Hypoxia activates multiple transcriptional pathways in mouse pheochromocytoma cells.

Mouse pheochromocytoma cells (MPCs) provide an excellent model system for investigating the effects of hypoxia on catecholamine enzyme genes and on transcription factors mediating stress responses. RT-PCR detects rapid, transient increases in PNMT mRNA in hypoxic MPC 712 cells. Additionally, elevation of mRNAs encoding transcription factors hypoxia inducible factor 1 (HIF-1) alpha subunit and Egr-1 are evident within 60 min incubation in anoxia. Therefore, hypoxia elicits rapid transcriptional responses in numerous genes expressed by chromaffin cells.

Serial head ultrasound studies in preterm infants: how many normal studies does one infant need to exclude significant abnormalities?

OBJECTIVE: We hypothesized that preterm infants with two normal head ultrasound (HUS) screening studies > or = 7 days apart would have subsequently normal follow-up studies. POPULATION: We reviewed reports of all HUS studies performed in preterm infants < or = 32 weeks gestation admitted to our nursery between January 1998 and July 2000. SETTING: Regional perinatal referral center. DESIGN: A normal HUS screening study was defined as either no findings; or grade I intraventricular hemorrhage (IVH) (Papile classification), germinal matrix irregularity or cyst, or normal but unequal ventricular size. An abnormal study was defined as any with IVH > or = grade II, periventricular leukomalacia (PVL), ventriculomegaly (VM), or periventricular echogenicity (PVE). RESULTS: Of 98 infants, 92 infants (94%) who had two normal HUS studies > or = 7 days apart had normal repeat studies subsequently, and six (6%) were abnormal. Four of the six abnormal infants were <25 weeks gestation at birth. One infant (27 weeks) became abnormal after culture-positive bacterial sepsis and necrotizing enterocolitis with bowel perforation requiring surgery. The remaining infant (29 weeks) had a question of PVE, and a normal repeat study. The positive predictive value for having a normal HUS after two previously normal studies > or = 7 days apart was 94% with a specificity of 86%. CONCLUSION: Stable premature infants > or = 25 weeks gestation without intervening deterioration may not need repeat screening HUSs after having had two normal studies > or = 7 days apart. Unstable or extremely premature infants <25 weeks gestation may be subject to late severe IVH, VM, and PVL, and therefore need a repeat study before hospital discharge, even if two initial studies > or = 7 days apart were normal.