Endoneurial blood flow in rat sciatic nerve during development.

Abstract

SUMMARY1. Endoneurial blood flow (EBF) in the sciatic nerve of rats aged 2-12 weeks was studied using microelectrode H2 polarography.2. EBF is highest in 2-week-old rats and progressively declines during development. Mean arterial pressure (MAP) is low at 2 weeks of age, gradually increases through the next 4 weeks, and is relatively constant thereafter. The decrease in EBF, in spite of an increase in MAP, occurs because the endoneurial vascular resistance is increasing faster than the MAP.3. The higher EBF in younger rats is not due to the smaller diameter of their nerves. Sural and tibial nerves of 12-week-old rats, with diameters comparable to that of the sciatic nerve of a 3-week-old rat, have EBFs similar to that of the sciatic nerve of a 12-week-old rat.4. There was no compelling evidence of autoregulation of EBF in 3-week-old rats over a MAP range from -40 to + 30 mmHg of the normal value.5. The increase of nerve vascular resistance with maturation is probably due to a decrease in capillary density and, to a lesser extent, to an increase in plasma viscosity and haematocrit.6. The higher EBF in immature rats is likely to be a developmentally adaptive mechanism which permits greater blood-nerve exchange of material to accommodate the greater metabolic needs of rapidly elongating and myelinating axons and proliferating Schwann cells.

Y1R control of sciatic nerve blood flow in the Wistar Kyoto rat

“…Axons of nerves receive approximately 15-20 mL/min/100 g of blood flow both in white matter of the brain (Sakurada et al, 1978) and in peripheral axons (Kihara et al, 1991;McManis et al, 1997). However, peripheral nerves do not autoregulate blood flow the way that the brain does (Kihara et al, 1991;McManis et al, 1997) so that axonal nerve blood flow changes with blood pressure.…”

“…However, peripheral nerves do not autoregulate blood flow the way that the brain does (Kihara et al, 1991;McManis et al, 1997) so that axonal nerve blood flow changes with blood pressure. Using Doppler ultrasound, we were able to detect a 156% increase in blood flow velocity through the sciatic nerve in response to a bolus infusion of saline.…”

“…Measures of steady-state sciatic nerve blood flow range from 10 to 15 ml/min/100 g in the healthy anesthetized rodent Kihara et al, 1991;Sugimoto et al, 1987). These earlier studies also indicate that the sciatic nerve is perfused in excess of metabolic requirements at baseline conditions (Kihara et al, 1991). Nonetheless, neural ischemia, as observed in diabetic neuropathy, is a major contributing etiology to neural pathology (Coppey et al, 2000;Low and Tuck, 1984;Terata et al, 1999;Tuck et al, 1984).…”

“…Measures of steady-state sciatic nerve blood flow range from 10 to 15 ml/min/100 g in the healthy anesthetized rodent Kihara et al, 1991;Sugimoto et al, 1987). These earlier studies also indicate that the sciatic nerve is perfused in excess of metabolic requirements at baseline conditions (Kihara et al, 1991).…”

“…Nerve blood flow patterns do not exhibit autoregulation in response to changes in blood pressure and are, therefore, dependent on mean arterial pressure (Kihara et al, 1991). Therefore, maintaining or constraining nerve blood flow to support metabolic needs requires additional stimuli.…”