Measurement of neuropeptide levels released by sciatic nerve stimulation from isolated rat hind limb vascular bed

Skeletal muscle contraction causes one of the biggest increases in blood flow in normal mammal tissues. Post-exercise hyperemia and vasodilation are part of the phenomenon called post-exercise hypotension (PEH). Although the mechanisms underlying this phenomenon are not fully known, changes in sympathetic and afferent nerve activity, baroreflex mechanism, histamine, prostaglandins, nitric oxide, endogenous opioid and thermoregulation are possible mechanisms that may be effective in the formation of PEH. In addition, the contribution of peripheral nerves has been suggested. Additively, direct electrical stimulation of the sciatic nerve caused a decrease in blood pressure. The role of vasodilator neuropeptides with perivascular localizations such as CGRP, SP and NKA, has been suggested in this phenomenon. It seems possible that some changes that occur during exercise (heat, pH change, stress, CO2 etc.) may also cause PEH. In this thesis, we investigated the nature of the decrease in perfusion pressure observed as a result of electrical stimulation of the motor nerve innervating the hindlimb muscles in the isolated-perfused rat hindlimb vascular bed by applying an "isolated experimental exercise" model. For this purpose, the rat hindlimb vascular bed was isolated as a whole and perfused with Krebs solution (perfusion rate; 5 mL/min) continuously gassed with 95% O2 + 5% CO2 in an organ bed whose temperature was kept constant at 37°C. Vascular bed perfusion pressure was increased with an α-agonist phenylephrine (2x10-5 M). Subsequently, endothelial integrity was tested with acetylcholine (0.1 g). First, vasodilator responses were obtained by stimulating the motor nerve. Then, the levels of the aforementioned neuropeptides were measured in the perfusates poured from the vascular bed. This procedure was also performed in the presence of capsaicin, which is reported to be a neuropeptide depletor. We obtained small but consistent vasodilator responses (14%) with motor nerve stimulation. It was observed that the developed response was not frequency dependent. Similar vasodilator responses were observed with direct stimulation of the hind leg muscles (17%). Interestingly, no NKA levels obtained after nerve or muscle stimulation, in experiments where neuropeptide levels were measured from the venous effluent. However, SP and CGRP levels were unable to be measured technically. On the other hand, an increase in lactic acid levels from venous outflow was seen after stimulation of motor nerves and muscle. Interestingly, lactic acid levels obtained by direct stimulation of leg muscles were found to be higher.