Effect of group B streptococcal meningitis on retinal and choroidal blood flow in newborn pigs.

PURPOSE: To assess the effect of group B streptococcal (GBS) meningitis on retinal blood flow (RetBF) and choroidal blood flow (ChBF) autoregulation in sedated newborn piglets (1 to 5 days of age). METHODS: Fourteen study animals injected with 0.5 ml heat-killed GBS (10(9)) were compared to 10 control animals injected with 0.5 ml saline. The site of injection for both groups was the cerebral lateral ventricles. RetBF and ChBF were measured by radioactive microspheres (141Ce, 51Cr, 113Sn, 85Sr, 95Nb, 46Sc) over a mean arterial blood pressure (MABP) range of 20 to 150 mm Hg. Hypertension and hypotension were induced 2 hours apart in random sequence on each animal by inflating balloon-tipped catheters placed at the descending aorta and the aortic root, respectively. RetBF and ChBF were measured 15 minutes before and after injection of GBS or saline (baseline) and during hypotension or hypertension. RESULTS: Fifth-order polynomial regression analyses of RetBF and ChBF (ml/100 g per minute) versus MABP showed that in control animals, blood flows were constant at MABP of 60 to 110 mm Hg for RetBF and was pressure passive above and below these ranges. However, no autoregulation was observed for ChBF throughout the MABP range. In contrast, RetBF of GBS-treated animals increased with increasing blood pressure throughout range of MABP studied, and absence of autoregulation was maintained in the choroid. Vascular resistance (mm Hg/ml per minute/100 g) increased as MABP was raised to maintain constant flow and was correlated linearly with MABP at 60 to 110 mm Hg (r = 0.6682, P = 0.0003) in RetBF of control animals but not in GBS-treated animals (r = -0.291, P = NS). Vascular resistance did not change with MABP for ChBF of control animals (r = -0.264, P = NS) but decreased as MABP was raised in GBS-treated animals (r = -0.548, P < 0.0001). GBS did not alter oxygen delivery, which varied directly with MABP in control animals (RetBF: r = 0.74, P < 0.001; ChBF: r = 0.68, P < 0.001) and in GBS-treated animals (RetBF: r = 0.55, P < 0.001; ChBF: r = 0.68, P < 0.001). CONCLUSION: Group B streptococcal meningitis significantly impairs eye blood flow autoregulation and may contribute to increased risk of retinal damage in infants with meningitis.

Dose-effect relationship of bilirubin on striatal synaptosomes in rats.

The uptake of tyrosine as precursor of dopamine in striatal nerve endings was studied in rat striatal synaptosomes to evaluate the role of different bilirubin concentrations on this mechanism of synaptic neurotransmission. Freshly prepared striatal synaptosomes obtained from adult male Sprague-Dawley rats (200-300 g) were homogenized in about 25 vol of 0.32 M sucrose and 5 nM Hepes at pH 7.4 and centrifugated at 12,000-16,000 rpm for 20 min. 14C tyrosine was evaporated under N2 and resuspended in tyrosine 100 microliters/ml. Different concentrations of crystalline bilirubin ranging from 70 to 140 microM at 10-min intervals were prepared. Eighty microliters of synaptosomes were added to 5 microliters of the different bilirubin concentrations and 20 microliters of 14C tyrosine. The results of this study show a statistically significant correlation between bilirubin levels and tyrosine uptake in rat synaptosomes (p < 0.05) supporting the hypothesis that the effect of bilirubin on neuronal excitability is dose-dependent.