Geology topics

Stephen D. McCormick

Publications and source records attributed to Stephen D. McCormick.

118 records · Page 7Linked to original sources

USGS2005

Distinct effects of 4-nonylphenol and estrogen-17β on expression of estrogen receptor α gene in smolting sockeye salmon

Xenoestrogens such as 4-nonylphenol (4-NP) have been shown to affect the parr–smolt transformation, but their mechanisms of action are not known. We therefore examined effects of 4-NP and estradiol-17β (E2) on expression of estrogen receptor (ER) α gene in the liver, gill, pituitary and brain of sockeye salmon to elucidate molecular mechanisms of 4-NP and E2 and developmental differences in response during smolting. Fish were treated twice within a week with 4-NP (15 and 150 mg/kg BW), E2 (2 mg/kg BW) or only vehicle at three stages of smolting, pre-smolting in March, early smolting in April and late smolting in May. The absolute amounts of ERα mRNA were determined by real-time PCR. The basal amounts of ERα mRNA peaked in April in the liver, gill and pituitary. In March, E2 extensively increased the amounts in the liver, while 4-NP had no effects at this stage. In contrast, 4-NP (but not E2) decreased liver ERα mRNA in April. 4-NP also decreased the amount of ERα mRNA in the gill in April. In the pituitary, 4-NP increased ERα mRNA in March but decreased it in May. There were no significant effects in the brain. Changes in basal ERα mRNA observed in this study indicate that estrogen responsiveness of tissues may change during salmon smolting. Furthermore, 4-NP and E2 have different effects on expression of ERα gene in the liver and gill during smolting, and the response is dependent on smolt stage.

Comparative Biochemistry and Physiology, Part C: T↗

USGS2005

Endocrine disruption of parr-smolt transformation and seawater tolerance of Atlantic salmon by 4-nonylphenol and 17β-estradiol

Sex steroids are known to interfere with the parr-smolt transformation of anadromous salmonids, and environmental estrogens such as nonylphenol have recently been implicated in reduced returns of Atlantic salmon in the wild. To determine the endocrine pathways by which estrogenic compounds affect smolt development and seawater tolerance, groups of juvenile Atlantic salmon were injected with one of five doses (0.5, 2, 10, 40 or 150 μg g −1 ) of branched 4-nonylphenol (NP), 2 μg g −1 of 17β- estradiol (E 2 ), or vehicle, during the parr-smolt transformation in April, and the treatment was repeated 4, 8, and 11 days after the first injection. Plasma was obtained for biochemical analysis 7 and 14 days after initiation of treatment. After 14 days of treatment, additional fish from each treatment group were exposed to seawater for 24 h to assess salinity tolerance. The E 2 treatment and the highest NP dose resulted in lower salinity tolerance and decreased plasma insulin-like growth factor I (IGF-I) levels, along with elevated levels of plasma vitellogenin and total calcium. Plasma growth hormone levels were elevated at intermediate NP doses only, and not affected by E 2 . After 7 days, plasma thyroxine (T 4 ) levels decreased in a strong, dose-dependent manner in response to nonylphenol, but after 14 days, this suppressive effect of T 4 occurred at the highest NP dose only. Similarly, E 2 decreased plasma T 4 levels at 7, but not 14 days. Plasma 3,3′,5-triodo- l -thyronine was reduced by E 2 and the highest NP dose after 7 and 14 days of treatment. Plasma cortisol levels were not affected by any of the treatments. The results indicate that the parr-smolt transformation and salinity tolerance can be compromised by exposure to estrogenic compounds. Suppression of plasma IGF-I levels is a likely endocrine pathway for the effects of estrogenic compounds on hypo-osmoregulatory capacity, and the detrimental effects of E 2 and NP on thyroid hormone levels are also likely to compromise the normal parr-smolt transformation of Atlantic salmon.

General and Comparative Endocrinology↗

USGS2001

Endocrine control of osmoregulation teleost fish

As the primary link between environmental change and physiological response, the neuroendocrine system is a critical part of osmoregulatory adaptations. Cortisol has been viewed as ‘the’ seawater-adapting hormone in fish and prolactin as ‘the’ fresh water adapting hormone. Recent evidence indicates that the growth hormone/insulin-like growth factor I axis is also important in seawater adaptation in several teleosts of widely differing evolutionary lineages. In salmonids, growth hormone acts in synergy with cortisol to increase seawater tolerance, at least partly through the upregulation of gill cortisol receptors. Cortisol under some conditions may promote ion uptake and interacts with prolactin during acclimation to fresh water. The osmoregulatory actions of growth hormone and prolactin are antagonistic. In some species, thyroid hormones support the action of growth hormone and cortisol in promoting seawater acclimation. Although a broad generalization that holds for all teleosts is unlikely, our current understanding indicates that growth hormone promotes acclimation to seawater, prolactin promotes acclimation to fresh water, and cortisol interacts with both of these hormones thus having a dual osmoregulatory function.

