Gonadotropin-releasing hormone (GnRH) is released episodically into the pituitary portal vessels and from hypothalamic tissue of male and female rats in vitro. Perfused primary cultures of rat hypothalamic neurons, as well as the GT1-1 GnRH neuronal cell line, spontaneously exhibited episodic GnRH secretion of comparable frequency to that observed with perifused hypothalami. Such pulsatile GnRH release from GT1 cells indicates that GnRH neurons generate rhythmic secretory activity in the absence of input from other cell types. In primary hypothalamic cultures, the frequency of GnRH pulses increased with the duration of culture. The spontaneous pulsatility in GnRH release was abolished in Ca2+-deficient medium and was markedly attenuated in the presence of nifedipine, an antagonist of voltage-sensitive Ca2' channels. The basal intracellular Ca2+ level of perifused GT1-1 cells cultured on coverslips was also dose-dependently reduced by nifedipine. Conversely, depolarization with high K+ increased intracellular Ca+ and GnRH release in an extracellular Ca2+-dependent and nifedipine-sensitive manner. The dihydropyridine Ca2+ channel agonist Bay K 8644 increased basal and K+-induced elevations of intracellular Ca2+ concentration and GnRH secretion. These findings demonstrate that pulsatile neuropeptide secretion is an intrinsic property of GnRH neuronal networks and is dependent on voltage-sensitive Ca2+ influx for its maintenance.The pulsatile secretion of gonadotropin-releasing hormone (GnRH) from hypothalamic nerve terminals adjacent to hypophyseal portal vessels in the median eminence is essential for the synthesis and secretion of gonadotropic hormones from the anterior pituitary gland (1). In contrast to other hypophysiotropic neurons, GnRH-producing cells are not concentrated in a discrete region of the hypothalamus but are distributed in the preoptic area and adjacent sites in the rostal portion of the hypothalamus (2). The majority of the GnRH neurons send projections to the median eminence and, despite their scattered locations, are interconnected to form a functional unit termed the GnRH pulse generator (3) that is responsible for the episodic release of GnRH and, consequently, of pituitary gonadotropins. Thus, pulses of luteinizing hormone secretion are elicited by preceding elevations of GnRH concentration in pituitary portal blood (4, 5), and a pulsatile mode of GnRH action is essential for the maintenance and control of normal gonadotropin profiles in the peripheral circulation (6).Changes in GnRH pulse frequency occur at puberty (7) and during the menstrual cycle (8), as well as after castration (9). Alterations in the pulsatile GnRH signal in several reproductive states may reflect a requirement not only for increased gonadotropin secretion but also for changes in the proportions of luteinizing hormone and follicle-stimulating hormone production under various physiological conditions. Thus, the pattern of GnRH secretion can differentially regulate the levels of gonadotropin subunit mRNAs in th...

No abstract

Summary Since sperm require high energy levels to perform their specialised function, it is vital that essential nutrients are available for spermatozoa when they develop, capacitate and acquire motility. However, they are vulnerable to a lack of energy and excess amounts of reactive oxygen species, which can impair sperm function, lead to immotility, acrosomal reaction impairment, DNA fragmentation and cell death. This monocentric, randomised, double‐blind, placebo‐controlled trial investigated the effect of 6 months of supplementation with l‐carnitine, acetyl‐l‐carnitine and other micronutrients on sperm quality in 104 subjects with oligo‐ and/or astheno‐ and/or teratozoospermia with or without varicocele. In 94 patients who completed the study, sperm concentration was significantly increased in supplemented patients compared to the placebo (p = .0186). Total sperm count also increased significantly (p = .0117) in the supplemented group as compared to the placebo group. Both, progressive and total motility were higher in supplemented patients (p = .0088 and p = .0120, respectively). Although pregnancy rate was not an endpoint of the study, of the 12 pregnancies that occurred during the follow‐up, 10 were reported in the supplementation group. In general, all these changes were more evident in varicocele patients. In conclusion, supplementation with metabolic and antioxidant compounds could be efficacious when included in strategies to improve fertility.

No abstract

Diet in human health is no longer simple nutrition, but in light of recent research, especially nutrigenomics, it is linked via evolution and genetics to cell health status capable of modulating apoptosis, detoxification, and appropriate gene response. Nutritional deficiency and disease especially lack of vitamins and minerals is well known, but more recently, epidemiological studies suggest a role of fruits and vegetables, as well as essential fatty acids and even red wine (French paradox), in protection against disease. In the early 1990s, various research groups started considering the use of antioxidants (e.g., melatonin, resveratrol, green tea, lipoic acid) and metabolic compounds (e.g., nicotinamide, acetyl-L-carnitine, creatine, coenzyme Q10) as possible candidates in neuroprotection. They were of course considered on par with snake oil salesman (women) at the time. The positive actions of nutritional supplements, minerals, and plant extracts in disease prevention are now mainstream and commercial health claims being made are subject to regulation in most countries. Apart from efficacy and finding, the right dosages, the safety, and especially the level of purification and lack of contamination are all issues that are important as their use becomes widespread. From the mechanistic point of view, most of the time these substances replenish the body's deficiency and restore normal function. However, they also exert actions that are not sensu stricto nutritive and could be considered pharmacological especially that, at times, higher intake than recommended (RDA) is needed to see these effects. Free radicals and neuroinflammation processes underlie many neurodegenerative conditions, even Parkinson's disease and Alzheimer's disease. Curcumin, carotenoids, acetyl-L-carnitine, coenzyme Q10, vitamin D, and polyphenols and other nutraceuticals have the potential to target multiple pathways in these conditions. In summary, augmenting neuroprotective pathways using diet and finding new natural substances that can be more efficacious, i.e., induction of health-promoting genes and reduction of the expression of disease-promoting genes, could be incorporated into neuroprotective strategies of the future.

The mechanism by which gamma-aminobutyric acid (GABA) stimulates the release of LH was analyzed in cultured female rat pituitary cells. In 3-h incubations, GABA (1-100 microM) caused a dose-dependent increase in LH release, with the maximal response about 16% of that evoked by 10 nM GnRH. GABA action was independent of the GnRH receptor, since 1 microM GnRH antagonist [( N-acetyl-D-p-Cl-Phe1,2,D-Trp3,D-Lys6,D-Ala10] GnRH), which completely inhibits GnRH action, did not affect the response to GABA. In studies on the effects of GABA receptor agonists and antagonists, 4,5,6,7-tetrahydoisoxazolo-[5,4-c]pyridin-3(2H)-one (THIP) and muscimol (GABAA agonists) gave similar response patterns, with the same maximal stimulation as GABA but much higher potencies. In contrast, the GABAB receptor agonist baclofen did not stimulate LH release. The GABAA receptor antagonist SR95531 caused dose-dependent inhibition of the LH-releasing effects of GABA and muscimol (10 microM), with complete blockade at 10 microM SR95531. T-Butylbicyclophosphorothionate, an inhibitor of the GABAA receptor-associated chloride channel, also dose-dependently reduced the releasing effect of 100 microM GABA. These results indicate that GABA action is mediated by the chloride channel-associated GABAA receptor. However, the other GABAA receptor antagonists, including bicuculline, picrotoxin, and strychnine, did not attenuate the LH-releasing effect of 100 microM GABA in concentrations up to 100 microM, suggesting that GABA action is mediated by nonclassical GABAA receptors. Incubation in the presence of nifedipine (1 microM) or in calcium-free medium inhibited the LH-releasing action of GABA, indicating that calcium influx through voltage-sensitive calcium channels (VSCC) is required for GABA-induced LH release. Such entry of Ca2+ would result from activation of VSCC by depolarization due to the increased Cl- conductance caused by GABAA receptor activation. In cell perfusion studies, the actions of GABA and muscimol were attenuated or abolished after repetitive stimulation, consistent with desensitization of the GABA receptors. These findings have demonstrated that the stimulation of LH release by GABA is independent of GnRH action, occurs via binding to nonclassical GABAA receptors, which rapidly desensitize, and is mediated by the activation of VSCC.

