A Mammalian Growth Hormone‐Releasing Hormone Increases Serum Growth Hormone Levels and Somatic Growth at Suboptimal Temperatures in Tilapia

Abstract

The effects of a mammalian growth hormone‐releasing hormone (GHRH), PrebGRF(1–78)OH (bGHRH), on growth and serum growth hormone (GH) levels were investigated in tilapias Oreochromis mossambicus andO. niloticus × O. aureus. Fish were injected intramuscularly or implanted intramuscularly (Silastic or cholesterol implants) with distilled water, 0.1 μg/kg bGHRH, 1.0 μg/kg bGHRH, 10.0 μg/kg bGHRH, or 100.0 μg/kg bGHRH and compared to untreated controls, fish implanted with 60 mg/kg 17α‐methyltestosterone (MT), or a combination of bGHRH concentrations plus either MT, 0.01 μg/kg of a thyroid hormone (T3), or 0.01 μg/kg of a glucocorticoid (DEX). The bGHRH increased serum GH levels in tilapia maintained at suboptimal temperatures (18 C). Serum GH levels were highest (5.3–0.45 ng/mL) for fish injected with 10.0 μg/kg bGHRH. Fish implanted with a Silastic implant containing 10.0 μg/kg bGHRH had significantly higher (4.35–0.35 ng/mL) serum GH levels than those with an equivalent dosage in a cholesterol implant. The addition of MT, thyroid hormones, and glucocorticoids did not increase serum GH levels above those obtained for fish receiving bGHRH alone. Tilapia reared at suboptimal temperatures and implanted with 10.0 μg/kg and 100.0 μg/kg bGHRH had significantly greater increases in weight and length than control fish. Fish implanted with bGHRH, MT or bGHRH plus MT had significantly higher moisture and protein content, while fat and ash contents were significantly lower than controls or sham‐implanted fish. Fish implanted with bGHRH or bGHRH plus MT had significantly higher gonadosomatic indices than fish implanted with MT alone, shams or non‐treated controls. This study demonstrates that a mammalian GHRH stimulates release of GH, promotes somatic and gonadal growth and may affect reproductive performance in tilapia.

Lack of growth enhancement by exogenous growth hormone treatment in yellow perch (Perca flavescens) in four separate experiments

“…The failure of bGH or homologous rypGH treatment to promote growth in yellow perch is in contrast to other fish species in which exogenous GH treatment markedly stimulates growth under both optimal (Weatherley and Gill, 1987;Skyrud et al, 1989;Silverstein et al, 2000;Hunt et al, 2000) and sub-optimal (Adelman, 1977;Kelly et al, 1996;Leedom et al, 2002) rearing conditions. Further, the GH treatments induced no increase in IGF-I levels in our studies, as has been shown in several other fish species (Cao et al, 1989;Funkenstein et al, 1989;Moriyama, 1995;Moriyama et al, 1995;Shamblott et al, 1995).…”

Characterization and sexual dimorphic expression of Cytochrome P450 genes in the hypothalamic–pituitary–gonad axis of yellow catfish

“…Control groups were injected only with 5% ethanol/95% saline solution. In previous studies, injection of 1-100 lg MT per gram body weight into fish body has been shown to affect gonadal development and induce female-to-male sex inversion (Kelly et al, 1996;Sarter et al, 2006;Tan-Fermin et al, 1994). When different doses of MT (0, 1, 10 and 100 lg/g body weight) were injected into female yellow catfish, the levels of 17b-estradiol (E2) and 11-ketotestosterone (11-KT) in the blood were measured using the fish E2 ELISA Kit and 11-KT ELISA Kit (Enzyme-linked Biotechnology Company, Shanghai) as described previously (Parikh et al, 2006).…”

Mammalian Growth Hormone‐Releasing Hormone Indirectly Stimulates Sex Steroid Production in Tilapia

“…It has been reported that synthetic human growth hormone-releasing hormone (h-GHRH) (Peter et al 1984) and bovine GHRH (bGHRH) (Kelly et al 1996a) stimulate GH release in vivo in teleost fish. To date, common carp Cyprinius carpio.…”

“…sockeye salmon Oncorhynchus nerka and the Thai catfish Clarias macrocephalus GHRH have been sequenced (Vaughan et al 1992;Parker et al 1993;McRory et al 1995). Various GHRHs have been shown to stimulate GH secretion by increasing plasma GH levels in goldfish Carassius auratus (Peter et al 1984) and the Mozambique tilapia Oreochromis mossambicus (Melamed et al 1995;Kelly et al 1996a) and have stimulated GH release from pituitary cells of goldfish (Vaughan et al 1992), rainbow trout Oncorhynchus mykiss (Luo and McKeown 1989, 1991a, 1991bLuo et al 1990) and the Mozambique tilapia (Melamed et al 1995). Le Bail et al (1991) were able to demonstrate GH release from the pituitary cells of the chinook salmon Oncorhynchus tshawytscha utilizing a h-GHRH, however, goldfish pituitaries were unresponsive to this peptide .…”

“…The gonad incubation studies also examined the effects of GnRH-a and hCG to determine the target sites for bGHRH. The GHRH employed was a potent mammalian GHRH analog that has been shown to increase tilapia GH levels in previous studies (Kelly et al 1996a).…”