Increased sympathetic activity during sleep and nocturnal hypertension in Type 2 diabetic patients with diabetic nephropathy

Aims To elucidate the putative factors involved in the blunted nocturnal blood pressure reduction in hypertensive Type 2 diabetic patients with diabetic nephropathy. Methods Extracellular fluid volume and fluid shift from interstitial to plasma volume (haematocrit), sympathetic nervous activity (plasma noradrenaline and adrenaline) and the internal 'body clock' (serum melatonin) were investigated in 31 hypertensive Type 2 diabetes mellitus (DM) patients with diabetic nephropathy (24 males, age 60 (45-73) years). All variables, except extracellular volume, were measured repeatedly with the patients lying awake in bed from 21:30 to 23:00 h (baseline) and during sleep from 23:00 to 07:00h. Using the median nocturnal blood pressure reduction (8.4%) as a guide, the patients were divided into groups; group 1 with the highest and group 2 with the lowest nocturnal blood pressure reduction. Results Haematocrit decreased from baseline to the sleep period in group 1 by a mean (95% confidence interval (CI)) of 1.7 (0.3-3.1)%, but it increased by 0.5 (-1.0-1.9)% in group 2, mean difference (95% CI), -2.1 (-4.0 to -0.2)% (P = 0.029). Noradrenaline decreased from baseline to the sleep period, mean (95% CI), by 13.3 (0.0-25.0)% in group 1 but rose by 7.7 (-9.7-28.4)% in group 2, mean difference (95% CI), -19.6 (-35-0.0)% (P = 0.049). The nocturnal blood pressure change correlated to the nocturnal change in both noradrenaline (r = 0.51, P = 0.004) and haematocrit (r = 0.42, P = 0.018). Adrenaline remained constant in both groups. Extracellular fluid volume and plasma melatonin levels were comparable in the two groups. Conclusion Sustained adrenergic activity during sleep is associated with blunted nocturnal blood pressure reduction in hypertensive Type 2 DM patients with diabetic nephropathy, probably mediated through a lack of peripheral vasodilatation whereas changes in extracellular fluid volume distribution and melatonin secretion have no impact.