Abstract
Although insulin degradation by insulin degrading enzymes in various tissues has been well studied, no report is yet available about insulin degradation by the rat pituitary.
Insulin degradation by the adenopituitary of male and female rats was observed using their hemipituitaries and homogenates. A medium containing 50μU/m/ or 25μU/m/ pork insulin was incubated with Krebs-Ringer bicarbonate buffer containing 2.5% BSA and 0.1% glucose.
The hemipituitaries were incubated in this medium and the IRI in the medium was measured before and after the incubation. Insulin degradation by the hemipituitaries increased in proportion to the incubation time. No degradation was observed on incubation at 4°C, but about 35% of the insulin in the medium was degraded with the hemipituitary during 60 min at 37°C. When the hemipituitary was heated for 10 min at 70°C before incubation, insulin degradation was apparently suppressed.
Comparisons were made on hemipituitaries of rats in the following groups; male and female rats fed and fasted for 48 hr, pregnant rats fed and fasted for 48 hr, and streptozotocine diabetic pregnant rats and streptozotocine diabetic non-pregnant rats. Insulin was degraded to the greatest degree (about 66%) by hemipituitaries of pregnant fed and fasted rats. Insulin degradation was more suppressed by hemipituitaries of rats in a fasting state than by those which had been fed.
The insulin degradation rate was lessened to the greatest degree (about 30%) in the case of hemipituitaries of streptozotocine diabetic non-pregnant rats.
The degradation of insulin in the hemipituitaries of male rats was less than that in female rats, although the difference was not significant.
The grade of insulin degradation in adenopituitary homogenates was intermediate between that of the liver and diaphragm muscle. Homogenates of these tissues showed a higher insulin degradation rate than the hemipituitary.
