Acute Caloric Restriction Leads to Loss of Hypoglycemic Counter-Regulation in Mice following Short-Term Refeeding

Abstract

Background: Hypoglycemia-associated autonomic failure (HAAF) is a maladaptive failure in glucose counter-regulation known to be caused by recurrent exposure to insulin-induced hypoglycemia. Fasting or caloric restriction is the only natural physiological process which induces prolonged moderate-to-severe hypoglycemia similar to the antecedent of HAAF. In this study we tested the hypothesis that exposure to fasting-induced hypoglycemia can cause HAAF-like symptoms in mice. Methods: Two groups of mice were used, an ad libitum (ad lib) fed group (n=6) and a caloric restriction (CR) group (n=6). CR mice were placed on 60% caloric restriction for 6 consecutive days. Ad lib mice were housed in an identical manner but fed ad libitum during this same period. Following 6 days of restriction, CR mice were given ad lib access to food for 16 h. After the 16 h period of refeeding, both CR and ad lib mice began a 6 h fast which was immediately followed by a hypoglycemic insulin tolerance test (ITT). ITTs consisted of a variable dose of insulin (1.4-1.75 U/kg, IP) which produced similar levels of hypoglycemia in each group (∼45 mg/dL). Results: As expected, mice exposed to 6 days of 60% CR lost ≈30% of their initial body weight, and experienced a gradual fall in blood glucose to an average minimum of 67.9 mg/dL. CR mice displayed a significantly reduced fasting glucose level relative to ad lib mice (102.7 and 171.0 mg/dL respectively, p = 0.0002) as well as reduced serum glucagon levels in response to the ITT (6.0 and 30.4 pg/mL respectively, p = 0.0182). Conclusions: Our results demonstrate that exposure to fasting-induced hypoglycemia produces HAAF-like symptoms in mice following refeeding. These results suggest that HAAF may be a result of an adaptive response to fasting which is inappropriately elicited during exposure to insulin-induced hypoglycemia. Further characterization of the effects of CR on the induction of deficits in glucose counterregulation warrants further investigation. Disclosure D. McDougal: None.