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      Thyroid and male reproduction

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          Abstract

          Male reproduction is governed by the classical hypothalamo-hypophyseal testicular axis: Hypothalamic gonadotropin releasing hormone (GnRH), pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) and the gonadal steroid, principally, testosterone. Thyroid hormones have been shown to exert a modulatory influence on this axis and consequently the sexual and spermatogenic function of man. This review will examine the modulatory influence of thyroid hormones on male reproduction.

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          Most cited references66

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          Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis.

          Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.
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            Thyroid hormone action in mitochondria.

            Triiodothyronine (T3) is considered a major regulator of mitochondrial activity. In this review, we show evidence of the existence of a direct T3 mitochondrial pathway, and try to clarify the respective importance of the nuclear and mitochondrial pathways for organelle activity. Numerous studies have reported short-term and delayed T3 stimulation of mitochondrial oxygen consumption. Convincing data indicate that an early influence occurs through an extra-nuclear mechanism insensitive to inhibitors of protein synthesis. Although it has been shown that diiodothyronines could actually be T3 mediators of this short-term influence, the detection of specific T3-binding sites, probably corresponding to a 28 kDa c-Erb Aalpha1 protein of the inner membrane, also supports a direct T3 influence. The more delayed influence of thyroid hormone upon mitochondrial respiration probably results from mechanisms elicited at the nuclear level, including changes in phospholipid turnover and stimulation of uncoupling protein expression, leading to an increased inner membrane proton leak. However, the involvement of a direct mitochondrial T3 pathway leading to a rapid stimulation of mitochondrial protein synthesis has to be considered. Both pathways are obviously involved in the T3 stimulation of mitochondrial genome transcription. First, a 43 kDa c-Erb Aalpha1 protein located in the mitochondrial matrix (p43), acting as a potent T3-dependent transcription factor of the mitochondrial genome, induces early stimulation of organelle transcription. In addition, T3 increases mitochondrial TFA expression, a mitochondrial transcription factor encoded by a nuclear gene. Similarly, the stimulation of mitochondriogenesis by thyroid hormone probably involves both pathways. In particular, the c-erb Aalpha gene simultaneously encodes a nuclear and a mitochondrial T3 receptor (p43), thus ensuring coordination of the expression of the mitochondrial genome and of nuclear genes encoding mitochondrial proteins. Recent studies concerning the physiological importance of the direct mitochondrial T3 pathway involving p43 led to the conclusion that it is not only involved in the regulation of fuel metabolism, but also in the regulation of cell differentiation. As the processes leading to or resulting from differentiation are energy-consuming, p43 coordination of metabolism and differentiation could be of significant importance in the regulation of development.
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              Reactive oxygen species and human spermatozoa. II. Depletion of adenosine triphosphate plays an important role in the inhibition of sperm motility.

              Under moderate conditions, reactive oxygen species (ROS) have been shown to inhibit sperm motility after several hours of incubation. The rapid decrease in flagellar beat frequency observed within the first hour of contact between ROS and spermatozoa was associated with a rapid loss of intracellular adenosine triphosphate (ATP). Motility of intact spermatozoa ceased when their ATP concentration was reduced by 85 +/- 5%. Axonemal damage was confirmed when ROS-treated spermatozoa could not reactivate motility after demembranation in a medium containing magnesium adenosine triphosphate (Mg.ATP). However, in conditions allowing rephosphorylation of the axonemes (addition of cyclic adenosine monophosphate, or cAMP, and protein kinase or sperm extracts to the demembranation medium), the motility could reactivate. Three lines of evidence suggested that ATP depletion induced by ROS treatment was responsible for the effects observed in spermatozoa. First, the rapid decrease in intracellular ATP observed after ROS treatment was closely followed by a decrease in beat frequency, loss of intact sperm motility, and axonemal damage due to insufficient phosphorylation. Second, incubation of spermatozoa with the combination pyruvate-lactate allowed maintenance of sperm ATP at a normal level and prevented the effects of ROS; furthermore, spermatozoa immobilized after ROS treatment, then supplemented with pyruvate-lactate, were able to reinitiate motility in parallel with an increase in their ATP level. Third, treatment of spermatozoa with rotenone, an ATP depleting agent, produced effects similar to ROS treatment and could also be reversed by the addition of pyruvate-lactate. These data are consistent with the conclusion that ROS treatment produced axonemal damage mostly as a result of ATP depletion.(ABSTRACT TRUNCATED AT 250 WORDS)
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                Author and article information

                Journal
                Indian J Endocrinol Metab
                Indian J Endocrinol Metab
                IJEM
                Indian Journal of Endocrinology and Metabolism
                Medknow Publications & Media Pvt Ltd (India )
                2230-8210
                2230-9500
                Jan-Feb 2014
                : 18
                : 1
                : 23-31
                Affiliations
                [1] Department of Reproductive Biology, All India Institute of Medical Sciences, New Delhi, Intern, India
                [1 ] University College of Medical Sciences, Delhi, India
                Author notes
                Correspondence Author: Prof. Anand Kumar, Department of Reproductive Biology, All India Institute of Medical Sciences, New Delhi - 110 029, India. E-mail: anandkumarrepbiol@ 123456hotmail.com
                Article
                IJEM-18-23
                10.4103/2230-8210.126523
                3968728
                24701426
                342f7826-9d6c-46c0-bcb2-06c99c070c33
                Copyright: © Indian Journal of Endocrinology and Metabolism

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Categories
                Review Article

                Endocrinology & Diabetes
                hyperthyroidism,hypothyroidism,leydig cells,sertoli cells,sperm function,tri-iodothyronine

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