American Zoologist↗

USGS2001

Gill Na+-K+-2Cl- cotransporter abundance and location in Atlantic salmon: Effects of seawater and smolting

Na + -K + -2Cl − cotransporter abundance and location was examined in the gills of Atlantic salmon ( Salmo salar ) during seawater acclimation and smolting. Western blots revealed three bands centered at 285, 160, and 120 kDa. The Na + -K + -2Cl − cotransporter was colocalized with Na + -K + -ATPase to chloride cells on both the primary filament and secondary lamellae. Parr acclimated to 30 parts per thousand seawater had increased gill Na + -K + -2Cl − cotransporter abundance, large and numerous Na + -K + -2Cl − cotransporter immunoreactive chloride cells on the primary filament, and reduced numbers on the secondary lamellae. Gill Na + -K + -2Cl − cotransporter levels were low in presmolts (February) and increased 3.3-fold in smolts (May), coincident with elevated seawater tolerance. Cotransporter levels decreased below presmolt values in postsmolts in freshwater (June). The size and number of immunoreactive chloride cells on the primary filament increased threefold during smolting and decreased in postsmolts. Gill Na + -K + -ATPase activity and Na + -K + -2Cl − cotransporter abundance increased in parallel during both seawater acclimation and smolting. These data indicate a direct role of the Na + -K + -2Cl − cotransporter in salt secretion by gill chloride cells of teleost fish.

American Journal of Physiology - Regulatory, Integ↗

USGS1998

Seasonal differences in plasma cortisol and gill corticosteroid receptors in upper and lower mode juvenile Atlantic salmon

Circulating plasma cortisol and gill corticosteroid receptors (CR) have been observed to change seasonally in conjunction with smolting in Atlantic salmon. To differentiate whether these changes are seasonal or ontogenic, juvenile Atlantic salmon parr were separated by size into upper (UM) and lower mode (LM) in September. At monthly intervals, the fish were sampled for plasma cortisol, gill Na + K + ATPase activity and CR abundance ( B max ) and dissociation constant ( k D ). UM were significantly larger than LM, and showed the silver appearance characteristic of smolts in April and May. Gill Na + K + ATPase activity of UM fish increased 6-fold during the spring; LM fish increased 1.5-fold. Plasma cortisol levels increased significantly (10-fold) in UM fish in May, but not in LM fish. Gill CR B max increased 5-fold over the duration of the study in both groups. CR k D was lowest in October and highest in May; a 1.8- and 2-fold increase in LM and UM, respectively. There were no significant differences in gill CR B max and k D between the two groups during the study, except in May, when k D was significantly greater and B max lower in UM than LM. Peak levels of gill Na + K + ATPase activity occur coincident with an increase in plasma cortisol concentration. Seasonal increases in CR B max and k D are similar in UM and LM fish and occur independent of smolting in juvenile Atlantic salmon. In UM fish, plasma cortisol increases in spring are concurrent with increased smolt characteristics.

Aquaculture↗

USGS1998

Atlantic salmon smolts are more responsive to an acute handling and confinement stress than parr

Atlantic salmon parr and smolts reared under a natural temperature and photoperiod regime were subjected to an acute handling and confinement stress in early May. Smolts had a mean plasma cortisol concentration of 10 ng/ml before stress and 242 ng/ml 3 h after initiation of stress which returned to pre-stress levels within 8 h. Parr had a plasma cortisol concentration of 4 ng/ml prior to stress which increased to 11 ng/ml 3 h after initiation of stress and returned to pre-stress levels within 8 h. Plasma glucose was significantly higher in parr and smolts 3 h after initiation of stress; in parr, plasma glucose returned to pre-stress levels within 8 h, but not until 48 h in smolts. Plasma chloride concentration in smolts decreased from 139 to 124 mM 3 h after initiation of stress but returned to pre-stress levels within 24 h; plasma chloride in parr was not altered by stress. Plasma thyroxine of parr and smolts peaked at 3 h after initiation of stress and returned to pre-stress levels within 8 h, but smolts had 72% higher levels at 3 h. Pre-smolts (February) and smolts (May) reared under constant temperature (8–10°C) were also subjected to a handling and confinement stress. Although peak levels of plasma cortisol 3 h after initiation of stress were twice as high in smolts, other physiological and endocrine responses were not substantially different between pre-smolts and smolts. The results demonstrate that Atlantic salmon smolts are more responsive to stress than parr and that developmental differences are more important than seasonal changes.

