No abstract

Impact activity is an important contributor to bone accrual. Children engaging in such activity have been shown to have greater bone mineral density (BMD) than their peers. This cross-sectional study was designed to quantify the association between BMD and impact activity in pre-pubescent girls, specifically examining for a dose-dependent relationship. Fifty 7-11-year-old Caucasian female gymnasts were grouped by hours of gymnastics participation during a 6-month period: LOW, 1-8 hours/week (hrs/wk); HIGH, >8 hrs/wk. They were compared with 20 controls, with height, weight, age, and Tanner stage averages matched to the gymnasts. Total body, forearm, hip, lumbar spine BMD, and body composition were measured by dual energy X-ray absorptiometry (DXA). Strength was measured by one repetition maximum testing, calcium intake was quantified by questionnaire, and physical activity was measured by questionnaire and activity monitors. Total and regional BMD were greater in the HIGH group than the controls (P<0.05). Furthermore, both total and forearm BMD were greater in the HIGH group than in the LOW group, and greater in the LOW group than in the controls (P<0.05). Simple regression analysis between hrs/wk of gymnastics activity versus total and regional BMD (using maturation-adjusted Z scores) yielded a positive slope for each site. R2 was greatest for hip BMD (R2 = 0.25), and least for lumbar spine (R2 = 0.10) (P<0.0001). In conclusion, in this group of pre-pubescent girls, we observed a dose-dependent relationship between BMD and hrs/wk of impact activity; even moderate doses of impact activity were associated with increased BMD.

The number of Leydig cells in the adult human testis declines as a function of increasing age, but whether these cells disappear by transforming into another cell type or by undergoing death and dissolution has not been resolved. This question was addressed in 30 men between 20 and 76 years of age who were known as a group to have experienced significant age-related loss of Leydig cells. If the loss of Leydig cells resulted from transformation into another cell type, other testicular interstitial cells in these men should have increased with age. Testes obtained at autopsy were perfused with glutaraldehyde less than 15 h after sudden death due to trauma or heart attack. Numbers of other interstitial cells were determined by quantitative histometric estimation of the proportion of testicular parenchyma occupied by other interstitial cell nuclei of measured average volume. Other interstitial cell nuclei declined significantly with advancing age (rho = -0.41, P less than 0.05). Mean number of other interstitial cell nuclei per individual was significantly reduced in the 15 men 50 yr old or older compared to the 15 younger men (460 +/- 34 million vs. 609 +/- 43 million; P less than 0.05). There was no tendency for individuals with reduced numbers of Leydig cells to have increased numbers of other interstitial cells. These findings argued against the persistence of Leydig cells in aged testes as dedifferentiated mesenchymal elements. Instead, light and electron microscopic observation of testes from these men revealed evidence of Leydig cell degeneration and dissolution.

We have used a RIA system for measuring LH in the plasma of domestic cats and characterized the component of LH secretion which is controlled by negative feedback inhibition. Blood samples were collected at 6- to 10-min intervals from animals with chronically indwelling venous cannulae. The inhibitory influence (negative feedback) of gonadal secretion was evidenced by the increased plasma concentrations of LH seen 24 h after castration in 9 animals and within 5 days in all 15 cats. Restoration of negative feedback by either short or long term administration of 17 beta-estradiol reduced LH concentrations to precastration levels. In castrated animals of both sexes, the plasma concentrations of LH fluctuated episodically, with increases occurring at intervals of 20-30 min, presumably a reflection of intermittent periods of LH release. The dynamics of this pattern of LH release were simulated by the iv injection of gonadotropin-releasing hormone. In combination with our additional observation that plasma concentrations of LH decreased rapidly after treatment with four different anesthetic agents, the observations are suggestive of episodic secretion of gonadotropin-releasing hormone in the absence of negative feedback. The mechanisms regulating tonic LH secretion in this reflex ovulator appear to be more sensitive to neural stimuli but qualitatively similar to those previously described for other species in which ovulation occurs spontaneously.