title: Effects of differing durations of antecedent hypoglycemia on counterregulatory responses to subsequent hypoglycemia in normal humans.
abstract: The aim of this study was to determine whether the duration of antecedent hypoglycemia regulates the magnitude of subsequent counterregulatory failure. A total of 31 lean healthy overnight-fasted individuals (16 men/15 women) were studied. There were 15 subjects (8 men/7 women) who underwent two separate 2-day randomized experiments separated by at least 2 months. On day 1, 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1)) euglycemic (5.2 +/- 0.1 mmol/l) or hypoglycemic (2.9 +/- 0.1 mmol/l) glucose clamps (prolonged hypoglycemia) were carried out in the morning and afternoon. Of the other subjects, 16 participated in a 2-day study in which day 1 consisted of morning and afternoon short-duration hypoglycemia experiments (hypoglycemic nadir of 2.9 +/- 0.1 mmol for 5 min), and 10 of these individuals underwent an additional 2-day study in which day 1 consisted of morning and afternoon intermediate-duration hypoglycemia (hypoglycemic nadir of 2.9 +/- 0.1 mmol for 30 min). The next morning (day 2) all subjects underwent an additional 2-h hyperinsulinemic-hypoglycemic clamp (2.9 +/- 0.1 mmol/l). The rate of fall of glucose (0.07 mmol/min) was carefully controlled during all hypoglycemic studies so that the glucose nadir was reached at 30 min. Despite equivalent day 2 plasma glucose and insulin levels, there were significant differences in counterregulatory physiological responses. Steady-state epinephrine, glucagon, growth hormone, cortisol, and pancreatic polypeptide levels were similarly significantly blunted (P < 0.01) by the differing duration day 1 hypoglycemia compared with day 1 euglycemia. Muscle sympathetic nerve activity and endogenous glucose production were also similarly blunted (P < 0.01) by day 1 hypoglycemia (relative to day 1 euglycemia). Day 2 hypoglycemic symptoms were significantly reduced (P < 0.01) after day 1 prolonged intermediate- but not short-duration hypoglycemia. In summary, two episodes of short-duration moderate hypoglycemia can produce significant blunting of key neuroendocrine and metabolic counterregulatory responses. Hypoglycemic symptom scores are reduced by prolonged but not short-duration prior hypoglycemia. We conclude that in healthy overnight fasted humans, 1) neuroendocrine, autonomic nervous system, and metabolic counterregulatory responses are sensitive to the blunting effects of even short-duration prior hypoglycemia, and 2) the duration of antecedent hypoglycemia results in a hierarchy of blunted physiological responses with hypoglycemic symptom awareness less vulnerable than neuroendocrine responses.
authors.affiliation: Department of Medicine, Vanderbilt University School of Medicine and Veterans Affairs Medical Center, Nashville, Tennessee, USA. steve.davis@mcmail.vanderbilt.edu
authors.forename: S N
authors.initials: SN
authors.lastname: Davis
authors.forename: S
authors.initials: S
authors.lastname: Mann
authors.forename: P
authors.initials: P
authors.lastname: Galassetti
authors.forename: R A
authors.initials: RA
authors.lastname: Neill
authors.forename: D
authors.initials: D
authors.lastname: Tate
authors.forename: A C
authors.initials: AC
authors.lastname: Ertl
authors.forename: F
authors.initials: F
authors.lastname: Costa
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D001794:Blood Pressure; D004837:Epinephrine / Q000097:blood; D005260:Female; D005934:Glucagon / Q000097:blood; D015309:Glucose Clamp Technique; D006339:Heart Rate; D006706:Homeostasis; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007003:Hypoglycemia / Q000097:blood* / Q000503:physiopathology; D007328:Insulin / Q000097:blood; D007700:Kinetics; D008297:Male; D009132:Muscles / Q000294:innervation; D010191:Pancreatic Polypeptide / Q000097:blood; D013564:Sympathetic Nervous System / Q000503:physiopathology; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D007328:Insulin; D019382:Human Growth Hormone; D010191:Pancreatic Polypeptide; D005934:Glucagon; D006854:Hydrocortisone; D004837:Epinephrine