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United States Department of Agriculture

Agricultural Research Service

Title: Serum Somatotropin, Insulin-Like Growth-Factor-I, and Antibody Production in Rainbow Trout (Oncorhynchus Mykiss) Treated with Sustained-Release Bovine Somatotropin (Rbst)

Authors
item Simpson, P - UNIV. OF IDAHO AVS
item Peterson, Brian
item Shelling, G - UNIV. OF IDAHO AVS
item Cain, K - UNIV. OF IDAHO CFW
item Hardy, R - UNIV. OF IDAHO AVS
item Overturff, K - USDA/ARS
item Ott, T - UNIV. OF IDAHO AVS

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2004
Publication Date: May 18, 2005
Citation: Biga, P.R., Peterson, B.C., Shelling, G.T., Cain, K.D., Hardy, R.W., Overturf, K., Ott, T.L. 2005. Serum somatotropin, insulin-like growth-factor-I, and antibody production in rainbow trout (Oncorhynchus mykiss) treated with sustained-release bovine somatotropin (rbST). Aquaculture 246:437-445.

Interpretive Summary: A study was conducted to examine the regulation of injected recombinant bovine somatotropin (rbST) in rainbow trout. Sixty-six rainbow trout (mean weight 550 ± 10 g) received either an injection of rbST (120 micrograms/g body weight) or saline on days 0 and 21. Blood samples were collected on days 0, 0.5, 1, 3, 7, and 28 of the study. As expected, rbST levels increased in circulation 12 h after treatment and continued to increase from day 0 to day 7 after treatment. Recombinant bST treatment increased serum insulin like growth factor-I (IGF-I) levels one week after treatment, while endogenous trout ST did not change during this time. These results suggest that the endogenous negative feedback control loop described in mammals is not activated by rbST in rainbow trout. However, it is demonstrated here that rbST does increase circulating IGF-I over time and rbST is detectable throughout the three-week injection period.

Technical Abstract: Previously, recombinant bovine somatotropin (rbST) increased growth rates in rainbow trout, Oncorhynchus mykiss. This response is thought to be under the control of the GH/IGF axis, as it is in mammals. However, the mechanisms regulating fish muscle growth are poorly understood. Therefore, an experiment was conducted to examine the growth-promoting effects of rbST in rainbow trout. Sixty-six rainbow trout (mean weight 550 ± 10 g) received either an injection (i.p.) of rbST (120 micrograms/g body weight) or vehicle on days 0 and 21. Blood samples were collected on days 0, 0.5, 1, 3, 7, and 28 and assayed in triplicate for rainbow trout somatotropin (tST), rbST, and IGF-I by radioimmunoassay. As expected, rbST levels increased (P<0.05) in circulation 12 h after treatment and continued to increase (P<0.05) from day 0 to day 7 after treatment. Recombinant bST treatment increased serum IGF-I levels (P<0.01) one week after treatment, while endogenous trout ST did not change during this time (P=0.28). Overall rbST increased circulating IGF-I while not affecting endogenous GH in the peripheral circulation. These results suggest that the endogenous negative feedback control loop described in mammals is not activated by rbST in rainbow trout, as rtST was unaffected by increased circulating rbST and IGF-I. However, it is demonstrated here that rbST does increase circulating IGF-I over time and rbST is detectable throughout the three-week injection period.

Last Modified: 7/22/2014
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