Biomedical subjects

E Dennison

Publications and source records attributed to E Dennison.

22 records · Page 2Linked to original sources

PubMed1998

Programming of growth hormone secretion and bone mineral density in elderly men: a hypothesis.

Epidemiological studies suggest that retarded growth in infancy is associated with low adult bone mass. The mechanism underlying this association is unknown, but the programming of GH secretion or sensitivity by environmental influences during early development may play a role. We examined this issue in a sample of 37 healthy men, aged 63-73 yr, whose weight gain in infancy had been recorded. Venous blood samples were obtained under standard conditions every 20 min over a 24-h period. Measurements were made of the GH secretory profile, insulin-like growth factor I (IGF-I), IGF-binding protein-1 and -3, and GH-binding protein. Bone mineral density was measured at the lumbar spine and femoral neck using dual energy x-ray absortiometry. There was a statistically significant association between peak GH concentration (r = 0.46; P < 0.01) and fasting IGF-I concentration (r = 0.46; P < 0.01) with femoral neck bone density. After allowing for the peak GH concentration, median GH was negatively (P < 0.05) associated with bone mineral density. Weight at 1 yr was not related to peak GH, but was strongly related to the median GH concentration (r = 0.42; P = 0.01). These observations are consistent with a dual effect of GH secretion on bone density. High peak GH values drive IGF-I production and maintain bone mineralization in adult life. However, integrated GH secretion, after adjusting for the effect of pulse amplitude, is negatively associated with bone density in adult life. This particular characteristic of the GH secretory profile correlates with growth during infancy and might be programmed by environmental factors during intrauterine or early postnatal life.

Adult↗

PubMed1997

Prenatal factors influencing long-term outcome.

Animal studies have shown that undernutrition before birth programmes persisting changes in a range of metabolic, physiological and structural parameters. Studies in humans have shown that men and women who had birth weights at the lower end of the normal range, who were thin or short at birth, or who were small in relation to placental size, have increased rates of coronary heart disease. This article suggests how fetal undernutrition at different stages of gestation may be linked to these patterns of early growth. Adaptations by the fetus to undernutrition are associated with changes in the concentrations of fetal placental hormones. Persisting changes in the level of hormone secretion and tissue sensitivity may link fetal undernutrition with adult disease.

Adult↗

PubMed1996

Systemically administered gonadotrophin-releasing hormone enhances copulatory behaviour in castrated, testosterone-treated hyperprolactinaemic male rats.

Hyperprolactinaemic male rats exhibit deficits in copulatory behaviour which can be reversed by a single injection of GnRH. We tested whether systemically administered GnRH can stimulate copulatory behaviour independently of LH-mediated increases in plasma testosterone levels. Gonadectomized, pituitary-grafted adult male Fischer 344 rats bearing implants of 5, 10 or 20 mm capsules of testosterone were administered a single injection of 500 ng GnRH or saline s.c., 30 min prior to copulation tests. Pituitary-grafted castrates displayed copulatory deficits, relative to sham-operated castrates with identical levels of testosterone replacement. Administration of 500 ng GnRH to pituitary-grafted castrates bearing 10 mm testosterone implants significantly increased the proportion of rats that mounted, intromitted and ejaculated during a 30 min test. This treatment also reduced significantly the latency of intromission and ejaculation, and increased significantly the frequency of intromission. The copulatory behaviour of the sexually unresponsive, pituitary-grafted castrates bearing 5 mm testosterone implants, or of the more sexually responsive castrates bearing 20 mm testosterone implants, was not altered significantly by GnRH injections. These results support the hypothesis that copulatory deficits in moderately hyperprolactinaemic rats are due in part to reduced hypothalamic GnRH release, and suggest that GnRH can stimulate sexual behaviour in these animals via mechanisms that are independent of luteinizing hormone-induced testosterone release. However, a threshold level of testosterone (achieved with 10 mm implants) appears to be required for GnRH to elicit this effect.

Animals↗

PubMedDate not supplied

The epidemiology of osteoporosis.

Osteoporosis is a skeletal disorder characterised by low bone mass and an increased susceptibility to fracture. The last two decades have seen an increase in our understanding of the epidemiology of fractures at the three most frequent sites (the hip, wrist and vertebral body). These new insights have led to the delineation of preventive strategies against these fractures for both the general population, and those individuals at highest risk. This review covers these descrptive epidemiological characteristics, as well as approaches to prevention.

Female↗