Physiologic Response to Glucagon at Varying Insulin Levels

The purpose of this research study is to test how different levels of insulin block the effect of glucagon. Insulin is a hormone that lowers blood glucose. Glucagon raises blood glucose. Both are natural hormones made by people without diabetes. Sensor-based blood glucose control studies have been done by our research group using glucagon in small doses to prevent hypoglycemia (low blood sugar). However, sometimes glucagon does not work to raise blood sugar. The investigators believe this is because of too much insulin in the body. This study will help determine how different levels of insulin in the body affect the ability of glucagon to raise blood sugar.

We investigators have been working on the development of a closed loop (artificial endocrine pancreas) insulin and glucagon infusion system since 2005 and are part of the Juvenile Diabetes Research Foundation Artificial Pancreas Consortium. As part of our studies, we give small doses of glucagon to prevent hypoglycemia. As we assessed the success and failure of glucagon administration during these studies, we found the use of glucagon reduced the frequency of hypoglycemia by about 75%. However, the fact that approximately 25% of administrations of glucagon are ineffective remains a concern.

The primary question to be addressed by this study is, in the setting of low dose subcutaneous glucagon administration, how do plasma glucagon and plasma insulin quantitatively interact? In other words, as the rate of insulin administration is increased, how much more glucagon is necessary to overcome the effect of insulin to prevent hypoglycemia? This study is designed to address this question. Subjects will be brought in to a Legacy Hospital for four 10 hour experiments on each of four separate days. On each study day, there will be a continuous infusion of a different rate of IV Regular insulin in order to achieve different steady state free insulin levels. At each insulin level, there will be four subcutaneous glucagon doses given. Octreotide will be infused by IV at a constant rate to suppress endogenous production of glucagon. A stable glucose isotope will also be infused to allow for measurement of hepatic glucose production and glucose turnover. Arterialized venous blood glucose will be measured by the HemoCue Glucose 201 Analyzer.

Eligibility Criteria:
Inclusion Criteria:

* Diagnosis of type 1 diabetes mellitus for at least 1 year
* Male or female subjects 21 to 65 years of age
* Current use of an insulin pump
* Willingness to sign informed consent and HIPAA documents and follow all study procedures

Exclusion Criteria:

* Pregnancy or Lactation: For women of childbearing potential: there is a requirement for a negative urine pregnancy test and for agreement to use contraception during the study and for at least 1 month after participating in the study
* Renal insufficiency (serum creatinine of 2.0 mg/dL or greater)
* Liver abnormalities: Serum ALT or AST equal to or greater than 3 times the upper limit of normal; hepatic synthetic insufficiency as defined as a serum albumin of less than 3.3 g/dL; or serum bilirubin of over 2
* Adrenal insufficiency
* Hematocrit of less than or equal to 34%
* A history of cerebrovascular disease or coronary artery disease regardless of the time since occurrence
* Congestive heart failure, NYHA class III or IV
* Cardiac rhythm disturbance characterized by: 2nd or 3rd degree heart block, bradycardia of less than 50 bpm (exception of bradycardia in an aerobic athlete), tachycardia of greater than 100 bpm, or any arrhythmia judged by the investigator to be exclusionary
* Any active infection
* Active foot ulceration
* Severe peripheral arterial disease characterized by ischemic rest pain or severe claudication
* Active alcohol abuse, substance abuse, or severe mental illness (as judged by the principal investigator)
* Active malignancy, except basal cell or squamous cell skin cancers
* Major surgical operation within 30 days prior to screening
* Seizure disorder
* Any concurrent illness, other than diabetes, that is not controlled by a stable therapeutic regimen
* Chronic usage of any immunosuppressive medication
* Current administration of oral or parenteral corticosteroids
* Use of an investigational drug within 30 days prior to screening
* Bleeding disorder, treatment with warfarin, or platelet count below 50,000
* Allergy to glucagon
* Past history of pheochromocytoma or a family history of MEN 2, neurofibromatosis, or von Hippel-Lindau disease
* Insulin resistance requiring more than 200 units per day