Carnitine is essential for energy metabolism and spermatozoa maturation. Combining L‐carnitine and L‐acetylcarnitine with micronutrients has been investigated as a treatment for infertility in men. We evaluated the effects of a therapeutic formulation, Proxeed Plus, on sperm parameters in oligoasthenozoospermic men. This prospective, randomised, double‐blind, placebo‐controlled clinical trial involved 175 males (19–44 years) with idiopathic oligoasthenozoospermia who failed to impregnate their partners (12 months). Males received Proxeed Plus or placebo for 3 and 6 months. Sperm volume, progressive motility and vitality significantly (p < 0.001) improved after 6 months compared to baseline. Sperm DNA fragmentation index significantly decreased compared to baseline (p < 0.001) and the 3‐month therapy (p = 0.014) in treated men. Increased seminal carnitine and α‐glucosidase concentration also positively correlated with improved progressive motility. Decreased DNA fragmentation index was the good predictor of progressive sperm motility >10%, and simultaneous measurement of changes in sperm vitality and DNA fragmentation index gave the highest probability of sperm motility 10% (AUC = 0.924; 95% CI = 0.852–0.996; p < 0.001). Logistic regression analyses revealed DNA fragmentation index decrease as the only independent predictor of sperm motility 10% (OR = 1.106; p = 0.034). We have demonstrated the beneficial effects of carnitine derivatives on progressive motility, vitality and sperm DNA fragmentation. Combining metabolic and micronutritive factors is beneficial for male infertility.

There is growing evidence that suggests that brain injury after amphetamine and methamphetamine (METH) administration is due to an increase in free radical formation and mitochondrial damage, which leads to a failure of cellular energy metabolism followed by a secondary excitotoxicity. Neuronal degeneration caused by drugs of abuse is also associated with decreased ATP synthesis. Defective mitochondrial oxidative phosphorylation and metabolic compromise also play an important role in atherogenesis, in the pathogenesis of Alzheimer's disease, Parkinson's disease, diabetes, and aging. The energy deficits in the central nervous system can lead to the generation of reactive oxygen and nitrogen species as indicated by increased activity of the free radical scavenging enzymes like catalase and superoxide dismutase. The METH‐induced dopaminergic neurotoxicity may be mediated by the generation of peroxynitrite and can be protected by antioxidants selenium, melatonin, and selective nNOS inhibitor, 7‐nitroindazole. L‐Carnitine (LC) is well known to carry long‐chain fatty acyl groups into mitochondria for β‐oxidation. It also plays a protective role in 3‐nitropropioinc acid (3‐NPA)‐induced neurotoxicity as demonstrated in vitro and in vivo. LC has also been utilized in detoxification efforts in fatty acid‐related metabolic disorders. In this study we have tested the hypothesis that enhancement of mitochondrial energy metabolism by LC could prevent the generation of peroxynitrite and free radicals produced by METH. Adult male C57BL/6N mice were divided into four groups. Group I served as control. Groups III and IV received LC (100 mg/kg, orally) for one week. Groups II and IV received 4 × 10 mg/kg METH i.p. at 2‐h intervals after one week of LC administration. LC treatment continued for one more week to groups III and IV. One week after METH administration, mice were sacrificed by decapitation, and striatum was dissected to measure the formation of 3‐nitrotyrosine (3‐NT) by HPLC/Coularry system. METH treatment produced significant formation of 3‐NT, a marker of peroxynitrite generation, in mice striatum. The pre‐ and post‐treatment of mice with LC significantly attenuated the production of 3‐NT in the striatum resulting from METH treatment. The protective effects by the compound LC in this study could be related to the prevention of the possible metabolic compromise by METH and the resulting energy deficits that lead to the generation of reactive oxygen and nitrogen species. These data further confirm our hypothesis that METH‐induced neurotoxicity is mediated by the production of peroxynitrite, and LC may reduce the peroxynitrite levels and protect against the underlying mechanism of METH toxicity, which are models for several neurodegenerative disorders like Parkinson's disease.