The epidemiology of hearing impairment in an Australian adult population.

BACKGROUND: This study measured the prevalence of hearing impairment, and major demographic factors that influence the prevalence, in a representative South Australian adult population sample aged > or = 15 years. METHODS: The study group was recruited from representative population surveys of South Australians. Participants in these surveys who reported a hearing disability were then recruited to an audiological study which measured air and bone conduction thresholds. In addition a sample of those people who reported no hearing disability were recruited to the audiological study. RESULTS: The data reported in this study are the first in Australia to assess the prevalence of hearing impairment from a representative population survey using audiological methods. The data show that 16.6% of the South Australian population have a hearing impairment in the better ear at > or = 25 dBHTL and 22.2% in the worse ear at the same level. The results obtained in this representative sample compare well with those obtained in the British Study of Hearing, although some differences were observed. CONCLUSIONS: Overall, there are only a few studies worldwide that have audiologically assessed the impairment of hearing from a representative population sample. The overall prevalence of hearing impairment in Australia is similar to that found in Great Britain, although there are some differences between the estimates of severity of impairment and some sex differences. The corroboration of the two studies reinforces the status of hearing impairment as the most common disability of adulthood. The present study also showed that there are a large number of Australians who may benefit from a more systematic community-based rehabilitation programme including the fitting of hearing aids. Secondly, the study identified the need for health goals and targets for hearing to be based on an epidemiological approach to the problem.

Normal rabbit intestinal cytosol as a source of binding protein for the 1,25-dihydroxyvitamin D3 assay.

Cytosol prepared from small intestine of vitamin D-sufficient rabbits contains a specific high-affinity binding protein for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). This binding protein sediments at 3.0-3.5 S in sucrose density gradients containing 0.3 M KCl. Scatchard analysis using intestinal cytosol demonstrated a Kd of 0.05 nM and a maximum binding capacity of 92 fmol/mg cytosol protein for 1,25(OH)2D3 at 4 degrees C. Competitive binding studies with various metabolites of vitamin D showed a relative binding affinity of this protein for 1,25(OH)2D3 greater than 25-hydroxyvitamin D3 greater than vitamin D3. With 200 micrograms of rabbit intestinal cytosol protein, as little as 1.0-2.5 pg of 1,25(OH)2D3 reproducibly displaced the tracer sterol from the binding protein. Analyses of human plasma 1,25(OH)2D3 content yielded values consistent with published results. The vitamin D-replete rabbit provides a convenient, plentiful, and inexpensive source of binding protein for 1,25(OH)2D3 assays.

Ontogenesis of the rabbit intestinal receptor for 1,25-dihydroxyvitamin D3--evidence for increased receptor content during late suckling and lactating periods.

The 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) intestinal receptor was not detected in term fetal rabbits. This receptor was present at 2 weeks postpartum and its concentration reached a maximum at 4 weeks of age, and declined to adult levels by 10 weeks postpartum. The 1,25(OH)2D3 intestinal receptor concentration was elevated at 2 weeks postpartum in lactating rabbits, but returned to normal adult concentrations by 4 weeks postpartum. In rabbits of various ages, only minor changes in the equilibrium dissociation constant of this receptor were observed. These data indicate that increasing the small intestine 1,25(OH)2D3 receptor concentration is one mechanism by which the rabbit adapts to periods of increased calcium demand.