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Michael F Smith, Rodney D Geisert, John J Parrish
The study of reproductive physiology in domestic ruminants has progressed from the whole animal to the molecular level in an amazingly short period of time. The volume of information on this subject is enormous; therefore, we have focused on domestic ruminants, with an emphasis on cattle. To date, artificial insemination (AI) is perhaps the most powerful technique that reproductive physiologists and geneticists have provided the livestock industry for genetic improvement. Early efforts to establish AI as a tool were initiated in Russia around 1899 and since that time major advances in methods of semen collection, evaluation of male fertility, cryopreservation of sperm, sex-sorted semen, and estrous cycle control have occurred...
April 19, 2018: Journal of Animal Science
Stine A Holmboe, Lærke Priskorn, Niels Jørgensen, Niels E Skakkebaek, Allan Linneberg, Anders Juul, Anna-Maria Andersson
Based on a large population of 1113 men aged 30-60 at baseline (mean: 44.1 years, standard deviation: 10.5), we investigated whether intra-individual changes in testosterone (T) and related reproductive hormones during a ten year period were dependent of marital status at baseline and follow-up. The studied men were part of a health survey in Denmark, conducted between 1982 and 1984 with a follow-up examination approximately ten years later. Data on reproductive hormones, measured in serum, and lifestyle and marital status were obtained at both time points...
June 2017: Psychoneuroendocrinology
J H Check
PURPOSE: To evaluate the influence of sleep on early pre-pubertal and pubertal development and to explore the importance of circadian rhythms and gonadotropin secretion. METHODS: Mechanisms of suppression and turning on of the hypothalamic gonadotropin releasing hormone (GnRH) pulse generator at different times in development are evaluated. Furthermore, the influence of neurotransmitters in controlling pubertal development is also considered. RESULTS: By the end of the first year, certain genes are activated that cause marked sensitivity of the GnRH pulse generator to negative feedback of circulating sex steroid...
2013: Clinical and Experimental Obstetrics & Gynecology
C R Barb, G J Hausman, R R Kraeling
The aim of this study was to determine if there is an age related reduction in the sensitivity of the negative feedback action of 17β-estradiol (estradiol) on luteinizing hormone (LH) secretion in the prepubertal gilt. Ovariectomized gilts at 90 (n=12), 150 (n=11) or 210 (n=12) days of age received estradiol benzoate (EB) osmotic pump implants 6/group and the remaining animals received vehicle control (C) implants except for 150-day C (n=5) on Day 0. On Day 10 blood samples were collected every 15 min for 8h and serum LH and estradiol concentrations were measured...
December 2010: Animal Reproduction Science
Ioannis E Messinis
Marked changes in hormone secretion occur from childhood to adulthood. Prior to puberty gonadotropin-releasing hormone (GnRH) secretion is markedly suppressed. At the onset of puberty, the hypothalamic gonadostat is derepressed and the amplitude of GnRH pulses increases. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels increase gradually during puberty stimulating follicle maturation and estrogen production in the ovaries. Only the negative feedback mechanism is powerful before puberty, while the positive feedback mechanism becomes active for the first time in late puberty...
December 2006: Annals of the New York Academy of Sciences
O Wasielewski, G Rosiński
The gonadostatic action of the peptides Neb-colloostatin (SIVPLGLPVPIGPIVVGPR) and Neb-TMOF (NPTNLH) from Neobellieria bullata was studied in female mealworm Tenebrio molitor. Both peptides potently inhibit ovarian development and terminal oocyte maturation of mated females during their first reproductive cycle. Injection of 4 mug of Neb-colloostatin or Neb-TMOFNeb-TMOF reduced, at day 4 of the cycle, the size of the terminal oocytes to about half or one third of the normal size in saline-injected controls...
