A parametric analysis of olanzapine-induced weight gain in female rats.

Rationale: Some novel antipsychotics, including olanzapine, induce weight gain and metabolic abnormalities, which represent the major adverse effects of these drugs. However, the mechanism(s) involved in such effects are unclear.

Objective: The aim of this study was to develop, in female rats, a parametric model of olanzapine-induced weight gain and metabolic abnormalities and evaluate it against clinical findings.

Methods: Female rats were administered olanzapine b.i.d. at doses of 0, 1, 2 and 4 mg/kg over 20 days, and a wide range of variables were recorded during and after drug administration.

Results: Olanzapine increased both 24 h and total food intake. This was associated with rapid onset weight gain and increased adiposity (assessed by visceral fat pad masses). Insulin, but not glucose, concentrations were elevated, with a significant increase in the HOMA-IR index, indicative of insulin resistance. A nonsignificant trend towards higher levels of leptin was observed. Paradoxically, there was a significant increase in adiponectin. All of these variables showed maximal increases at either 1 or 2 mg/kg and attenuated effects at 4 mg/kg. Prolactin levels were also increased by olanzapine. However, for this variable, there was a clear dose-response curve, with the maximal effect at the highest dose (4 mg/kg).

Conclusions: These data suggest that aspects of olanzapine-induced weight gain and metabolic abnormalities can possibly be modelled in female rats. It is suggested that olanzapine-induced hyperphagia acts as an initial stimulus which leads to weight gain, enhanced visceral adiposity and subsequent insulin resistance, although the latter may be ameliorated by compensatory responses in adiponectin levels. Prolactin elevation appears likely not to be involved in the weight gain, adiposity and metabolic changes seen in this model.