Pharmacodynamic characterization of insulin on MDMA-induced thermogenesis

Abstract

Sympathomimetic drugs (MDMA; ecstasy) induce a potentially catastrophic hyperthermia that involves free fatty acid (FFA) activation of mitochondrial uncoupling proteins (UCP). Insulin is an important regulator of plasma FFA levels, although its role in thermogenesis is unclear. The aims of the present study were 1) to characterize the pharmacodynamic effects of MDMA on plasma insulin and glucose, 2) to examine the effects of insulin on MDMA-induced thermogenesis and 3) to examine MDMA-induced thermogenesis in an animal model of insulin resistance, the obese Zucker rat. Insulin levels peaked 15 min after MDMA (40 mg/kg, s.c.), which preceded the peak temperature change at 60 min. Plasma glucose levels also peaked 15 min. after MDMA and remained elevated throughout the 90-min. monitoring period. Insulin pretreatment (10 units/kg, s.c.) 30 min. before a low dose of MDMA (5 mg/kg, s.c.) potentiated the thermogenic response. Insulin resistant, fa/fa (obese) Zucker rats demonstrated an attenuated thermogenic response to MDMA (40 mg/kg, s.c.). Consistent with the role for FFA in UCP3 expression, immunoblot analysis showed significantly increased levels of UCP3 protein obese compared to lean Zucker skeletal muscle. In conclusion, the results of the present study suggest a potential role of insulin signaling in sympathomimetic-induced thermogenesis.

Fig. 1

Effects of MDMA (40 mg/kg, sc) on plasma insulin levels and rectal (core) temperature (A) and blood glucose levels (B). Each point represents the mean ± S.E.M. (n=6-7). *Indicates significantly different from all other time points (P<0.01).

Fig. 2

Effects of insulin on body temperature effects of a low MDMA dose (5 mg/kg, sc). Insulin (10 units/kg, sc) was administered 15 min. before MDMA. Glucose (1 g/kg, ip) was administered 15 min. after MDMA. Each point represents the mean ± S.E.M. (n=6). *Indicates significantly different from all other treatment groups (P<0.001); **indicates significantly different from normal saline (NS)-NS only (P<0.01); and ˆindicates significantly different from NS-NS and insulin-glucose-MDMA (P<0.05).

Fig.3

Effects of MDMA (40 mg/kg, sc) on rectal temperature in fa/fa (obese) and Fa/-(lean) Zucker rats. MDMA was administered at time 0. Each point represents the mean ± S.E.M. (n=6). *Indicates significantly different from all other time points (P<0.05).

Fig.4

Effects of MDMA (40 mg/kg, sc) on plasma FFA (A) and glucose (B) levels in fa/fa (obese) and Fa/- (lean) Zucker rats. FFA and glucose levels were determined 60 min. post- MDMA or saline administration. Each column represents the mean ± S.E.M. (n=5-6). *Indicates significantly different from saline controls within a treatment group (P<0.05).

Fig.5

UCP3 protein levels in fa/fa (obese) and Fa/- (lean) Zucker rats. Gastrocnemius skeletal muscle (SKM) and brown adipose tissue (BAT) were harvested and lysates prepared from isolated mitochondria. UCP3 protein was detected via immunoblotting (upper panels). SDS-PAGE gels were stained for protein loading controls (lower panels).