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The atrazine metabolite diaminochlorotriazine suppresses LH release from murine L?T2 cells by suppressing GnRH-induced intracellular calcium transients.

ABSTRACT: The primary metabolite of the herbicide atrazine (ATRA), diaminochlorotriazine (DACT), has been suggested to cause disruption in the hypothalamic-pituitary-gonadal axis leading to inhibition of luteinizing hormone (LH) release. DACT is a reactive electrophile known to form covalent protein adducts both in vitro and in vivo following ATRA exposure and maybe targeting proteins involved in GnRH-induced calcium signaling and subsequent LH release. To test this hypothesis, L?T2 pituitary cells were exposed to 300 ?M DACT for 24 hrs and examined by fluorescence microscopy for GnRH-induced changes in intracellular calcium and LH release. L?T2 cells exposed to DACT had markedly diminished GnRH-induced intracellular calcium transients and a significant decreased LH release in response to GnRH. DACT appeared to cause a selective decrease in caffeine-sensitive ryanodine receptor-operated calcium stores in L?T2 cells, rather than in thapsigargin-sensitive ER calcium stores. This sensitivity correlated with the formation of covalent protein adducts by DACT, as determined by mass spectrometry. ERp57 was identified by mass spectrometry as a target of DACT adduction in the ER that could potentially mediate the effects of DACT on inhibition of GnRH-induced calcium signaling and inhibition of LH release. Intracellular calcium responses to GnRH and release of LH were restored in DACT-treated cells with the addition of a calcium ionophore (A23187). These data suggest that DACT forms adducts on proteins involved in calcium handling within the ER and that dysfunction in this critical signaling system is associated with loss of normal sensitivity to GnRH and subsequent decreased release of LH.

SUBMITTER: Dooley GP

PROVIDER: S-EPMC3774316 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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The atrazine metabolite diaminochlorotriazine suppresses LH release from murine LβT2 cells by suppressing GnRH-induced intracellular calcium transients.

Dooley Gregory P GP Tjalkens Ronald B RB Hanneman William H WH

Toxicology research 20130501 3

The primary metabolite of the herbicide atrazine (ATRA), diaminochlorotriazine (DACT), has been suggested to cause disruption in the hypothalamic-pituitary-gonadal axis leading to inhibition of luteinizing hormone (LH) release. DACT is a reactive electrophile known to form covalent protein adducts both <i>in vitro</i> and <i>in vivo</i> following ATRA exposure and maybe targeting proteins involved in GnRH-induced calcium signaling and subsequent LH release. To test this hypothesis, LβT2 pituitar ...[more]

PMID: 24052811

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Project description:BackgroundRisk factors associated with a suboptimal response to Gonadotropin-releasing hormone (GnRH) agonists include a high or low body mass index (BMI), prolonged use of oral contraceptive pills, and low luteinizing hormone (LH) levels on either the start or trigger days of controlled ovarian stimulation (COS). However, this approach may increase the need for a dual trigger and may also result in a higher incidence of ovarian hyperstimulation syndrome (OHSS) in hyper-responders. We aimed to investigate whether the maximum LH level during stimulation can serve as a predictive factor for achieving an optimal oocyte yield using the GnRH agonist trigger alone.MethodsWe retrospectively reviewed all antagonist protocols or progestin-primed ovarian stimulation (PPOS) protocols triggered with GnRH agonist only between May 2012 and December 2022. Subjects were divided into three groups, depending on basal LH level and LH maximum level. The freeze-all strategy was implemented in all cycles: Group 1, consistently low LH levels throughout COS; Group 2, low basal LH level with high LH max level during COS; Group 3, consistently high LH levels throughout COS. The primary outcome was the oocyte yield rate. The secondary outcome includes the number of collected oocytes, suboptimal response to GnRH agonist trigger, oocyte maturity rate, fertilized rate, clinical pregnancy rate, ongoing pregnancy rate, and live birth rate. The pregnancy outcomes were calculated for the first FET cycle.ResultsFollowing confounder adjustment, multivariable regression analysis showed that Group 1 (cycles with consistently low LH levels throughout COS) remains an independent predictor of suboptimal response (OR: 6.99; 95% CI 1.035-47.274). Group 1 (b = -12.72; 95% CI -20.9 to -4.55) and BMI (b = -0.25; 95% CI -0.5 to -0.004) were negatively associated with oocyte yield rate. Patients with low basal LH but high LH max levels had similar clinical outcomes compared to those with high LH max levels through COS.ConclusionsThe maximum LH level during COS may serve as an indicator of LH reserve and could be a more reliable predictor of achieving an optimal oocyte yield when compared to relying solely on the basal LH level. In the case of hyper-responders where trigger agents (agonist-only or dual trigger) are being considered, we propose a novel strategy that incorporates the maximum LH level, rather than just the basal or trigger-day LH level, as a reference for assessing LH reserve. This approach aims to minimize the risk of obtaining suboptimal oocyte yield and improve overall treatment outcomes.

