title: Feeding reduces activity of growth hormone-releasing hormone and somatostatin neurons.
abstract: Secretion of growth hormone (GH) is synchronized among castrate male cattle (steers) around feeding when access to feed is restricted to a 2-hr period each day. Typically, concentrations of GH increase before and decrease after feeding. Our objectives were to determine whether i) concentrations of GH decrease in blood after start of feeding; ii) activity of immunoreactive growth hormone-releasing hormone (GHRH-ir) neurons decreases in the arcuate nucleus (ARC) after feeding; iii) activity of immunoreactive somatostatin (SS-ir) neurons in the periventricular nucleus (PeVN) and ARC increase after feeding; and iv) GHRH stimulates release of GH to a similar magnitude at 0900 and at 1300 hr, in steers fed between 1000 and 1200 hr. Blood samples were collected at 20-min intervals from 0700 to 1300 hr. Groups of steers were euthanized at 0700, 0900, 1100, and 1300 hr (n = 5 per group). Dual-label immunohistochemistry was performed on free-floating sections of hypothalami using antibodies directed against Fos and Fos-related antigens (Fos/FRA) as a marker of neuronal activity in immunoreactive GHRH and SS neurons. Concentrations of GH were high before and decreased after feeding. The percentage of SS-ir neurons containing Fos/FRA-ir in the PeVN was 50% lower (P<0.01) at 1100 hr and 36% lower (P<0.05) at 1300 hr than at 0900 hr. There was no change in percentage of SS-ir neurons containing Fos/FRA-ir in the ARC. The percentage of GHRH-ir neurons containing Fos/FRA-ir in the ARC was 66% lower (P<0.05) at 1100 hr and 65% lower (P<0.05) at 1300 hr than at 0700 hr. In contrast, the number of GHRH-ir neurons increased from 0700 to 1300 hr. GHRH-induced release of GH was suppressed at 1300 hr compared with 0900 hr. In conclusion, reduced basal and GHRH-induced secretion of GH after feeding was associated with decreased activity of GHRH neurons in the ARC and decreased activity of SS neurons in the PeVN.
authors.affiliation: Department of Animal Science, Michigan State University, East Lansing 48824-1225, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: McMahon
authors.forename: L T
authors.initials: LT
authors.lastname: Chapin
authors.forename: K J
authors.initials: KJ
authors.lastname: Lookingland
authors.forename: R P
authors.initials: RP
authors.lastname: Radcliff
authors.forename: H A
authors.initials: HA
authors.lastname: Tucker
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000378:metabolism; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism; D004435:Eating; D013006:Growth Hormone / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism*; D008297:Male; D020644:Midline Thalamic Nuclei / Q000166:cytology / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism*; D013194:Staining and Labeling / Q000379:methods
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone