Plasma Glucose and Insulin Concentrations and Feeding Behavior in Ponies2

Abstract

The hypothesis that changes in blood glucose concentrations and(or) utilization rate affect feeding behavior in ponies was tested. Ponies (n = 4) were fasted for 4 h, then given iv injections of 50% glucose [.2 g glucose/BW.75 kg (low dose, LD) or 1.0 g glucose/BW.75 kg (high dose, HD)] or an equal volume of normal saline (HDS; LDS) 5 min before being allowed access to pelleted feed. Blood samples were drawn at regular intervals pre- and post-treatment and analyzed for plasma glucose (PG), immunoreactive insulin (IRI) and glucagon concentrations. All glucose-treated animals immediately ate meals of size (HD = .67 +/- .23 kg, LD = .62 +/- .30 kg) and duration (HD = 54 +/- 19 min; LD = 49 +/- 16 min) comparable to those observed after saline injections (HDS = .58 +/- .29 kg in 48 +/- 16 min. LDS = .58 +/- .10 g in 50 +/- 15 min). There was a tendency, however, to prolong the interval between the first and second meal (first intermeal interval) after glucose injections (LD = 62 +/- 16 min, P less than .10; HD = 65 +/- 12 min, P less than .05) relative to saline treatment (LDS = 44 +/- 15 min; HDS = 35 +/- 8 min). Glucose-treated ponies PG was elevated (P less than .01) at the time of refeeding (LD = 122 +/- 14 mg/100 ml; HD = 259 +/- 69 mg/100 ml) relative to controls (84 +/- 2 mg/100 ml) as was 11.2 ng/ml; control = 2.67 +/- 2.20 ng/ml). The concentration of glucagon did not change significantly with either feeding of glucose treatment. The animal's PG and IRI dropped to within or below control ranges by 35 (LD) or 65 min (HD) post-treatment. The results indicated that, in ponies, intravenous glucose loads can prolong the duration of satiety experienced after a meal. Exogenously-induced hyperglycemia and resultant hyperinsulinemia do not, however, affect the first meal size or duration of ponies after a 4 h fast.