• Samia A. Eleiwe Department of Anatomy; AlKindi College of Medicine; University of Baghdad, Iraq.
  • Nibras Hatim Khamees Department of Anatomy, School of Medicine, Faculty of Medical Sciences, University of Sulaimani, Kurdistan Region, Iraq.
  • Shilan Hussein Karim Department of Anatomy, School of Medicine, Faculty of Medical Sciences, University of Sulaimani, Kurdistan Region, Iraq.



Thyroid, Melatonin, Darkness, Endocrine



The thyroid glands function and structure are influenced by several psychomotor stimulants like: temperature, drugs, chemicals and light. The purpose of this study was to investigate the effect of continuous darkness on the thyroid glands of male rats. Despite so many previous works to explore the effect of exogenous or endogenous melatonin on thyroid, there are few studies dealing with the outcome of progressively increasing phases of darkness on thyroid architecture, according to the available literatures.


This work is intended to study the effect of rising period of continuous darkness on thyroid tissues in adult male rats.


Adult Wister albino rats were kept in total 24 hours darkness for successive 4 phases. These rats were divided into 8 groups. Group II, III, IV and V were cited in continuous darkness for 2, 4, 6 and 8 weeks in that order. Group Iɑ, Group Ib, Group Ic , and Group Id were control groups of group II, III, IV and V likewise. After the last day of the dark phase dedicated for each group, the animals were sacrificed under effect of anesthesia. The thyroid gland was separated, weighed and right lobe was practiced to study its structural changes.


The results illustrated no key structural effect by short and medium phases of darkness, while on long phases; there was detrimental effect on thyroid tissues.


The continuous darkness for a long time has undesirable histological and anatomical changes on the thyroid tissues of the adult male rats in a manner correlated with the length of publicity.


- Cass H. Let There Be Dark—and Melatonin. Science News. 2006. Available from: http:// magazine/article/1677-let-there-be-dark-and-melatonin ‎

- Richard . "Thyroid gland", in Clinical anatomy by regions.8th ed. Lippincott Wiliams &Wilkins. p. 817.

- Bowen R. The Pineal Gland and Melatonin. 2003; Available from: .

- Blask DE, Hill SM, Dauchy RT, Xiang S, Yuan L, Duplessis T, et al. Circadian regulation of molecular, dietary, and metabolic signaling mechanisms of human breast cancer growth by the nocturnal melatonin signal and the consequences of its disruption by light at night. J Pineal Res. 2011; 51(3): 259-69. DOI:

- Grande E, Díez JJ, Zafon C, Capdevila J. Thyroid Cancer: Molecular Aspects and New Therapeutic Strategies. J Thyroid Res. 2012; 2012:10. DOI:

- Sullivan MC, Roman SA, Sosa JA. Clinical and Economic Outcomes of Thyroid Surgery in Elderly Patients: A Systematic Review. J Thyroid Res. 2012; 2012:7. DOI:

- El-Kaissi S, Wall JR. Determinants of Extraocular Muscle Volume in Patients with Graves' Disease. J Thyroid Res. 2012; 2012:4. DOI:

- Kamath C, Adlan MA, Premawardhana LD. The Role of Thyrotrophin Receptor Antibody Assays in Graves’ Disease. J Thyroid Res. 2012: 2012:8. DOI:

- Davies TF, Latif R,Yin X. New Genetic Insights from Autoimmune Thyroid Disease. J Thyroid Res. 2012;2012:6. DOI:

- Schaarschmidt J, Paschke S, Özerden M, Jäschke H, Huth S, Eszlinger M, et al. Late Manifestation of Subclinical Hyperthyroidism After Goitrogenesis in an Index Patient with a N670S TSH Receptor Germline Mutation Masquerading as TSH Receptor Antibody Negative Graves' Disease. Horm Metab Res. 2012; 44(13):962-5. DOI:

- Eleiwe SA, Mobarak HJ, Al-Taii AA. Exogenous Melatonin Induces Histological changes In The Male rat Thymus. Iraqi Journal of Medical Sciences. 2008;6(2):74-80.

- Bancroft JD, Stevens A. Theory and practice of Histological Techniques. Edinburgh: Churchill Livingstone; 1987. p. 482-502.

- Baker FJ, Silverton RE, Pallister CJ. Baker and Silverton´s Introduction to Medical Laboratory Technology. 7th ed. UK: Hodder Education Publishers; 1998.

- Aherne, W. A. and Dunnill, M. S. (1982): Morphometry. London: Edward Arnold, P 46-59.

- Daniel W. Biostatistics: A Foundation for analysis in the health sciences. 9th ed. New York: John Wiley; 2008. P. 273-295.

