Effect of Twice Daily Administration of GH-releasing Peptide-2 for 10 Days on Growth Performance, Plasma GH Responses and Insulin-like Growth Factor-1 Concentrations in Swine

V Nou,H.G Lee,H Inoue,H Kuwayama,H Hidari,N Matsunaga

doi:10.5713/ajas.2003.1193

Abstract

An increase in frequency of administration of exogenous growth hormone (GH) or GH-releasing hormone was reported to be a model to increase blood circulating insulin-like growth factor-1 (IGF-1) and to improve growth performance in animals. We have investigated the effect of twice daily administration of GH-releasing peptide-2 (GHRP-2) on growth performance, GH responsiveness and plasma insulin-like growth factor IGF-1 in swine. We administered to eight swine, 3 control and 5 treatment, a twice daily s.c. injections of GHRP-2 (30 µg/kg BW) for a period of 10 days. Every day blood samples immediately taken before injections of GHRP-2 or saline, at 08:00 h and 16:00 h, were measured for IGF-1 concentrations. Blood samples for GH assay were collected every 20 min on days 1, 6 and 10, from 1 hour before and 3 h after GHRP-2 or saline injections at 08:00 h. GH peak concentrations and GH area under curve (GH AUC) on day 1, 6 and 10 in treatment group of swine were higher than those in control swine (p<0.05). Twice daily administration of GHRP-2 caused a significantly attenuation (p<0.05) of GH peak concentrations (80.25±13.87, 39.73±5.72 and 27.57±6.06 ng/ml for day 1, 6 and 10, respectively) and GH AUCs (3,536.15±738.35, 1,310.31±203.55 and 934.37±208.99 ng/ml for day 1, 6 and 10, respectively). However, there was no significant difference in GH peak concentration and GH AUC between day 6 and 10. Plasma IGF-1 concentration levels were higher in treatment than control group of swine (p<0.05) after 3 days of the treatment, and the levels reached a plateau from day 3 to 10 of experiment. Growth performance did not alter by GHRP-2 administration, even though a numerical increase of body weight gain and feed efficiency was observed. These results indicate that twice daily administration of GHRP-2 for 10 days in swine did not significantly influence on growth performance, caused an overall attenuation of GH response, and that elevation of plasma GH concentrations caused by GHRP-2 administration increased plasma IGF-1 concentrations, even though an attenuation of GH response was observed. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 8 : 1193-1198)

Highlights

Growth hormone releasing peptide-2 (GHRP-2) is a potent growth hormone (GH) secretagogue and its GHreleasing activity has been generally effective in various animals as well as human (Sawada et al, 1994; Wu et al., 1994; Bowers and Granda-Ayala, 2001)
Growth performance did not alter by GHRP-2 administration, even though a numerical increase of body weight gain and feed efficiency was observed. These results indicate that twice daily administration of GHRP-2 for 10 days in swine did not significantly influence on growth performance, caused an overall attenuation of GH response, and that elevation of plasma GH concentrations caused by GHRP-2 administration increased plasma insulin-like growth factor-1 (IGF-1) concentrations, even though an attenuation of GH response was observed
It has been previously reported that increasing in frequency of GH or GHRH administration was a model to increase in GH response, blood circulating IGF-1 and in turn enhanced growth performance (Jansson et al, 1982; Kensinger et al, 1987; Jorgensen et al, 1990, 1991)

Summary

INTRODUCTION

Growth hormone releasing peptide-2 (GHRP-2) is a potent growth hormone (GH) secretagogue and its GHreleasing activity has been generally effective in various animals as well as human (Sawada et al, 1994; Wu et al., 1994; Bowers and Granda-Ayala, 2001). Twice daily or continuous administration of GHRP-2 has been reported to increase plasma IGF-1 concentrations in cows (Roh et al, 1996; Lee et al, 2000). Increases in frequency of GH administration had been reported to effectively generate an increase in plasma IGF-1 concentrations (Jorgensen et al, 1990, 1991) and promote growth (Jansson et al, 1982). In swine, improved growth performance was positively related to increasing GH responses and IGF-1 concentrations after. The present study was to conduct to investigate the effect of twice daily s.c. administration of GHRP-2, at the same dose as described in swine above for a period of 10 days, on growth performance, GH responsiveness, and on the release of plasma IGF-1 concentrations in swine

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION