Insulin sensitivity in cardiological syndrome X.

OBJECTIVES

To test whether cardiological syndrome X is an insulin-resistant state. SETTING, DESIGN AND SUBJECTS: The coronary care unit of a referral centre for angina pectoris in Pisa, Italy. A case-control study, involving 10 patients with unequivocal (angiographycally proven) cardiological syndrome X, but normal glucose tolerance, blood pressure and lipid levels, and 13 matched healthy subjects.

MAIN OUTCOME MEASURES: Insulin sensitivity and pattern of substrate oxidation (assessed by the euglycaemic insulin clamp technique in combination with indirect calorimetry).

RESULTS

Fasting plasma glucose and insulin levels were 5.05 +/- 0.11 versus 4.88 +/- 0.11 mmol l-1 and 68 +/- 10 versus 56 +/- 6 pmol l-1, respectively (controls versus patients, ns). During the insulin clamp, glucose disposal rate was nearly identical in patients and controls (25.9 +/- 1.8 and 27.2 +/- 1.8 mumol kg-1 min-1, respectively. P = 0.88). Non-oxidative glucose disposal accounted for similar proportions of total glucose uptake (59 versus 53%, patients versus controls, ns). Resting energy expenditure (13.7 +/- 0.6 versus 13.8 +/- 0.8 cal kg-1 min-1, ns) and insulin-induced thermogenesis were similar in the two groups. Fasting plasma NEFA concentrations (0.64 +/- 0.09 and 0.64 +/- 0.06 mmol l-1, patients and controls, ns) fell in a similar time-course and to virtually identical nadirs (0.13 +/- 0.02 and 0.14 +/- 0.02 mmol l-1) after insulin infusion. Fasting plasma potassium was similar in patients and controls (3.99 +/- 0.10 and 4.16 +/- 0.04 mmol l-1, ns), and insulin induced equivalent hypokalaemia (-14 versus -19%).

CONCLUSIONS

None of the in vivo actions of insulin were impaired in patients with 'pure' syndrome X when compared to matched controls. Therefore, we conclude that cardiological syndrome X is not an insulin resistant state per se, and that any decrease in insulin sensitivity found in this condition is likely to be secondary.