Project description:BackgroundLuteinizing hormone secreted by the anterior pituitary gland regulates gonadal function. Luteinizing hormone secretion is regulated both by alterations in gonadotrope responsiveness to hypothalamic gonadotropin releasing hormone and by alterations in gonadotropin releasing hormone secretion. The mechanisms that determine gonadotrope responsiveness are unknown but may involve regulators of G protein signaling (RGSs). These proteins act by antagonizing or abbreviating interaction of Galpha proteins with effectors such as phospholipase Cbeta. Previously, we reported that gonadotropin releasing hormone-stimulated second messenger inositol trisphosphate production was inhibited when RGS3 and gonadotropin releasing hormone receptor cDNAs were co-transfected into the COS cell line. Here, we present evidence for RGS3 inhibition of gonadotropin releasing hormone-induced luteinizing hormone secretion from cultured rat pituitary cells.ResultsA truncated version of RGS3 (RGS3T = RGS3 314-519) inhibited gonadotropin releasing hormone-stimulated inositol trisphosphate production more potently than did RSG3 in gonadotropin releasing hormone receptor-bearing COS cells. An RSG3/glutathione-S-transferase fusion protein bound more 35S-Gqalpha than any other member of the G protein family tested. Adenoviral-mediated RGS3 gene transfer in pituitary gonadotropes inhibited gonadotropin releasing hormone-stimulated luteinizing hormone secretion in a dose-related fashion. Adeno-RGS3 also inhibited gonadotropin releasing hormone stimulated 3H-inositol phosphate accumulation, consistent with a molecular site of action at the Gqalpha protein.ConclusionsRGS3 inhibits gonadotropin releasing hormone-stimulated second messenger production (inositol trisphosphate) as well as luteinizing hormone secretion from rat pituitary gonadotropes apparently by binding and suppressing the transduction properties of Gqalpha protein function. A version of RGS3 that is amino-terminally truncated is even more potent than intact RGS3 at inhibiting gonadotropin releasing hormone-stimulated inositol trisphosphate production.

Project description:Kisspeptin modulates GnRH secretion in mammals and peripheral administration of 10-amino acid fragment of kisspeptin (Kp10) induces LH release and ovulation in cattle. Experiments were done to determine if iv administration of kisspeptin will activate GnRH neurons (i.e., after crossing the blood-brain barrier) and if pre-treatment with a GnRH receptor blocker will alter kisspeptin-induced LH release (from gonadotrophs) and ovulation. In Experiment 1, cows (n = 3 per group) were given human-Kisspeptin10 (hKp10; 3 x 15 mg iv at 60-min intervals) or normal saline and euthanized 150 min after treatment was initiated. Every 20th free-floating section (50 μm thickness) from the preoptic area to hypothalamus was double immunostained to colocalize GnRH- (DAB) and activated neurons (cFOS; Nickel-DAB). Kisspeptin induced plasma LH release from 15 to 150 min (P = 0.01) but the proportion of activated GnRH neurons did not differ between groups (5.8% and 3.5%, respectively; P = 0.11). Immunogold electron microscopy detected close contacts between kisspeptin fibers and GnRH terminals in the median eminence. In Experiment 2, pubertal heifers (n = 5 per group) were treated with 1) hKp10 iv, 2) Cetrorelix (GnRH antagonist; im) + hKp10 iv or 3) saline on Day 6 of the follicular wave under low-progesterone condition. A rise in plasma LH concentration was detected from 15 to 240 min in the hKp10 group but not in cetrorelix or control group (P<0.001). Ovulations were detected only in the hKp10 group (4/5; P = 0.02). Cetrorelix treatment was associated with regression of the preovulatory dominant follicle and emergence of a new follicular wave 3.4±0.75 days after the treatment in all five heifers. Results support the hypothesis that the effect of peripheral kisspeptin is mediated downstream of GnRH synthesis and does not involve GnRH-independent LH release from gonadotrophs. Peripheral kisspeptin may release pre-synthesized GnRH from the nerve terminals in areas outside the blood-brain barrier.

Dataset Information

The atrazine metabolite diaminochlorotriazine suppresses LH release from murine L?T2 cells by suppressing GnRH-induced intracellular calcium transients.

Publications

The atrazine metabolite diaminochlorotriazine suppresses LH release from murine LβT2 cells by suppressing GnRH-induced intracellular calcium transients.

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