Female infertility is a very real medical problem in developing countries. The female reproductive system is very sensitive to different harmful environmental factors. A major advancement in technology was followed by an increased use of chemicals that could seriously impair female fertility. Some chemicals are counteractive with estrogen . There is a potential danger in the increased use of different food additives like MSG .
The results of this study revealed observable alterations in the structure of the ovary of MSG-treated rats. The ovary showed an increase in the cellularity of tunica albuginea. The stromal cells appeared vacuolated and arranged in clusters. Some atretic follicles were present whereas other types of follicles were distorted, having a degenerated oocyte surrounded by disorganized cells of follicular granulosa cells with darkly stained nuclei and vacuolated theca folliculi cells. Some follicles had markedly degenerated granulosa cells and multiple vacuoles. The blood vessels contained hyaline eosinophilic material in their lumina and their walls were thickened and contained hypertrophied smooth muscle cells. These results were in agreement with those of other investigators who reported that MSG treatment in the neonatal female rats resulted in cystic degeneration of the ovaries, with the appearance of many atretic follicles, abundant interstitium, and hyalinosis of arteriola . Prolonged administration of high doses of MSG induced degenerative and atrophic changes in rat ovaries as MSG had a dose-dependent toxic effect on the oocyte and follicular cells .
Other authors attributed the toxic effect of MSG on the female reproductive system to its direct effect on nuclei of the hypothalamus. Rats treated with MSG showed a decrease in cytosol estrogen receptors in the arcuate median eminence region . It was found that reduction of endogenous production of ovarian estrogen by the follicular zona granulosa initiated widespread atrophic reproductive tract changes. Ovarian atrophy was associated with inactive interstitial glands, reduction in the numbers of follicles and interstitial stromal cell hypertrophy or hyperplasia. These stromal cells may be collections of theca cells remaining after atresia . Anovulatory follicular cysts may develop, forming an immature ovum that may lead to infertility . Similarly, other investigators have reported that nicotine inhibits the release of gonadotrophins, FSH, and LH from the pituitary, acting through the hypothalamus, blocking the neural stimulus to GnRH . In females, FSH stimulates the growth of Graafian follicles and LH is required for its maturation and ovulation. Thus, a decrease in gondatrophins is reflected in atrophy of both gonads in structure and function .
Glutamate receptors are present in different tissues including the hypothalamus, endocrine system, ovaries, and uterus . Glutamate receptors play a very important role in the pathogenesis of disorders induced by MSG. Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system [25–27]. There are two basic types of glutamate receptors: ionotropic and metabotropic [28,29]. The neurotoxicity of MSG is related to glutamate receptor activation . Sustained high-concentration MSG could alter the ionic permeability of neural membranes for calcium and induce persistent depolarization. This excessive activation of glutamate receptors and overloading with intracellular calcium could induce neural death, including nuclei of the hypothalamus .
In this study, the immune reaction to iNOS was highly positive in the granulosa cells and in the stromal cells of the treated group. Nitric oxide is an important biological messenger in animals. It is synthesized from l-arginine by enzyme nitric oxide synthase (NOS), which exists in multiple isoforms in a wide range of mammalian cells. Nitric oxide is considered a vital molecule controlling the hypothalamic–pituitary–gonadal axis . The NOS had been classified depending on the tissue of origin, the functional and structural properties in neuronal constitutive NOS, endothelial constitutive NOS (eNOS), and iNOS. iNOS is expressed in response to inflammatory cytokines and lipopolysaccarides .
Results from different studies have indicated that rat granulosa cells from primary, secondary, and small antral follicles and rat stroma, thecal, and luteal cells express eNOS. In contrast, iNOS was barely detectable . eNOS and iNOS from aortic endothelial cells showed an increased expression in ovariectomized compared with intact pigs . It has been proposed that locally produced NO may help modulate follicle development and possibly prevent apoptosis, at least at low concentrations, whereas high levels might promote cell death by means of peroxynitrite formation .
It has been reported that a reduction in the level of gonadotrophins, known as inhibiting factors of apoptosis in granulosa cells, results in apoptosis and shrinkage of granulosa cells. Apoptosis of granulosa cells could be considered another reason for the reduction of the FSH level [37,38]. In addition, MSG induces oxidative stress in different organs including the thymus. MSG increased rat thymocytes apoptosis by decreasing BCL-2 expression in rat thymocytes , caused a significant increase in lipid peroxidation, glucose, and ascorbic acid and a decrease in the glutathione content in the hepatocytes. Oxidative stress and hyperglycemia observed after the administration of MSG seem to be because of the metabolic products of MSG .
In this study, a concomitant administration of diltiazem and MSG in the prophylactic group resulted in improved histological and immunohistochemical changes instead of pictures. Many apparently healthy follicles at different stages of development were seen and separated by dilated congested blood vessels. This was in accordance with the observations of other authors who reported that the pretreatment with diltiazem prevented the development of morphological and functional disorders of ovaries following MSG toxicity because calcium overload played an important role in the mechanisms of this toxicity [14,18]. Diltiazem has been shown to be a potent vasodilator by inducing relaxation of smooth muscles and the resultant decrease in peripheral vascular resistance. Diltiazem is used in the treatment of the vascular smooth muscle dysfunction because of calcium overload .