March 2007: Archives of Insect Biochemistry and Physiology
N Lima, H Cavaliere, M Knobel, A Halpern, G Medeiros-Neto
OBJECTIVE: In obese men, sex hormone-binding globulin (SHBG) as well as total testosterone (TT) levels are decreased. Data concerning serum free testosterone (FT) levels in obese men are discordant. FT levels are decreased in only some morbidly obese men, consistent with an impairment of the feedback regulatory mechanism. In this study we aimed to verify serum levels of TT and FT in two groups of obese men (BMI < 35.0 kg/m2 and BMI > 35.1 kg/m2) before and after weight loss. DESIGN: Two groups of obese men (group 1: BMI < or = 35 kg/m2; and group 2: BMI > or =35...
November 2000: International Journal of Obesity and related Metabolic Disorders
S E Dolgin
Prenatal sonography uncovers many fetal ovarian masses that previously would have gone unrecognized. This challenges clinicians to learn the natural history of these asymptomatic lesions so as to provide the best care postnatally. Spontaneous resolution of simple ovarian cysts is expected by about 6 months of age, which is attributed to predicted changes in the postnatal hormonal milieu. After birth, levels of human chorionic gonadotropin (HCG) and estrogen plummet. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) rise until about 3 months of age and then fall as the "gonadostat" matures...
August 2000: Seminars in Pediatric Surgery
A R Genazzani, F Bernardi, P Monteleone, S Luisi, M Luisi
Puberty results from withdrawal of the "gonadostat" mechanisms and from increased gonadotropin sensitivity to GnRH. It has been hypothesized that GnRH release may be modulated by a non-steroid-mediated mechanism. Modifications of neuropeptides, neurotransmitters, and neurosteroids may underlie the onset of pubertal processes. Neuropeptides mainly involved in the control of GnRH release are opioids, neuropeptide Y (NPY), galanin, and corticotropin-releasing factor (CRF), whereas neurotransmitters are noradrenaline, dopamine, serotonin, melatonin and gamma-aminobutyric acid (GABA)...
2000: Annals of the New York Academy of Sciences
Sh N Galimov, G R Valeeva
Characteristics of spermatogenesis, morphometric changes in the Leydig's and Sertoli's cells, and fertility of albino rats exposed to various doses of 2.4-D were investigated. Chronic injection of the herbicide led to transitional sterility against pronounced disorders of spermatogenesis, hyperplasia of sertolicytes and predominance of low-active forms of the Leydig's cells. An assumption concerning possible role of altered gonadostat in genesis of the reproductive disorders is offered.
1999: Aviakosmicheskaia i Ekologicheskaia Meditsina, Aerospace and Environmental Medicine
O V Slaetna, H I Khodorovs'kyĭ
Results of experimental investigations of the effect of the epiphysectomy and brain lateral septal nucleus (LSN) destruction on the morphofunctional conditions of the genital system of juvenile female white rats kept under different illumination conditions are described. The analysis of consequences of epiphysectomy and LSN destruction as well as of these operative influences taken together shows that the morphofunctional condition of the female genital apparatus changes more intensively in rats kept under the constant illumination and less intensively in those kept under variation of light and darkness, which affected the estradiol production function of rats...
January 1995: Fiziolohichnyĭ Zhurnal
B Bidzińska, D Jedrzejuk
Gonadal steroids and beta-endorphin (beta-EP) (and probably other - EOP endogenous opioid peptides) play a role of the pivotal hormones involved in integration of several neurophysiological mechanisms. The reproductive system could be disturbed at hypothalamic level by interference of beta-EP and GnRH secretion and/or at pituitary level with response of gonadotropes to GnRH. Gonadal steroids, through a feedback mechanism, may exert similar effect on hypothalamus and/or pituitary. The action of EOP on the hypothalamo-pituitary-gonadal axis may be influenced by physiological and pathological changes in gonadal steroids during puberty, menstrual cycle in females, menopause, in case of idiopathic delayed puberty, in patients with gonadal dysgenesis or after castration...
1995: Postȩpy Higieny i Medycyny Doświadczalnej
V A Giagulli, J M Kaufman, A Vermeulen
In obese men, sex hormone-binding globulin levels (SHBG) as well as total plasma testosterone (T) levels are decreased. Data concerning the levels of nonprotein-bound testosterone (FT) are discordant, with some researchers reporting normal levels, and other reporting decreased levels. The latter imply an impairment of the feedback regulation mechanism of FT levels. We investigated whether an eventual decrease in FT levels and, hence, functional impairment of the gonadostat might occur only at a more severe degree of obesity than that required for a decrease in SHBG and total T levels...
