A transient ghrelin surge occurs just before feeding in a scheduled meal-fed sheep
Section snippets
Animals and diets
Experiment 1. Four Suffolk rams, aged 1–2 years, weighing approximately 51.3±0.5 kg (mean ± SE) were used. They were fitted with a jugular catheter on the left jugular vein at least one day before the experimental day as described previously [17]. Animals were kept in metabolism crates in a controlled environment chamber at 20 °C under a 12-h light-dark cycle (07:30–19:30, light; 19:30–07:30, dark). The rams were fed a sufficient quantity of alfalfa hay cubes to meet 120–125% of their daily
TR-FIA of ghrelin and GH
The standard curves of rat ghrelin and ovine GH are shown in Fig. 1. The competitive TR-FIA of ghrelin had a standard curve ranging from 0.01 to 10 ng/mL with a sensitivity of 0.025 ng/mL. The intra- and interassay variations of ghrelin were 6.9% and 5.5%, respectively. The median inhibitory concentration (IC50) of ghrelin in TR-FIA system was 0.831 ng/mL. Recovery of ghrelin from ovine plasma was 97.6%. Addition of ovine plasma resulted in displacement of the ghrelin tracer in a dose–response
Experiment 1: Diurnal rhythm of plasma ghrelin and GH concentrations in a scheduled meal-fed sheep
Changes in plasma ghrelin and GH concentrations in sheep fed a diet once daily are presented in Fig. 2. In this experiment blood samples were obtained from animals at 10 min intervals for 3 h period from 1 h before feeding (08:00) to 2 h after feeding (11:00), and at 2 h intervals for 21 h period from 11:00 to 08:00 on the second day, respectively. Ghrelin levels were relatively high 1 h before feeding on the first day. They rose from this time to a peak just before feeding, and then declined to a
Experiment 2: Changes in plasma ghrelin and GH concentrations in the pseudo-feeding sheep
Changes in plasma ghrelin and GH concentrations during the 3 h period of 08:00–11:00 in fed- and pseudo-feeding sheep are presented in Fig. 3. In fed-sheep, plasma ghrelin concentrations increased just before feeding, then decreased during feeding in the same manner as described in Experiment 1 (Fig. 3A). In the pseudo-fed sheep, plasma ghrelin levels just before pseudo-feeding tended to increase (P<0.1) comparing to values at 1 h before pseudo-feeding as seen in the fed sheep and reached the
Discussion
Sheep used in the experiment were trained to the feeding schedule employed, it was noticed, (a) a transient surge of plasma ghrelin occurred in the pre-feeding period, (b) the single surge of ghrelin could increase plasma GH during feeding in scheduled-meal-fed sheep.
In Experiment 1, drastic increases in plasma ghrelin occurred just before feeding in a scheduled-meal feeding. Such a drastic change in blood ghrelin has not been reported. In addition, the plasma ghrelin changed from the maximum
Acknowledgements
We acknowledge the NIDDK's National Hormone and Pituitary Program, and Dr. A.F. Parlow for the ovine GH radioimmunoassay kit.
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