A preliminary investigation of the effect of bovine growth hormone on growth and muscle composition of coho salmon (Oncorhynchus kisutch)

Effects of recombinant salmon type II growth hormone and bovine growth hormone on growth of coho salmon (Oncorhynchus kisutch)

A comparison of the efficacy of salmon and bovine growth hormone to stimulate growth of coho salmon juveniles was performed. Oncorhynchus nerka (sockeye salmon) type II growth hormone (nGH2) was produced using a bacterial expression system, yielding approximately 25 mg of refolded recombinant protein per litre of cells. The purified nGH2 and bovine growth hormone (bGH) were tested in juvenile O. kisutch (coho salmon) over 24 weeks. Weekly intraperitoneal injections of 0.1 and 0.5 μg/g nGH2 resulted in a dose-dependent increase in weight and fork length compared to control fish injected with bovine serum albumin (BSA). Application of 0.5 μg/g bGH resulted in the same stimulation of growth as did 0.5 μg/g nGH2, indicating these proteins were equipotent. Following 6 weeks of treatment and a subsequent rest period of 7 weeks, coho salmon were further treated with bGH at 0.5 μg/g. A prior treatment with bGH did not reduce growth-promoting activity of bGH in subsequent treatments. Throughout the experiment, condition factor decreased at similar rates for all treatment groups. These data show that bGH, which is widely available, can be used to elevate growth rate in juvenile salmon comparably to homologous GH, and validate the use of bGH in physiological or ecological experiments where rapid growth is desired compared to that seen in wild type.

Sarcopenia and piscines: the case for indeterminate-growing fish as unique genetic model organisms in aging and longevity research

Sarcopenia and dynapenia pose significant problems for the aged, especially as life expectancy rises in developed countries. Current therapies are marginally efficacious at best, and barriers to breakthroughs in treatment may result from currently employed model organisms. Here, we argue that the use of indeterminate-growing teleost fish in skeletal muscle aging research may lead to therapeutic advancements not possible with current mammalian models. Evidence from a comparative approach utilizing the subfamily Danioninae suggests that the indeterminate growth paradigm of many teleosts arises from adult muscle stem cells with greater proliferative capacity, even in spite of smaller progenitor populations. We hypothesize that paired-box transcription factors, Pax3/7, are involved with this enhanced self-renewal and that prolonged expression of these factors may allow some fish species to escape, or at least forestall, sarcopenia/dynapenia. Future research efforts should focus on the experimental validation of these genes as key factors in indeterminate growth, both in the context of muscle stem cell proliferation and in prevention of skeletal muscle senescence.

Growth hormone differentially regulates growth and growth-related gene expression in closely related fish species

Zebrafish (Danio rerio) have become an important model organism for developmental biology and human health studies. We recently demonstrated differential growth patterns between the zebrafish and a close relative the giant danio (Danio aequipinnatus), where the giant danio appears to exhibit indeterminate growth similar to most fish species important for commercial production, while zebrafish exhibit determinate growth more similar to mammalian growth. This study focused on evaluating muscle growth regulation differences in adult zebrafish and giant danio utilizing growth hormone treatment as a mode of growth manipulation. Growth hormone treatment resulted in increased overall growth in giant danio, but failed to increase growth in the zebrafish. Growth hormone treatment increased muscle IGF-I and GHrI gene expression in both species, but to a larger degree in the giant danio. In contrast, zebrafish exhibited a larger increase in IrA and IGF-IrB gene expression in muscle in response to GH treatment. In addition muscle myostatin levels were differentially regulated between the two species, with a down-regulation observed in rapidly growing, GH-treated giant danio and an up-regulation in zebrafish not actively growing in response to GH. This is the first report of differential expression of growth-regulating genes in closely related fish species exhibiting opposing growth paradigms. These results further support the role that the zebrafish and giant danio can play important model organisms for determinate and indeterminate growth.

