Thiazide induced hypotension: the role of plasma volume reduction and the urinary kallikrein system

Therapeutic roles of thiazides and loop diuretics in blood pressure control and renal protection against chronic kidney disease

Fluid overload secondary to loss of functional nephron mass can elevate blood pressure, which is characteristic of hypertension shown in chronic kidney disease (CKD). Therefore, it is logical to use diuretics at appropriate dose to lower blood pressure in patients with CKD and hypertension. Despite the theoretical background on the use of diuretics in CKD, there have been no definitive data on the effectiveness or safety of diuretics as first-line therapy for the management of hypertension in patients with CKD. Results from some clinical trials have demonstrated that diuretics would not lower blood pressure. They could even worsen electrolyte imbalance and kidney function when they are administered in patients with CKD. Major clinical practice guidelines on management of blood pressure or CKD have stated that evidence for benefits of thiazide diuretics is not conclusive yet in patients with advanced CKD, although loop diuretics are often effective for volume control at lower glomerular filtration rate. Recently, evidence for diuretics as effective blood pressure lowering agents in patients with advanced CKD is increasing. Renoprotective effect of thiazide or loop diuretics might represent a consequence of their influence on blood pressure or their ability to potentiate the effect of renin-angiotensin system blockade by making intraglomerular pressure more renin-angiotensin system-dependent, although their direct benefit on renal function remains controversial. This review summarizes recent data on the possible role of diuretics in lowering blood pressure, slowing the progression of kidney disease, and reducing cardiovascular risk in CKD patients.

Intracellular Ca2+ contributes to K+-induced increase in renal kallikrein secretion

We have reported that natriuretic effects of K(+) are involved in enhancement of renal kallikrein-kinin system. The study was aimed to examine 1) comparison of augmentative effects of K(+) on urinary KK excretion with non-specific washout effects by trichlormethiazide (thiazide), polyethyleneglycol 200 (PEG) and rapid physiological saline infusion, 2) contribution of Ca(2+) on the K(+)-induced increase in renal kallikrein secretion. Renal kallikrein activities were measured as fluorescence activities of methylcoumarinylamide-labeled synthetic substrate of tissue kallikrein (TK). Increases in urinary TK excretion were simultaneously observed with diuresis caused by thiazide, PEG, and rapid saline infusion. K(+) infusion increased urinary TK excretion with a diuretic response same as the control. K(+), but not thiazide, showed an early increase in renal TK secretion dose dependently in the kidney slices. Increases in renal TK secretion persisted during treatment with K(+). Neither voltage-dependent Ca(2+)-channel blockers such as verapamil and nifedipine nor simultaneous treatment of EDTA affected on the K(+)-induced increase in renal TK secretion. While, EDTA decreased the K(+)-induced increases in renal TK secretion with time. Caffeine also had an early effect on the increase in renal TK secretion. K(+)-induced increases in renal TK secretion was demonstrated even after treatment with ryanodine or depletion of caffeine-sensitive intracellular Ca(2+) by thapsigargin. It was indicated that the increase in renal TK secretion by K(+) depends on the intracellular Ca(2+) and the caffeine-sensitive release of intracellular Ca(2+) may not be involved in this response. Mechanisms for the K(+)-induced increase in renal TK secretion needs to be further elucidated.