M. Yonetani et al., EFFECT OF HEMORRHAGIC HYPOTENSION ON EXTRACELLULAR LEVEL OF DOPAMINE,CORTICAL OXYGEN-PRESSURE AND BLOOD-FLOW IN BRAIN OF NEWBORN PIGLETS, Neuroscience letters, 180(2), 1994, pp. 247-252
The present study describes the relationships between extracellular st
riatal dopamine, cortical oxygen pressure and blood flow in brain of n
ewborn piglets during hemorrhagic hypotension. Cerebral oxygen pressur
e was measured optically by the oxygen dependent quenching of phosphor
escence; extracellular dopamine by in vivo microdialysis; striatal blo
od flow was monitored by a laser Doppler. Following a 2 h stabilizatio
n period after implanting the microdialysis and laser Doppler probes i
n the striatum, the mean arterial blood pressure (MABP) was decreased
in stepwise manner from 87 +/- 4 Torr (control) to 35 +/- 5 Torr, duri
ng 63 min. The whole blood was then reinfused and measurements were co
ntinued for 45 min. Statistically significant decrease in blood flow,
10%, was observed when arterial blood pressure decreased to about 53 T
orr. With further decrease blood pressure to 35 Torr, blood flow decre
ased to about 35% of control (P < 0.01). Cortical oxygen pressure decr
eased almost proportional to decrease in blood pressure. The progressi
ve decrease in MABP from 87 +/- 4 Torr to 65 +/- 6, 52 +/- 7, and 35 /- 5 Torr resulted in cortical oxygen pressure decreasing from 45 +/-
4 Torr to 33 +/- 3 Torr (P < 0.05), 24 +/- 4 Torr (P < 0.01) and 13 +/
- 3 Torr (P < 0.01). The levels of extracellular dopamine in the stria
tum increased with decreasing cortical oxygen pressure. As cortical ox
ygen decreased, the extracellular dopamine increased to 230%, 420% and
3200% of control, respectively. Our results show that in mild hypoten
sion total blood flow is well maintained but oxygen pressure in the mi
crovasculature decreases, possibly due to heterogeneity in the regulat
ory mechanism. The decrease in cortical oxygen pressure in striatum is
parallel to increase in striatal dopamine which then can be use as ea
rly indicator of brain hypoxia.