Effects of short-term growth hormone treatment on liver and muscle transcriptomes in rainbow trout (Oncorhynchus mykiss)

Although studies have established that exogenous growth hormone (GH) treatment stimulates growth in fish, its effects on target tissue gene expression are not well characterized. We assessed the effects of Posilac (Monsanto, St. Louis, MO), a recombinant bovine GH, on tissue transcript levels in rainbow trout selected from two high-growth rate and two low-growth rate families. Transcript abundance was measured in liver and muscle with the Genome Research in Atlantic Salmon Project (GRASP) 16K cDNA microarray. A selection of the genes identified as altered by the microarray and transcripts for insulin-like growth factors, growth hormone receptors (GHRs), and myostatins were measured by real-time PCR in the liver, muscle, brain, kidney, intestine, stomach, gill, and heart. In general, transcripts identified as differentially regulated in the muscle on the microarray showed similar directional changes of expression in the other nonhepatic tissues. A total of 114 and 66 transcripts were identified by microarray as differentially expressed with GH treatment across growth rate for muscle and liver, respectively. The largest proportion of these transcripts represented novel transcripts, followed by immune and metabolism-related genes. We have identified a number of genes related to lipid metabolism, supporting a modulation in lipid metabolism following GH treatment. Most notable among the growth-axis genes measured by real-time PCR were increases in GHR1 and -2 transcripts in liver and muscle. Our results indicate that short-term GH treatment activates the immune system, shifts the metabolic sectors, and modulates growth-regulating genes.

Zebrafish and giant danio as models for muscle growth: determinate vs. indeterminate growth as determined by morphometric analysis

The zebrafish has become an important genetic model, but their small size makes them impractical for traditional physiological studies. In contrast, the closely related giant danio is larger and can be utilized for physiological studies that can also make use of the extensive zebrafish genomic resources. In addition, the giant danio and zebrafish appear to exhibit different growth types, indicating the potential for developing a comparative muscle growth model system. Therefore, the present study was conducted to compare and characterize the muscle growth pattern of zebrafish and giant danio. Morphometric analyses demonstrated that giant danio exhibit an increased growth rate compared with zebrafish, starting as early as 2 wk posthatch. Total myotome area, mean fiber area, and total fiber number all exhibited positive correlations with larvae length in giant danio but not in zebrafish. Morphometric analysis of giant danio and zebrafish larvae demonstrated faster, more efficient growth in giant danio larvae. Similar to larger teleosts, adult giant danio exhibited increased growth rates in response to growth hormone, suggesting that giant danio exhibit indeterminate growth. In contrast, adult zebrafish do not exhibit mosaic hyperplasia, nor do they respond to growth hormone, suggesting they exhibit determinate growth like mammals. These results demonstrate that giant danio and zebrafish can be utilized as a direct comparative model system for muscle growth studies, with zebrafish serving as a model organism for determinate growth and giant danio for indeterminate growth.

Cloning of the growth hormone cDNA of alligator gar Atractosteus spatula and its expression through larval development

The alligator gar (Atractosteus spatula) is the largest freshwater fish inhabiting rivers draining into the Gulf of Mexico. This primitive fish shows a fast growth rate since its early larval stages. This is attributed to the action of growth hormone (GH), an anterior pituitary gland hormone responsible for linear growth in vertebrates that can also be expressed in extrapituitary adult tissues and in fish embryos. The present research was aimed at obtaining the GH coding sequence of the alligator gar and studying its expression through larval development. A cDNA was obtained by RT-PCR, cloned and sequenced. The alligator gar GH cDNA sequence shares 98% nucleotide similarity with that reported for Lepisosteus osseus, indicating a very slow evolution of the GH within the primitive fish, in contrast with the burst of changes observed in euteleosts. Using RT-PCR and RNA nuclease protection assays, GH transcripts were detected at very high levels in eggs, embryos and in several larval stages. These data suggest that the GH may play an important role during embryogenesis in fish. The better understanding of alligator gar larval physiology will facilitate the culture of larvae and juvenile gar and consequently may allow the restoration of their natural populations.

Effect of dietary vitamin E level on growth, tissue lipid peroxidation, and erythrocyte fragility of transgenic coho salmon, Oncorhynchus kisutch

This study was conducted to investigate the effect of dietary vitamin E concentration on growth performance, iron-catalyzed lipid peroxidation in liver and muscle tissue, and erythrocyte fragility of transgenic growth hormone coho salmon (Oncorhynchus kisutch). Fish were fed one of four isoenergetic and isonitrogenous experimental diets that contained either 11, 29, 50, or 105 IU of vitamin E/kg. Following the 10-week feeding trial, no significant (P>0.05) diet-related differences were detected in growth, whole body proximate composition or erythrocyte fragility. The vitamin E contents of liver and muscle, however, were affected by the dietary treatment. Fish fed diets containing > or =50 IU of vitamin E/kg had significantly increased vitamin E concentrations in their tissues. Iron-catalyzed lipid peroxidation of liver and muscle tissue of fish fed elevated dietary vitamin E (> or =50 IU vitamin E/kg diet) was significantly lower (P<0.05) than that noted for fish fed the diet containing no supplemental vitamin E. The results indicated that changes in tissue lipid peroxidation measurements precede clinical signs of sub-optimal vitamin E intake.