Aquaculture↗

USGS1995

Circulating growth hormone, cortisol and thyroxine levels after 24 h seawater challenge of yearling coho salmon at different developmental stages

The response of the endocrine system to short-term exposure to sea water (SW) was examined before, during and after the parr-smolt transformation of coho salmon. Five transfers of yearling coho salmon ( Oncorhynchus kisutch ) from fresh water (FW) to FW, or from FW to SW for 24 h were carried out between March and September. Condition factor declined significantly in late April, and gill Na + , K + -ATPase activity was elevated between late March and early June. Increases in plasma osmolality after transfer to SW were high in early March, low from late March — early June and slightly higher in September. In fish transferred from FW to FW, plasma levels of thyroxine (T 4 ) were elevated in late March-late April, and plasma levels of cortisol were high in late March-early June; both hormones declined to early March levels thereafter. Growth hormone (GH) levels increased in late March and remained elevated for the duration of the study. A significant linear correlation existed between plasma cortisol and growth hormone levels in FW to FW transferred fish. After SW transfer, T 4 levels were significantly lower than values in FW controls in early March and were significantly higher than FW control levels in early June and early September. Cortisol levels increased significantly after each transfer except in late April. However, compared with the early March and early September transfers, the magnitude of the elevation was reduced in late March. GH levels were significantly elevated above FW control levels after seawater transfer in late April only, despite a trend for mean GH levels to be higher after transfer in June and September. Thus, minimal increases in cortisol, and increases in GH occur after SW transfer of functional (optimally hypo-osmoregulating) smolts.

Aquaculture↗

USGS1994

Physiology of seawater acclimation in the striped bass, Morone saxatilis (Walbaum)

Several experiments were performed to investigate the physiology of seawater acclimation in the striped bass, Morone saxatilis . Transfer of fish from fresh water (FW) to seawater (SW; 31–32 ppt) induced only a minimal disturbance of osmotic homeostasis. Ambient salinity did not affect plasma thyroxine, but plasma cortisol remained elevated for 24h after SW transfer. Gill and opercular membrane chloride cell density and Na + ,K + -ATPase activity were relatively high and unaffected by salinity. Average chloride cell size, however, was slightly increased (16%) in SW-acclimated fish. Gill succinate dehydrogenase activity was higher in SW-acclimated fish than in FW fish. Kidney Na + , K + -ATPase activity was slightly lower (16%) in SW fish than in FW fish. Posterior intestinal Na + ,K + -ATPase activity and water transport capacity (J v ) did not change upon SW transfer, whereas middle intestinal Na + ,K + -ATPase activity increased 35% after transfer and was correlated with an increase in J v (110%). As salinity induced only minor changes in the osmoregulatory organs examined, it is proposed that the intrinsic euryhalinity of the striped bass may be related to a high degree of “preparedness” for hypoosmoregulation that is uncommon among teleosts studied to data.

Fish Physiology and Biochemistry↗

USGS1994

Physiological and hormonal differences among Atlantic salmon parr and smolts reared in the wild, and hatchery smolts

Atlantic salmon which had been released as fry in tributaries of the Connecticut River (Northeastern USA) were captured during the migratory period (9 May to 6 June) 1 to 2 years later. Migrants (smolts) were captured above a dam on the main-stem; non-migrants (parr) were captured in two tributaries. Migrants were significantly larger than non-migrants (16.9 and 13.0 cm, respectively), but had a 20% lower condition factor. Relative to non-migrants, migrants had significantly higher gill Na + , K + -ATPase activity (5-fold), plasma glucose (1.8-fold), plasma thyroxine (8-fold), plasma cortisol (5-fold) and plasma growth hormone (100-fold). There were no significant differences in plasma [Na + ], [K + ] and [Ca 2+ ] between migrants and non-migrants. Most of the differences seen between non-migrants and migrants were similar to those that occurred seasonally in a captive (hatchery) population of the same stock of Atlantic salmon. However, hatchery smolts had lower levels of plasma thyroxine and exhibited no significant change in plasma growth hormone from February to June. The large differences between migrants and non-migrants may be related to both the parr-smolt transformation and migration.

Aquaculture↗

USGS1993

Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review

Osmoregulatory actions of growth hormone (GH) and its mode of action in salmonids are reviewed. We present evidence suggesting that insulin-like growth factor I (IGF-I) mediates some of the actions of GH on seawater acclimation. Plasma concentration and turnover of GH rise following exposure to seawater. Exogenous GH ( in vivo ) increases gill Na + ,K + -ATPase activity and the number of gill chloride cells, and inhibits an increase in plasma osmolarity and ions following transfer of fish to seawater. A single class of high affinity GH receptors is present in the liver, gill, intestine, and kidney. The levels of IGF-I mRNA in the liver, gill and kidney increased after GH-injection. After transfer to seawater, IGF-I mRNA increased in the gill and kidney following the rise in plasma GH, although no significant change was seen in the liver. Injection of IGF-I improved the ability of the fish to maintain plasma sodium levels after transfer to seawater. GH treatment also sensitizes the interrenal to adrenocorticotropin (ACTH), increasing cortisol secretion. Both cortisol and IGF-I may be involved in mediating the action of GH in seawater adaptation, although studies on the effect of GH on osmoregulatory physiology of non-salmonid species are limited. An integrated model of the osmoregulatory actions of GH is presented, and areas in need of research are outlined.

Fish Physiology and Biochemistry↗