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Gonadostat control

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
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
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
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
R Bhanot, M Wilkinson
We have examined (1) the effects of naloxone and an opiate peptide, FK 33-824, on LH and FSH secretion in immature male and female rats and (2) the influence of sexual maturation on the ability of this peptide to inhibit LH secretion. FK 33-824 potently inhibits LH secretion in the 48-h-gonadectomized rat. This effect could be blocked by coinjection of naloxone, suggesting that the peptide exerts its influence through opiate receptors. An endogenous opiate component in the control of LH secretion was demonstrated by examining the effect of naloxone injection alone...
August 1983: Endocrinology
S R Ojeda, L I Aguado, S Smith
The advent of female puberty represents the culmination of a diversity of developmental processes which affect all components of the reproductive axis. Development of neuroendocrine reproductive functions proceeds in a harmonious and interrelated manner. No unique 'trigger' of puberty can be discerned, but rather puberty represents the climax of a cascade of events, finely interconnected throughout the continuum of sexual maturation. A resetting of the hypothalamic 'gonadostat' to steroid negative feedback appears to be a phenomenon associated with puberty, but not its cause...
October 1983: Neuroendocrinology
R P Kelch, S L Kaplan, M M Ghumbach
Clomiphene citrate, an "anti-estrogen" with mild estrogenic properties, inhibits rather than stimulates gonadotropin excretion in prepubertal and early pubertal children. These and other data suggest that the sensitivity of the hypothalamic-pituitary "gonadostat" decreases at the onset of puberty. To test this hypothesis further, the daily excretion of urinary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was determined in 19 children (5 "short normals" and 14 with isolated human growth hormone (HGH) deficiency) who were given ethinyl estradiol (EE) 1...
May 1973: Journal of Clinical Investigation
K Kula, S Dulko, M Pawlikowski, K Imieliński, J Słowikowska
Principal parameters of gonadostat function were determined in 15 female-to-male (F-M) and 7 male-to-female (M-F) transsexual patients (T), all homosexuals. The data were compared with normal heterosexual controls of the respective sex. Anamnesis revealed prolongation of the menstrual cycles in F-M patients, mainly in those taking previously medication with depot-testosterone. However, also in patients with no previous medication the basal body temperature chart revealed anovulatory cycles (all 4 examined patients)...
June 1986: Experimental and Clinical Endocrinology
D H Olster, D L Foster
The gonadostat hypothesis, i.e. that a decrease in response to the inhibitory feedback action of gonadal steroids occurs during puberty, was tested in the male lamb. Also investigated was whether a simultaneous steroid-independent rise in gonadotropin secretion could be the underlying mechanism for the reduction in steroid feedback sensitivity during puberty. Sexual maturation in intact Suffolk lambs was characterized by increases in all of the following parameters: Serum FSH and LH and LH pulse frequency (during 4-7 weeks of age), testicular size and testosterone (T) concentrations (during 7-28 weeks of age)...
June 1986: Endocrinology
K D Ryan, S L Robinson, S H Tritt, A J Zeleznik
The purpose of this study was to examine the role of circulating 17 beta-estradiol in the regulation of pituitary gonadotropin secretion and, hence, ovarian maturation in immature female ferrets. The hypersensitive negative feedback relationship between the ovaries and the hypothalamo-pituitary axis in developing ferrets was disrupted by infusion of a specific antiserum to 17 beta-estradiol. The effect of this treatment on gonadotropin secretion and ovarian morphology was contrasted with that observed in intact age-matched control females treated with a nonimmune gamma-globulin preparation...
April 1988: Endocrinology
H G Bohnet, H J Wiest, H G Dahlén, H P Schneider
The magnitude and frequency of episodic LH-fluctuations have been observed to change during the different phases of the menstrual cycle. A hypothalamic control center appears to be responsible for these variations. Disturbances of the hypothalamus often make themselves known through a lack of LH-episodes. Ahypothalamic derangement in women with functional amenorrhoea can result in a disregulation of gonadotropins as well as prolactin, thereby leading to hyperprolactinemia. One finds an inverse relationship between high prolactin secretion and cessation of or decreased pulsatile LH-secretion (spiking)...
November 1975: Endokrinologie
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