Effects of recombinant equine somatotropin on wound healing, carbohydrate and lipid metabolism, and endogenous somatotropin responses to secretagogues in geldings

The primary purpose of this experiment was to assess the possible beneficia l effects of recombinant equine somatotropin (reST) administration on wound healing in adult geldings. The effects of the 21-d reST treatment on carbo hydrate and lipid metabolism and on endogenous ST characteristics were moni tored as well. Single, full-thickness skin incisions (7.62 x 7.62 cm) were made in the pectoral region of all geldings on d 0. Treated geldings receiv ed reST at 20 mu g/kg BW i.m., and control geldings received vehicle (10 mM sodium berate) at equivalent volumes daily from d 0 (immediately after sur gery) through d 20. Tracings of the wounds were made with acetate transpare ncies, and wound areas were calculated via a digital analyzer. In addition to once-daily blood samples collected at specified days throughout the trea tment period, an i.v. glucose tolerance test was performed on d 16, and thr ee assessments of endogenous ST secretion were performed in the 2 d immedia tely following the end of treatment: epinephrine administration during the morning of d 21, an exercise test during the afternoon of d 21, and i.v. as partic acid infusion on d 22. There was no effect (P > .1) of reST treatmen t on wound healing as assessed by changes in wound areas. Daily plasma ST, IGF-I, glucose, and insulin concentrations were higher (P < .05) and urea-n itrogen concentrations were lower (P < .001) in geldings receiving reST rel ative to controls. Glucose, NEFA, and insulin concentrations were all highe r (P < .01) in reST-treated geldings before glucose infusion on d 16, and t he responses to glucose were greater (P < .05) as well. Epinephrine adminis tration increased (P < .02) ST concentrations in control geldings on d 21 b ut not in reST-treated geldings; a similar suppressive effect of reST treat ment was observed for the ST response to exercise (P < .001). After asparti c acid infusion on d 22, reST-treated geldings had a much smaller (P < .001 ) ST response than did control geldings. In conclusion, reST administered t o geldings at 20 mu g/kg BW i.m. caused hyperglycemia, hyperinsulinemia, in sulin insensitivity, mobilization of fatty acids, and an apparent negative feedback on the pituitary's ST response to various stimuli known to induce ST secretion. However, there was no beneficial effect of reST treatment wit h the wound model used in this experiment.