Dynamics of GHRH in third-ventricle cerebrospinal fluid of cattle: Relationship with serum concentrations of GH and responses to appetite-regulating peptides

Thomas, M.G.; Amstalden, M.; Hallford, D.M.; Silver, G.A.; Garcia, M.D.; Keisler, D.H.; Williams, G.L.

doi:10.1016/j.domaniend.2009.05.006

« Previous Next »Domestic Animal Endocrinology
Volume 37, Issue 4 , Pages 196-205, November 2009

Dynamics of GHRH in third-ventricle cerebrospinal fluid of cattle: Relationship with serum concentrations of GH and responses to appetite-regulating peptides

M.G. Thomas
- Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, USA
- Corresponding author. Department of Animal and Range Sciences, MSC 3I, Knox Hall 328, 2980 South Espina St, New Mexico State University, Las Cruces, NM 88003, USA. Tel.: +1 575 646 3427; fax: +1 575 646 3488.
M. Amstalden
- Department of Animal Science, Texas A&M University, College Station, TX 77843-2471, USA
D.M. Hallford
- Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, USA
G.A. Silver
- Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, USA
M.D. Garcia
- Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, USA
- Present address: Department of Animal Sciences, 105 J.B. Francioni Hall, Louisiana State University, Baton Rouge, LA 70803.
D.H. Keisler
- Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA
G.L. Williams
- Texas AgriLife Research Station, Beeville, TX 78102, USA

Received 11 February 2009; received in revised form 27 May 2009; accepted 28 May 2009. published online 27 July 2009.

Abstract

Objectives were to (1) characterize the relationship of third-ventricle (IIIV) cerebrospinal fluid (CSF) concentrations of growth hormone–releasing hormone (GHRH) with concentrations of GH in the peripheral circulation; and (2) assess the influence of acute administration of appetite-regulating peptides leptin (anti-orexigenic) and neuropeptide Y (NPY; orexigenic) on the release of GHRH. Six mature beef cows fitted with IIIV and jugular vein cannulae were treated intracerebroventricularly with saline, and leptin (600μg) and NPY (500μg) in saline, in a replicated 3×3 Latin square design. Third-ventricle CSF and blood were collected 10min before and continued 220min after treatments. Mean concentrations of GHRH and frequency of pulses after treatments were 2.2±0.13ng/mL and 1.2±0.15 pulses/220min, respectively. These measures were not influenced by treatments. Concentrations of GHRH in CSF were weakly correlated (r=0.15; P<0.03) with serum concentrations of GH; however, 58% of the GH pulses were preceded by a pulse of GHRH and 90% of the GHRH pulses occurred within 20min preceding a pulse of GH. Leptin tended (P<0.10) to suppress GH area under the curve (AUC) compared to saline. Concomitantly, NPY tended (P<0.10) to increase GH AUC, which appeared to be a consequence of increased (P<0.05) pulse amplitude. Infusion of NPY also increased (P<0.05) AUC of GHRH relative to saline. No differences were detected among treatments in serum concentrations of insulin-like growth factor-I or its AUC. Sampling CSF from the IIIV appears to be a viable procedure for assessing hypothalamic release of GHRH coincident with anterior pituitary gland secretion of GH in cattle. These data also demonstrate the differential responsiveness of the GH axis to appetite-regulating peptides.