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Title: Protein turnover in Salmonids : sexual maturation and hormonal control
Author: Martin, Niall M. B.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1990
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Aspects of tissue protein metabolism were studied in different groups of Atlantic salmon (Salmo salar). Firstly, 2 groups of sea water salmon were fasted for 3 and 5 days, prior to the measurement of tissue fractional rates of protein synthesis (ks, %day), using the method of 3H-phenylalanine flooding. The sensitivity of liver and gill to a short-term fast was indicated by their reduced rates of ks, while in other tissues such as ventricle, stomach and red muscle protein synthesis was unaffected. Both liver and gill are tissues which show the greatest capacities to synthesise protein, expressed by their high RNA contents. The response of tissue protein metabolism to sexual maturation was investigated in 2 groups of salmon undergoing river migration, tissues were analysed in both July salmon (sexually maturing) and in more mature October salmon. White muscle contributed most of the amino acids required during maturation, denoted by the high loss of protein and RNA from the flesh of the salmon by October. Red muscle, gill and ventricle were tissues which were protected during maturation, showing only slight changes in rates of protein metabolism. Liver, stomach and ovary on the other hand increased their RNA and protein contents, and showed increased rates of protein synthesis. The liver however, displayed a greater increase in its RNA concentration than protein i.e. the liver by October had increased its capacity to produce large amounts of export proteins. Despite the overall loss by stomach and other visceral tissues of protein and RNA, the stomach by October showed a dramatic 5-6 fold increase in its rate of protein synthesis. It was concluded that smooth muscle may have a particular role or function in the sexually mature fish. Factors controlling these in vivo changes in protein synthesis were investigated using rainbow trout (Oncorhynchus mykiss) isolated hepatocytes and a smooth muscle preparation in vitro . Anabolic actions on hepatocyte protein synthesis were exhibited by insulin, thyroxine and in the absence of fetal calf serum by triiodothyronine. The synthetic glucocorticoid, dexamethasone, unlike its actions in muscle, also exhibited an anabolic action on hepatocytes, by raising RNA and protein levels in cells from immature fish, while increasing protein synthesis rates in liver cells of sexually mature fish. Estradiol, like dexamethasone, stimulated rates of protein synthesis over 24 hours. However, hydroxyprogesterone caused no change in protein synthesis and decreased the effect of estradiol. Estradiol also increased protein synthesis rates in smooth muscle by some 30%. However, hydroxyprogesterone, as in liver cells, caused no stimulation of protein synthesis and again decreased the estradiol stimulated ks. It was proposed that estradiol is one of the factors involved in increasing the ks in the stomach of the sexually maturing salmon, while progesterone regulates the action of estradiol towards the end of sexual maturation, when such an effect of estradiol on liver and smooth muscle ks is unnecessary.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available