Glutamate Supply Reactivates Ovarian Function while Increases Serum Insulin and Triiodothyronine Concentrations in Criollo x Saanen-Alpine Yearlings’ Goats during the Anestrous Season

Abstract

The possible effect of glutamate supplementation upon ovarian reactivation and serum concentrations of insulin (INS) and triiodothyronine (T3) in anestrous yearling goats was evaluated. Goats (n = 32, 12 mo., 26° North, 1117 m) with a similar live weight (LW) and body condition score (BCS) were blood sampled twice per week for two weeks (2 × 1 week × 2 weeks) to confirm the anestrus status (<1 ng P4/mL; RIA). Thereafter, goats were randomly assigned to either 1) Glutamate (GLUT; n = 16, LW = 27.1 ± 1.09 kg, 3.5 ± 0.18 units, IV-supplemented with 7 mg of glutamate kg−1 LW), or 2) Control (CONT; n = 16; LW = 29.2 ± 1.09 kg; BCS = 3.5 ± 0.18, IV saline). During the treatment period, 16 goats (eight/group) were blood sampled twice per week for six weeks. Such serum samples (2 × 1 week × 6 weeks) were quantified by their P4 content to evaluate the ovarian-luteal activity, whereas a sample subset (1 × 1 week × 6 weeks) was used to quantify their INS & T3 content to evaluate their metabolic status. Neither LW (28.19 kg; p > 0.05) nor BCS (3.51 units; p > 0.05) differed between treatments. Goats depicting ovarian reactivation favored the GLUT group (50 vs. 12.5%; p < 0.05). Neither INS (1.72 ± 0.15 ng mL−1) nor T3 (2.32 ± 0.11 ng mL−1) differed between treatments, yet a treatment x time interaction regarding INS & T3 concentration across time favored (p < 0.05) the GLUT group. The results unveil exogenous glutamate as an interesting modulator not only of ovarian reactivation, but of metabolic hormone synthesis.

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

“…The last, in turn, may have increased the LH-pulse, while augmenting the ovarian activity. Whereas diverse studies support the positive effects of glutamate administration upon the reproductive outcomes in diverse species, either male [28] or female [10,24,29,30], other studies have also demonstrated an interesting interplay between glutamatergic signaling and sexual male-to-female behavior [28,31]. Some components of the rams' sexual behavior such as ano-genital sniffing, vocalizations, mounting, intromission, and ejaculation are also observed in rodents [32][33][34].…”

“…Since the LH pulse frequency showed a non-parametric distribution, a Kruskal-Wallis test was used to analyze the variable LH-PULSE. The response variables were evaluated for normality using the Shapiro-Wilk test, and log 10 , transformed for basal and mean LH concentrations as well as for LH pulse amplitude. When a significant effect of the treatment x time interaction occurred, the data were compared across time.…”

“…At a central level, the glutamatergic systems (i.e., ligand-receptors), have been involved in the control of pulsatile GnRH secretion, and the pre-ovulatory surge of gonadotropins (LH and FSH) [ 9 ]. Interestingly, the glutamatergic neurons that have been associated in the control of the GnRH neurons are also responsive to kisspeptin, an essential peptide in the regulation of the hypothalamic–pituitary–gonad (HPG) axis, promoting an increase in GnRH pulses [ 8 , 9 , 10 ]. While domestic sheep and goats have shown great potential as large animal models, sheep have been mainly used to perform preclinical and translational studies in reproductive research, while goats have been used in a more limited fashion [ 10 ].…”

Effect of Social Rank upon Estrus Induction and Some Reproductive Outcomes in Anestrus Goats Treated With Progesterone + eCG

“…Our findings agree with previous studies where high hierarchy females had a faster and higher response than low hierarchy females regarding LH pulse frequency and estrus activity [ 7 ]. Some biological triggers of such increased ovarian function include reproductive hormones such as follicle stimulating hormone (FSH) or LH [ 32 , 39 , 40 ], metabolic endocrine cues such as leptin [ 41 ], insulin-like growth factor-1 [ 42 ], insulin–triiodothyronine [ 43 ], the somatotropic GH-IGF-1 axis [ 44 ], some defined neuroendocrine hints such as the kiss-1, kisspeptin, gpr-54 complex, kisspeptinergic neurons, and GnRH release [ 32 , 45 ], some other genomic signals such as the OCT2, TTF1, and EAP1 hypothalamic genes [ 32 , 46 ], and even specific nutritional molecules such as glutamate [ 47 , 48 ] and β-carotene [ 40 , 49 ].…”

Does Size Matters? Relationships among Social Dominance and Some Morphometric Traits upon Out-of-Season Reproductive Outcomes in Anestrus Dairy Goats Treated with P4 + eCG

“…The wide distribution of glutamate receptors in different central nervous system synapses sets this neurotransmitter as a key regulator of a myriad of physiological processes [43,44]. Indeed, while exogenous glutamate administration activated reproductive function in pre-pubertal females, through increases in serum insulin, triiodothyronine [45], and cholesterol [46], in adult anestrus females, glutamate supply also reactivated reproductive function, with concomitant increases in serum insulin and triiodothyronine [47]. Therefore, the possible involvement of glutamatergic and kisspeptinergic neurons as activators of the GnRH neurons in the HSR goats, which also displayed the largest live weights and body measures, could be a conceivably occurring scenario, in the observed out-of-season reproductive outcomes in the HSR-females.…”