- Afzal R. Melatonin: Miracles far beyond the pineal gland. Indian J Endocr Metab. 2012;16(4):672-4. DOI:

- Kvetnoy IM. Extrapineal melatonin: location and role within diffuse neuroendocrine system. Histochem J. 1999;31(1):1-12. DOI:

- Dardente H. Melatonin-Dependent Timing of Seasonal Reproduction by the Pars Tuberalis: Pivotal Roles for Long Day lengths and Thyroid Hormones. J Neuroendocrinol. 2012;24(2):249-66. DOI:

- Wolden-Hanson, T.; Mitton, D. R.; McCants, R. L.; Yellon, S. M.; Wilkinson, C. W.; Matsumoto, A. M. and Rasmussen, D. D. (2000): "Daily melatonin administration to middle-aged male rats suppresses body weight, intra-abdominal adiposity, and plasma leptin and insulin independent of food intake and total body fat. Endocrinology. 2000;141(2):487–97. DOI:

- Fleur SE. Daily rhythms in glucose metabolism: suprachiasmatic nucleus output to peripheral tissue. J Neuroendocrinol. 2003;15:315–22. DOI:

- Tan DX, Manchester LC, Fuentes-Broto L, Paredes SD, Reiter RJ. Significance and application of melatonin in the regulation of brown adipose tissue metabolism: relation to human obesity. Obes Rev 2011;12(3):167–88. DOI:

- Association Medical Association. Decreased Melatonin Secretion Associated With Higher Risk of Developing Type 2 Diabetes. 2013; Available from:

- Sugden D, Davidson K, Hough KA, Teck MT. Melatonin, melatonin receptors and melanophores: a moving story. Pigment Cell Res. 2004;17(5):454–60. DOI:

- Slominski RM, Reiter RJ, Schlabritz-Loutsevitch N, Ostrom RS, Slominski AT. Melatonin membrane receptors in peripheral tissues: Distribution and functions. Mol Cell Endocrinol. 2012;351:152-66. DOI:

- Anisimov VN, Alimova IN, Baturin DA, Popovich IG, Zabezhinski MA, Rosenfeld SV, et al. Dose-dependent effect of melatonin on life span and spontaneous tumor incidence in female SHR mice. Exp Gerontol. 2003;38(4):449–61. DOI:

- Succu S, Berlinguer F, Pasciu V, Satta V, Leoni GG, Naitana S. Melatonin protects ram spermatozoa from cryopreservation injuries in a dose-dependent manner. Journal of Pineal Research. 2011;50(3):310-8 DOI:

- Bahadori MH, Ramazani M, Asghari-Nohadani Z. Melatonin dose- dependent effect on oocyte maturation capacity, in vitro fertilization and blastocyst development in mouse. KOWSAR MEDICAL JOURNAL SUMMER 2011;16(2):67-71.

- Fawcett DW. Bloom and Fawcett: Concise Histology [Paperback] 2002.

- Stevens A, Lowe J. PATHOLOGY: Mosby; 2000.

- González A, Alvarez-García V, Martínez-Campa C, Alonso-González C, Cos S. Melatonin promotes differentiation of 3T3-L1 fibroblasts. Journal of Pineal Research. 2012;52(1):21-20. DOI:

- Xie YF, Zhang JC, Liu SJ, Dai LB, Du GW. Effect of melatonin on proliferation and apoptosis of fibroblasts in human hypertrophic scar. Zhonghua Shao Shang Za Zhi. 2011;27(6):422-6.

- Olatunji-Bello II, Sofola OA. Effect of continuous light and darkness exposures on the pituitary – gonadal axis and thyroid activity in male rats. Afr J Biomed Res. 2001;4:119 – 22. DOI:

- Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis Of Diseases. 7th ed: Elsevier Saunders; 2005. P. 880.

- Forsling ML, Wheeler MJ, Williams AJ. The effect of melatonin administration on pituitary hormone secretion in man. Clinical Endocrinology- Oxf. 1999;51(5):637-42. DOI:

- Korde JP, Srivastava RS, Mishra SC, Sharma AK. Time dependent immunomodulatory response of exogenous melatonin to killed Pasteurella multocida (P52 strain) vaccine in albino rats. Indian-J-Physiol-Pharmacol. 2005;49(2):227-35.






How to Cite

Eleiwe S, Khamees N, Karim S. CONTINUOUS DARKNESS INDUCES STRUCTURAL CHANGES IN THYROID GLAND OF ADULT MALE RATS. JSMC [Internet]. 2014 Jun. 1 [cited 2024 Feb. 29];4(1):1-9. Available from:

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