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Plasma Glucose and Insulin Concentrations and Feeding Behavior in Ponies^1,2,

University of Pennsylvania³, Kennett Square 19348

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
(low dose, LD) or 1.0 g
(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<.10; HD = 65 ± 12 min, P<.05) relative to saline treatment (LDS = 44 ± 15 min; HDS = 35 ± 8 min). Glucose-treated ponies PG was elevated (P<.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 IRI (LD = 7.08 ± 4.34 ng/ml; HD = 10.42 ± 11.2 ng/ml; control = 2.67 ± 2.20 ng/ml). The concentration of glucagon did not change significantly with either feeding or 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.

¹ This research was supported in part by grants in aid from the Fund for the Study of Feeding Behavior, Dept. of Clin. Studies, School of Vet. Med., Univ. of Pennsylvania and NIH Training Grant GM-02051.

² The authors are grateful to Ms. Terri Wilkinson for her technical assistance.

³ Section of Med., School of Vet. Med.