early development.

Influence of cortisol on developmental rhythms during embryogenesis in a tropical damselfish.

Newly-spawned teleost eggs can vary widely in their maternal endowment of a variety of hormones, including cortisol. Field and laboratory experiments have shown that initial egg cortisol concentrations directly influence the size at hatching of the benthic spawning damselfish, Pomacentrus amboinensis. The present study examines the mechanism by which cortisol influences larval size at hatching by investigating the growth and developmental rhythms throughout embryogenesis. Newly spawned eggs of P. amboinensis were collected from natural benthic nests, and half of each clutch was incubated in a moderate level of cortisol (2.7 x 10(-6) M, equivalent to a concentration of 0.79 pg/egg). Cortisol was found to have no affect on the rate of cell-pulsations up to epiboly (18 hr post-fertilization), with cells pulsing at a mean rate of 56-60 pulses/min. Cortisol had an affect on the relative growth rate from the start of gastrulation to knot formation. Growth in the cortisol-supplemented embryos was pulsed, with periods of fast growth punctuated by long periods of stasis. Overall growth rates during this period were lower in the cortisol-supplemented embryos despite their higher growth during active periods. Pulse rates of somite cells and contraction rhythms of myotomes and the heart were twice as high in cortisol-supplemented embryos than controls. Despite this, cortisol-supplemented eggs developed at the same rate as controls and hatched at the same time. This study suggests that the maternal endowment of cortisol to eggs plays a vital role in determining the embryonic rhythms by which embryos grow and may be directly influencing metabolism.

Stress responsiveness of the pituitary-interrenal axis during early life stages of common carp (Cyprinus carpio).

Whole-body levels of ACTH, alpha-MSH and cortisol in eggs and larvae of the common carp (Cyprinus carpio) were determined periodically up until 168 h after fertilisation. ACTH, alpha-MSH and cortisol immunoreactivity was detected in unfertilised eggs, and endogenous production of ACTH and alpha-MSH was observed 24 h after fertilisation and that of cortisol 36 h after fertilisation. ACTH immunoreactivity reached peak levels before hatching (56-72 h after fertilisation) and remained relatively stable thereafter, while alpha-MSH immunoreactivity started to increase after hatching. At 36 h after fertilisation, whole-body cortisol levels increased rapidly reaching peak levels at the end of hatching (72 h after fertilisation), remaining stable until the end of the experiment. From 50 h after fertilisation onwards, embryos and larvae increased their whole-body cortisol levels when subjected to handling (mechanical pressure during egg stage or netting during the larval stage). It is concluded that the pituitary-interrenal axis in carp is fully functional at the time of hatching. No indications of a stress non-responsive period after hatching were observed. To characterise ACTH and alpha-MSH immunoreactivities in carp larvae, whole-body homogenates were analysed by HPLC, with pituitary homogenates of adult carp serving as a reference. ACTH and alpha-MSH immunoreactivity in carp larvae homogenates consisted of three and two products respectively. HPLC of adult carp pituitaries revealed the presence of two ACTH immunoreactive products, which may represent a phosphorylated and a non-phosphorylated ACTH variant, while the three alpha-MSH peaks most likely represent des-acetylated, mono-acetylated and di-acetylated alpha-MSH, the latter being the predominant form. In carp larvae, however, one of the ACTH immunoreactive products co-eluted with the non-phosphorylated ACTH, while the two alpha-MSH products identified co-eluted with des-acetylated and mono-acetylated alpha-MSH, indicating that POMC processing at this stage of development is different from prohormone processing in adult fish.

Stress induced elevation of plasma cortisol in adult female coho salmon (Oncorhynchus kisutch), is reflected in egg cortisol content, but does not appear to affect early development

Circulating levels of cortisol, the major corticosteroid among teleosts, increase in response to environmental Stressors. Cortisol has also been reported to be present in the freshly ovulated eggs of a number of teleost species. Since environmental Stressors have been implicated in the decrease of egg quality in salmonids, this study was conducted to investigate possible connections between egg cortisol content and subsequent viability. A physical Stressor applied to a single group of adult female coho salmon (Oncorhynchus kisutch), during the final two weeks of oogenesis appeared to result in significantly elevated plasma cortisol levels (227.5 ± 61.5 ng/ml) above those observed in a single group of control animals (141.0 ± 42.7 ng/ml), although other factors cannot be ruled out. Mean egg cortisol content (25.3 ± 0.77 ng/g) was significantly higher in the disturbed than in the undisturbed females (9.90 ± 0.94 ng/g), suggesting that cortisol content in eggs of salmonids is reflective of plasma levels during late oogenesis. Gonadosomatic index was unaffected by the treatment, although there was some evidence to suggest that elevated cortisol levels may have hastened ovulation in the experimental group. Paired groups of eggs from single females having either unmanipulated (37.0 ± 5.4 ng/g) or artificially elevated (232.7 ± 13.9 ng/g) levels of cortisol showed no significant differences in terms of time to, or synchrony of hatch, yolk sac to body weight ratio at hatch, growth from hatch to 52 days post fertilization (dpf), or percent mortality. Cortisol was seen to clear rapidly from eggs in both experimental and control groups soon after fertilization, and there was no significant difference observed between groups by 8 dpf, suggesting that maternal cortisol clears from developing embryonic salmon by the late eyed stage and may not be a factor in later development.

魚類未受精卵中の甲状腺ホルモンとコルチゾル

魚類未受精卵中の甲状腺ホルモンとコルチゾル