GROWTH HORMONE REGULATES INTESTINAL NUTRIENT TRANSPORTERS IN MOZAMBIQUE TILAPIA Oreochromis mossambicus
Tilapia, one of the main finfish cultured worldwide, exhibit excellent growth in captivity. In vertebrates, including fish, the endocrine system orchestrates the production and release of hormones by integrating sensory information with an array of physiological functions in nearly every organ . Growth is largely regulated by g rowth hormone (GH), which is secreted by the pituitary gland. Once in circulation, GH can bind to its receptor (GHR) in target tissues, such as muscle, liver and intestine, to initiate physiological responses that include cell proliferation and differentiation, nutrient uptake, and protein synthesis . The intestine is the primary site for the uptake of nutrients required for growth. Proteins that transport oligopeptides, amino acids, sugars, water, and ions facilitate the uptake of nutrients across the intestinal epithelium. Little is known, however, on how GH affects intestinal nutrient uptake.
Our laboratory has developed a model for investigating whole-organism effects of GH by employing the Mozambique tilapia ( Oreochromis mossambicus). In this model, we surgically remove the pituitary gland (hypophysectomy; Hx ) and replace GH via intraperitoneal injections. With this approach, we showed that GHR expression in muscle, liver, and intestine of Hx fish was dramatically reduced following hypophysectomy ; an effect that was recovered by replacement with GH. Next , we showed that GH stimulates the expression of intestinal PEPT1, PEPT2, and GLUT2. These results indicate that GH is a key regulator of peptide and sugar transport in the intestine of tilapia. Alternatively, NKCC2 and SLC7 were suppressed by Hx and unaffected by GH; thus the expression of the Na+/K+/Cl- co-transporter, and amino acid transport is seemingly under the control of a pituitary factor other than GH.
[Supported by HATCH (#HAW02051-H), NOAA (#NA18OAR4170347), NIH (1R21DK111775-01) and NSF (IOS-1755016 and -1755131)]
