Testosterone Levels in Men
Testosteron-Info.comFree testosterone vs bioavailable testosterone Iranmanesh, Johannes D. Testosterone Te is metabolized in the hypothalamus and pituitary gland, where untransformed steroid haloperidol im dose activated products participate in feedback regulation of GnRH and LH secretion. LH and Te dynamics were assessed by: Genetic inactivation of the type II isozyme in mice and in rare patients with male pseudohermaphroditism type II enzyme inhibitors elevate both Te and LH concentrations, indicating feedback adaptations 145. On the other hand, transgenic mutation of the type I gene is lethal in murine progeny due to a parturitional defect 6.
Test Directory Search - Central Oahu(H)
Ali Iranmanesh, Johannes D. Testosterone Te is metabolized in the hypothalamus and pituitary gland, where untransformed steroid and activated products participate in feedback regulation of GnRH and LH secretion. LH and Te dynamics were assessed by: Genetic inactivation of the type II isozyme in mice and in rare patients with male pseudohermaphroditism type II enzyme inhibitors elevate both Te and LH concentrations, indicating feedback adaptations 1 , 4 , 5.
On the other hand, transgenic mutation of the type I gene is lethal in murine progeny due to a parturitional defect 6. Genetic deficiency of the type I enzyme has not been described clinically. The secretion of LH is subject to prominent negative feedback by Te, inferentially via combined actions of Te and its immediate metabolites, estradiol and DHT 8 — The rationale for antagonizing the activities of both enzymes is their significant but unequal topographic representation within the central nervous system-gonadotrope-testicular axis Nine healthy young men participated.
Each subject provided voluntary written informed consent approved by the Institutional Review Board. Food and Drug Administration. Entry criteria included an unremarkable medical history, physical examination, and biochemical measures of renal, hepatic, hematologic, and metabolic function and a normal prostate-specific antigen. Exclusion criteria included acute or chronic systemic disease, alcohol or drug abuse, psychiatric illness, use of any prescription medications, unprotected intercourse for 6 wk after drug administration, and failure to provide written informed voluntary consent.
Volunteers were reimbursed for the time spent in participation. Subjects received placebo and dutasteride 5 mg orally once and then 1 mg daily for 10 d single-blind in that order based upon the prolonged kinetics of this inhibitor Study sessions were separated by 3 wk or more. Beginning at h the next morning d 10 , blood samples 1. Meals were served at , , and h. Ambulation was permitted to the lavatory only. Cigarettes and caffeine-containing beverages were disallowed. Median within and between-assay coefficients of variation were 5.
Assay sensitivity was 0. Bioavailable and dialyzably free Te concentrations were assayed exactly as reported Absolute peak maximum and interpulse nadir minimum concentrations and the frequency number per 24 h of discrete LH and Te pulses were estimated by model-free Cluster analysis Basal and pulsatile secretion rates and slow-phase half-lives of LH and Te were estimated after GnRH injection by deconvolution analysis To normalize comparisons among subjects and between hormones, ApEn is first computed on the measured time series and then recalculated each of times that the series is shuffled randomly rearranged by order without replacement or loss This procedure allows calculation of the mean ratio of observed to empirically random ApEn.
A ratio of unity is mean random, whereas lower ApEn ratios denote more ordered nonrandom patterns. Cross-ApEn provides an analogous statistic to quantitate the relative pattern regularity of two coupled time series Lower cross-ApEn ratios denote greater pattern synchrony between the interlinked signals.
Derived data were first subjected to logarithmic transformation. Figure 1A illustrates paired LH and total Te concentration profiles of the median responder in the group. Data reflect sampling every 10 min for 24 h on the last day of administration of placebo and dutasteride.
By visual inspection, exposure to dutasteride compared with placebo increased Te concentrations without affecting those of LH. Estradiol concentrations did not change viz.
SHBG also remained similar viz. A, Illustrative profiles of paired LH top and total Te bottom concentrations monitored by sampling blood every 10 min for 24 h in a young man administered placebo Pl, left and dutasteride Du, right. The profiles shown are from the median responder in the cohort.
B, Total, bioavailable, and free Te concentrations in h serum pools collected after placebo and dutasteride administration in nine young men. P values are parametric estimates. FSH, prolactin, and estradiol did not differ by intervention data not shown. In contrast, administration of dutasteride compared with placebo elevated each of total, bioavailable, and free Te concentrations; viz.
Cluster analysis was used as a model-free tool to quantitate pulsatile hormone release. There were two major findings. Dutasteride compared with placebo did not change LH pulsatility, and dutasteride selectively augmented nadir Te concentrations Table 1. Principal measures of model-free cluster pulse identification in h LH and Te concentration profiles. To distinguish basal and pulsatile secretion of LH and Te, biexponential deconvolution analysis was applied to the GnRH-stimulated time series.
Because the time of the GnRH-induced LH pulse is known a priori , this strategy allows valid simultaneous assessment of intercorrelated secretion and elimination parameters 35 , Statistical comparisons indicated that basal, pulsatile, and total LH secretion rates did not differ after dutasteride and placebo administration Fig. Deconvolution-based estimates of basal nonpulsatile , pulsatile mass secreted in bursts , and total basal plus pulsatile LH A and Te B secretion after GnRH injection in young men administered placebo Pl and dutasteride Du.
