Prevention of the Development of Hyperglycemia in Sand Rats by Adrenal Medullectomy

Summary

In sand rats high caloric food intake leads to hyperinsulinism, hyperglycemia, impaired insulin action on glucose metabolism in muscle and adipose tissue as well as to reduced hormone sensitive lipolysis associated with high circulating triglycerides and FFA-levels. Some of our results concerning glucose metabolism in muscle have already implicated that high epinephrine activity could contribute to the development of these metabolic disturbances. To clarify this question we have taken the adrenodemedullated sand rat as a model. Body weight, plasma insulin and glucose levels of adrenodemedullated sand rats and of a control group of sham-operated animals were checked over 3 months after operation. Thereafter the animals were decapitated and the hormone sensitivity of adenylate cyclase in adipose tissue as well as of cAMP secretion was examined.

Epinephrine in the circulation of the adrenodemedullated sand rats was not detectable, whereas in sham-operated animals its level was 0.99 ± 0.19 ng/ml. The norepinephrine level in adrenodemedullated animals amounted to 0.84 ± 0.22 ng/ml, thus being definitely lower than that of the controls (2.64±0.32 ng/ml). During the first 5 post-operative weeks the body weight differed between the two groups, but thereafter it was practically the same. Adrenal medullectomy prevented the development of hyperglycemia and significantly reduced the degree of hyperinsulinism. The norepinephrine action on adenylate cyclase activity of adipose tissue was significantly enhanced, and the insulin action on cAMP release was only slightly affected when the adrenal medulla was resected. In comparable experiments with young Wistar rats blood glucose and IRI-levels as well as norepinephrine and insulin action on adenylate cyclase activity and cAMP secretion were not significantly influenced by adrenal medullectomy. Our results support the significance of adrenergic activity for the excessive level of plasma insulin and the development of hyperglycemia in sand rats on a high caloric diet.

Key-Words:

Sand Rat - Adrenal Medullectomy - Sham Operated Animals - Hyperglycemia - Hyperinsulinism - Adipose Tissue