Response to chronic insulin administration: effect of area postrema ablation

The effects of daily administration of protamine zinc insulin (PZI) on plasma insulin and glucose levels and on food intake and body weight of rats with lesions of the area postrema and adjacent caudal-medial portions of the nucleus of the solitary tract (APX rats) were examined. Prior to insulin treatment, APX rats weighted less and had lower plasma immunoreactive insulin (IRI) levels than nonlesioned controls but did not differ from controls in plasma glucose levels. Five daily injections of 5 U/kg PZI raised plasma IRI and lowered plasma glucose levels similarly for both lesioned and nonlesioned rats. When injected with increasing doses of PZI over a 30-day period, both lesioned and nonlesioned rats showed increases of food intake and rate of weight gain in response to 8 U/kg PZI. These data indicate that APX does not affect either physiological or behavioral responses to chronic peripheral insulin administration.