Jean Smal

Stimulation of parr-smolt transformation by hormonal treatment in Atlantic salmon (Salmo salar L.)

Abstract Atlantic salmon reared under natural conditions in a fresh water (FW) hatchery at Le Conquet (Brittany, 48°N) were treated with different hormones in order to trigger or advance the parr-smolt transformation and to improve seawater (SW) adaptability. In the first experiment, juveniles were implanted with ovine growth hormone (oGH) pellets (7 μ g/g body weight for pre-smolts, 25 μ g/g for parr) and compared with sham-operated and control salmon at different times of the year. Different results were observed following direct exposure to full salinity (35‰) SW depending on the date of treatment. Prior to smoltification (November, December and February), pre-smolts treated with oGH had higher gill Na + ,K + -ATPase activity in FW, lower plasma osmolarity after SW transfer, and higher growth rate in SW compared with sham and control fish. However, for pre-smolts and smolts treated during April, May or June, there was no difference between treated and untreated fish. At any time of year, oGH-implanted parr survived SW transfer better than sham and control fish. Using a recombinant trout growth hormone (rtGH) at lower doses (0.28 and 1.4 μ g/g), a high percentage survival was observed after direct SW transfer for both pre-smolts (100% after 30 days in SW compared with 86% in sham) and parr (65% compared with 0%). rtGH is at least 10 times more efficient than oGH for increasing gill Na + ,K + -ATPase and salinity tolerance. Treatments with cortisol (8 μ g/g in silastic pellets), 3,5,3′-triiodo-L-thyronine (T 3 , 20 mg/kg of food during 6 weeks), ovine prolactin (oPRL, 7 μ g/g) and oGH (7 μ g/g) were used on pre-smolts in October (8 months old). After direct SW exposure, only oGH-treated fish (alone or in combination with other hormones) were able to adapt, survive and grow. Both oPRL and oGH treatment increased gill Na + ,K + -ATPase activity in fish in FW; however, there was no improvement of SW adaptability in oPRL-implanted salmon.

A trout growth hormone is expressed, correctly folded and partially glycosylated in the leaves but not the seeds of transgenic plants

The growth hormone gene of the rainbow trout (tGH-II) was expressed in leaves of transgenic tobacco plants and seeds of transgenicArabidopsis plants using tissue-specific promoters. Although in the leaves and the seeds comparble amounts of tGH-II mRNA could be detected, the protein could only be identified in the tobacco leaves. Passage of the hormone into the secretory pathway, mediated by the signal sequence of the extracellular tobacco PRI-b (pathogenesis-related) protein, resulted in correct disulphide bridge formation and (partial) glycosylation of the hormone. In contrast, cytoplasmic expression resulted in misfolding and partial breakdown of the protein. The data demonstrate that synthesis, folding and glycosylation of heterologous proteins in plants is dependent both on subcellular location as well as on the tissue or cell type in which the protein is expressed.

The effects of gonadal development and sex steroids on growth hormone secretion in the male tilapia hybrid (Oreochromis niloticus × O. aureus)

Profiles of plasma growth hormone (GH) in male tilapia hybrid (Oreochromis niloticus x O. aureus) were measured and compared at different times of the year. The profiles did not appear to be repetitive, however, differences in their nature were observed at the different seasons; the most erratic profiles were seen in the height of the reproductive season (July), while the peaks were more subdued in the spring and disappeared in the autumn. Peaks in male fish were more prominent than in the females when measured in July. Perifused pituitary fragments from fish with a high GSI responded to salmon gonadotropin-releasing hormone (sGnRH) analog (10 nM-1 μM), while those from fish with a low GSI barely responded to even the highest dose. Exposure of perifused pituitary fragments from sexually-regressed fish to carp growth hormone-releasing hormone (cGHRH; 0.1 μM) or sGnRH (I μM) stimulated GH release only after injection of the fish with methyl testosterone (MT; 3 injections of 0.4 mg kg 1). The same MT pretreatment did not alter the response to dopamine (DA; 1 or 10 μM). GH pituitary content in MT-treated fish was lower than in control fish, which may be explained by the higher circulating GH levels in these fish, but does not account for the increased response to the releasing hormones. Castration abolished the response of cultured pituitary cells to sGnRH (I fM-100 nM) without altering either their basal rate of secretion or circulating GH levels. Addition of steroids to the culture medium (MT or estradiol at 10 nM for 2 days) enabled a GH response to sGnRH stimulation in cells from sexually regressed fish. Pituitary cells which had not been exposed to steroids failed to respond to sGnRH, although their response to forskolin or TPA was similar to that of steroid-exposed cells. It would appear, therefore, that at least one of the effects of the sex steroids on the response to GnRH is exerted proximally to the formation of cAMP, or PKC, presumably at the level of the receptor. An increase in the number of receptors to the GH-releasing hormones, following steroid exposure, would explain also the changing nature of the GH secretory profile in different stages of the reproductive season.

Protein uptake by intestinal macrophages and eosinophilic granulocytes in trout: An in vivo study

Summary— A homologous protein, recombinant trout somatotropin (rtST) and its heterologous counterpart, native bovine somatotropin (bST), were administered anally to juvenile rainbow trout (Oncorhynchus mykiss). Plasma levels of rtST, determioned by radio‐immunoassay, peaked between 15 and 60 min and remained high until 2 h after administration. Immunogold labelling was used to follow the routes of transfer of rtST and bST, and to observe potential interaction between the hormones and the cells constituting the first line of non‐specific defence, ie the macrophages infiltrated between epithelial cells, or dispersed in the subepithelial lamina propria, and eosinophilic granulocytes (EGCs) of the lamina propria, whose properties have been considered to be similar to mammalian mast cells. Macrophages were immunolabelled for the homologous and heterologous proteins. EGCs took up to the heterologous but not the homologous protein. This finding was confirmed using indirect immunofluorescence assay. EGCs could internalize foreign proteins transferred from the intestinal lumen to the lamina propria.