Submitted to: General and Comparative Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2005
Publication Date: 2/6/2006
Citation: Picha, M., Silverstein, J., Borski, R. 2006. Discordant regulation of hepatic IGF-I mRNA and circulating IGF-I during compensatory growth in a teleost, the hybrid striped bass (morone chrysops x morone saxatilis). General and Comparative Endocrinology. 147(2):196-205. Interpretive Summary: Compensatory growth is a term used to describe the subsequent rapid growth displayed by animals that have had their growth restricted for a time. The hormonal changes that regulate the growth system during the rapid compensatory growth are not well know, however if these changes were defined we could possibly improve growth rates by manipulating regulatory hormone levels. The hormone insulin-like growth factor (IGF-I) is a central molecule in the growth axis. Changes in the blood levels of this hormone are correlated with fish growth rates. In this study with hybrid striped bass, feed restriction was used to hold back growth of some fish. After 4 weeks, feeding was restored to normal daily levels and fish that had been restricted grew more rapidly and more efficiently and they ate more feed than controls that had been fed daily. An inverse relationship between blood levels and the mRNA levels of IGF-I typically not seen under normal growing conditions was apparent. These results may suggest approaches to defining compensatory growth characteristics.
Technical Abstract: Compensatory growth (CG) is a period of growth that exceeds normal rates after animals are alleviated of certain growth-stunting conditions. Little is known, however, about the endocrine control of CG in teleosts. So, our aim was to induce CG in juvenile hybrid striped bass (HSB, Morone chrysops x Morone saxatilis) through manipulations in feeding regimen, and then determine whether changes in circulating insulin-like growth factor-I (IGF-I) and hepatic IGF-I gene expression accompany the CG response. A considerable catabolic state was induced after 4 weeks of reduced feeding in which HSB were fed a total of two times (once each in the 2nd and 3rd week). Negative energy balance was evidenced through weight loss (-3.4 % BW) and a significant drop in hepatosomatic index (HSI) from a value of 3.71 to 1.46. Upon realimentation, in which HSB were fed ad libitum 2X/day, a significant CG response was observed over a 4-week period. The CG response was characterized by an elevated specific growth rate, hyperphagia, restoration of the HSI and an improvement in feed conversion, all relative to controls that were fed normally throughout the experiment. Moreover, the CG response and catabolic state preceding it were marked by a discordant regulation in the expression of hepatic IGF-I mRNA and plasma IGF-I levels, the latter parameter paralleling changes in growth. The catabolic state was accompanied by an 82% increase in hepatic IGF-I mRNA while levels of plasma IGF-I were significantly depressed relative to controls. During the subsequent CG response, however, hepatic IGF-I mRNA decreased by 61% while plasma IGF-I increased by 86%. This inverse relationship may suggest a novel mechanism through which CG is achieved: hepatic IGF-I mRNA is accumulated and stored during periods of catabolism so, when conditions improve, this pool might be rapidly translated and released into circulation.