Goats as Valuable Animal Model to Test the Targeted Glutamate Supplementation upon Antral Follicle Number, Ovulation Rate, and LH-Pulsatility

Abstract

The potential effect of intravenous administration of glutamate on the ovarian activity and the LH secretion pattern, considering the anestrous yearling goat as an animal model, were assessed. In late April, yearling goats (n = 20) were randomly assigned to either (1) Glutamate supplemented (GLUT; n = 10, Live Weight (LW) = 29.6 ± 1.02 kg, Body Condition (BCS) = 3.4 ± 0.2 units; i.v. supplemented with 7 mg GLUT kg−1 LW) or (2) Non-supplemented (CONT; n = 10; LW = 29.2 ± 1.07 kg, BCS = 3.5 ± 0.2 units; i.v. saline). The oats were estrus-synchronized; blood sampling (6 h × 15 min) was carried out for LH quantification. Response variables included pulsatility (PULSE), time to first pulse (TTFP), amplitude (AMPL), nadir (NAD), and area under the curve (AUC) of LH. Ovaries were ultra-sonographically scanned to assess ovulation rate (OR), number of antral follicles (AF), and total ovarian activity (TOA = OR + AF). LH-PULSE was quantified with the Munro algorithm; significant treatment x time interactions were evaluated across time. The variables LW and BCS did not differ (p > 0.05) between the experimental groups. Nevertheless, OR (1.77 vs. 0.87 ± 0.20 units), TOA (4.11 vs. 1.87 ± 0.47 units) and LH-PULSE (5.0 vs. 2.2 pulses 6 h-1) favored (p < 0.05) to the GLUT group. Our results reveal that targeted glutamate supplementation, the main central nervous system neurotransmitter, arose as an interesting strategy to enhance the hypothalamic–hypophyseal–ovarian response considering the anestrous-yearling goat as an animal model, with thought-provoking while promising translational applications.

Effect of one or two fixed glutamate doses on follicular development, ovarian-intraovarian blood flow, ovulatory rate, and corpus luteum quality in goats with a low body condition score

“…Glutamate is an AA that acts as an excitatory neurotransmitter and stimulates GnRH production and release ( Chiang and Park, 2020 ). Under normal conditions, its activity is regulated by steroid hormones ( Barth et al, 2015 ; Porter et al, 2021 ), and supplementation with this amino acid has been shown to be effective in reducing the negative feedback effects of E2 ( Luna-García et al, 2022 ).…”

“…LW acted on the factors that promoted negative feedback, reducing its effects on the HPO axis, proving that glutamate intervenes as a signal for the beginning of the breeding season ( Meza-Herrera et al, 2020 ). As described by Luna-García et al (2022) , glutamate possibly acts by decreasing the action of dopamine on kisspeptin-producing neurons, activating the hypothalamic centers that synthesize and release GnRH, which promotes an increase in LH pulses and acts on ovarian activity.…”

“…Metabolic signals observed in animals with adequate body weight and BCS are not known to influence the effects exerted by glutamate because interactions between these factors have not been reported ( Torres-Moreno et al, 2009 ; Meza-Herrera et al, 2020 ; Luna-García et al, 2022 ). We observed that the action of glutamate was not accompanied by changes in glycemia or cholesterol in animals with low BCS, suggesting that the involvement of other metabolic signals in addition to those of live weight and BCS may be related to ovarian reactivation in goats supplemented with glutamate ( Meza-Herrera et al, 2020 ).…”

“…In goats, glutamate can act on centers that promote reproductive activity during puberty, the estrous cycle, and seasonal anestrus. Two doses of l-glutamate supplementation were tested in goats: 0.175 mg/kg LW of l-glutamate, which improved the ovulation rate in cyclic goats ( Meza-Herrera et al, 2014b ), and 7 mg/kg LW of l-glutamate, which stimulated ovarian activity, induced an early onset of puberty ( Torres-Moreno et al, 2009 ; Meza-Herrera et al, 2011 ), decreased the negative feedback effects of estradiol (E2) ( Meza-Herrera et al, 2020 ), and increased LH pulses ( Luna-García et al, 2022 ). In addition, the aforementioned dose improved reproductive behavior and male effects in rams ( Calderón-Leyva et al, 2018 ) and positively affected their sperm production during the natural period of sexual rest ( Calderon-Leyva et al, 2017 ).…”

“…According to Gilbreath et al (2021) , the use of AAs can be a strategy that improves fertility and promotes reproductive efficiency in the ruminant production sector. In the literature, it has been reported that, administration of l-glutamate decrease the effects of negative feedback on hypothalamic centers that suppress GnRH release ( Meza-Herrera et al, 2020 ; Luna-García et al, 2022 ).…”