Disruption of Blood Flow Autoregulation in the Middle Cerebral Artery Bed in Rats with Carotid Artery Stenosis

Carotid artery stenosis results in chronic cerebral hypoperfusion and dysfunctions of cerebral vasculature. The aim of the work was to evaluate changes in cerebral blood flow regulation in rats two days after bilateral stenosis of the common carotid arteries. Carotid stenosis (CS group) was performed using silver clamps (decrease in volume blood flow rate (VBFR) by 70–80%), sham-operated rats served as a control (CON). Blood flow velocity in large branches of the right middle cerebral artery was recorded by laser speckle-contrast visualization (after thinning of the skull) under urethane anesthesia and artificial ventilation with subsequent calculation of vessel diameter and VBFR. Tests with respiratory hypercapnia (5% and 10% CO2) and gradual bleeding (five-fold blood sampling from the inferior vena cava, 5% of the circulating blood volume at 5-min intervals) were performed. Blood biochemical parameters (lipoprotein profile and urea/creatinine levels) did not differ between the CON and CS groups. The mean arterial pressure in the baseline and its changes during the interventions also did not differ between the two groups. Hypercapnia resulted in a comparable increase in VBFR in the CON and CS groups. In CS rats, bleeding induced a decrease in VBFR, while VBFR did not decrease in the CON group. Using spectral analysis, low-frequency (0.1 Hz) oscillations of blood flow velocity were explored in the arteries; such frequency peak was absent in the spectrum of mean arterial pressure. The power of such oscillations increased during blood loss in the CON group but not in the CS group. Thus, narrowing the carotid arteries leads to disruption of compensatory capabilities of cerebral blood flow regulation with gradual decrease in arterial pressure due to blood loss, as well as to suppression of vasomotions of cerebral arterial tone.