The effects of recombinant bovine somatotropin (rbST) on tissue IGF-I, IGF-I receptor, and GH mRNA levels in rainbow trout, Oncorhynchus mykiss

Numerous studies demonstrated that rbST increased growth rates in several fish species, and several species exhibit GH production in tissues other than the pituitary. The role of tissue GH and IGF-I in regulating fish growth is poorly understood. Therefore an experiment was conducted to examine the effects of rbST treatment on tissue GH, IGF-I, and IGF-I receptor-A (rA) expression in rainbow trout. Rainbow trout (550 +/- 10 g) received either intra-peritoneal injections of rbST (120 microg/g body weight) or vehicle on days 0 and 21, and tissue samples were collected on days 0, 0.5, 1, 3, 7, and 28 (n = 6/day/trt). Total RNA was isolated and assayed for steady-state levels of IGF-I, IGF-IrA, and GH mRNA using quantitative RT-PCR. Insulin-like growth factor-I mRNA levels increased in liver, gill, gonad, muscle, brain, and intestine in response to rbST treatment (P < 0.10). Liver IGF-I mRNA increased (P < 0.01) 0.5 day after treatment and remained elevated throughout the trial. Intestine IGF-I mRNA increased (P < 0.05) in treated fish from day 1 to day 3, then decreased to day 7 and increased again at day 28, and remained elevated above control levels throughout the trial. Gill IGF-I mRNA levels increased (P < 0.05) 1 day after treatment and remained elevated throughout the trial. Heart IGF-IrA mRNA levels decreased (P < 0.05) while gonad GH mRNA levels increased (P < 0.10) following rbST treatment. These results demonstrate that rbST treatment increased IGF-I mRNA levels in extra-hepatic tissues, and decreased heart IGF-IrA and increased gonad GH mRNA levels. Because the primary source for endocrine IGF-I is liver, the increased IGF-I mRNA reported in extra-hepatic tissues may indicate local paracrine/autocrine actions for IGF-I for local physiological functions.

Photoperiod regulation of plasma growth hormone levels during induced smoltification of underyearling Atlantic salmon

Earlier studies have established that increased daylength increases plasma growth hormone (GH) levels during spring smoltification of yearling Atlantic salmon. Recently, the Atlantic salmon aquaculture industry has started the production of underyearling ("summer") smolts. This involves fast juvenile growth on continuous light (24L), the transfer of juveniles over 8 cm in length to short day (12L) for 6 weeks in the summer, followed by transfer to 24L for another 6 weeks before transfer to seawater in late October. Three groups were studied in fresh water from July to the following May in order to elucidate the GH response to this photoperiod manipulation: one group was kept on 24L throughout (long-day group), while the other two groups were exposed to short day from July 15th. Of these, one was brought back onto long day on September 1st (winter group) while the other was kept on short day (short-day group). Plasma GH levels of the long-day group were around 1.6 ng/ml throughout the study. The short-day transfer suppressed GH levels to 0.7 ng/ml within 2 weeks (short-day and winter groups). The long-day transfer (winter group) increased GH levels to 11 ng/ml within 3 weeks, and this elevation of GH levels was sustained for about 3 months, before declining to pretreatment levels. The study demonstrates that underyearling Atlantic salmon react to increased daylength in a way similar to traditional yearling smolts. It also demonstrates for the first time that decreased daylength can suppress plasma GH levels in fish. It is concluded that winter photoperiod manipulation causes an out-of-season initiation and completion of the parr-smolt transformation of underyearling Atlantic salmon and that growth hormone plays a major role in this process.

Growth hormone, sexual maturity and steroids in male carp (Cyprinus carpio)

