Light reduction and the electroretinogram of preterm infants.

AIMS: To examine the effects of light on retinal development and function in preterm infants as measured by the electroretinogram (ERG). Secondary outcomes included visual acuity testing, the incidence of retinopathy of prematurity, and general wellbeing, reflected in feeding tolerance, rate of weight gain, and length of hospital stay. METHODS: Eligibility criteria for enrollment were birthweight < or = 1250 g and gestational age < or = 31 weeks. Sixty one infants were randomly allocated by 6 hours after birth to a control or treatment group which wore 97% light filtering goggles for a minimum of four weeks or until the infant reached 31 weeks postmenstrual age. RESULTS: There were no significant differences between the two groups in the numbers of electroretinograms performed at 36 weeks of postmenstrual age. Although the sample size was not large enough to exclude clinically important differences in secondary outcomes, no significant differences were observed between the groups in visual acuity testing at 4-6 months corrected age, incidence of retinopathy of prematurity, weight gain, or length of stay. CONCLUSION: These data support the safety and feasibility of this intervention. A much larger study will be needed to determine whether light reduction to the eyes of very low birthweight infants will reduce the incidence of retinopathy of prematurity or enhance general well-being.

Alterations in myometrial stress during ovine pregnancy and the puerperium.

Substantial alterations occur in female reproductive tissues to ensure the successful outcome of and recovery from pregnancy. Although sheep have been widely used to study several aspects of pregnancy, little information is available regarding alterations in myometrial function. We therefore characterized the alterations that occur in ovine myometrial stress-generating capacity and examined mechanisms that might account for these changes. Length-force relations were determined for longitudinal myometrial strips from nonpregnant (n = 6), pregnant (n = 11; 67-140 days gestation), and postpartum (n = 6) ewes. Active stress (force per cross-sectional area) was calculated at optimal length for maximal force as determined from length-force relations. Stimulation by 65 mM KCl resulted in 3.5 times greater stress in strips from late-pregnant vs. nonpregnant ewes, 1.20 +/- 0.16 vs. 0.34 +/- 0.04 x 10(5) N/m2 (+/- SE; P < 0.05), respectively. Responses returned to values seen in strips from nonpregnant ewes within 2 wk postpartum. Increases in stress were not associated with differences in the phosphorylated myosin light-chain fraction or the amount of smooth muscle bundles. Although basal prostacyclin production was 15-fold greater in myometrium from nonpregnant vs. pregnant ewes (222 +/- 28 vs. 14.9 +/- 2.0 pg.mg wet wt-1.h-1), cyclooxygenase inhibition did not potentiate stress responses in strips from nonpregnant animals. However, smooth muscle contents of actin (26.0 +/- 1.8 vs. 19.1 +/- 2.2 micrograms/mg wet wt) and myosin heavy chain (5.5 +/- 0.4 vs. 2.0 +/- 0.3 microgram/mg wet wt) were greater (P < 0.04) in myometrium from late-pregnant vs. nonpregnant ewes. Myometrial growth during ovine pregnancy is associated with reversibly augmented contractile properties that appear to primarily reflect increased cellular contents of contractile proteins.

Myometrial angiotensin II receptor subtypes change during ovine pregnancy.

Although regulation of angiotensin II receptor (AT) binding in vascular and uterine smooth muscle is similar in nonpregnant animals, studies suggest it may differ during pregnancy. We, therefore, examined binding characteristics of myometrial AT receptors in nulliparous (n = 7), pregnant (n = 24, 110-139 d of gestation), and postpartum (n = 21, 5 to > or = 130 d) sheep and compared this to vascular receptor binding. We also determined if changes in myometrial binding reflect alterations in receptor subtype. By using plasma membrane preparations from myometrium and medial layer of abdominal aorta, we determined receptor density and affinity employing radioligand binding; myometrial AT receptor subtypes were assessed by inhibiting [125I]-ANG II binding with subtype-specific antagonists. Compared to nulliparous ewes, myometrial AT receptor density fell approximately 90% during pregnancy (1,486 +/- 167 vs. 130 +/- 16 fmol/mg protein) and returned to nulliparous values > or = 4 wk postpartum; vascular binding was unchanged. Nulliparous myometrium expressed predominantly AT2 receptors (AT1/AT2 congruent to 15%/85%), whereas AT1 receptors predominated during pregnancy (AT1/AT2 congruent to 80%/20%). By 5 d postpartum AT1/AT2 congruent to 40%/60%, and > 4 wk postpartum AT2 receptors again predominated (AT1/AT2 congruent to 15%/85%). In studies of ANG II-induced force generation, myometrium from pregnant ewes (n = 10) demonstrated dose-dependent increases in force (P < 0.001), which were inhibited with an AT1 receptor antagonist. Postpartum myometrial responses were less at doses > or = 10(-9) M (P < 0.05) and unaffected by AT2 receptor antagonists. Vascular and myometrial AT receptor binding are differentially regulated during ovine pregnancy, the latter primarily reflecting decreases in AT2 receptor expression. This is the first description of reversible changes in AT receptor subtype in adult mammals.