Serum insulin concentrations, insulin sensitivity, and endothelial function in essential hypertension and non-insulin-dependent diabetes mellitus
A series of studies is described in which specific and conventional insulin immunoassays, the hyperinsulinaemic clamp technique and forearm venous occlusion plethysmography with local intra-arterial infusions have been used to investigate: the effect of insulin assay specificity on the relationships among serum insulin concentrations, insulin sensitivity, and blood pressure in diabetic and non-diabetic subjects with and without essential hypertension (Chapter 5) the effect of sustained physiological activation of the renin-angiotensin system induced by moderate dietary sodium restriction on insulin sensitivity in patients with non-insulin-dependent diabetes mellitus (Chapter 6) the relationship between endothelial function and insulin sensitivity in healthy subjects (Chapter 7) Prior to these investigations, preliminary studies (Chapters 3 and 4) were performed in order to validate aspects of the clinical physiological techniques required for the measurement of blood flow and insulin sensitivity. The reproducibility of bilateral forearm venous occlusion plethysmography Studies using this technique to measure changes in forearm blood flow (FBF) during intra-arterial infusions of vasoactive substances often report changes in blood flow ratio (expressing responses in the intervention arm as a ratio of responses in the control arm) rather than absolute values for flow. However, unilateral measurements are reported by other investigators, and the possibility was considered that the method used for expressing responses might influence the conclusions reached. A reproducibility study was performed (Chapter 3) which demonstrated that the between-day intra-subject variability of bilateral forearm venous occlusion plethysmography (FBF ratios) was less than that of unilateral FBF measurements. The bilateral technique was used thereafter where possible.