Sex differences in African-Americans regarding sensitivity to insulin's glucoregulatory and antilipolytic actions.
OBJECTIVE
The purpose of this study was to determine if there are sex differences in African-Americans regarding the effect of obesity on sensitivity to insulin as a glucoregulatory and antilipolytic hormone.


METHODS
Data from study participants, 127 nondiabetic African-Americans (mean age 32 +/- 4 years), included anthropometric measurements, an oral glucose tolerance test (OGTT), a 2-h euglycemic-hyperinsulinemic clamp, and a fasting triglyceride level. Sensitivity to insulin as a glucoregulatory hormone was determined by M/FFM, where M is the mean glucose infusion rate during the second hour of the clamp and FFM is fat-free mass. Sensitivity to insulin's antilipolytic action was assessed during the OGTT by the percent suppression of free fatty acid (FFA) concentrations between 0 and 120 min. The higher the suppression of FFAs, the greater the sensitivity to insulin's antilipolytic action.


RESULTS
The participants were classified by BMI into three groups: nonobese (31 men, 24 women), obese (17 men, 14 women), and severely obese (12 men, 29 women). The women had higher percentages of body fat (P < 0.001), and the men had greater FFM (P < 0.001). The M/FFM values for men versus women in each BMI group were nonobese, 8.8 +/- 2.8 vs. 10.8 +/- 4.4; obese, 7.2 +/- 3.4 vs. 8.5 +/- 3.4; and severely obese, 4.7 +/- 2.1 vs. 6.1 +/- 2.2. The difference between the BMI groups was significant (P < 0.001), as was the difference between men and women (P < 0.01). In addition, there was a significant sex difference in percent suppression of FFAS (P < 0.001). The men and women had similar fasting insulin and FFA concentrations; however, in the men only, the percent suppression of FFA declined with increasing obesity (nonobese, 83 +/- 15%; obese, 73 +/- 18%; and severely obese, 69 +/- 19%; P = 0.02). The women in all three BMI groups had lower FFA levels of 86-88%.


CONCLUSIONS
Obese African-American men and women are resistant to insulin as a glucoregulatory hormone, but only obese men are resistant to insulin's antilipolytic action; obese African-American women are sensitive to insulin's antilipolytic action. The combined presence of sensitivity to insulin's antilipolytic action with resistance to insulin's glucoregulatory action in obese African-American women may contribute to their high prevalence of obesity and type 2 diabetes.
Sumner
A E
AE
Institute for Women's Health, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania, USA. annes@intra.niddk.nih.gov
Kushner
H
H
Sherif
K D
KD
Tulenko
T N
TN
Falkner
B
B
Marsh
J B
JB
D000328:Adult; D000704:Analysis of Variance; D044383:Black People; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism*; D015331:Cohort Studies; D005260:Female; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006706:Homeostasis; D006801:Humans; D006946:Hyperinsulinism; D007262:Infusions, Intravenous; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D008066:Lipolysis / Q000187:drug effects*; D008137:Longitudinal Studies; D008297:Male; D008657:Metabolic Clearance Rate; D015143:Philadelphia; D012044:Regression Analysis; D012727:Sex Characteristics; D001741:Black or African American
D001786:Blood Glucose; D007328:Insulin