Abstract
The aim of the present study was to examine the growth hormone (GH) response to the combined and repeated administrations of growth hormone-releasing peptide-2 (GHRP-2) plus growth hormone releasing hormone (GHRH) in swine. Six cross-bred castrated male swine, 130-135 days of age were used in this study. Animals were given a single intravenous (i.v.) injection of either GHRP-2 (30μg/kg BW), GHRH (1μg/kg BW) and GHRP-2 (30μg/kg BW) plus GHRH (1μg/kg BW) or 5ml saline (served as control) in random order with two days apart. GHRP-2 or GHRH alone and in combination with together stimulated the release of GH in swine. The peak concentrations of GH and areas under the GH response curve (GH AUC) for 120min after these treatments were significantly higher (P<0.01) than those in controls. The combined administration of these two peptides [GHRP-2 (30μg/kg BW) and GHRH (1μg/kg BW)] resulted in a GH AUC significantly greater than the arithmetic sum of those following their separate administrations (P<0.05), demonstrating the synergistic effect for GH release. GH responses to two successive i.v. injections of GHRP-2 (30μg/kg BW) plus GHRH (1μg/kg BW) at 2h interval in swine were increased after each injection; however, peak concentration of GH and GH AUC for 120min after the second injection were significantly lower (P<0.01) than those after the first injection. These results of the present study indicated that the combined administration of GHRP-2 and GHRH synergistically stimulates the release of GH in swine, and the GH responses to the co-administration of these two peptides decrease after the repeated injection. These findings suggest that GHRP-2 and GHRH act through different receptors and intracellular signal transduction and can be used together for stimulating further release of GH in swine.