Samples of pituitary, blood plasma and gonad were taken from male carp. The growth hormones (GH) in the pituitary and plasma were measured in fish of various body weights (BW) and degrees of gonad development, and compared with the levels of 17 beta-estradiol (E2), testosterone (T), 17 alpha-hydroprogesterone (17-P), 11-ketotesterone (11-KT) and progesterone (P) in the testes and plasma. The gonadosomatic index increased rapidly with BW from 100 to 600 g, and then decreased at 900 g. The pituitary GH did not change with BW, but plasma GH was higher in fish weighing 300 +/- 50 and 600 +/- 50 g, than in fish weighing 900 +/- 50 g. In fish weighing 150 +/- 50 to 300 +/- 50 g, the level of T rose significantly in the testes (2.27 ng g-1) and plasma (1.3 ng g-1); E2 was very low in both testes (0-30 pg g-1) and plasma (11-28 pg ml-1), increasing as BW rose from 150 to 600 g. The level of P rose mainly at BW of 300 +/- 50 and 600 +/- 50 g: from 0 to 25 ng g-1 in the testes and from 0 to 17 ng ml-1 in the plasma. The level 17-P rose from 2.5 to 20 ng g-1 in the testes at 600 +/- 50 g BW, but no significant change was recorded in the plasma. The level of 11-KT rose significantly in the tests of fish at 300, 600 and 900 g (0.5-6 ng g-1). The application of different steroids (E2, T and 17-P) on a primary culture of pituitary cells led to the release of GH. Release was significantly higher (P < 0.05) after 4 h at steroid concentrations of 10(-6) M.

Recombinant flounder growth hormone from Escherichia coli: overexpression, efficient recovery, and growth-promoting effect on juvenile flounder by oral administration

An efficient production method for recombinant flounder growth hormone (r-fGH) from Escherichia coli was developed and the biological activity of purified r-fGH was examined using juvenile flounder. The use of bicistronic construction in the expression plasmid resulted in the production of over 40% of the E. coli cellular protein as r-fGH. The r-fGH was recovered from cell lysates following inclusion body washing, solubilization and refolding in sodium dodecylsulfate (SDS) solution, and removal of contaminated proteins with secondary butanol treatment. The SDS content in purified r-fGH solution was adjusted to appropriate levels by diafiltration. More than 47% of the r-fGH was recovered from the E. coli cell lysates and the purity of recovered r-fGH was 98%. The oral administration of purified r-fGH to juvenile flounder, once a week for 4 weeks at a dosage of 40 micrograms r-fGH g-1 fish body weight, resulted in significant increases both in weight and length. These results of overexpression, simple purification with high recovery yield and purity, and good growth-promoting activity of the r-fGH suggest that the production scheme described in this study is useful for the potential application of r-fGH in fish farming.

Growth hormone, gonad development, and steroid levels in female carp

The pituitary and plasma growth hormone (GH) levels of female carp (Cyprinus carpio L.) were measured in fish of various sizes and degrees of maturity, and were matched against the levels of 17 beta-estradiol (E2), testosterone (T), 17 alpha-hydroxyprogesterone (17-P), and progesterone (P) in the ovary and plasma. The short-term action of the above hormones and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20-P) on the release of GH was examined in vitro in primary culture pituitary cells. The gonadosomatic index (%GSI) increased rapidly in specimens when they had attained 900 +/- 50 g body weight (BW). The pituitary and plasma GH levels increased between 150 and 600 g BW (when oocytes reached the stage at which lipoprotein appeared in the cytoplasm), but at 900 g BW (with oocytes in vitellogenesis) the plasma GH dropped, while pituitary GH remained high. E2 increased with BW, reaching its maximum at 600 and 900 g BW in the ovary and plasma, respectively. Similar patterns were found in the levels of T and P, both hormones reaching their maximum levels at 900 g BW. The level of 17-P was very low and did not increase in proportion to BW. The application of various concentrations of different steroids on a primary culture of pituitary cells led to release of GH. The highest degrees of release were obtained from 10(-6) and 10(-7) M E2, 10(-6) M T, 10(-7) M 17-P and 10(-8) M 17,20-P. In all these cases, hormone treatment effected higher release of GH than was found in the control. A model of the relationship between GH and the steroids associated with maturation is proposed.

Bombesin acts to suppress feeding behavior and alter serum growth hormone in goldfish

The acute effects of a single injection of bombesin (BBS) on feeding behavior and serum growth hormone (GH) levels in goldfish were examined. When injected intraperitoneally (IP), BBS (0.5-100 ng/g) caused a dose-dependent decrease in food intake within 30 and 45 min of administration; maximal suppression was achieved at 50 ng/g BBS and was accompanied by an elevation in serum GH levels. Associated with IP injection of BBS was a pronounced spitting out behavior in which food pellets were taken into the oral cavity but immediately expelled. When injected into goldfish deprived of food for 72 h, 50 ng/g BBS was still potent in suppressing feeding behavior and increasing serum GH. Additionally, IP injection of BBS (10 or 100 ng/g) into groups of fish caused a significant increase in circulating serum GH levels at 1.5 h postinjection. Finally, when injected into the third brain ventricle (ICV), 60 ng/g BBS also caused a suppression in food intake and a concomitant increase in serum GH. Groups of fish injected ICV with 5 or 50 ng/g BBS also exhibited a graded increase in serum GH levels at 45 min postinjection. Overall, these data are the first to demonstrate in any lower vertebrate that a neuropeptide acts to suppress food intake and cause concomitant alterations in circulating serum GH levels, following either peripheral or central administration.

