Acetaminophen as a marker of gastric emptying in ponies

Gastric emptying was evaluated in ponies using the acetaminophen (AP) method. Fifteen minutes after i.v. administration of metoclopramide, erythromycin, yohimbine, atropine or saline, the ponies were given AP by stomach tube. Blood samples for AP analysis were collected at baseline and 15, 30, 45, 60, 75, 90, 105 and 120 min after AP administration. Time to reach peak serum concentration (Tmax), maximum serum concentration (Cmax) and area under the AP serum concentration vs. time curve (AUC) were determined for each treatment group. In the control group, Tmax was 31 min and this decreased significantly (P < 0.05) following the administration of metoclopramide. Atropine significantly increased Tmax and decreased Cmax and AUC. Yohimbine significantly increased AUC. Erythromycin did not significantly change any parameter. This study indicates that acetaminophen can be used to evaluate gastric emptying in ponies. The method is easy to perform and is minimally invasive. Metoclopramide stimulated gastric emptying of liquid in healthy, fasting ponies. Atropine significantly delayed, while erythromycin had little effect on, gastric emptying. Yohimbine increased the cumulative absorption of AP.