J Korean Pain Soc.  2004 Dec;17(2):113-118. 10.3344/jkps.2004.17.2.113.

Repeated Intraplantar Injection of Low-pH Saline Produce Mechanical Hyperalgesia in Rat

• Woo YC

• KMID: 2104839
• DOI: http://doi.org/10.3344/jkps.2004.17.2.113

Abstract

BACKGROUND
The purpose of this study was to characterize an animal model of persistent mechanical hyperalgesia induced by repeated intraplantar injection of low pH saline. METHODS: Saline, at pHs of 4, 5, 7 and 7.4, was intraplantarily injected into the hind paw twice, 5 days apart. To quantify the hyperalgesia, the withdrawal threshold (WT) to mechanical stimuli was measured on the following schedule: before the first injection; 2 h and 4 h after the first injection; before the second injection and 4 h and weekly (6 weeks) after the second injection. The paw withdrawal latency to radiant heat was also measured with pH 4 saline. Mechanical hyperalgesia (MH) due to an intraplantar, subcutaneous injection was compared with that of a gastrocnemius muscle injection at pH 4. RESULTS: Two unilateral injections of pH 4 and 5 saline solutions caused bilateral mechanical, but not heat hyperalgesia, which lasted 3 4 weeks. An intraplantar injection of pH 4 saline showed a higher WT than the gastrocnemius muscle injection 4 hours after the second injection, but there was no significant difference between the two. CONCLUSIONS: Repeated intraplantar injections of low pH saline produced bilateral long-lasting MH in rats, but there was no significant difference in the WT between muscle and subcutaneous injections.

Keyword

acid; muscle injection; pain; subcutaneous injection

MeSH Terms

Animals
Appointments and Schedules
Hot Temperature
Hydrogen-Ion Concentration
Hyperalgesia*
Injections, Subcutaneous
Models, Animal
Muscle, Skeletal
Rats*