The end-product method of measuring whole-body protein turnover: a review of published results and a comparison with those obtained by leucine infusion.

The present review summarizes the results of all published papers on whole-body protein turnover in man measured by [15N]glycine and the end-product method using both urea and ammonia. It begins with a short account of the underlying assumptions and the justification for the use of [15N]glycine. The results are then compared with those of a large sample of measurements by the 'gold standard' precursor method with continuous infusion of [13C]leucine. The pros and cons of the two methods are compared and it is suggested that there is a place for further work by the less invasive end-product method, particularly for population studies of the genetic, environmental and functional determinants of whole-body rates of protein synthesis.

Relationship of maternal protein turnover and lean body mass during pregnancy and birth length.

Epidemiological evidence shows that small size at birth is associated with an increased risk of developing cardiovascular and metabolic disease in adult life. We have examined the relationships between size at birth and maternal body composition and protein turnover in normal pregnant women. A group of 27 multiparous Caucasian women with singleton pregnancies were studied at around 18 and 28 weeks' gestation. Body composition was determined by anthropometry, and whole-body protein turnover was estimated by using a single oral dose of [(15)N]glycine and the end-product method. The baby's weight and length were measured within 48 h of birth. Mothers with a greater lean body mass had higher rates of protein turnover at 18 weeks' gestation. This association was largely accounted for by differences in the mother's visceral, rather than muscle, mass. Mothers who had higher protein turnover at 18 weeks' gestation had babies that were longer at birth. After adjustment for the duration of gestation and the baby's sex, 26% of the variation in length at birth was accounted for by maternal protein synthesis at 18 weeks' gestation. Maternal protein intake was not associated with the baby's birth length. Thus the mother's ability to nourish her fetus is influenced by her body composition and her rate of protein turnover. Dietary intake does not adequately characterize this ability.

Whole body protein turnover can be measured non-invasively in women using the end product method with [15N]glycine to show changes with the menstrual cycle and pregnancy.

OBJECTIVES: To assess the effect of the menstrual cycle and pregnancy on whole body protein turnover. DESIGN AND SUBJECTS: Whole body protein turnover was determined using oral [15N]glycine in normal women from enrichment measured in urine at days 7 and 14 of the menstrual cycle and in pregnant women at 17-20 weeks and 30-32 weeks gestation. RESULTS: Nitrogen flux was 38.2 (5.8) mg N/kg/h using a single dose and 31.1+/-4.1 mg N/kg/h with prime-intermittent doses-the same as in men using the same methods. Nitrogen flux around the time of ovulation, 32.3 (8.2) mg N/kg/h, was greater than at day 7, 26.8 (3.0) mg N/kg/h (P<0.05). For women taking the contraceptive pill flux at day 7, 22.7 (0.2) mg N/kg/h, and day 14, 21.3 (2.1) mg N/kg/h, were similar, but were lower at day 14 than for women not taking the pill (P<0.05). Protein synthesis increased between mid and late pregnancy (1.7-2.0 g N/h; P=0.012), but not when expressed in relation to body weight CONCLUSIONS: Protein turnover can be measured reproducibly in women using a non-invasive method, provided care is taken to standardize the conditions, and especially the duration over which urine is collected. There is an increase around the time of ovulation when hormonal levels are at their highest and during pregnancy the results obtained are similar to those reported using [13C]leucine. SPONSORSHIP: University of Southampton and Medical Research Council.

Growth in infancy, infant feeding, childhood living conditions, and Helicobacter pylori infection at age 70.

AIM: To examine childhood correlates of Helicobacter pylori infection in adults. DESIGN: Follow up study of men and women whose birth weight, weight at age 1 year, and feeding in infancy were recorded by health visitors. Data on childhood housing conditions were obtained by recall. SUBJECTS: 631 men and 389 women born in Hertfordshire during 1920-30 and still living in the east or northwest districts of the county. MAIN OUTCOME MEASURES: Serum H pylori IgG antibodies measured by enzyme linked immunosorbent assay. RESULTS: Independent of their current social class, subjects were more likely to be H pylori seropositive if they had large numbers of siblings (p < 0.0001), and if they had lived in a crowded house (p = 0.001), or shared a bedroom or bed in childhood (p = 0.02). Low weight at 1 year was associated with increased seropositivity rates in men (p = 0.0002), but not women (p = 0.8). Men and women who were breast fed in infancy were less likely to be seropositive than those who were bottle fed (p = 0.08). CONCLUSIONS: The findings support the current view that H pylori infection is often acquired in childhood by close person to person contact, and persists into adult life. H pylori infection may be a cause of failure to thrive in infancy, especially in boys. Alternatively, small infants may be more susceptible to infection. Breast feeding may prevent early infection.

Cigarette smoking and bone mineral density in the elderly.

OBJECTIVE: To test the hypothesis that cigarette smoking is associated with reduced bone mineral density in elderly men and women. DESIGN: Cross sectional study. SUBJECTS: These comprised 224 men and 186 women aged 61-73 years, born and resident in East Hertfordshire. MEASUREMENTS: Lumbar spine and femoral neck bone mineral density (BMD) were determined by dual energy x ray absorptiometry. RESULTS: After adjusting for potential confounding variables, men who were current smokers were found to have a lumbar spine BMD that was 7.3% (95% CI 0.4, 14.2) lower than men who had never smoked. Similarly, women who were current smokers had a BMD value that was 7.7% (95% CI 0.3, 15.6) lower than in women who had never smoked. The difference at the femoral neck was smaller and not statistically significant. For both men and women, each decade of smoking was associated with a reduction of 0.015 g/cm2 in BMD at the lumbar spine (95% CI: men 0.002, 0.027; women 0.003, 0.028). At the femoral neck the reduction in BMD was 0.011 g/cm2 (95% CI 0.003, 0.020) for men and 0.004 g/cm2 (95% CI -0.003, 0.012) for women with each decade of smoking. CONCLUSIONS: The results show an adverse effect of smoking on BMD which was most noticeable at the lumbar spine, and seemed stronger in men than women. This effect could not be explained by differences in life style between smokers and nonsmokers.

Weight in infancy and prevalence of coronary heart disease in adult life.

OBJECTIVE: To determine whether low birth weight and low weight at 1 year are followed by an increased prevalence of coronary heart disease in adult life. DESIGN: A follow up study of men born during 1920-30 whose birth weights and weights at 1 year were recorded. SETTING: Hertfordshire, England. SUBJECTS: 290 men born and still living in East Hertfordshire. MAIN OUTCOME MEASURE: The prevalence of coronary heart disease, defined by the Rose/WHO chest pain questionnaire, standard electrocardiographic criteria, or history of coronary artery angioplasty or graft surgery. RESULTS: 42 (14%) men had coronary heart disease. Their mean birth weight, 7.9 lb (3600 g), was the same as that of the other men. Their mean weight at 1 year, 21.8 lb (9.9 kg), was 1 lb (454 g) lower (95% confidence interval 0.1 to 1.8, P = 0.02). Percentages of men with coronary heart disease fell from 27% in those who weighed 18 lb (8.2 kg) or less at 1 year to 9% in those who weighed more than 26 lb (11.8 kg) (P value for trend = 0.03). This trend occurred in both smokers and non-smokers and within each social class. CONCLUSION: These findings add to the evidence that coronary heart disease is "programmed" during early growth.