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J. M. Shrimpton

Publications and source records attributed to J. M. Shrimpton.

14 recordsLinked to original sources
USGS2008

Are we missing a mineralocorticoid in teleost fish? Effects of cortisol, deoxycorticosterone and aldosterone on osmoregulation, gill Na + ,K + -ATPase activity and isoform mRNA levels in Atlantic salmon

It has long been held that cortisol, acting through a single receptor, carries out both glucocorticoid and mineralocorticoid actions in teleost fish. The recent finding that fish express a gene with high sequence similarity to the mammalian mineralocorticoid receptor (MR) suggests the possibility that a hormone other than cortisol carries out some mineralocorticoid functions in fish. To test for this possibility, we examined the effect of in vivo cortisol, 11-deoxycorticosterone (DOC) and aldosterone on salinity tolerance, gill Na + ,K + -ATPase (NKA) activity and mRNA levels of NKA α1a and α1b in Atlantic salmon. Cortisol treatment for 6–14 days resulted in increased, physiological levels of cortisol, increased gill NKA activity and improved salinity tolerance (lower plasma chloride after a 24 h seawater challenge), whereas DOC and aldosterone had no effect on either NKA activity or salinity tolerance. NKA α1a and α1b mRNA levels, which increase in response to fresh water and seawater acclimation, respectively, were both upregulated by cortisol, whereas DOC and aldosterone were without effect. Cortisol, DOC and aldosterone had no effect on gill glucocorticoid receptor GR1, GR2 and MR mRNA levels, although there was some indication of possible upregulation of GR1 by cortisol (p = 0.07). The putative GR blocker RU486 inhibited cortisol-induced increases in salinity tolerance, NKA activity and NKA α1a and α1b transcription, whereas the putative MR blocker spironolactone had no effect. The results provide support that cortisol, and not DOC or aldosterone, is involved in regulating the mineralocorticoid functions of ion uptake and salt secretion in teleost fish.

General and Comparative Endocrinology↗
USGS2007

Effect of daily oscillation in temperature and increased suspended sediment on growth and smolting in juvenile chinook salmon, Oncorhynchus tshawytscha

We examined the effect of temperature oscillation and increased suspended sediment concentration on growth and smolting in juvenile ocean-type chinook salmon (Oncorhynchus tshawytscha). Fish were ponded on February 26; each treatment group had three replicates of 250 fish. Mean temperatures for the entire experiment were 12.3????C for all tanks with a total of 1348 and 1341 degree days for the constant temperature and oscillating temperature tanks, respectively. Daily fluctuation in temperature averaged 7.5????C in the variable temperature groups and less than 1????C for the constant temperature group. Starting on April 5, bentonite clay was added each day to tanks as a pulse event to achieve a suspended sediment concentration of 200??mg l- 1; clay cleared from the tanks within approximately 8??h. Fish were sampled at approximately two??week intervals from ponding until mid-June. On the last sample date, June 12, a single gill arch was removed and fixed for histological examination of gill morphology. By early May, significant differences were seen in size between the groups; control > temperature = sediment > (temperature ?? sediment). This relationship was consistent throughout the experiment except for the last sample date when the temperature group had a mean weight significantly greater than the sediment group. Gill Na+,K+-ATPase activity was not affected by daily temperature oscillations, but groups subjected to increased suspended sediment had significantly lower enzyme activities compared to controls. Mean cell size for gill chloride cells did not differ between groups. Plasma cortisol increased significantly during the spring, but there were no significant differences between groups. ?? 2007 Elsevier B.V. All rights reserved.

Aquaculture↗
USGS2007

Differential hormonal responses of Atlantic salmon parr and smolt to increased daylength: A possible developmental basis for smolting

In order to elucidate the developmental basis for smolting, Atlantic salmon, Salmo salar, parr (< 11.5??cm) and smolts (> 12.5??cm) were exposed to natural daylength (LDN) and increased daylength (LD16:8) starting in late February and gill Na+,K+-ATPase activity and circulating hormone levels monitored from January to May. Gill Na+,K+-ATPase activity remained low and constant in both groups of parr. In smolts, gill Na+,K+-ATPase began increasing in late February in both photoperiods, but was significantly higher in the LD16:8 group from March through April. Smolts exposed to LD16:8 had dramatically elevated plasma GH within one week of increased daylength that remained high through April, whereas plasma GH of LDN smolts increased steadily beginning in late February and peaking in late April. Plasma GH levels of parr remained low in spring and did not respond to increased daylength. Plasma insulin-like growth factor I (IGF-I) levels were substantially higher in smolts than parr in January. Plasma IGF-I levels of parr increased steadily from January to May, but there was no influence of increased daylength. In smolts, plasma IGF-I of LD16:8 fish initially decreased in early March then increased in late March and April, whereas plasma IGF-I of LDN smolts increased steadily to peak levels in early April. Plasma cortisol was low in parr throughout spring and did not differ between photoperiod treatments. Plasma cortisol of LD16:8 smolts increased in early March and remained elevated through April, whereas in LDN smolts plasma cortisol did not increase until early April and peaked in late April. Plasma thyroid hormones were generally higher in smolts than in parr, but there was no clear effect of increased daylength in parr or smolts. The greater capacity of the GH/IGF-I and cortisol axes to respond to increased daylength may be a critical factor underlying smolt development. ?? 2007 Elsevier B.V. All rights reserved.

