Ritmo diário de genes relacionados com o eixo somatotrópico e resposta gênica causada pela aplicação única de GH em Tilápia

Abstract

With the aim of assess the existence of biological rhythms and the effects of exogenous GH administration on the somatotropic axis of tilapia (Oreochromis niloticus) fed either at ML or at MD, two experiments were performed at the University of Murcia-ES, using 96 animals (48 fish per experiment) with an average body weight of 88.97 ± 36.8 g (mean ± S.D.). In both experiments, we evaluated the mRNA expression, by means of qPCR, of gh in the pituitary; pacap-1a and pacap-1b in the hypothalamus; ghr-1, ghr-2, igf-1, igf-2a and igf-2r in the liver; and ghr-1, ghr-2, igf-1ra e igf-2r in the muscle. In addition, plasma GH was evaluated by means of ELISA. In the first experiment, the animals were divided into 8 groups (n=6), 4 of them were fed at ML and 4 were fed at MD. Samples from pituitary, hypothalamus, liver, muscle and plasma were collected every 6 hours (ZT3, ZT9, ZT15 and ZT21). In each time point, all animals from one of the groups fed at ML and one of the groups fed at MD were collected. Data from gene expression and plasma GH were subjected to Cosinor test (p<0.05) to detect the presence of daily rhythms. Only ghr-1 and ghr-2 in ML-fed animals displayed significant rhythms in liver, located at a similar acrophase (2:59 hrs). In muscle, only ghr-1 showed a significant rhythm, with an acrophase at 4:10 and 9:01 in fish fed at ML and MD, respectively. In the second experiment, fish were divided into 8 groups (n=6), with 4 groups being fed at ML and 4 fed at MD. In 2 groups fed at ML, one group was injected with GH and the other with saline solution (control), both at ZT3; for the other 2 groups, one was injected with GH and the other with saline solution, both at ZT15. The same procedure was performed with the fish fed at MD. Data were subjected to one-way ANOVA followed by a Tukey post hoc test (p<0.05) to check for statistically significant differences between groups and an F-test to check for differences between each injected groups and its respective control. GH administration did not induce any effect on the genes studied in hypothalamus and pituitary. igf-2a gene expression in the liver and igf-2r expression in the muscle, in animals fed at ML, were stimulated by GH administration at ZT15. ghr2 was stimulated, both in liver and muscle, by GH administration at ZT15, although the response was higher in animals fed at ML than in fish fed at MD.