Background
Experimental and clinical data have shown an increase of collateral vessel growth in hindlimb ischemia and cardiovascular disease after treatment with cytokins affecting proliferation or survival time of monocystes. Recently, this concept of “arteriogenesis” was also adapted to the cerebrovascular system by measuring an increase of the left posterior cerebral artery after three-vessel occlusion in rats and treatment with granulocyte-macrophage colony-stimulating factor (GM-CSF). Since it remained questionable to what extend this increase of the vessel diameter does contribute to a better collateral circulation, we investigated whether the observed normalization of brain perfusion was also based on growth of resistance vessel.
Methods
Male Sprague-Dawley rats received after bilateral internal carotid artery (ICA) occlusion a daily injection for 7 weeks of 10 μg/kg GM-CSF (GM-CSF group) or isotonic saline in control animals. To evaluate the effect of bilateral ICA occlusion a sham group was added. Cerebral blood flow (CBF) was repeatedly measured by laser-Doppler flowmetry scanning under resting conditions and after azetazolamide application. At the end of the observation period resting CBF was measured by iodo[14C]antipyrine autoradiography. Vessel density was evaluated on brain sections 7 weeks after bilateral ICA occlusion as was the number of precapillary microvessels detected by á-smooth muscle actin (α-SMA) immunohistochemistry.
Results
Resting CBF was not affected by bilateral ICA occlusion (GM-CSF group: 102±14 ml/100 g/min, control group: 90±8 ml/100 g/min, sham group: 100±9 ml/100g/min). However, the response to acetazolamide was abrogated in saline-treated control animals 2 weeks (2.0±4.0 %, sham: 7.8±6.1 %) and 5 weeks (2.2±3.7 %, sham: 10.8±8.4 %) after bilateral ICA occlusion. GM-CSF treatment resulted in a normalization of the CBF response to azetazolamide after 5 weeks of treatment (17.2±9.3 %). This recovery was accompanied by a slight increase in the number of cortical capillaries counted in individual observation fields (GM-CSF group: 95.1±3.2, control group: 92.6±6.1 and sham group: 92.5±2.9) and a significant increase of á-SMA positive vessels in individual observation fields (GM-CSF group: 101±52, control group: 50±33 and sham group: 50±38, p<0.05).
Conclusions
The increase in the number of small resistance vessels after GM-CSF treatment under conditions of mild hypoperfusion might well explain the normalization of brain perfusion. Thus, GM-CSF treatment seems to be a promising therapeutic approach in patients with chronic impairment of CBF.