October 1994: Journal of Clinical Endocrinology and Metabolism
A Vermeulen
Aging is accompanied by important changes in the production and secretion of hormones. These partly arise from changes in the peripheral endocrine glands themselves but are also partly the consequence of changes in the neuro-endocrine regulating centers of the hormone secretion. Considering e.g. the male gonads, we know that the reduced androgen secretion (and the diminished spermatogenesis) along the ageing process is the consequence of changes in the testes, such as the reduced number of Leydig- and Sertoli-cells, as well as a reduced testicular blood-perfusion...
1994: Verhandelingen—Koninklijke Academie Voor Geneeskunde Van België
P Marrama, C Carani, G F Baraghini, A Volpe, D Zini, M F Celani, V Montanini
The role which testicular hormones have on the decrease of sexual function in ageing men is still uncertain, but of primary interest. Previously, it has been known that the impairment of Leydig cell activity is a causal factor in the decreasing sexual function in ageing men. The present study is an evaluation of some chronobiological aspects, which directly or indirectly concern the 'Gonadostat' in ageing men, in order to determine of any change of the hypothalamic-pituitary axis occurs during the ageing process...
August 1982: Maturitas
D F Wittenberg
Four male cousins showed clinical and biochemical features of X-linked recessive congenital adrenocortical hypoplasia. In addition, they showed varying degrees of androgenic precocity. One was virilised at birth. Another showed advanced growth and skeletal maturation. The remaining two had genital measurements greater than normal for age and showed raised testosterone levels, although pituitary gonadotrophins seemed normal and there was no response to luteinising hormone-releasing hormone testing. It is suggested that in X-linked adrenal hypoplasia, intrauterine adrenal androgen deficiency results in abnormal priming of the pituitary 'gonadostat', leading to an abnormal feedback with excess testosterone production and nonprogressive virilisation...
August 1981: Archives of Disease in Childhood
T M Plant, D S Zorub
The neuroendocrine basis underlying timing of the onset of puberty in rhesus monkeys is examined in this review. The immediate stimulus responsible for the initiation of the pubertal process originates within the central nervous system and is relayed to the pituitary-gonadal axis by an intermittent pattern of gonadotropin releasing hormone (GnRH) secretion, which is viewed as being generated by a neural oscillator resident within the hypothalamus. While results of recent studies in male rhesus monkeys suggest that this hypothalamic oscillator is fully functional by the neonatal stage of ontogeny, sexual maturity in this species is not attained until after 3 to 4 yr of prepubertal development...
1982: Journal of Animal Science
W W Andrews, J P Advis, S R Ojeda
Several experiments were performed to study the changes in the negative feedback of estradiol on gonadotropin secretion around the time of puberty in the female rat. Ovariectomy of juvenile, first diestrus, or adult animals elevated FSH and LH levels 2 and/or 4 days later. Estradiol administered via Silastic capsules, at several dose levels, was much more effective in preventing the postcastration rise of gonadotropins in juvenile than in the older animals. A dose of estradiol that inhibited gonadotropin levels in juvenile rats, but not in adult animals, maintained preovariectomy serum estradiol levels more efficiently in the adult rats...
December 1981: Endocrinology
E Terasawa, W E Bridson, T E Nass, J J Noonan, D J Dierschke
Developmental changes in LH release patterns were observed longitudinally in female rhesus monkeys at 10-65 months of age. The average ages of menarche and first ovulation in this experiment (n = 14) were 31.1 +/- 2.6 and 47.0 +/- 2.6 months (mean +/- SE), respectively. To assess the ovarian influence on developmental changes in LH, data were simultaneously obtained from neonatally ovariectomized animals at similar ages. The estimation of circulating LH was made with RIA as well as biological assay. During the prepubertal period (10-20 months of age), basal LH was very low, and there was no circadian fluctuation of LH in gonadally intact monkeys...
December 1984: Endocrinology
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