Aortocaval fistula delays gastric emptying of liquid test meal in awake rat

Abstract

Arteriovenous (AV) anastomoses disrupt cardiovascular and renal homeostasis, 25 eliciting hemodynamic adjustments, resetting the humoral pattern, and inducing cardiac 26 hypertrophy. Because acute circulatory imbalance alters gut motor behavior, we studied the 27 effects of AV fistula placement on the gastric emptying (GE) of a liquid meal in awake rats. After 28 laparotomy, we created an aortocaval fistula (ACF) by aorta and cava wall puncture with a 21-, 29 23-, or 26-gauge needle. The ACF was not created in the control group, which underwent sham 30 surgery. After 12, 24, or 48 h, mean arterial pressure (MAP), heart rate (HR), and central venous 31 pressure (CVP) were continuously recorded, and cardiac output (CO) was estimated by thermal 32 dilution. The rats were then gavage-fed a test meal (i.e., phenol red in glucose solution), and 33 fractional dye retention was determined 10, 20, or 30 min later. The effect of prior bleeding on 34 ACF-induced GE delay, the role of neuroautonomic pathways, and changes in plasma hormone 35 levels (i.e., angiotensin II, arginine vasopressin, atrial natriuretic peptide, corticosterone, and 36 oxytocin) were evaluated. Compared with the sham group, ACF rats exhibited arterial 37 hypotension, higher (p < 0.05) HR, CVP, and CO values, and increased (p < 0.05) gastric dye 38 retention, a phenomenon prevented by bilateral subdiaphragmatic vagotomy and 39 hexamethonium treatment. Pirenzepine also impaired the occurrence of gastric delay in virtue 40 of ACF. In addition to causing hyperkinetic circulation, ACF placement delayed the GE of liquid 41 in awake rats, an effect that likely involves a parasympathetic pathway.