The role of endothelium‐derived hyperpolarizing factor (EDHF) in the regulation of blood flow in vivo was examined in the mesenteric and hindlimb circulations of anaesthetized rats. Basal mesenteric conductance decreased from 57 ± 5 to 20 ± 6 μl min−1 mmHg−1 when nitric oxide (NO) production was inhibited, and combined blockade of intermediate‐ and small‐conductance Ca2+‐activated K+ (KCa) channels with charybdotoxin (ChTx) and apamin had no further effect. Basal hindlimb conductance was reduced from 39 ± 3 to 22 ± 2 μl min−1 mmHg−1 by NO synthesis inhibition, with no effect of the KCa channel blockers. Endothelial stimulation with acetylcholine (ACh) infusion directly into the mesenteric bed increased conductance by 20 ± 2 μl min−1 mmHg−1. Blockade of NO synthesis decreased this conductance to 15 ± 1 μl min−1 mmHg−1, leaving the response attributable to EDHF. This was reduced to 2 ± 1 μl min−1 mmHg−1 by ChTx plus apamin but not by iberiotoxin, which selectively blocks large‐conductance KCa channels. Similar results were obtained when bradykinin (BK) was used to stimulate the endothelium. Nitroprusside, which directly relaxes smooth muscle, evoked an increase in conductance that was resistant to all blockers tested. ACh‐induced increases in hindlimb conductance were reduced from 19 ± 1 to 12 ± 1 μl min−1 mmHg−1 by NO synthesis inhibition and further reduced to 2 ± 2 μl min−1 mmHg−1 by ChTx plus apamin. In contrast to NO, ChTx‐ and apamin‐sensitive EDHF appears to contribute little to basal conductance in rat mesenteric and hindlimb beds. However, EDHF accounts for a significant component of the conductance increase during endothelial stimulation by ACh and BK. In these beds, intermediate‐ and small‐conductance KCa channels underpin EDHF‐mediated vasodilatation.

Umbilical cord occlusion (UCO), a known risk factor for perinatal brain damage, causes severe fetal asphyxia leading to oxidative stress, lipid peroxidation, and cell death. We have determined the effects of two 10-min UCO on the distribution of the lipid peroxidation marker 4-hydroxynonenal (4-HNE) and the activated form of the apoptosis marker caspase-3 in the brains of late-gestation fetal sheep. UCO caused asphyxia, hypertension, and bradycardia, but these parameters normalized 2 h after the occlusion. At postmortem, 48 h after the second UCO there were significantly higher numbers of 4-HNE-positive cells in all layers of the hippocampus and cerebellum, the parietal cortex, substantia nigra, caudate nucleus, putamen, and thalamus compared with control brains. 4-HNE immunoreactivity was also found in white matter tracts of the subcallosal bundle, external medullary lamina, reticular thalamic nucleus, and cerebellar fiber tracts only in UCO brains. Double-labeling identified these cells as predominantly neurons and astrocytes, with oligodendrocytes showing lower levels of 4-HNE immunoreactivity. After UCO, the number of caspase-3-immunoposotive cells was increased significantly in the hippocampal CA1, molecular layer and dentate gyrus, ventrolateral thalamic nucleus, substantia nigra, putamen, and cerebellar granular and molecular layers compared with controls. Double-labeling revealed caspase-3 immunoreactivity was mainly in neurons, and to lesser extent in astrocytes and oligodendrocytes. Pyknotic cell numbers were significantly increased in hippocampal CA1 and CA3, parietal cortex, caudate nucleus, putamen, and cerebellar Purkinje cells after UCO. These data indicate that brief asphyxia induces widespread lipid peroxidation involving all cell types of the fetal brain and apoptosis in both neurons and glia. Abbreviations UCO, umbilical cord occlusion 4-HNE, 4-hydroxynonenal ROS, reactive oxygen species TBARS, thiobarbituric acid-reactive substances PFA, paraformaldehyde NGS, normal goat serum GFAP, glial fibrillary acidic protein CNPase, 2', 3'-cyclic nucleotide 3'-phosphodiesterase MAP-2, microtubule associated protein Asphyxia and hypoxia are threats faced by the fetus in utero and are implicated in long-term postnatal sequelae such as mental retardation, seizure disorders and cerebral palsy (1). In particular, white matter injury is thought to result from insults that cause CNS inflammation and oxidative stress (2, 3). The brain is relatively deficient in oxidative defenses and highly susceptible to free radical damage (4). ROS alter the structure and function of proteins and DNA, and activate cysteine proteases (caspases), leading to apoptotic cell death (5). Hydroxyl radical, in particular, causes lipid peroxidation by rearranging double bonds in fatty acid side chains, and other radicals trigger the destruction of adjacent fatty acid molecules (4). Peroxidation of lipids leads to formation of cytotoxic reactive aldehydes, including malondialdehyde and 4-HNE (6). Cell membrane lipid composition makes so...