Exogenous endothelin-1 improves microvascular oxygen balance during focal cerebral ischemia in the rat

We tested the hypothesis that endothelin-1 (ET-1), a cerebrovasoconstrictive peptide, would alter microvascular oxygen balance during focal cerebral ischemia. In this study, male Wistar rats were placed in control (n=9) and ET-1-treated (n=9) groups. Cortical ischemia was induced by middle cerebral artery (MCA) occlusion in isoflurane (1.4%) anesthetized rats. Forty minutes after MCA occlusion, 10(-7) M ET-1 or saline was applied to the ischemic cortex (IC) for a period of 20 min; the fluid was changed every 5 min. After 1 h of ischemia, regional cerebral blood flow (rCBF) was determined using a 14C-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined microspectrophotometrically. The cerebral blood flow (45% control, 45% ET-l) and oxygen consumption (24% control, 44% ET-1) of the IC were significantly lower than the contralateral cortex. ET-1 of 10(-7) M did not cause a statistically significant alteration in regional cerebral blood flow or oxygen consumption of the IC, but did increase the average venous O(2) saturation of the IC from 50 +/- 1% to 55 +/- 2% (p<0.04). A significant (p<0.05) increase was observed in O(2) supply/consumption ratio in the ET-1-treated IC (2.79 +/- 0.26 ml O(2)/min/100 g in ET-1-treated IC vs. 2.41 +/- 0.12 ml O(2)/min/100 g in the control IC) compared to the control IC. ET-1 also significantly lowered the frequency of small veins with less than 50% O(2) saturation in the IC (39 out of 70 veins in IC vs. 17 out of 70 veins in ET-1-treated IC). Thus, the exogenous application of 10(-7) M ET-1 improved microvascular oxygen supply/consumption balance during focal cerebral ischemia.

Endothelin peptides in brain diseases

Recently, scientists interested in diseases of the human brain have paid much attention to the endothelin group of peptides. Under normal conditions they are found in some types of neurons and in endothelial cells of microvessels but not in glial cells. This review focuses on the endothelin peptides and their involvement in various brain diseases. Particular attention is paid to their expression in reactive astrocytes seen in many pathological conditions of the human brain. Endothelin-1 is a very potent vasoconstrictor which may be involved in the vasospasm occurring in subarachnoid haemorrhage. Intracerebral injection or application to cerebral arteries in animals will cause a focal necrosis, apparently due to severe vasoconstriction. Reactive astrocytes occurring in cases with infarcts, lacunae, Alzheimer's disease, progressive multifocal leukoencephalopathy (PML) and subacute sclerosing panencephalitis (SSPE) express endothelin-like immunoreactivity. Astrocytes in vitro may produce, store and release endothelins. To some extent astrocytes grown in vitro mimic reactive astrocytes in vivo since in cultures astrocytes are removed from their natural environment which may trigger reactive responses. Therefore, in vivo reactive astrocytes may produce, store and release endothelins just as in vitro. If endothelins are released from reactive astrocytes they may act as mitogens and may influence microcirculation by inducing vasoconstriction of intracerebral arterioles. In such ways endothelins may contribute to the final lesions seen in cases with infarcts, lacunae, traumatic conditions, Alzheimer's disease and inflammatory diseases of the brain.

Reactions of astrocytes and microglial cells around hematogenous metastases of the human brain. Expression of endothelin-like immunoreactivity in reactive astrocytes and activation of microglial cells

An immunohistochemical study was made on the peritumoral gliosis which is produced around hematogenous metastases of the human brain. The material was derived from 73 autopsy cases with different primary malignancies and six control cases without evidence of brain disease. Reactive astrocytes of hypertrophic and gemistocytic types were present around and within all the metastases. Eighty-five percent of the cases with metastases showed expression of endothelin-like immunoreactivity in the peritumoral astrocytes. Such immunoreactive astrocytes were not present in the normal controls but have previously been found in reactive astrocytes around infarcts, lacunas, inflammatory and degenerative brain diseases. The endothelin-like immunoreactivity probably reflects an increased intracellular content of endothelin. If this peptide is released from the reactive astrocytes it may act as a mitogen and influence microcirculation by inducing vasoconstriction. Activation of microglial cells, detected by ferritin immunohistochemistry, was another frequent and widespread glial cell alteration around the metastases. In conclusion, the reactive gliosis, which is formed around metastases involves activated astrocytes as well as activated microglial cells. Both cell types can release numerous biologically active compounds which may influence the structure and function of the brain tissue around the metastases.