The goal of this clinical trial is to clarify (i) the contribution of brain insulin action on regulation of systemic metabolism, (ii) sex-specific differences in the central regulation and (iii) the influence of the menstrual cycle in women. Therefore, participants will undergo oral glucose tolerance tests combined with a double tracer dilution technique. This approach will be compared between days with insulin delivery to the brain as nasal spray and days with placebo spray.
This research project aims to investigate to what extent brain insulin action is responsible for the control of postprandial metabolism compared to direct effects of insulin in peripheral target tissues. Furthermore, the study will investigate sex differences and the influence of the menstrual cycle on brain-derived coordination of postprandial signaling for metabolic control. Therefore, insulin action in the brain will be introduced by application of insulin as nasal spray (on one day) versus carrier solution as placebo nasal spray (on another day) in a randomized, blinded fashion. Spray administration will be performed 15 minutes before a 75 gram oral glucose tolerance test that will introduce a postprandial state. On placebo day, the known spillover of tiny amounts of nasal insulin into the systemic circulation will be mimicked by an appropriate i.v. insulin bolus. This approach will be combined with a double-tracer dilution technique. Labeled glucose (\[6,6-2H\]glucose) will be infused 120 minutes before and during the OGTT (180 min) and will be used to address endogenous glucose production. The glucose drink from the OGTT will be enriched with \[U-13C6\]glucose to compute the glucose appearance rate (Ra). Basal endogenous glucose production will be calculated as well as post-load endogenous glucose production and rates of glucose disappearances (Rd). Using this approach, brain-derived regulation of postprandial metabolism including endogenous glucose production, glucose disappearance, insulin secretion, and secretion of proglucagon-cleavage products (incretins) will be examined.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Enrollment
31
Subjects will undergo a 75 g OGTT (180 min) combined with a double tracer dilution. The double-tracer dilution technique will be used to quantify endogenous glucose production, glucose appearance and disappearance rate. \[6,6-2H\]glucose will be infused for a total of 300 minutes,while the infusion will start 120 minutes prior the OGTT and will last until the end of the OGTT. Intranasal insulin will be administered 15 minutes prior to the start of the OGTT. The drink consumed at time point 0 min contains 75 gram glucose, enriched with \[U-13C6\]-glucose.
Subjects will undergo a 75 g OGTT (180 min) combined with a double tracer dilution. The double-tracer dilution technique will be used to quantify endogenous glucose production, glucose appearance and disappearance rate. \[6,6-2H\]glucose will be infused for a total of 300 minutes,while the infusion will start 120 minutes prior the OGTT and will last until the end of the OGTT. Placebo spray will be administered 15 minutes prior to the start of the OGTT. The drink consumed at time point 0 min contains 75 gram glucose, enriched with \[U-13C6\]-glucose. To mimic insulin spill-over from nasal spray into systemic circulation, an i.v. insulin bolus of 3 mU × kg-1. will be administered over ten minutes starting at time point -15 minutes on the placebo spray day. On the insulin spray day a comparable amount of saline will be infused.
Universityhospital Ulm
Ulm, Germany
Endogenous glucose production
Effect of intranasal insulin versus placebo on endogenous glucose production assessed with Steele's non-steady state model during an oral glucose tolerance test combined with double-tracer dilution technique.
Time frame: -120 minutes - 180 minutes during oral glucose tolerance test
Rate of glucose disappearance
Effect of intranasal insulin versus placebo on rate of glucose disappearance (Rd) assessed with Steele's non-steady state model during an oral glucose tolerance test combined with double-tracer dilution technique.
Time frame: -120 minutes - 180 minutes during oral glucose tolerance test
Proglucagon cleavage products
Effect of intranasal insulin versus placebo on secretion of proglucagon cleavage products assessed by oral glucose tolerance test.
Time frame: 0-120 minutes during oral glucose tolerance test
Glucose tolerance
Effect of intranasal insulin versus placebo on glucose tolerance assessed as area under the glucose curve (0-120 minutes) and glucose levels at timepoint 120 minutes during the 75 g oral glucose tolerance test.
Time frame: 0-120 minutes during oral glucose tolerance test
Whole-body insulin sensitivity
Effect of intranasal insulin versus placebo on whole-body insulin sensitivity, assessed from glucose and insulin measurements during the 75 g OGTT.
Time frame: 0-120 minutes during oral glucose tolerance test
Insulin secretion
Effect of intranasal insulin versus placebo on insulin secretion assessed from glucose and insulin/C-peptide measurements during the 75 g oral glucose tolerance test.
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Time frame: 0-180 minutes during oral glucose tolerance test
Post-absorptive energy expenditure
Effect of intranasal insulin versus placebo on post-absorptive energy expenditure assessed by indirect calorimetry at timepoint 30 min and 180 min during an oral glucose tolerance test combined with double-tracer dilution technique.
Time frame: 30 minutes and 180 minutes during oral glucose tolerance test
Sex differences
Explore sex differences in the brain-derived regulation of postprandial metabolism during the 75 g oral glucose tolerance tests. Outcomes 1-7 will be compared between sexes.
Time frame: -120 minutes - 180 minutes during oral glucose tolerance test
Menstrual cycle effects
Differences between the follicular and the luteal phase of the menstrual cycle in the brain-derived regulation of postprandial metabolism during the 75 g oral glucose tolerance tests: Outcomes 1-7 will be compared between the phases of the menstrual cycle.
Time frame: -120 minutes - 180 minutes during oral glucose tolerance test
Autonomic nervous system activity
Effect of intranasal insulin versus placebo on autonomic nervous system activity assessed by heart rate variability using an 3-channel ECG at timepoint -15 min until 180 min during an oral glucose tolerance test combined with double-tracer dilution technique.
Time frame: -15 minutes - 180 minutes during oral glucose tolerance test