Cardiovascular and T2-T4 dorsal horn cell responses to gallbladder distention in the cat

Abstract

Effects of gallbladder distention on blood pressure, heart rate, and T2-T4 dorsal horn cell activity were determined in 18 cats anesthetized with alpha-chloralose. Distention of the gallbladder (10-100 mm Hg) increased blood pressure in 17 of 18 cats, but heart rate was altered in only 2. The gallbladder pressure-blood pressure relation was derived for 11 cats. Pressor responses were greater with greater distending pressures over the gallbladder pressure range of 20-80 mm Hg. The maximum increase in blood pressure was 21 +/- 6 mm Hg at a gallbladder pressure of 80 mm Hg. Effects of gallbladder distention were tested on 64 T2-T4 dorsal horn neurons which met the following criteria: they had a somatic receptive field and were excited or inhibited by electrical stimulation of the left greater splanchnic nerve. In addition, all 64 neurons responded to stimulation of cardiopulmonary sympathetic afferent fibers. Gallbladder distention excited 17 cells and inhibited 9 cells. Responses usually consisted of phasic and tonic components. Significant increases or decreases in cell activity were elicited at a gallbladder pressure of 40 mm Hg. Pressor responses as well as changes in cell activity were abolished or greatly attenuated when both greater splanchnic nerves were sectioned. Vagotomy had no effect. Gallbladder pressure thresholds for a change in blood pressure (27 +/- 3 mm Hg) and cell activity (29 +/- 4 mm Hg) were not significantly different. Cells responding to gallbladder distention were located in laminae IV-VII of the T2-T4 segments. We conclude that gallbladder distention alters cell activity in the upper thoracic spinal cord and increases blood pressure. These findings may explain the phenomenon of chest pain which results from disease of the gallbladder.