P values reflect paired comparisons. Biexponential deconvolution analysis see Subjects and Methods allowed concomitant estimation of the slow-phase half-life of elimination of LH and Te Fig.
Statistical comparisons indicated that dutasteride did not affect the kinetics of either LH or Te. Deconvolution estimates of the slow-phase half-lives of LH and Te elimination following GnRH injection after exposure to placebo Pl and dutasteride Du. See data presentation in Fig. Cosinor analysis was applied to quantitate the h rhythmic variation in LH and Te concentrations. This analytical outcome is consistent with higher mean and interpulse nadir Te concentrations ApEn analysis provides a scale-free measure of the feedback-dependent regularity of hormone secretion patterns As shown in Fig.
In addition, the relative pattern synchrony of LH-driven Te release and Te-inhibited LH secretion did not differ between interventions, as quantitated by cross-ApEn of the ordered pairs. Dutasteride exposure did not alter either of these physiological relationships. ApEn calculations left , which define signal regularity orderliness under modulation by negative feedback. Dutasteride administration did not affect ApEn values or the foregoing physiological relationships.
Virtually nothing is known about the regulation of basal nonpulsatile Te secretion in the human or experimental animal. This adaptation in Te production occurred without measurable changes in the h concentration, pulsatility, nyctohemeral rhythmicity, pattern regularity, half-life, or amount of GnRH-stimulated LH secretion.
At present, we are unaware of any other well-defined nonpathological mechanisms that selectively drive the basal time-invariant mode of Te production. However, recent clinical studies of the dynamics of Te secretion indicate that aging increases basal Te secretion and decreases pulsatile Te secretion 25 , A plausible inference, therefore, is that basal hormone secretion is sparingly regulated physiologically and may be constitutive in pathological states.
Direct sampling of the human spermatic vein has disclosed an admixture of pulsatile and nonpulsatile Te secretion 46 , The current computation of fractional basal Te secretion falls within the foregoing range and was unaffected by dutasteride administration. In addition, the calculated half-life of Te disappearance Fig. A speculative explanation is that inhibition of types I vs. II reductase exerts an opposing effect on estradiol synthesis, resulting in no net change. An LH pulse stimulates an increase in Te concentrations after a time delay of about 40 min, followed by a decline to baseline 45—60 min later 40 , 47 , 49 , Thus, basal, unlike pulsatile, Te production does not appear to depend so acutely on LH pulses.
In this regard, numerous testicular paracrine and autocrine factors, including sex steroids, neurotransmitters, and peptides, can modulate Leydig cell steroidogenesis under in vitro conditions For example, Te, estradiol, and cytokines inhibit and growth factors enhance LH-stimulated androgen biosynthesis 53 — Estradiol and SHBG concentrations did not change.
By way of precedence, administration of DHT in vivo inhibits exogenous gonadotropin-stimulated ovarian steroidogenesis in the Rhesus monkey In corollary, the cross-ApEn statistic quantitates adaptations in coupling between two functionally interlinked signals By way of qualifications, first, the current cohort size confers greater than 0.
The consistency of estimated LH kinetics in the presence of dutasteride and placebo would further argue against any major change in bioactivity. This is because more biopotent LH molecules manifest an alkaline isoelectric profile due to reduced sialic acid content and exhibit more rapid disappearance from the circulation 59 , Third, given the prolonged residence time of dutasteride, the drug was always given on the second study session.
Although an order effect cannot be excluded absolutely, it would have occurred only for Te and not LH or estradiol measurements. Test-retest analyses in young men studied three times without intervention establish high intraindividual reproducibility of estimates h LH secretion The proximate mechanism entails stimulation of basal nonpulsatile Te secretion.
This adaptation accounts for augmentation of interpulse nadir, daily mean, and the mesor of h rhythmic Te concentrations. Amplified basal Te secretion is selective, in that dutasteride does not alter the amplitude of the h Te rhythm, the slow-phase half-life of Te, Te secretory regularity, and any of multiple measures of LH dynamics.
Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide.
Sign In or Create an Account. Close mobile search navigation Article navigation. View large Download slide. Hypothalamic sites of action for testosterone, dihydrotestosterone, and estrogen in the regulation of luteinizing hormone secretion in male sheep. On the role of dihydrotestosterone in regulating luteinizing hormone secretion in man. Differential regulation of gonadotropin-releasing hormone secretion and gene expression by androgen: Contemporary aspects of discrete peak detection algorithms: The paradigm of the luteinizing hormone pulse signal in men.
Sie haben zu viele Anfragen gesendet, sodass Linguee Ihren Computer ausgesperrt hat.
The amount of SHBG and albumin in serum and the total testosterone concentration determine the distribution of free and bioavailable testosterone. DHT has a greater affinity to SHBG than does testosterone. the total testosterone concentration determine the distribution of free and bioavailable testosterone. Febr. Men with low serum testosterone levels had a significantly higher .. (U test or t- test) for men with testosterone levels, vs.! nmol/L and .. total, free and bioavailable testosterone and of SHBG in middle-aged men com-.