Various areas in the central nervous system are responsible for inhibiting ascending pain transmission within the spinal cord through the activity of inhibitory neurotransmitters, which include serotonin, norepinephrine, enkephalins, γ-amino butyric acid and adenosine.
The ETB receptor has been clearly demonstrated to inhibit thick ascending limb and collecting duct (CD) Na reabsorption, while the role of the nephron ETA receptor in modulating tubule Na and/or water transport remains uncertain [ 6].
The present study, therefore, suggests that the descending LC/SC system can inhibit visceral nociceptive signals ascending through the STT and the DC pathways.
Loop diuretics like furosemide increase urinary flow rate and urinary excretion of sodium, potassium and chloride by inhibiting Na+ K+ 2Cl− symporter in the thick ascending loop and by inhibiting carbonic anhydrase enzyme.
The calcium binding to the Ca-sensing receptor expressed in the thick ascending limb inhibits the Na,K, 2CL cotransporter, which decreases both sodium reabsorption and thus influences blood pressure [39].
According to this theory, stimuli travelling ascending pathways may inhibit the nociceptive signals from painful stimulus through various endogenous mechanisms located along the spino-thalamic tract [ 77].
Loop diuretics are administered to inhibit sodium reabsorption in the thick ascending limb of the loop of Henle and are intended to increase natriuresis.
Previous studies have shown that the loop diuretic furosemide, which inhibits reabsorption in the medullary thick ascending limb, increased medullary oxygen tension by reducing oxygen consumption rather than by increasing medullary blood flow [ 18, 19].
The dopamine D1 receptor agonist fenoldopam (1 μM) inhibited sodium chloride transport in the thick ascending limb by 42±5%.
20-HETE is a potent vasoconstrictor and inhibits sodium transport in the proximal tubule and thick ascending loop of Henle (TALH), whereas EETs are endothelium-derived relaxing factors that dilate small arterioles and inhibit sodium transport in the proximal tubule and the collecting duct [ 1].