Hormonal replacement therapy in fish:human growth hormone gene function in hypophysectomized carp

Transgenic common carp,Cyprinus carpio, produced by the microinjection of fertilized eggs with a linearized chimeric plasmid pMThGH, a human growth hormone (hGH) gene with a mouse metallothionein-1 (MT) gene promoter in pBR322, were used to produce F1 and F2 transgenics. Following hypophysectomy of the transgenic F2 common carp, non-transgenic common carp and non-transgenic crucian carp, growth was monitored for up to 110 days. In addition, recombinant hGH was injected subcutaenously into a group of the non-transgenic crucian carp. Growth rate analyses indicated that (1) hypophysectomy of non-transgenic common carp and crucian carp results in the cessation of growth, (2) hGH administration can stimulate the growth of hypophysectomized crucian carp and (3) hypophysectomized hGH-transgenic common carp continue to grow in the absence of their own growth hormone, suggesting that the hGH-transgene is being expressed in tissues other than the pituitary.

Effect of insulin in the diet on the growth of European eels (Anguilla anguilla L.)

The effect of oral administration of insulin, in various concentrations, on the growth of European eels (Anguilla anguilla L.) was studied. In order to determine whether the insulin penetrated through the stomach or gills to the blood system, 5 ml insulin, suspended in an 0.6% solution of NaCl, was inserted via the mouth of eels, and the insulin content in the blood measured by radioimmunoassay immediately, and at one and two hours after administration. A control group was given 0.6% NaCl alone. Significantly increased levels of insulin in the blood plasma were found in eels which received high insulin concentrations compared to the control group. Eels administered 20 ppm and 40 ppm insulin in the diet grew significantly faster than a control group fed a diet without insulin, and a group fed 5 ppm insulin.

The effects of ovine growth hormone on protein turnover in rainbow trout

Ovine growth hormone (oGH) was administered to rainbow trout via an intraperitoneal cholesterol implant. After 21 days, plasma oGH levels were recorded as control group, less than 2 ng ml-1, i.e., not detectable, and oGH group, 19.2 +/- 2.8 ng ml-1. oGH-treated fish exhibited significantly increased whole-body growth rates, whole-body protein accretion rates, stimulated tissue protein synthesis, and tissue protein accretion rates. A dramatic decrease in white muscle protein concentration was also observed after oGH treatment. In some tissues (liver and stomach), elevated protein synthesis rates were the result of higher RNA/protein ratios. However, in other tissues (gill and ventricle), increased RNA activity accounted for the differences in rates of protein synthesis. The growth promoting effects of oGH on both whole-body and tissue protein turnover were generally accompanied with no change in the efficiency of deposition of newly synthesized protein. For the same ration size, the oGH group showed higher retentions of ingested nitrogen. It is concluded that oGH significantly enhances whole-body growth rates as a result of the stimulatory effect on protein synthesis rates with little effect on protein degradation.

An enkephalin analog stimulates growth of tilapia

A synthetic enkephalin analog (Tyr-D-Trp-Ala-D-Phe-NH2) was administered to juvenile hybrid tilapia (Tilapia nilotica ×T. aurea) by immersing the fish for 15 minutes per week into one of two doses of the hormone for 8 weeks. Growth, food conversion efficiency, body weight, specific growth rate, food conversion efficiency and feed consumption were all significantly increased as a result of enkephalin treatment. The low dose (10µg/100 ml water) of enkephalin analog had a better stimulation effect than that of the high dose (100µg/100 ml water). Liver protein and protein/DNA ratio were higher in both treatment groups than in the control group. Tissue-body indices and muscle proximate composition were similar in the treatment and control groups. The growth stimulation in fish treated with the enkephalin analog was possibly mediated by an increase in growth hormone secretion.

