Effects of hyperlipidemia on gallbladder motility in dogs

Background: The pathogenesis of gallbladder mucocele is unknown in the dog. It has been proposed that hyperlipidemia could impair gallbladder motility and contribute to gallbladder mucocele formation.

Objectives: The objective of this study was to compare gallbladder motility in dogs with hyperlipidemia to healthy, control dogs using ultrasonography. We hypothesized that hyperlipidemic dogs have decreased gallbladder motility, defined by increased fasting gallbladder volume (GBV) and decreased gallbladder ejection fractions at 60 (EF60) and 120 minutes (EF120) compared to controls.

Animals: 26 hyperlipidemic dogs, 28 healthy control dogs Methods: Twenty-six hyperlipidemic and 28 healthy, age-matched control dogs were prospectively enrolled. Hyperlipidemia was defined as hypercholesterolemia (>332 mg/dL) and/or hypertriglyceridemia (>143 mg/dL). Dogs with both primary and secondary causes of hyperlipidemia were included. All dogs were fasted for at least 12 hours prior to collection of plasma biochemistry and pre-prandial ultrasound. Ultrasound was performed on dogs in the fasted state as well as at 60 and 120 minutes after being fed 10g/kg of a high fat diet (Hill's a/d diet; Hill's Pet Nutrition, Topeka, Kansas, USA). GBVs and EFs were calculated using the following formulas: GBV = (0.52 x L x W x H)/kg and EF = ((GBV0- GBV60,120)/GBV0) x 100, respectively. GBV0, GBV60, GBV120, EF60 and EF120 were compared between dogs with hyperlipidemia and controls using the Wilcoxon rank sum test. Statistical significance was set to p<0.05.

Results: Hypercholesterolemia and hypertriglyceridemia were present in 15/26 (58%) and 21/26 (81%) hyperlipidemic dogs, respectively and 10/26 (38%) had elevations in both parameters. The median age in both groups was 10 years. Median (range) cholesterol concentration was 346 mg/dL (181-1372 mg/dL) and 238 mg/dL (153-324) in hyperlipidemic and control dogs, respectively. Median triglyceride concentration was 330 mg/dL (52-2213) and 65.5 mg/dL (32-142) in hyperlipidemic and control dogs, respectively. Eleven (42%) hyperlipidemic dogs were considered severely hyperlipidemic based on the triglyceride and/or cholesterol concentrations above 500 mg/dL. There were significant differences in GBV0 and GBV60 between hyperlipidemic and control dogs. Dogs with severe hyperlipidemia had significantly larger GBVs at all time points. Dogs with hypercholesterolemia also had significantly greater GBVs at all times compared to dogs without hypercholesterolemia. Median EF60 and EF120 were not significantly different between hyperlipidemic and control dogs nor severely hyperlipidemic and mildly hyperlipidemic dogs.

Conclusions: Hyperlipidemic dogs have significantly greater fasting and postprandial GBVs but similar ejection fractions when compared to control dogs. Gallbladder emptying is unaltered in hyperlipidemic dogs, but gallbladder volume is higher in hyperlipidemic dogs after feeding. This distention could contribute to bile retention of bile and potentially gallbladder disease.