Vj. Ruth et al., ADENOSINE AND CEREBROVASCULAR HYPEREMIA DURING INSULIN-INDUCED HYPOGLYCEMIA IN NEWBORN PIGLET, The American journal of physiology, 265(5), 1993, pp. 80001762-80001768
The present study tested the hypothesis that adenosine is involved in
mediating the hyperemic response of the newborn brain to hypoglycemia.
By use of the cranial window and microdialysis-H-2 clearance methodol
ogies, changes in the diameter of pial arterioles (25-50 mum), extrace
llular adenosine concentrations ([ADO]), and local cerebral blood flow
(CBF) were examined in isoflurane-anesthetized piglets subjected to i
nsulin-induced hypoglycemia. Blood glucose concentrations ranged from
10 to 18 mg/dl after insulin administration (25 IU/kg iv). Local CBF i
n the frontal cortex increased 36 +/- 12% (P = 0.014) at 30 min of hyp
oglycemia (group 1, n = 12; control = 43 +/- 3 ml.min-1.100 g-1). The
mean increase in dialysate [ADO] sampled concurrently from the same co
rtical area was 59 +/- 29% (P = 0.011; control = 0.11 +/- 0.02 muM). A
t 30 min of hypoglycemia, pial diameters increased 55 +/- 10% (P = 0.0
01; group 2, n = 9). The [ADO] in cranial window cerebrospinal fluid (
CSF) increased 217 +/- 71% (P = 0.04) in response to hypoglycemia (gro
up 3, n = 8; control = 0.016 +/- 0.006 muM). Local administration of a
n adenosine antagonist, 10 muM 8-sulfophenyltheophylline, to the cereb
ral cortex before hypoglycemia caused a 38% reduction (P = 0.011) in t
he pial arteriolar response at 30 min of hypoglycemia (group 4, n = 9)
. Similarly, local superfusion of CSF with 3.7 mM glucose attenuated t
he hypoglycemia-induced pial dilation 33% (P = 0.039; group 5, n = 9).
Perfusion of microdialysis probes with 3.7 mM glucose in the CSF abol
ished the hypoglycemia-induced increase in dialysate [ADO] (group 1).
Pial arteriolar diameters did not change when normoglycemic blood gluc
ose levels were maintained by intravenous glucose after insulin admini
stration (group 6, n = 6). These findings in newborn piglets indicate
that hypoglycemia promotes increases in cerebral extracellular [ADO],
which contribute to the observed pial dilation and parenchymal hyperem
ia.