Serum insulin changes in arteriosclerotic breeder female rats versus non-arteriosclerotic virgin rats

Immunoreactive serum insulin (IRI), glucose, free fatty acids (FFA), and corticosterone (Cmpd. B) were measured in non-arteriosclerotic virgin versus arteriosclerotic, breeder female rats exhibiting normal 4-day cycles. In the arteriosclerotic breeder females, the normal increase in IRI during proestrus and estrus did not occur. The IRI levels during these times were comparable to the minimal levels found during metestrus in the non-arteriosclerotic virgin rats and were even lower than the IRI levels or ovariectomized rats. Since both young and old non-arteriosclerotic virgin rats had similar IRI patterns, the lack of cyclic insulin change in the arteriosclerotic breeder rats is not considered to be age-related. Instead, these changes are ascribed to hypothalamic-pituitary-adrenal hyperactivity associated with repeated reproductive activity and the development of arteriosclerosis.