Aquaculture↗
USGS2005

Seasonal changes in androgen levels in stream- and hatchery-reared Atlantic salmon parr and their relationship to smolting

In stream-reared Atlantic salmon Salmo salar, plasma androgens were significantly greater in mature male parr than immature males and females in October, but had declined by January and did not differ significantly from immature fish throughout the spring. Immature fish in March were significantly larger and had greater gill Na+,K+-ATPase activity than their previously mature counterparts. Bimodal growth distribution was seen in hatchery-reared Atlantic salmon and a proportion of the male fish in the lower mode matured. Plasma testosterone (T) and 11-ketotestosterone (11-KT) were significantly elevated from September to December in mature male (1+ year) parr. In January, plasma androgens had declined in mature males and did not differ significantly from immature fish. By May all the hatchery fish were large enough to smolt and a proportion of the previously mature males had increased gill Na+,K+-ATPase activity. Therefore elevated androgens in the previous autumn do not prevent smolting. Parr with higher plasma T and 11-KT in April and May, that are presumably beginning to mature, had lower gill Na+,K+-ATPase activity, indicating that future maturation and associated increases in androgens may inhibit smolting. ?? 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.

Journal of Fish Biology↗
USGS2002

Effects of an advanced temperature cycle on smolt development and endocrinology indicate that temperature is not a zeitgeber for smolting in Atlantic salmon

Atlantic salmon ( Salmo salar ) juveniles were reared under simulated conditions of normal photoperiod (LDN) or short days (LD 9:15) and ambient temperature (AMB: normal temperature increases in April) or an advanced temperature cycle (ADV: temperature increases in February). Under both photoperiod conditions, the timing of increased and peak levels of gill Na + ,K + -ATPase activity were not altered by temperature,although the rate of increase was initially greater under ADV. ADV/LD 9:15 resulted in peak gill Na + ,K + -ATPase activity that was half of that seen under normal photoperiod and temperature conditions. Plasma growth hormone (GH) levels increased threefold in late March under ADV/LDN,but not under ADV/LD 9:15, indicating that there is a photoperiod-dependent effect of temperature on levels of this hormone. Plasma insulin-like growth factor I (IGF-I) increased in spring in all groups, with increases occurring significantly earlier in the ADV/LDN group. In each photoperiod condition, the advanced temperature cycle resulted in large decreases in plasma thyroxine(T 4 ) levels in March, which subsequently recovered, whereas plasma 3,5,3′-triiodo-L-thyronine (T 3 ) levels were not substantially affected by either photoperiod or temperature. There was no consistent pattern of change in plasma cortisol levels. The results do not provide support for the role of temperature as a zeitgeber, but do indicate that temperature has a role in the timing of smolting by affecting the rate of development and interacting with the photoperiod.

Journal of Experimental Biology↗
USGS1999

Responsiveness of gill Na+/K+-ATPase to cortisol is related to gill corticosteroid receptor concentrations in juvenile rainbow trout

A positive relationship between receptor concentration and tissue responsiveness is an often-assumed and rarely tested principle in endocrinology. In salmonids, seasonal changes in levels of plasma cortisol and gill corticosteroid receptors (CRs) during the spring indicate a potential role for this hormone in the parr–smolt transformation. It is not known whether these seasonal changes result in alterations in gill responsiveness to cortisol. The relationship between CR concentration and tissue responsiveness was, therefore, examined in the gills of juvenile rainbow trout ( Oncorhynchus mykiss ). Gill CR concentration ( B max ) and affinity ( K d ) were assessed using a radioligand binding assay with the synthetic glucocorticoid triamcinolone acetonide. Gill responsiveness to cortisol was quantified by measuring in vitro Na + /K + -ATPase activity. Gill CR concentration was manipulated by stress or hormonal treatments. Repeated handling stresses resulted in a significant reduction in CR numbers. The decrease in CR B max corresponded to a reduction in gill responsiveness to cortisol. Triiodothyronine, but not growth hormone, treatment was found to increase CR B max significantly. The increase in CR numbers was correlated with a marked increase in gill responsiveness to cortisol. A significant positive linear relationship exists between the in vitro gill Na + /K + -ATPase activity response to cortisol and CR B max ( r 2 =0.614, P <0.001). We have demonstrated that binding sites for cortisol in the gills of rainbow trout have high affinity, high specificity and saturable binding and that the number of binding sites is correlated with the tissue response to cortisol.

