Effects of ghrelin on growth hormone secretion in vivo in ruminants.
Ghrelin, a novel endogenous growth hormone (GH) secretagogue, has been shown to exert very potent and specific GH-releasing activity in rats and humans. However, little is known about its GH-releasing activity and endocrine effects in domestic animals. To clarify the effect of ghrelin on GH secretion in vivo in ruminants, plasma GH responses to intra-arterial and intra-hypothalamic injections of rat ghrelin (rGhrelin) were examined in goats and cattle. The intra-arterial injection of 1 microg/kg BW of rGhrelin in ovariectomized goats failed to stimulate GH release, however, a dosage of 3 microg/kg BW significantly increased plasma GH concentrations (P<0.05). GH levels peaked at 15 min after the injection, then decreased to basal concentrations within 1 h after the injection. However, the secretory response to 3 microg/kg BW of rGhrelin was weaker than that of growth hormone-releasing hormone (GHRH) (0.25 microg/kg BW) (P<0.05). An infusion of 10 nmol of ghrelin into the medial basal hypothalamus (arcuate nucleus) significantly stimulated the release of GH in male calves (P<0.05). GH levels began to rise just after the infusions and peaked at 10 min, then decreased to the basal concentrations within 1 h after the injection. The present results show that ghrelin stimulates GH release in ruminants.
Hashizume
Tsutomu
T
Faculty of Agriculture, Iwate University, Morioka, Iwate 020-8550, Japan. hashi@iwate-u.ac.jp
Horiuchi
Mami
M
Nonaka
Sumie
S
Kasuya
Etsuko
E
Kojima
Masayasu
M
Hosoda
Hiroshi
H
Kangawa
Kenji
K
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism; D002417:Cattle; D005260:Female; D054439:Ghrelin; D006041:Goats / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage*; D007269:Injections, Intra-Arterial; D008297:Male; D036361:Peptide Hormones / Q000008:administration & dosage*; D051381:Rats
D054439:Ghrelin; D036361:Peptide Hormones; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone