Effects of neutering on hormonal concentrations and energy requirements in male and female cats.

OBJECTIVE To determine whether changes in concentrations of hormones involved in glucose and fatty acid homeostasis are responsible for the increased probability that neutered cats will develop obesity and diabetes mellitus. ANIMALS 10 male and 10 female weight-maintained adult cats. PROCEDURE Results of glucose tolerance tests and concentrations of hormones and nonesterified fatty acids (NEFA) were examined before and 4, 8, and 16 weeks after neutering. RESULTS Caloric requirements for weight maintenance were significantly decreased 8 and 16 weeks after neutering in females. Glucose concentrations during a glucose tolerance test did not change in neutered females or males. The area under the curve (AUC) for insulin was significantly higher in males, compared with females, before neutering. However, the AUC for insulin increased and was significantly higher 4 and 8 weeks after neutering in females. The AUC for insulin did not change in neutered male cats. Leptin concentrations did not change in females but increased significantly in males 8 and 16 weeks after neutering. Thyroxine concentrations did not change after neutering; however, free thyroxine concentration was significantly higher in females than males before neutering. Baseline concentrations of NEFA were significantly higher in female than male cats before but not after neutering. Suppression of NEFA concentrations after glucose administration decreased successively in male cats after neutering, suggesting decreased insulin sensitivity. CONCLUSIONS AND CLINICAL RELEVANCE Changes in NEFA suppression, caloric intake, and leptin concentrations may be indicators of, and possible risk factors for, the development of obesity in cats after neutering.