Metabolic effects of sodium restriction and thiazides in tetraplegic patients

Mechanism of Thiazide Diuretic Arterial Pressure Reduction: The Search Continues

Thiazide diuretic (TZD)-mediated chronic reduction of arterial pressure is thought to occur through decreased total peripheral vascular resistance. Further, the decreased peripheral vascular resistance is accomplished through TZD activation of an extrarenal target, resulting in inhibition of vascular constriction. However, despite greater than five decades of investigation, little progress has been made into the identification of the TZD extrarenal target. Proposed mechanisms range from direct inhibition of constrictor and activation of relaxant signaling pathways in the vascular smooth muscle to indirect inhibition through decreased neurogenic and hormonal regulatory pathways. Surprisingly, particularly in view of this lack of progress, comprehensive reviews of the subject are absent. Moreover, even though it is well recognized that 1) several types of hypertension are insensitive to TZD reduction of arterial pressure and, further, TZD fail to reduce arterial pressure in normotensive subjects and animals, and 2) different mechanisms underlie acute and chronic TZD, findings derived from these models and parameters remain largely undifferentiated. This review 1) comprehensively describes findings associated with TZD reduction of arterial pressure; 2) differentiates between observations in TZD-sensitive and TZD-insensitive hypertension, normotensive subjects/animals, and acute and chronic effects of TZD; 3) critically evaluates proposed TZD extrarenal targets; 4) proposes guiding parameters for relevant investigations into extrarenal TZD target identification; and 5) proposes a working model for TZD chronic reduction of arterial pressure through vascular dilation.

The cardiovascular, endocrine and renal response of tetraplegic and paraplegic subjects to dietary sodium restriction

1. The effects of change from a high to low sodium diet upon renal sodium and water excretion and hormone responses were studied in patients with dissociated sympathetic control (DS, tetraplegic) and controls with sympathetic control largely intact (IS, paraplegic). 2. Total and fractional urinary sodium excretion fell in response to sodium restriction in both groups, but the fall in fractional sodium excretion was greater in the DS group compared with the IS group (DS, 1.34 +/- 0.12 to 0.42 +/- 0.05%; IS, 0.96 +/- 0.08 to 0.52 +/- 0.06%). 3. Supine mean arterial pressure fell during the low salt period in the DS group (80.2 +/- 2.7 to 74.4 +/- 2.3 mmHg) but was unaffected by salt restriction in the IS group (101 +/- 2.3 to 98.8 +/- 2.7 mmHg). In the DS group, creatinine clearance remained constant throughout the low salt period (103.7 +/- 7.9 to 98.3 +/- 9.7 ml min-1), but fell during salt restriction in the IS group (101.4 +/- 8.5 to 83.2 +/- 5 ml min-1). 4. Plasma renin activity was lower during salt loading in DS subjects but increased more rapidly and to higher levels in response to salt restriction (DS, 1021 +/- 142 to 4439 +/- 355; IS, 1765 +/- 269 to 3683 +/- 465 pg angiotensin I ml-1 h-1). Plasma atrial natriuretic peptide concentration was higher in the DS group during salt loading and salt restriction (DS, 37.6 +/- 5.6 to 22 +/- 3.8; IS, 20.2 +/- 2.3 to 11 +/- 1.6 pg ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Hyponatremia in spinal cord injury

Hypoosmolar hyponatremia (serum Na+ less than 130 mmol/L) has proven a common and incompletely explained phenomenon in the spinal cord injured patient. When present, it has generally been preceded by excessive fluid intake and environmental/dietary factors which reversibly restrict free water excretion. We have attempted to more fully characterize the determinants of SCI-associated hyponatremia by retrospectively analyzing its features and treatment response in a series of 14 hyponatremic SCI patients. In most instances, hyponatremia could be attributed to uncontrolled fluid intake in the presence of an acute or semiacute illness and thus stimuli for non-osmotic releases of arginine vasopressin. Treatment measures generally included administration of 3% saline, with all patients recovering uneventfully from their episode of hyponatremia.