Effects of salt-loading hypertension on nociception in rats

Abstract

BackgroundThere is on going controversy on the effect of experimentally induced hypertension on nociception. The effect of salt-loading-induced hypertension on pain was studied in male rats.MethodTwenty-four male Sprague-Dawley rats (160–280 g) were divided into two groups. Group A (n = 12) was treated with normal-feed diet (control), while group B (n = 12) was treated with 8% salt-loaded diet for 10 weeks. After 10 weeks of the treatment, six rats each from groups A and B were used for blood pressure measurement, while the remaining six rats were used for both the tail-flick and formalin tests. Thermal and chemical pain test were assessed using tail immersion test (tail flick) and formalin test pain paradigms at onset of salt-loading diet and after 10 weeks of salt loading.ResultsChronic administration of salt-loading diet caused significant increases (P < 0.001) in systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure. Moreover, salt-loading-induced hypertension was found to significantly reduce pain sensitivity in the tail-immersion test (P < 0.001) and in the early and late phase of the formalin test (P < 0.01). However, the hypoalgesia was higher in the late phase (94.8%) than in the early phase (56.8%) of the formalin test.ConclusionThe present study suggests that high salt-loading-induced hypertension causes hypoalgesia in rats, which might be due more to reduction in inflammatory response.

Biocompatibility of Four Common Orthopedic Biomaterials Following a High-Salt Diet: An In Vivo Study

“…According to Safe ® Company (Safe S.A.S, Augy, France) which provided food for laboratory animals, we determined that the NaCl amount in the basic food ranged between 0.25% and 0.27% of food weight. Since most high-salt diets that were used in the scientific literature were composed with levels up to 8% NaCl [ 65 , 66 ], this value was chosen as a reference. In accordance with Oloyo et al, food pellets usually given to rats were mixed with water to form a smooth paste, then salt (7.75% of the total food weight) was added to reach the desired salt concentration of 8% and pellets were reconstituted before being dried for 24 h [ 67 ].…”

Epidural administration of neostigmine-loaded nanofibers provides extended analgesia in rats

“…The formalin test is usually used for evaluation of anti-nociceptive drugs which are administrated intrathecally against the high intensity of chemical pain stimulus. In order to avoid interaction of both techniques’ effects on the same animals, it is better to evaluate the formalin test at least 7 days after the tail-flick test, because the tail-flick test has no impact on the formalin test results after this period [ 20 ]. Therfore, in this study the formalin test was performed 7 days after the tail flick test.…”