Effect of fasting on hormones and metabolites in plasma of fast-growing, lean and slow-growing obese pigs.

Plasma concentrations of glucose, free fatty acids (FFA), insulin and growth hormone (GH) were determined immediately after food removal and then hourly for 24 hours. Blood was sampled from six lean and six obese pigs at 10 weeks of age via indwelling catheters. Plasma glucose decreased but was similar in both pig strains shortly after feed removal; at the end of the 24-hr fast, plasma glucose was higher (P less than .01) in lean pigs. Plasma FFA concentrations were similar in lean and obese pigs and increased five-fold within 24 hr of fasting. Plasma insulin was higher (P less than .05) in obese pigs than in lean pigs immediately after food removal only (21.4 +/- 3.0 vs 9.8 +/- 2.4 microU/ml). Pattern of GH secretion over 24 hr was episodic; average plasma GH was lower in obese pigs than in lean pigs (2.8 +/- .7 vs 9.4 +/- 1.9 ng/ml). In summary, FFA mobilization was similar in lean and obese pigs, GH concentrations were lower in plasma of obese pigs and relative differences in plasma glucose and insulin between pig strains were influenced by time after feed removal.