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Biomedical subjects

J Barrett

Publications and source records attributed to J Barrett.

At least 397 records · Page 22Linked to original sources
PubMedDate not supplied

Short cervix: a cause of preterm delivery in young adolescents?

OBJECTIVE: To test the hypothesis that at midgestation younger adolescents (<16 years of age at conception) have shorter cervices than older adolescents (16-19 years of age at conception). METHODS: At midgestation (22.9 +/- 2.4 weeks) we measured cervical length by transvaginal ultrasound in a group of 46 13-19-year-old participants in an intensive, adolescent-oriented, antenatal program. Subjects were also comprehensively screened and treated for other recognized physiologic, microbiologic, obstetric, behavioral, and psychosocial factors associated with preterm delivery. Univariate, bivariate, and logistic regression analyses were used. RESULTS: The 18 younger adolescents had significantly shorter cervices than the 28 older adolescents (30 +/- 11 mm vs. 39 +/- 8 mm; P = 0.002). The younger adolescents' cervices were also more likely to be < or =25 mm long (33% and 4%, respectively; P = 0.02) and to exhibit funneling (39% vs. 4%; P = 0.01). Teenagers with cervices < or =25 mm long were younger, thinner, more apt to report vaginal bleeding and substance abuse, and to be treated for preterm labor (71% vs. 21%; P = 0.005). Logistic regression analyses revealed that age <16 years at conception (odds ratio = 13.7; 95% CI: 1.3-151.4) and substance abuse (odds ratio = 8.5; 95% CI: 1.2-62.8) were associated with cervical length < or =25 mm. Cervical length < or =25 mm was the only significant predictor of preterm delivery (odds ratio = 26.2; 95% CI: 2.1-333.6; P = 0.01) in this population of adolescents who were routinely treated for other recognized causes of preterm delivery. CONCLUSIONS: Cervical length < or =25 mm and cervical funneling may be complications of conception prior to 16 years of age. Randomized trials are needed to determine if younger adolescents benefit preferentially from ultrasound screening for short cervix at midgestation.

Adolescent↗
PubMedDate not supplied

Chlorophyll-protein complexes of brown algae: P700 reaction centre and light-harvesting complexes.

Thylakoid membranes from several brown algae have been fragmented with the non-ionic detergent, Triton X-100. Three intrinsic chlorophyll-protein complexes with different pigment compositions have been isolated by sucrose density gradient centrifugation. Brown algae contain the photosystem 1 reaction-centre complex, a P700-chlorophyll a-protein which has similar spectroscopic and chemical properties to those of higher plants. This complex represents about 10--20% of the total chlorophyll in all species; the Acrocarpia paniculata complex has a chlorophyll/P700 ratio of 38. Two main light-harvesting complexes have also been isolated, which have properties unique to brown algae. The heavier of these, an orange fraction, is a fucoxanthin-chlorophyll a/c-protein; this complex contains most of the fucoxanthin and has only chlorophyll c2. The other, a green fraction, is a chlorophyll a/c-protein enriched in violaxanthin. Neither of these complexes possesses detectable photosystem 1 or photosystem 2 activities. Both of these complexes efficiently transfer light energy to chlorophyll a, indicating that the molecular arrangement of their pigments is similar to that in vivo. Differential extraction of thylakoid membranes indicates that the P700-chlorophyll a-protein is the complex most firmly embedded in the membrane, but the fucoxanthin-chlorophyll a/c-protein is the least firmly bound. We suggest that the fucoxanthin complex is the most variable component of the photosynthetic unit of brown algal chloroplasts.

Cell Membrane↗