ARS | Publication request: EFFECTS OF RESTRICTED FEED INTAKE ON PLASMA LEVELS OF IGF-I AND ABUNDANCE OF HEPATIC IGF-I AND GH RECEPTOR MRNA IN CHANNEL CATFISH

Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 2, 2005
Publication Date: July 24, 2005
Citation: Peterson, B.C., Small, B.C. 2005. Effects of restricted feed intake on plasma levels of igf-i and abundance of hepatic igf-i and gh receptor mrna in channel catfish. American Society of Animal Science Vol. 83 Suppl. 1, p. 283.

Technical Abstract: Feed restriction and fasting of catfish are common management strategies during periods of environmental stress and disease. We have previously reported roles for GH and IGF-I in growth regulation of channel catfish, but effects of restricted feeding on the somatotropic axis are not known. Research was conducted to examine abundance of hepatic IGF-I and GH receptor (GHR) mRNA and plasma IGF-I in fed, restricted, and fasted channel catfish. One hundred and twenty fish (60.0 +/- 0.2 g) were randomly assigned to one of three treatments with four replicates each. The treatments were: 1) fed control (commercial catfish diet fed daily), 2) restricted (commercial diet fed every other day), and fasted (no feed). All fish were weighed and bled from the caudal vasculature on day 0, 21, and 42. On d 42, liver samples were excised from 8 fish per treatment (2 fish/tank), RNA was isolated, and relative abundance of hepatic IGF-I and GHR mRNA was determined by real time RT-PCR. Final weights of the fed control, restricted, and fasted fish were 110.4, 78.8, and 40.6 g, respectively. Plasma levels of IGF-I were higher (P < 0.001) in the fed and restricted fish (7.5 +/- 0.8 and 5.5 +/- 0.6 ng/ml, respectively) compared to fasted fish (1.4 +/- 0.6 ng/ml) at day 21. By d 42, differences in plasma levels of IGF-I were less dramatic between treatments, but tended to remain higher in fed controls (P < 0.01). Abundance of liver IGF-I mRNA was similar (P > 0.05) among treatments. However, GHR mRNA abundance decreased 60% in the both restricted and fasted fish compared to fed controls (P < 0.001). Results showed that restricting feed intake decreased plasma IGF-I without a significant change in abundance of IGF-I mRNA. Results also demonstrated that GHR mRNA is down regulated when feed is limited. Higher plasma levels of IGF-I in the fed controls support IGF-I's role in growth regulation of channel catfish. One of the mechanisms through which growth may be inhibited in food restricted catfish is through a reduction in GHR and thus IGF-I.