Influence of a high osmolality, high salt concentration, and bitter taste on the reticular groove reflex in the adult cow

Abstract

Objective – To determine if the reticular groove reflex can be triggered in the adult cow by a high osmolality, a high salt concentration, or a bitter taste. Design – Clinical trial. Animals – 4 fistulated Holstein Friesian cows, between 3 and 10 years old. Procedures – Cows were administered test solutions of hypertonic dextrose, hypertonic sodium chloride, hypertonic sodium bicarbonate, and bitter MgSO4. All solutions included dextrose and acetaminophen. Negative and positive controls were obtained by inserting solutions in the ventral rumen sac and in the abomasum. Plasma samples were taken during 6 hours after administration in order to determine the concentrations of glucose and acetaminophen. Results – Area under the curve between 0 and 60 minutes and between 0 and 120 minutes, maximum serum concentrations (Cmax,μg/ml) and time until maximum serum concentrations (Tmax,min.) for acetaminophen and glucose were calculated for each of the test solutions. None of the test solutions differed significantly from the negative control when looking at area under the curve. Only Cmax acet. for the hypertonic dextrose solution (25.5 μg/ml) was significantly (P = 0.0471) higher than for the negative control (17.1 μg/ml). Cmax acet. for the hypertonic dextrose solution was also significantly (P = 0.0000) lower than for the positive control (55.8 μg/ml). Tmax acet. was at 202.5 minutes, which is slightly later (P = 0.0949) than for the negative control (135 minutes), but significantly later (P = 0.0010) than for the positive control (47.5 minutes). No significant differences were found between the test solutions and the negative control for glucose. Conclusions – None of the test solutions were able to trigger the reticular groove reflex. Results form earlier studies, that concluded that they could activate the reticular groove reflex with sodium chloride and sodium bicarbonate, could not been repeated and were probably caused by closure of the groove as result of hypovolemia and other factors than closure of the esophageal groove.