Journal of Experimental Biology↗
USGS1998

Regulation of gill cytosolic corticosteroid receptors in juvenile Atlantic salmon: Interaction effects of growth hormone with prolactand triiodothyronine

The potential effects of growth hormone (GH), prolactin (Prl), and triiodothyronine (T 3 ) on gill Na + ,K + -ATPase activity and corticosteroid receptor (CR) concentration ( B max ) and dissociation constant ( K d ) were examined in juvenile Atlantic salmon ( Salmo salar ). Compared to controls, fish injected with GH (ovine, 5.0 μg g −1 ) had significantly greater gill Na + ,K + -ATPase activity after 7 and 14 days. Gill CR B max and K d were significantly elevated on day 7, but not day 14. T 3 also significantly increased CR B max . The effect of GH on CR B max was also additive with T 3 (5.0 μg g −1 ) treatment. There was a synergistic effect on CR B max when purified coho salmon GH (csGH, 0.1 μg g −1 ) was injected in combination with T 3 (1.6 μg g −1 ). Prl (ovine, 5.0 μg g −1 ; purified coho salmon, 0.1 μg g −1 ) did not significantly alter gill CR B max . Although Prl limited the increase in CR B max by GH, the effect was not signicant. T 3 and Prl did not have an effect on K d . GH significantly increased gill Na + ,K + -ATPase activity, T 3 administration did not have a significant effect, and Prl-treated fish had significantly lower gill Na + ,K + -ATPase activity. The results indicate that T 3 acts additively with GH, while Prl has no effect in regulating CR B max . An increase in cytosolic CR by GH and T 3 , but not Prl, may regulate gill responsiveness to cortisol and be an important mechanism in the endocrine control of physiological changes during the parr–smolt transformation.

General and Comparative Endocrinology↗
USGS1998

Repeated acute stress reduces growth rate of Atlantic salmon parr and alters plasma levels of growth hormone, insulin-like growth factor I and cortisol

Atlantic salmon ( Salmo salar ) parr were subjected to acute handling stresses and growth-monitored for at least 30 days. In fish stressed twice daily, growth rate in weight was 61% lower than controls after 11 days (1.00 vs. 2.57% day −1 ) and over a 30 day period it was 50% lower than controls (1.53 vs. 3.07% day −1 ). In fish stressed once daily, growth rate was 18% lower than controls after 10 days (2.17 vs. 2.63% day −1 ) and over a 30-day period it was 34% lower than controls (1.71 vs. 2.59% day −1 ). In fish stressed once daily, food consumption was reduced by 62% and 37% after 17 and 37 days, respectively. At the end of 40 days of acute stress once daily, control and stressed fish were sampled 1 h prior to, 3 and 7 h after a stress event. Plasma growth hormone levels were significantly higher in the stressed group than in the controls prior to and 7 h after stress. Plasma insulin-like growth factor I (IGF-I) levels were higher in the stressed group only 3 and 7 h after stress. Plasma cortisol levels were lower in the stressed group prior to and 3 h after stress. The results indicate that acute stressors decrease growth of Atlantic salmon parr, with increasing frequency of stress having a more rapid and greater effect.

Aquaculture↗
USGS1995

Increases in gill cytosolic corticosteroid receptor abundance and saltwater tolerance in juvenile coho salmon (Oncorhynchus kisutch) treated with growth hormone and placental lactogen

Juvenile coho salmon ( Oncorhynchus kisutch ) were injected with one of two recombinant bovine hormones, growth hormone (bGH; 5.0 and 0.5 μg · g -1 body wt) or placental lactogen (bPL; 5.0, 0.5, μg · g -1 body wt) to determine the effect on growth, plasma cortisol concentration, cytosolic corticosteroid receptors (CR) in the gills, and the development of hypoosmoregulatory ability. One week following a single injection or six weekly injections of bGH or bPL, the first were measured and samplest for CR concentration and Na + , K + . ATPase activity in the gills. Fish were also challenged with salt water (salinity 25%) for 24 hr to determine saltwater tolerance at the end of the 6-week treatment. Treatment with bPL and bGH significantly increased weight and length of the fish. The 0.05-μg bPL dose significantly elevated plasma cortisol concentration, whereas all other hormone treatments did not affect cortisol levels. bPL and bGH also significantly increased CR concentration and Na + , K + -ATPase activity in the gills. The perturbation in plasma sodium concentration was least in animals receiving the highest dose bPL and the bGH-treated animals following transfer to seawater. An increase in cytosolic CR by bGH and bPL may increase responsiveness of the gills to cortisol and partially accout for the increase in Na + , K + -ATPase activity and greater ability to regulate plasma sodium in seawater as exhibited by the experimental groups.

General and Comparative Endocrinology↗