Calcium channel antagonists have found widespread use in the treatment of cardiovascular abnormalities. They have been used experimentally in a range of disorders besides the cardiovascular system; for example, it has been reported that diltiazem attenuates acute hepatocellular damage in the perfused rat liver induced by D-galactosamine and CCl4. Also, calcium channel antagonists prolong the survival time in various animal models of endotoxic shock . The addition of a calcium chelator maintained the DNA integrity of cooled pig oocytes .
Thus, in this study, administration of MSG to adult female rats resulted in histological and immunohistochemical alterations, suggesting harmful effects on the function of the ovary. Pretreatment with diltiazem prevented the development of these alterations caused by MSG. These results suggest that the safety profile of MSG should be reexamined and that calcium overload plays an important role in the mechanisms of MSG toxicity.
1. Mahesh VB, Brann DW. Regulatory role of excitatory amino acids in reproduction Endocrine. 2005;28:271–280
2. Nayanatara AK, Vinodini NA, Damodar G, Ahemed B, Ramaswamy CR, Shabarianth AM, Ramesh BM. Role of ascorbic acid in monosodium glutamate mediated effect on testicular weight, sperm morphology and sperm count in rat testis J Chin Clin Med. 2008;3:1–5
3. Mozeš Š, Šefčíkova Z, Lenhardt L, Raček L. Obesity and changes of alkaline phosphatase activity in the small intestine of 40- and 80-day-old rats subjected to early postnatal overfeeding or monosodium glutamate Physiol Res. 2004;53:177–186
4. Ehlers I, Niggemann B, Binder C, Zuberbier T. Role of nonallergic hypersensitivity reactions in children with chronic urticaria Allergy. 1998;53:1074–1077
5. Gobatto CA, Mello MAR, Souza CT, Ribeiro IA. The monosodium glutamate (MSG) obese rat as a model for the study of exercise in obesity Res Commun Mol Pathol Pharmacol. 2002;111:89–101
6. Onakewhor JUE, Oforofuo IAO, Singh SP. Chronic administration of monosodium glutamate induces oligozoospermia and glycogen accumulation in Wistar rat testes Afr J Reprod Health. 1998;2:190–197
7. Eweka AO, Adjene JO. Histological studies of the effects of monosodium glutamate on the geniculate body of adult Wistar rat Electron J Biomed. 2007;22:9–13
8. Gao J, Wu J, Zhao XN, Zhang WN, Zhang YY, Zhang ZX. Transplacental neurotoxic effects of monosodium glutamate on structures and functions of specific brain areas of filial mice Acta Physiol Sinica. 1994;46:44–51
9. Ćirić M, Najman S, Bojanić V, Cekić S, Neśić M, Puškaš N. Neonatal influence of monosodium glutamate on the somatometric parameters of rats Gen Physiol Biophys. 2009;28:155–161
10. Kuznetsova EG, Amstislavskaya TG, Bulygina VV, Il'nitskaya SI, Tibeikina MA, Skrinskaya YA. Effects of administration of sodium glutamate during the neonatal period on behavior and blood corticosterone levels in male mice Neurosci Behav Physiol. 2007;37:827–833
11. Eweka AO, Eweka A, Om'Iniabohs FAE. Histological studies of the effects of monosodium glutamate of the fallopian tubes of adult female Wistar rats North Am J Med Sci. 2010;2:146–149
12. Hubscher CH, Brooks DL, Johnson JR. A quantitative method for assessing stages of the rat estrous cycle Biotech Histochem. 2005;80:79–87
13. Eweka AO, Eweka A, Om'Iniabohs FAE. Histological studies of the effects of monosodium glutamate on the ovaries of adult Wistar rats Internet J Gynecol Obstetrics. 2007;8:1–7
14. Bojanić V, Bojanić Z, Najman S, Savić T, Jakovljević V, Najman S, Jancić S. Diltiazem prevention of toxic effects of monosodium glutamate on ovaries in rats Gen Physiol Biophys. 2009;28:149–154
15. Bancroft JD, Gamble M Theory and practice of histological techniques. 20076th ed London, UK Churchill Livingstone
16. Kiernan JA Histological and histochemical methods: theory and practice. 20013rd ed Oxford A Hodder Arnold Publication
17. Adjene JO, Agoreyo FO. Effects of halofantrine hydrochloride (halfan) on the histology of the ovary of mature female Wistar rats Afr J Reprod Health. 2003;7:113–120
18. Bojanic V. The efficiency of diltiazem in prevention of monosodium glutamate toxicity on ovaries in rats Arch Oncol. 2001;9:25–26
