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A submaximal dose of the GnRH antagonist ganirelix was used to assess outflow of GnRH, by calculating the difference between LH output during the control arm and ganirelix arm. Ketoconazole (a steroidogenic inhibitor) was used to estimate feedback, by the difference in LH output during the ketoconazole and control arm. High-dose ganirelix and repeated LH infusions were used to measure testicular responsivity. Blood sampling was performed at 10-minute intervals.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>There were age-related, but not body composition\u2013related decreases in estimated GnRH secretion, the feedback strength of Te on LH, and Leydig cell responsivity to LH, accompanied by changes in approximate entropy. Bioavailable Te levels were negatively related to both age and computed tomography (CT)\u2013estimated abdominal visceral mass (AVF), without interaction between these variables. The LH response to a submaximal dose of GnRH was independent of age and AVF.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Advancing age is associated with (1) attenuated bioavailable Te secretion caused by diminished GnRH outflow and not by decreased GnRH responsivity of the gonadotrope, (2) diminished testicular responsivity to infused LH pulses, and (3) partial compensation by diminished Te feedback on central gonadotropic regulation.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1210\/clinem\/dgz246","type":"journal-article","created":{"date-parts":[[2019,12,9]],"date-time":"2019-12-09T09:07:19Z","timestamp":1575882439000},"page":"e628-e641","source":"Crossref","is-referenced-by-count":19,"title":["Dynamic Interactions Between LH and Testosterone in Healthy Community-Dwelling Men: Impact of Age and Body Composition"],"prefix":"10.1210","volume":"105","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6276-2834","authenticated-orcid":false,"given":"Ferdinand","family":"Roelfsema","sequence":"first","affiliation":[{"name":"Department of Internal Medicine, Section Endocrinology and Metabolism, Leiden University Medical Center , Leiden,","place":["The Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter Y","family":"Liu","sequence":"additional","affiliation":[{"name":"Department of Medicine, David Geffen School of Medicine at UCLA, Harbor-UCLA Medical Center and Los Angeles Biomedical Research Institute , Los Angeles, California"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paul Y","family":"Takahashi","sequence":"additional","affiliation":[{"name":"Department of Primary Care Internal Medicine, Mayo Clinic , Rochester, Minnesota"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rebecca J","family":"Yang","sequence":"additional","affiliation":[{"name":"Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities , Mayo Clinic, Rochester, Minnesota"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Johannes D","family":"Veldhuis","sequence":"additional","affiliation":[{"name":"Endocrine Research Unit, Mayo School of Graduate Medical Education, Center for Translational Science Activities , Mayo Clinic, Rochester, Minnesota"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"80","published-online":{"date-parts":[[2019,12,2]]},"reference":[{"issue":"9","key":"2026041420195078700_CIT0001","doi-asserted-by":"crossref","first-page":"1502","DOI":"10.1111\/j.0002-8614.2004.52413.x","article-title":"Changes in sexual function in middle-aged and older men: longitudinal data from the Massachusetts Male Aging Study","volume":"52","author":"Araujo","year":"2004","journal-title":"J Am Geriatr Soc."},{"issue":"2","key":"2026041420195078700_CIT0002","doi-asserted-by":"crossref","first-page":"145","DOI":"10.1530\/eje.0.1490145","article-title":"The associations of age, lifestyle factors and chronic disease with testosterone in men: the Troms\u00f8 Study","volume":"149","author":"Svartberg","year":"2003","journal-title":"Eur J Endocrinol."},{"key":"2026041420195078700_CIT0003","first-page":"285","article-title":"The hypothalamo-pituitary unit, testis, and male accessory organs.","volume-title":"Reproductive Endocrinology","author":"Liu","year":"2018"},{"issue":"7","key":"2026041420195078700_CIT0004","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1016\/0895-4356(91)90028-8","article-title":"An examination of research design effects on the association of testosterone and male aging: results of a meta-analysis","volume":"44","author":"Gray","year":"1991","journal-title":"J Clin Epidemiol."},{"issue":"2","key":"2026041420195078700_CIT0005","doi-asserted-by":"crossref","first-page":"724","DOI":"10.1210\/jcem.86.2.7219","article-title":"Longitudinal effects of aging on serum total and free testosterone levels in healthy men. 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