Reproductive Hormones

3 Key excerpts on "Reproductive Hormones"

• 

  eBook - ePub

  Clinical Biochemistry of Domestic Animals

  • Jiro J. Kaneko(Author)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  Murphy, 1964 ). These techniques have added new dimensions to the study of reproductive mechanisms. The assay systems are sensitive, specific, relatively inexpensive, and require small amounts of assay material. They have been of special value for studying endocrinological reproductive functions in domestic animals in that they have made possible the study of dynamic endocrine changes through the assay of serial blood samples from the same animal. Radioimmunoassay and competitive protein binding techniques are suitable not only for physiological research, but also as diagnostic aids for the identification and elucidation of clinical reproductive problems. In clinical practice, these methods are becoming important from both a diagnostic and therapy-monitoring point of view.

  Because this book deals with clinical biochemistry in domestic animals, the main emphasis of the chapter is on the determination of hormones and the use of the data as diagnostic aids. General reproductive endocrinology in domestic species is broadly covered. Readers specifically interested in this subject are referred to specialized books dealing with this matter.

  A Definition of Hormones

  Hormones are chemical substances synthesized and secreted by ductless endocrine glands directly into the bloodstream, by which they are carried to other parts of the body, where they regulate (decrease or increase) the rates of specific biochemical processes. The endocrine glands include the pituitary (the adenohypophysis and neurohypophysis), thyroid, parathyroid, adrenal cortex and medulla, islets of Langerhans of the pancreas, ovary, testis, placenta, and pineal gland.

  B Chemical Classes of Reproductive Hormones

  1 Protein Hormones

  a Releasing Hormones.

  Several types of hormones are involved in the regulation of reproduction. Releasing hormones are peptide hormones which are produced within the hypothalamus and transferred via the hypothalamohypophyseal portal veins to the adenohypophysis, where they regulate the synthesis and/or release of adenohypophyseal hormones. The gonadotropin-releasing hormone (Gn-RH), a decapeptide with the sequence pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2 , regulates the release of two important Reproductive Hormones, namely, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Thyrotropin-releasing hormone, a tripeptide (pGlu-His-Pro-NH2

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  eBook - ePub

  Biochemistry of Andrology

  • Marco Aurélio Gouveia Alves, Pedro Fontes Oliveira(Authors)
  • 2017(Publication Date)
  • Bentham Science Publishers

    (Publisher)

  Hormonal Control of Male Reproductive Function

  Maria J. Meneses

  1 , 2

  ,

  Ana D. Martins

  1 , *

  1 Department of Microscopy, Laboratory of Cell Biology, Institute of Biomedical Sciences Abel Salazar (ICBAS) and Unit for Multidisciplinary Research in Biomedicine (UMIB), University of Porto, 4050-313 Porto, Portugal

  2 ProRegeM PhD Program, CEDOC – Chronic Diseases Research Center and NOVA Medical School, New University of Lisbon, 1150-082 Lisboa, Portugal

  Abstract

  Hormones are key regulators of the reproductive system. These signaling molecules are transported in the blood stream to reach target organs in order to regulate physiologic processes and their function. The most relevant hormones for male reproductive system are those involved in the hypothalamus-pituitary-gonads axis. Through several stimuli, anterior pituitary produces luteinizing hormone and follicle-stimulating hormone that act on testicular cells modulating both steroidogenesis and spermatogenesis. In fact, steroidogenesis, namely the production of testosterone, is crucial for the normal occurrence of spermatogenesis and for feedback actions to the pituitary and hypothalamus. However, spermatogenesis and Sertoli cells are also important to the regulation of this axis through the production of activin and inhibin B that, along with testosterone, also transmit feedback to the brain. Interestingly, in the last years, new intervenient have appeared in the regulation of male reproductive function with the discovery that adipose tissue is an endocrine organ and thus also produces hormones that may be important for this process. Along with the latter, gut hormones, which are related with the nutrient homeostasis, also modulate the function of testicular cells. In some cases, this interaction was only found due to metabolic disorders, like hyper- or hypothyroidism, obesity or diabetes mellitus. Herein, we propose to discuss the action and function of these hormones that interact with male reproductive system.

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  eBook - ePub

  Reproductive Biology of Teleost Fishes

  • Robert J. Wootton, Carl Smith(Authors)
  • 2014(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  et al., 2010). These hormones are transported in the bloodstream to the target cells in the gonads. In the gonads, FSH and LH stimulate cells to produce steroid hormones, including androgens, oestrogens and progestagens, which then regulate the processes of oogenesis and spermatogenesis (Planas & Swanson, 2008). Another important function of these steroid hormones produced in the gonads is to provide information to the brain on the present state of the gonads. The steroids have both positive and negative feedback effects on the BPG reproductive axis.

  Levels of analysis

  In analyses of the hormonal control of reproduction, decisions have to be made about the levels within the BPG axis that are to form the focus of the study. One essential of such studies is that they are accompanied by histological studies on the status of the gonads. The highest focus of analysis is the level of GnRH in the brain and the rate of transmission to the pituitary. The effect of the GnRH on the pituitary cells will depend on the density of the receptors for GnRH in the gonadotrophic cells. The rate of synthesis of GTHs can be monitored by the level of expression of the mRNAs for GTHs and the levels of GTHs in the pituitary. Plasma levels of GTHs will indicate their availability to the target organs, the gonads. However, the effect of the GTHs at the level of the gonads will depend on the density of the receptors for FSH and LH in the target cells. These target cells include the steroidogenic cells, the Leydig cells in the testis, and the theca and granulosa cells of the ovary. The levels of activity of the enzymes in the steroidogenic pathway will determine the rate of production of sex steroid hormones. This rate of synthesis will then determine the levels of sex steroids in the blood plasma, but also the levels available for paracrine functions within the gonad. The effect of the sex steroids will depend on the concentration of suitable receptors in the target cells, whether within the gonad or in extragonadal sites such as the liver, pituitary and brain. The effect of sex steroids may also be mediated by growth factors such as insulin-like growth factors (IGFs) and activin. The ultimate goal of the studies is to develop quantitative models that predict the sequence of gonadal maturation under natural conditions or under the conditions imposed in aquaculture facilities. The interpretation of the studies on the endocrinology of reproduction in teleosts, which now use the highly developed techniques of molecular biology, has been hampered by the unsophisticated analyses of the quantitative results and the lack of predictive, quantitative models based on the experimental results.

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