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At least 217 records · Page 12Linked to original sources
PubMed1996

Mechanism of lithium-induced polyuria in the rat.

While many studies have demonstrated a nephrogenic diabetes insipidus syndrome (NDI) with prolonged lithium (Li) treatment, experiments in the isolated rat papillary collecting duct have suggested that the defect may be due to a circulating factor that inhibits the action of arginine vasopressin (AVP). Since Li-treatment can produce a form of hyperparathyroidism and parathyroid hormone (PTH) can act as a partial agonist to AVP, in vivo and in vitro studies were performed on rats made polyuric by daily intraperitoneal (i.p.) Li (4 mmol/kg) treatment. Li-treatment for three weeks produced an increase in PTH (194 +/- 20 compared with 118 +/- 18 pg/ml in control rats; P < 0.01) as well as an increase in the plasma calcium concentration (2.38 +/- 0.05 compared with 2.25 +/- 0.04 mmol/liter; P < 0.05). Clearance studies were performed on water loaded Li-treated and control rats, and the defect in urine concentration was only observed with a low physiological concentration of AVP (10 mU/kg body wt over 5 min). Maximal urine osmolality was 328 +/- 31 compared with 613 +/- 81 mOsm/kg (P < 0.05) in controls. There was no detectable difference with a prolonged maximal physiological AVP concentration (10 mU bolus and 50 mU/kg body wt per hr) and papillary solute concentrations were unchanged. When Li-treated rats had been parathyroidectomized (PTX), a significant difference in urine concentration with the low AVP concentration could not be demonstrated when compared to non-PTX control rats. In the isolated papillary collecting duct preparation a medium was used that contained fresh plasma from Li-treated or control rats, both intact and PTX. Experiments using plasma from Li-treated intact rats produced only a 25.4 +/- 5.1% increase in diffusional water permeability with the addition of AVP (200 microU/ml) compared to 52.6 +/- 9.0% in control rats (P < 0.01). However, when plasma from Li-treated PTX rats was used, the AVP induced increase in water permeability (54.7 +/- 11.2%) was not significantly different from that observed in PTX control rats. These studies show that the NDI-like defect in Li-treatment is small and easily overcome by higher concentrations of AVP and suggests that the concentration defect is at least in part due to increased circulating levels of PTH acting as a partial agonist to AVP and thereby inhibiting its hydroosmotic action.

Animals↗
PubMed1995

Antidiuretic hormone levels and polyuria in spinal cord injury. A preliminary report.

Chronic cervical spinal cord injury is characterized by defects in sodium and water homeostasis and defects of adaptive hormonal responses. The plasma osmolality is maintained in a relatively narrow range, the lower limit of which is determined by osmotic threshold for vasopressin release and the upper limit by the third threshold. Antidiuretic hormone as an important mediator of fluid and electrolyte balance was well investigated in able bodied children comparing children with normal voiding pattern and children with enuresis. The normal subjects were found to have higher plasma ADH at night, not detected in the group with enuresis. The findings were similar in elderly patients with increased diuresis at night, suggesting an important role of ADH in nocturnal decrease of urine output. Investigators studied the effect of rapid tilt on plasma ADH in tetraplegic compared with normal subjects, but there are no data available in the literature regarding ADH and its effects on water and electrolyte balance in healthy tetraplegic subjects with a normal lifestyle. We decided to undertake a pilot study to attempt to establish baseline ADH levels in this subject group, to better understand and manage tetraplegic patients with water and electrolyte dysregulation. Our preliminary data suggest that these individuals lack the normal diurnal variation of ADH, a phenomenon similar to that demonstrated in enuretic children and elderly, and furthermore appear to have generally depressed ADH levels.

Adult↗