Growth hormone stimulates hepatic thyroxine 5'-monodeiodinase activity and 3,5,3'-triiodothyronine levels in rainbow trout (Salmo gairdneri)

Intraperitoneal injection of rainbow trout (Salmo gairdneri) with 0.4 microgram/g of human growth hormone (hGH) increased plasma levels of 3,5,3'-triiodo-L-thyronine (T3) and Vmax of the hepatic microsomal 5'-monodeiodinase enzyme (5'D) that converts thyroxine (T4) to T3, with no effect on Km or plasma T4 levels. A dose of 0.4 microgram hGH/g increased both plasma T3 and Vmax as early as 8 hr postinjection (pi). Maximal levels for both parameters occurred at 24 hr pi and significant stimulation was sustained to 48 hr pi. In trout injected with hGH over a dose range of 0.1-1.0 microgram/g and sampled at 24 hr pi, both Vmax and plasma T3 increased in a dose-dependent manner. It is concluded that the increase in the level of functional hepatic 5'D may contribute to the rapid hGH-induced elevation in plasma T3.

Interaction between ovine growth hormone and triiodo-L-thyronine on metabolic reserves of rainbow trout,Salmo gairdneri

Rainbow trout (Salmo gairneri) were given slow-release coconut oil implants which contained triiodo-L-thyronine (T3) and were subsequently administered ovine growth hormone (oGH) (either 0.24 or 2.5 μg/g body weight) or saline every seventh day for four injections. The purpose of the study was to examine the interactions between oGH and T3 on several aspects of the metabolism in rainbow trout.Trout treated with T3 alone had higher carcass water content, lower liver glycogen, higher plasma T3 levels and lower plasma cholesterol, triglyceride and protein levels compared with the controls implanted with coconut oil implants alone. Trout treated with oGH alone had higher condition factors, lowered carcass total lipid content, elevated liver lipid and RNA content, and elevated plasma T3 and L-thyroxine (T4) levels compared with the coconut oil-implanted and saline-injected controls. Trout treated with T3 and oGH had lower liver glycogen content, higher plasma T3 and fatty acid levels and lower plasma T4, cholesterol and triglyceride levels compared with the controls given coconut oil implants and saline injections alone. There were no apparent effects of either hormone alone or in combination on liver: body mass ratios, liver DNA content, liver RNA:DNA ratios, liver RNA:protein ratios, liver protein:DNA ratios and liver protein content.The data suggest an interaction between oGH and T3 as regards the regulation of condition factor, carcass water content, carcass and liver total lipid content, liver RNA content, plasma fatty acid and plasma protein content.

Plasma kinetics of injected recombinant chicken somatotropin in juvenile coho salmon (Oncorhynchus kisutch) using a homologous radioimmunoassay

Although somatotropins are potent growth promoters in salmonids, there is little information on how these proteins are metabolized by poikilotherms. In the present study, the plasma uptake and clearance rates of recombinant chicken somatotropin (rcGH) were investigated in juvenile coho salmon (Oncorhynchus kisutch). Two doses of rcGH were administered by intraperitoneal (ip) or intramuscular (im) injection and blood samples were collected over a period of 32 days. A specific radioimmunoassay was validated and used to discriminate rcGH from endogenous somatotropin. Plasma rcGH concentration was proportional to the dose delivered, but uptake and clearance rates were found to be independent of dose (between 0.5 and 5.0 μg/g). Absorption of rcGH into the plasma was faster from the im site, but the peak levels attained were similar after im or ip treatment (using the same dose) as was area under the curve. Plasma half-life was calculated from the declining phase of the uptake/clearance profile but the results were biased by the concurrent uptake of rcGH from the ip or im reservoir of material, resulting in an over-estimation of the true half-life value. Effective treatment doses and intervals are discussed.

Effects of cortisol and growth hormone replacement on osmoregulation in hypophysectomized coho salmon (Oncorhynchus kisutch)

Both cortisol and GH were able to reverse partially the effects of hypophysectomy on coho salmon (Oncorhynchus kisutch) as judged by improved seawater (SW) tolerance after long-term treatment; however, neither hormone significantly restored gill Na+, Na+,K+-ATPase activity. In the first experiment, gill Na+,K+-ATPase activity remained low in hypophysectomized (Hx) coho treated with cortisol (15 micrograms/g body wt, suspended in cocoa butter) for 96 hr (48 hr in fresh water followed by 48 hr in seawater). In addition, plasma sodium levels were higher in the cortisol-treated Hx animals compared with those in untreated controls. In the second experiment, treatment with cortisol-filled Silastic capsules and implants of bovine GH (mixed with cholesterol in a ratio calculated to yield a dose of 1.5 microgram/g body wt/week) for 12 days also failed to alter gill Na+,K+-ATPase activity, but did reduce plasma sodium levels in animals transferred to SW for 48 hr. These results suggest that these hormones may be involved in the development of hypoosmoregulatory ability in coho salmon. However, the failure of either hormone to restore gill Na+,K+-ATPase activity suggests that a combination of these hormones and/or an additional hormone(s) acting in a synchronized fashion may be required for full effectiveness.

