ABSTRACT
The present study examines the effect of concanavalin A (Con A) on the blood insulin and glucose levels of rats. Male and female rats treated with Con A (62.5-500 mug/kg) for three days showed a dose-and time-dependent hyperinsulinemia that lasted more than 48 h. Male rats were more sensitive to Con A. Thus, 6 h after treatment with Con A the circulating insulin levels in male rats had increased by 85 percent (control: 10.2 + 0.9 mU/l and Con A-treated: 18.8 + 1 mU/l) compared to only 38 percent (control: 7.5 + 0.2 mU/l; Con A-treated: 10.3 + mU/l) in females. An identical response was seen after 12 h. Con A (250 mug/kg) produced time-dependent hypoglycemia in both sexes but more pronounced in males. There was no correlation between the hypoglycemia and hyperinsulinemia described above. The Con A-induced hyperinsulinemia in rats of both sexes was abolished in gonadectomized animals (intact males: +101 + 17 percent vs orchiectomized males: -5 + 3 percent; intact females: +86 + 23 percent vs ovariectomized females: -18 + 7.2 percent). Pretreating intact male and female rats with human chorionic gonadotropin also significantly inhibited the Con A-induced hyperinsulinemia. Estradiol (10 mug/kg, im) significantly blocked the Con A-induced increase in circulating insulin in male rats (101 + 17 percent for controls vs 32 + 5.3 percent for estradiol-treated animals, P<0.05) while testosterone (10 mg/kg, im) had no similar effect on intact female rats. Pretreating Con A-injected rats with opioid antagonists such as naloxone (1 mg/kg, sc) and naltrexone (5 mg/kg, sc) blocked the hyperinsulinemia produced by the lectin in males (control: +101 + 17 percent vs naloxone-treated: +5 + 14 percent, or naltrexone-treated: -23 + 45 percent) and females (control: +86 + 23 por cent vs naloxone-treated: +21 + 20 percent, or naltrexone-treated: -18 + 11 percent). These results demonstrate that Con A increases the levels of circulating insulin in rats and that this response is opioid-dependent and hormonally regulated.