Relative roles of inhibin B and sex steroids in the negative feedback regulation of follicle-stimulating hormone in men across the full spectrum of seminiferous epithelium function

CONTEXT AND OBJECTIVE: Our aim was to explore the relative roles of gonadal sex steroids and inhibin B in the regulation of FSH across a spectrum of seminiferous epithelium function. SUBJECTS: The study included three groups: group I, healthy men (n = 31); group II, men with idiopathic hypogonadotropic hypogonadism receiving pulsatile GnRH (n = 12) selected to represent a spectrum of seminiferous tubular development, testicular size, and baseline inhibin B levels; and group III, men with functional anorchia (n = 3) receiving testosterone replacement. DESIGN: Subjects were studied before and after 3 d of acute sex steroid withdrawal. SETTING: The study was conducted at the Mallinckrodt General Clinical Research Center of Massachusetts General Hospital. INTERVENTIONS: Acute biochemical castration was achieved using high-dose ketoconazole (groups I and II) or withdrawal of androgen therapy (group III). MAIN OUTCOME MEASURES: The relationship between FSH and inhibin B in both normal and castrate sex steroid milieu was measured. RESULTS: In both normal and castrate sex steroid milieus, there was a negative relationship between inhibin B and FSH, best described by a logarithmic model. Acute biochemical castration resulted in the most dramatic increases in FSH in men with the lowest baseline inhibin B levels. CONCLUSIONS: We came to the following conclusions: 1) in the human male, inhibin B is the principal gonadal feedback regulator of FSH secretion unless seminiferous tubular function is severely compromised, and a logarithmic model best describes this relationship; and 2) sex steroid inhibition of FSH secretion is most apparent when serum inhibin B levels fall well below the normal range.     

Inhibins in childhood and puberty

Inhibin is a heterodimeric glycoprotein that consists of an alpha-subunit linked to either a betaA subunit (inhibin A) or to a betaB subunit (inhibin B) and it exists in at least six different isoforms. These isoforms can not be measured separately by immunoassays. In boys, serum inhibin B levels change in concert with the increase in gonadotrophins. Associated with the postnatal activation of gonadotrophin secretion, the early inhibin B secretion is sustained until the age of 18-24 months; thereafter serum concentrations subside. In boys, between Tanner stages G1 and G2, serum inhibin B concentration again increases, but then plateaus. Inhibin A levels in human males are below the detection limit, but in girls, during the postnatal activation of gonadotrophin secretion, both serum inhibin A and inhibin B concentrations are measurable. Serum inhibin B levels correlate positively with age several years before the clinical onset of puberty, suggesting increasing follicular activity in late prepuberty. During female puberty, the inhibin B level increases from Tanner stage B1 through stage B3, suggesting high follicular activity before the development of ovulatory menstrual cycles, but serum inhibin A levels become measurable later in puberty, in agreement with the idea that inhibin A is mainly produced by the corpus luteum.     

Comparison of drug-related problem risk assessment tools for older adults: a systematic review

European Journal of Clinical Pharmacology - This study aims to systematically review studies describing screening tools that assess the risk for drug-related problems (DRPs) in older adults...     

Serum androgen bioactivity in adolescence: a longitudinal study of boys with constitutional delay of puberty

We have examined the relationship between serum androgen bioactivity, as measured with a recombinant cell bioassay, and progression of puberty in 14 boys with constitutional delay of puberty. Six boys were followed up without treatment (control group), and eight boys received low-dose (1 mg/kg) testosterone enanthate im for 0-6 months together with an aromatase inhibitor, letrozole, 2.5 mg orally once a day for 0-12 months (treatment group). In the control group, serum androgen bioactivity increased during the course of puberty (P < 0.001). During 0-12 months of the study, the boys in the treatment group had higher androgen bioactivity levels (P < 0.05) and faster rate of pubic hair growth than the control boys (P < 0.05). Overall, the average serum androgen bioactivity during 12 months of follow-up correlated strongly with the concomitant changes in Tanner genital (r(S) = 0.89; n = 13; P < 0.005) and pubic hair stages (r(S) = 0.79; n = 13; P < 0.01). In conclusion, our results suggest that circulating androgen bioactivity mediates the tempo of pubertal maturation and that the combination of testosterone and letrozole given to boys with constitutional delay of puberty accelerates puberty.     

Hippocampal A beta 42 levels correlate with spatial memory deficit in APP and PS1 double transgenic mice

We investigated the role of hippocampal amyloid pathology in spatial learning impairment of a new mouse line carrying mutated human amyloid precursor protein (APP) and presenilin-1 (PS1) transgenes. The APP + PS1 mice were tested in spatial navigation in the water maze and in position discrimination in the T-maze at ages of 3-4 and 11-12 months, before and after the appearance of first amyloid plaques. The APP + PS1 mice were impaired in water maze acquisition and retention only at the age of 11-12 months, but performed equally to controls in the T-maze task at both ages. In the impaired older age group, the levels of total Abeta1-42 in the hippocampus of APP + PS1 mice correlated negatively with the retention score. Here we show for the first time that the age-dependent impairment in memory retention in the traditional water maze of APP + PS1 mice correlates with the amount of total Abeta in hippocampus even at a stage when the amyloid deposits cover less than 1% of the hippocampal volume.     

Blood levels of leukotrienes (LTC4, D4, E4, B4) and synthesis of leukotriene B4 by peripheral leukocytes in children with acute A and B hepatitis

Leukotrienes (LTs) are cell-membrane derived lipid inflammatory mediators, synthesized and eliminated by the liver. LTs have effects on liver cells in some pathological conditions. In this study, we measured plasma endogenous and liberated leukotriene (LT) concentration in peripheral blood leukocytes stimulated in vitro by the calcium ionophore (CaA23187) and platelet-activating factor (PAF). Production of LTs was measured in type A (n=37) and type B (n=10) acute hepatitis patients and control subjects (n=10). LTs levels were measured by high performance liquid chromatography (HPLC) and radioimmunoassay (RIA). The concentration of LTB4 measured in plasma and stimulated peripheral blood leukocyte supernatants of children with hepatitis A infection was found to be statistically elevated and in positive correlation with serum alanine aminotransferase (ALT) levels. In plasma samples of hepatitis B patients, LTC4 and LTE4 were measured in significantly elevated concentrations. These results suggest that LTB4 may be a critical mediator of hepatitis A virus-induced hepatocellular injury.     

Polyorchidism: a case report and review of the literature.

We report on a case of polyorchidism associated with left-sided inguinal hernia and hydrocele. Biopsies of both testes revealed normal histological pattern. After the hernia repair and hydrocelectomy both testes were left at their original places in the scrotum and fixed. Polyorchidism and its management are discussed briefly.     

Roentgen ray fluorescence method for determination of iodine in tissue

A roentgen ray fluorescence method was developed for the quantitative determination of iodine concentration in tissue. The method is based on the use of two beams, of which one excites the K roentgen rays of iodine, while the other does not. The concentration of iodine was determined from the difference between the counting rates of the fluorescent and the scattered radiation. The measurements were carried out with standard equipment consisting of a generator, a NaI)Tl)-detector and a scaler. An accuracy of 0.1 mg I per g was obtained with the radiation exposure of about 1 R.