Effects of cortisol and growth hormone on osmoregulation in pre- and desmoltified coho salmon (Oncorhynchus kisutch)

Salmonid species which undergo smoltification show a concurrent enhancement in saltwater (SW) osmoregulatory ability. This developmental change is marked by an increase in SW tolerance and gill Na+,K+-ATPase activity which appears to result, in part, from an increase in gill chloride cell density. Previous studies have suggested that cortisol and growth hormone (GH) may stimulate SW osmoregulatory mechanisms in salmonids. In this study, these hormones were examined for their ability to induce smoltification-associated osmoregulatory changes in pre- and desmoltified coho salmon (Oncorhynchus kisutch). Cortisol treatment for 12 days increased gill Na+,K+-ATPase activity in presmolts and gill residual (Na+,K+-independent) ATPase activity in both groups. Chloride cell density in presmolt primary and secondary lamellae and in desmolt secondary lamellae was increased as well. The rise in plasma sodium levels in fish transferred to SW was reduced only in desmolts. Treatment with bovine GH for 12-13 days increased gill Na+,K+-ATPase activity in presmolts and in desmolts. However, GH treatment in either group did not increase gill residual ATPase activity or alter plasma sodium levels in SW-transferred animals. Gill chloride cell density in presmolts also was unaffected (desmolts were not examined). Thus, both cortisol and GH are partially able to produce changes similar to those observed during smoltification. The contrasting effects of these hormones on gill chloride cell density and gill residual ATPase activity suggest that cortisol may stimulate chloride cell proliferation and/or differentiation, whereas GH may act specifically to increase gill Na+,K+-ATPase activity.

Effects of thyroxin, cortisol, growth hormone, and prolactin on lipid metabolism of coho salmon, Oncorhynchus kisutch, during smoltification

Juvenile coho salmon, Oncorhynchus kisutch, were either immersed in thyroxin-containing water (T4; 20 micrograms/ml) or implanted with cortisol (5 mg), bovine growth hormone (GH; 1.5 microgram/g body wt), or ovine prolactin (PRL; 1.5 microgram/g body wt), both early and late in smoltification. T4 and cortisol treatment stimulated lipid mobilization in parr. T4-stimulated lipid mobilization was indicated by decreased total lipids, primarily as triacylglycerols, and increased lipolytic enzyme (triacylglycerol lipase) activity in the liver and dark muscle. T4-stimulated lipid mobilization from mesenteric fat was indicated by decreased total tissue mass and by increased lipase activity. Cortisol caused significant reductions in total lipid concentration and triacylglycerol content of the liver and dark muscle; these effects were accompanied by increased lipase activity. Cortisol treatment did not affect mesenteric fat total lipid concentration, total tissue mass, or triacylglycerol content. However, cortisol implantation did enhance mesenteric fat lipase activity. Thyroxin and cortisol treatment failed to elicit alterations in the pattern of tissue lipid mobilization of smolts. GH stimulated lipid mobilization from coho salmon parr. Depletion of liver total lipids was accompanied by increased lipolytic enzyme (triacylglycerol lipase) activity. GH had limited effects on dark muscle and mesenteric fat. In smolts, GH had virtually no effect on lipid mobilization. PRL strongly stimulated lipid mobilization in parr; this effect was evident in all depots studied (liver, dark muscle, mesenteric fat). Decreases in total lipid concentration, or in total tissue mass (mesenteric fat), were accompanied by increased lipase activity and generally resulted in reduced tissue triacylglycerol content. Smolts appeared refractory to PRL treatment. Smolts (characteristically possessing elevated liver lipase activity) that were hypophysectomized exhibited low levels of liver lipase activity. Cortisol replacement restored enzyme activity to approximately the same levels as those observed in sham-operated controls. GH replacement restored lipase activity, but not to the levels observed in sham-operated controls. These results indicate that T4, cortisol, GH, and PRL all stimulate lipid mobilization in developing salmon by enhancement of lipolysis and suggest that T4, cortisol, GH, and PRL are among the factors which contribute to smoltification-associated lipid depletion.

