Assessment of endogenous growth hormone pulsatility in gelded yearling horses using deconvolution analysis.
OBJECTIVE
Defining normal Growth Hormone (GH) secretory dynamics in the horse is necessary to understand altered GH dynamics related to issues like welfare and disease.


METHODS
Twelve healthy yearlings and two mature Standardbreds were used to quantify GH secretion. Endogenous GH half-life was determined after administration of 1.0 µg/kg BW GH releasing hormone (GHRH). Exogenous GH half-life was determined after administration of 20 µg/kg BW recombinant equine GH (reGH) with and without suppression of endogenous GH secretion by somatostatin infusion (50 µg/m(2)/h). Pulse detection algorithm (Cluster) as well as deconvolution analysis was used to quantify GH secretory dynamics based on GH concentration-time series sampled every 5 min from 22:00 till 06:00 h. In addition, reproducibility, impact of sampling frequency and influence of altering initial GH half-life on parameter estimates were studied.


RESULTS
Mean endogenous GH half-life of 17.7 ± 4.4 (SD) min and mean exogenous half-life of 26.0 ± 2.9 min were found. The mean number of GH secretion peaks in 8 h was 12 ± 3.2. Ninety-nine percent of the total amount of GH secreted occurred in pulses, basal secretion was 0.012 ± 0.014 µg/L/min and half-life was 8.9 ± 2.6 min. Compared with a 5-min sampling frequency, 20- and 30-min sampling underestimated the number of secretory events by 45% and 100%, respectively.


CONCLUSIONS
The deconvolution model used was valid to GH time series in Standardbreds. As in man, the equine pituitary gland secretes GH in volleys consisting of multiple secretory bursts, without measurable intervening tonic secretion. The required GH sampling frequency for the horse should be around 3 min.


CONCLUSIONS
Defining normal GH secretory dynamics in the horse will make it possible to detect alterations in the GH axis due to pathophysiologic mechanisms as well as abuse of reGH.
Department of Equine Sciences, Medicine Section, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands. e.roelfsema@uu.nl
Ellen
E
de Graaf-Roelfsema
Paula P
PP
Veldhuis
Klien G
KG
van Dam
Paul P C A
PP
Menheere
Hans A
HA
Keizer
Michael L
ML
Johnson
Eric
E
van Breda
Inge D
ID
Wijnberg
Johannes H
JH
van der Kolk
D000465:Algorithms; D000818:Animals; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage; D006207:Half-Life; D006736:Horses; D008297:Male
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone