Abstract
A negative energy balance (NEB) is detrimental to reproduction in animals. A suggested link between NEB and reproductive failure is the gastrointestinal hormone ghrelin, because of the association between ghrelin and the hypothalamo-pituitary-gonadal axis. The [D-Lys3]-Growth Hormone Releasing Peptide-6 ([D-Lys3]-GHRP-6) is a ghrelin antagonist that acts on ghrelin receptors (GHS-R1). The objective of this study was to evaluate the effect of [D-Lys3]-GHRP-6 on reproduction variables in feed restricted ewes. Two experiments were conducted. Experiment I was conducted for 30 days; and Experiment II for 13 days. In both experiments the ewes (n = 18) were randomly assigned to: Control (CO): fed to meet maintenance requirements; Feed restriction (FR): 80% of maintenance restriction; or Ghrelin antagonist (GA): feed restricted and daily subcutaneous of 7.5μg/kg of [D-Lys3]-GHRP-6. Plasma was collected to measure hormones and metabolite concentration. In Experiment II, the hypothalamus and ovaries were collected on day 13. In both Experiments, sheep allocated to the FR and GA treatments decreased their body weight compared with sheep in the CO group (P < 0.06); progesterone however, did not differ between treatments (P > 0.10). Experiment I: Plasma ghrelin concentration was greater (P < 0.01) in FR and GA compared with CO ewes. Plasma non-esterified fatty acids concentration was greater (P < 0.01) in GA and FR than CO. Experiment II: Kisspeptin1-Receptor (Kiss1-R) mRNA expression was greater in FR (P < 0.01) and tended to be greater in GA (P = 0.10) compared with CO ewes. The neuro peptide-Y (NPY) mRNA expression was greater (P = 0.03) in FR than CO; and tended to be greater (P = 0.06) compared with GA ewes. Growth hormone releasing hormone (GhRH) mRNA expression was greater in GA (P = 0.04) and tended to be greater in FR (P = 0.07) compared with CO ewes. Feed restriction increased GhRH, NPY, and Kiss-R mRNA expression in hypothalamus without affecting reproductive variables.Ghrelin antagonist may prevent an increase inNPY expression in ewes.
Highlights
Ruminants affected by a negative energy balance (NEB) are subjected to metabolic change [1]
We did not found differences in the expression of the estrogen receptor 1 (ER1), estrogen receptor 2 (ER2), NPY1R, NPY2R, ARP, POMC, cocaine and amphetamine regulated transcript (CART), melanocortin receptor 3 (MCR3), and melanocortin receptor 4 (MCR4) mRNA, we suggest that it is possible that the ewes energy reserves, and or the 13 days of food restriction was insufficient time to observe these changes
In our results we found that Growth hormone releasing hormone (GhRH) mRNA relative expression was greater in Feed restriction (FR) and Ghrelin antagonist (GA) groups, even when the ghrelin receptor was blocked by [D-Lys-3]-GHRP-6
Summary
Ruminants affected by a negative energy balance (NEB) are subjected to metabolic change [1]. The binding of ghrelin to GHS-R1a stimulates growth hormone (GH) secretion [5], up-regulates growth hormone release hormone (GHRH) [6], and increases food intake regulating energy balance [7]. Ghrelin inhibits the secretion of gonadotropin release hormone (GnRH) in the hypothalamus of rats [8]. The release of GnRH by the hypothalamus stimulates LH synthesis and secretion from the hypophysis. When both hormones, GnRH and LH, are affected there is a dysfunction on the reproductive cycle [10]. Fertility and reproductive behavior of the animals are compromised Another possible mechanism of how ghrelin regulates reproduction is by suppressing kisspeptin (Kiss1) secretion. Kisspeptin is a hypothalamic neuropeptide that stimulates GnRH release [11]
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