The effect of 3,3',5-triiodo-L-thyronine and 17-α-methyltestosterone on growth and body composition of the glass stage of the eel (Anguilla anguilla L)

This study was undertaken to determine the influence of orally administered 3,3',5-triiodo-L-thyronine (T3) or 17-α-methyltestosterone (MT) on growth and body composition of the eel (Anguilla anguilla L.) during the glass stage.Elvers receiving 20 or 40 ppm of T3 in the food weighed significantly more (P < 0.05) than controls. However, after 61 days of treatment a dosage of 60 ppm was not efficacious.Terminal percentages of body protein were significantly lower (P < 0.05) in elvers that received 20 ppm or 40 ppm T3 in their diets, than in the control. Crude body fat content was higher (P < 0.05) in elvers receiving 20 ppm (29% fat) or 40 ppm (28% fat), than in the controls (26% fat). Compared to the control, diets containing T3 at 20 or 40 ppm increased the body glucose concentration.Glass eels fed a diet containing 1 or 10 ppm MT grew significantly more slowly (P < 0.05) than the controls.Total body protein content was higher (P < 0.05), but total body crude fat content was lower (P < 0.05) in elvers fed a diet with 1 or 10 ppm MT compared to the controls. Total body glucose concentration of elvers administered 10 ppm MT was significantly lower (P < 0.05) than that of the control groups.

Hormonal effects on L-proline transport in coho salmon (Oncorhynchus kisutch) intestine

The hormonal control of proline transport in pyloric ceca was studied in regard to the effects of cortisol, growth hormone (GH), epinephrine, and 3-isobutyl-1-methylxanthine (IBMX). Cortisol pellets implanted in yearling freshwater (FW) salmon for 2 weeks elevated plasma cortisol levels six times above that of control fish. The maximal influx (Jmax) and the half-saturation constant (Kt) of proline influx were twofold greater in cortisol-treated fish than the values in controls; the apparent passive permeability coefficient (Pa) was significantly reduced in the former group. FW salmon implanted with GH for 2 weeks showed increased body weight gain and a higher Jmax of proline influx compared with that of control fish. GH treatment resulted in a higher Pa of proline influx as well as in a 30% increase in area-specific intestinal dry weight. Thus, GH and cortisol may play a regulatory role in intestinal amino acid absorption during salmon development. The in vitro effects of epinephrine and the phosphodiesterase inhibitor, IBMX, on short-circuit current (Isc) and proline influx in salmon intestine were examined. Epinephrine (10(-6) M) caused a rapid increase in negative Isc (mucosa, ground). Pyloric ceca preincubated with epinephrine for 30 min showed reduced total proline influx compared with influx in paired control tissues. Epinephrine increased and IBMX decreased the Kt of proline influx; IBMX also reduced Jmax. The possible interaction between the effects of epinephrine and IBMX on ion transport and Na+-coupled proline influx are discussed.

Effect of mammalian growth hormone on amino nitrogen mobilization in the eel

Hypophysectomy decreased plasma amino nitrogen (PAN) levels of Japanese eels. In contrast, administration of bovine or ovine growth hormone (GH; 2 micrograms/g) produced a delayed increase in PAN levels of both intact and hypophysectomized eels 48 hr after GH injection. The minimum dose of GH required to elevate PAN levels was found to be 0.1-1 micrograms/g body wt. The fact that GH treatment also increased PAN of hepatectomized eels indicates that the increased PAN was at least partly caused by the increased mobilization of amino nitrogen from body protein. GH also increased plasma free fatty acid content of intact and hypophysectomized eels 48 hr after GH injection in one experiment of the present study, but this effect was not reproducible in other experiments. No effect of GH administration was observed either in plasma glucose and lipid of intact and hypophysectomized eels 48 hr after the injection.

In vivo and in vitro effects of growth hormone on the incorporation of [14C]leucine into protein of liver and muscle of the eel

In vivo administration of ovine GH (2 micrograms/g body wt) increased [14C]leucine incorporation into protein of the liver, skeletal muscle, and opercular muscle of hypophysectomized eels. Addition of ovine GH into the medium (5 micrograms/ml) slightly increased [14C]leucine incorporation into protein of liver slices during 5 hr in vitro incubation, but did not affect protein synthesis from [14C]leucine in opercular muscle. In vivo pretreatment with ovine GH (2 micrograms/g body wt) 48 hr prior to tissue preparation clearly increased [14C]leucine incorporation into protein of liver slices in vitro. However, no statistically significant change was observed for in vitro incorporation of [14C]leucine into protein of opercular muscle of hypophysectomized eels which had been previously treated with ovine GH (2 micrograms/g body wt). These results indicate that ovine GH has a protein anabolic action in the liver and muscle of the eel and that compared to mammals a rather long lag period is needed to elicit such protein anabolic actions of GH in these animals.