National Autonomous University of Mexico, Mexico
Fernando García Lacy received his degree of Veterinary Doctor and Master´s from the National Autonomous University of Mexico. He is dedicated to private practice in sport horses. He is a Professor at the same University.
Insulin has been instilled intra-articularly by some clinicians to treat horses for osteoarthritis, even though its local (synovial) and systemic effects and therapeutic dose are not known. Insulin, in concentrations up to 50 ng/mL induces mitosis of equine chondrocytes in vitro and enhances production of type II collagen by the chondrocytes. Insulin like growth factor 1 (IGF-1) is the most important growth factor in the equine joint, it has the greater mytotic effect on equine chondrocytes. For this study, we adapted the dosage used in vitro to in vivo use. We found that insulin, when administered intra-articularly, does not change significantly the composition of synovial fluid of the treated joint, whereas changes in intraarticular (IA) concentrations of glucose and insulin, and blood glucose levels were seen. The concentration of insulin in the joint was measured by using high-performance liquid chromatography (HPLC), which provided pharmacokinetic values, such as area under the curve, half-life, time of maximum concentration, and residence time. For this study, 6 mixed breed horses were administered three different doses of insulin into one antebrachiocarpal joint (10, 15 and 20 IU) and isotonic saline was administered into the contralateral antebrachiocarpal joint. The blood glucose concentration was found to be significantly changed through time for all 3 doses (P<0.0001). No significant differences in protein concentration and cell count in synovial fluid were found between treated and control (SSF) joints (P>0.05), and no significant difference in synovial glucose concentrations was found between treated and control joints (P>0.05). HPLC revealed that the pharmacokinetic values were dose dependant, but there was no significant difference in concentration of blood glucose between the three different doses (P=0.9851). Intraarticular (IA) injection of insulin enhances IGF-1 expression on the synovial fluid. The insulin used in this study proved to be inocuous to the equine joint, but, because the lowest concentration of blood glucose was seen one hour post injection, the horse should be monitored for about one hour after injection, and no more than 20 IU for a 350-400 kg horse should be administered.