19. Kiss P, Hauser D, Tamas A, Lubics A, Racz B, Horvath Z, et al. Changes in open-field activity and novelty-seeking behavior in periadolescent rats neonatally treated with monosodium glutamate Neurotoxicity Res. 2007;12:85–93
20. Long GG, Cohen IR, Gries CL, Young JK, Francis PC, Capen CC. Proliferative lesions of ovarian granulosa cells and reversible hormonal changes induced in rats by a selective estrogen receptor modulator Toxicol Pathol. 2001;29:403–410
21. Tsujioka S, Ban Y, Wise LD, Tsuchiya T, Sato T, Matsue K, et al. Collaborative work on evaluation of ovarian toxicity. 3): Effects of 2- or 4-week repeated-dose toxicity and fertility studies with tamoxifen in female rats J Toxicol Sci. 2009;34:SP43–SP51
22. Audi SS, Abraham ME, Borker AS. Effect of cigarette smoke on body weight, food intake and reproductive organs in adult albino rats Indian J Exp Biol. 2006;44:562–565
23. Ganong WF The gonads: development and function of the reproductive system. Review of Medical Physiology. 198713th ed Norwalk Appleton & Lange
24. Gill S, Barker M, Pulido O. Neuroexcitatory targets in the female reproductive system of the nonhuman primate (Macaca fascicularis
) Toxicol Pathol. 2008;36:478–484
25. Robinson MB. Acute regulation of sodium-dependent glutamate transporters: a focus on constitutive and regulated trafficking Handb Exp Pharmacol. 2006;175:251–275
26. Schlett K. Glutamate as a modulator of embryonic and adult neurogenesis Curr Top Med Chem. 2006;6:949–960
27. Greenwood SM, Connolly CN. Dendritic and mitochondrial changes during glutamate excitotoxicity Neuropharmacology. 2007;53:891–898
28. Weston MC, Gertler C, Mayer ML, Rosenmund C. Interdomain interactions in AMPA and kainate receptors regulate affinity for glutamate J Neurosci. 2006;26:7650–7658
29. Gerber U, Gee CE, Benquet P. Metabotropic glutamate receptors: intracellular signaling pathways Curr Opin Pharmacol. 2007;7:56–61
30. Beas Zárate C, Rivera Huizar SV, Martinez Contreras A, Feria Velasco A, Armendariz Borunda J. Changes in NMDA-receptor gene expression are associated with neurotoxicity induced neonatally by glutamate in the rat brain Neurochem Int. 2001;39:1–10
31. Bojanic V Experimental study of pathogenesis of monosodium glutamate-induced obesity. 1998 Serbia Faculty of Medicine, University of Nis
32. Dixit VD, Parvizi N. Nitric oxide and the control of reproduction Anim Reprod Sci. 2001;65:1–16
33. Hefler LA, Gregg AR. Inducible and endothelial nitric oxide synthase: genetic background affects ovulation in mice Fertil Steril. 2002;77:147–151
34. Zackrisson U, Mikuni M, Wallin A, Delbro D, Hedin L, Brannström M. Cell-specific localization of nitric oxide synthases (NOS) in the rat ovary during follicular development, ovulation and luteal formation Hum Reprod. 1996;11:2667–2673
35. Jablonka Shariff A, Olson LM. The role of nitric oxide in oocyte meiotic maturation and ovulation: meiotic abnormalities of endothelial nitric oxide synthase knock-out mouse oocytes Endocrinology. 1998;139:2944–2954
36. Tamanini C, Basini G, Grasselli F, Tirelli M. Nitric oxide and the ovary J Anim Sci. 2002;81(Suppl 2):E1–E7
37. Pocar P, Augustin R, Gandolfi F, Fischer B. Toxic effects of in vitro exposure to p-tert-octylphenol on bovine oocyte maturation and developmental competence Biol Reprod. 2003;69:462–468
38. Parent AS, Matagne V, Bourguignon JP. Control of puberty by excitatory amino acid neurotransmitters and its clinical implications Endocrine. 2005;28:281–285
39. Pavlovic V, Pavlovic D, Kocic G, Sokolovic D, Jevtovic Stoimenov T, Cekic S, Velickovic D. Effect of monosodium glutamate on oxidative stress and apoptosis in rat thymus Mol Cell Biochem. 2007;303:161–166
40. Kawatra R, Ahluwalia P. Role of sodium in oxidative stress induced by monosodium glutamate in adult male mice Toxicol Int. 2004;11:9–13
41. Gotze S, Auch Schwelk W, Bossaller C, Thelen J, Fleck E. Preventive effects of diltiazem on cyclosporin A-induced vascular smooth muscle dysfunction Transpl Int. 1994;7:157–162
42. Mustafa SB, Olson MS. Effects of calcium channel antagonists on LPS-induced hepatic iNOS expression Am J Physiol Gastrointest Liver Physiol. 1999;277:G351–G360
43. Mattioli M, Barboni B, Luisa G, Loi P. Cold-induced calcium elevation triggers DNA fragmentation in immature pig oocytes Mol Reprod Dev. 2003;65:289–297