title: Combined administration of ghrelin and GHRH synergistically stimulates GH release in Holstein preweaning calves.
abstract: Ghrelin is a gut peptide which participates in growth regulation through its somatotropic, lipogenic and orexigenic effects. Synergism of ghrelin and growth hormone-releasing hormone (GHRH) on growth hormone (GH) secretion has been reported in humans and rats, but not in domestic animals in vivo. In this study, effects of a combination of ghrelin and GHRH on plasma GH and other metabolic parameters, and changes in plasma active and total ghrelin levels were studied in Holstein bull calves before and after weaning. Six calves were intravenously injected with vehicle (0.1% BSA-saline), ghrelin (1 microg/kg BW), GHRH (0.25 microg/kg BW) or a combination of ghrelin plus GHRH at the age of 5 weeks and 10 weeks (weaning at 6 weeks of age). Ghrelin stimulated GH release with similar potency as GHRH and their combined administration synergistically stimulated GH release in preweaning calves. After weaning, GH responses to ghrelin and GHRH became greater compared with the values of preweaning calves, but a synergistic effect of ghrelin and GHRH was not observed. The GH areas under the concentration curves for 2h post-injection were greater in weaned than in preweaning calves (P<0.05) if ghrelin or GHRH were injected alone, but were similar if ghrelin and GHRH were injected together. Basal plasma active and total ghrelin levels did not change around weaning, but transiently increased after ghrelin injection. Basal plasma insulin, glucose and non-esterified fatty acid levels were reduced after weaning, but no changes by treatments were observed. In conclusion, ghrelin and GHRH synergistically stimulated GH release in preweaning calves, but this effect was lost after weaning.
authors.affiliation: Department of Animal Science, Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-11, Inada, Obihiro 080-8555, Japan.
authors.forename: Hnin
authors.initials: H
authors.lastname: ThidarMyint
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yoshida
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ito
authors.forename: Maolong
authors.initials: M
authors.lastname: He
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Inoue
authors.forename: Hideto
authors.initials: H
authors.lastname: Kuwayama
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle / Q000097:blood / Q000502:physiology*; D004357:Drug Synergism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D054439:Ghrelin / Q000097:blood / Q000494:pharmacology*; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007328:Insulin / Q000097:blood / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D011897:Random Allocation
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D054439:Ghrelin; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone