Relationship between insulin sensitivity and degree of obesity in mild hypertension

Eighteen patients with mild hypertension (diastolic blood pressure ≥ 90 and <104 mm Hg) and 15 normotensive control subjects were studied. Insulin tolerance tests (ITT) and fasting plasma insulin (FPI) level measurements were performed to evaluate insulin sensitivity. Insulin sensitivity, as measured with the ITT, showed a strong correlation with body mass index (BMI) in the hypertensive and control groups (r = -0.68, p < 0.01 and r = -0.61, p < 0.01, respectively). The fasting insulin levels also correlated significantly with BMI in both groups (r = 0.55, p < 0.05 in the hypertensive and r = 0.76, p < 0.01 in the control group). Insulin sensitivity in the hypertensive subjects whose BMI was ≤27.0 kg/m² (nonobese), as measured with the ITT and FPI, was not different from the nonobese normal controls (K(itt), 5.36 ± 1.74% min ¹ versus 5.61 ± 1.66% min ¹, respectively, p > 0.2; FPI, 5.8 ± 3.4 μU/ml versus 7.1 ± 2.5 μU/ml, respectively, p > 0.2). Also, insulin sensitivity, as measured with the ITT, was not statistically significantly different between hypertensive and normotensive obese subjects (K(itt), 2.82 ± 1.55% versus 3.90 ± 0.67% min ¹, respectively, p > 0.1). When fasting plasma insulin levels were compared, a higher level was observed in the obese normotensive subjects than in the obese hypertensive group (FPI, 19.8 ± 10.0 μU/ml and 11.5 ± 4.9 μU/ml, p < 0.05). The obese hypertensive individuals had higher FPI levels and significantly lower K(itt) values than nonobese hypertensives (K(itt), 2.82 ± 1.55% min ¹ versus 5.36 ± 1.66, respectively, p < 0.01; FPI, 11.5 ± 4.9 μU/ml versus 5.8 ± 3.4 μU/ml, respectively, p < 0.05). The slope of the regression line between K(itt) and BMI (as obtained from regression analysis) was smaller in the control groups (-0.19) than in the hypertensive groups (-0.55). The slope between FPI and BMI, however, was of greater magnitude in the control groups: 1.41 and 0.84 (control and hypertensive groups, respectively). We conclude that in mild hypertension, insulin sensitivity is a function of the degree of adiposity and that a significant degree of insulin resistance was not present in our group of mildly hypertensive subjects.