Lithium and the antidiuretic hormone

Renal concentrating capacity in long-term lithium treatment and after withdrawal of lithium

The urinary concentrating capacity was estimated with the DDAVP test in 87 patients receiving lithium therapy, which was discontinued in all patients. The test was repeated three and eight weeks after withdrawal of lithium in 75 patients and one year after withdrawal in 27 patients. Of the 87 patients, 52 were also treated with neuroleptics, which treatment was continued throughout the study. Two control groups, consisting of 30 patients receiving only neuroleptics and 30 healthy subjects, were studied on one occasion with the DDAVP test. Lithium-treated patients had significantly lower concentrating capacity and higher serum creatinine than healthy subjects at all examinations. Small but statistically significant correlations were found between urinary osmolality and total dose of lithium, between urinary osmolality and duration of lithium treatment, between the highest serum lithium concentration recorded and urinary osmolality after withdrawal of lithium and between the daily dose of lithium and urinary osmolality, while patients were still on lithium. The concentrating capacity improved significantly during the first two months after withdrawal of lithium, but not later. One year after withdrawal of lithium, 17 of 27 patients still had a concentrating capacity below 800 mOsm/kg. Patients receiving lithium and neuroleptics had lower concentrating capacity than patients treated with lithium alone, and patients treated with neuroleptics alone had lower concentrating capacity than healthy subjects.

Evidence for circulating vasopressin-like peptides in a case of polyuria

Plasma immunoreactive vasopressin (iAVP) was studied by RIA in a patient suffering from polyuria during chronic treatment with lithium. The combined use of two antisera specific for different regions of the AVP molecule allowed us to detect circulating forms which are modified in the acyclic tripeptide portion. In this lithium-treated patient, iAVP was abnormally low with respect to plasma osmolality. However, iAVP increased during hypertonic saline infusion, probably through an osmosensitive mechanism. A remarkable finding was that contrary to the observations made in healthy subjects and in another patient with diabetes insipidus, iAVP measured with the antiserum specific for the acyclic portion of the AVP molecule was below the values measured with the antiserum specific for the hexapeptide ring. This unusual immunoreactivity profile suggests that the plasma of this polyuric lithium-treated patient contains vasopressin-like peptides which differ from arginine vasopressin in the structure of the C-terminal tripeptide tail.

Chlorpromazine increases the lowered response to antidiuretic hormone in rats with lithium-induced diabetes insipidus

The interaction between chlorpromazine (CPZ) and lithium on renal concentrating ability was studied in rats fed a Li-containing diet for 8 weeks (plasma-Li 0.6-0.7 mmol/l). CPZ (15 mg/kg daily orally) reduced the polydipsia and increased the ability to concentrate the urine upon water deprivation in rats treated with lithium. CPZ also reduced systolic blood pressure, but had no effect on the glomerular filtration rate or plasma levels of arginine vasopressin (AVP) in hydrated rats treated with lithium. However, CPZ prevented the rise in plasma AVP levels observed in lithium-polyuric rats in response to dehydration. During anaesthesia CPZ partially restored the impaired anti-diuretic response to exogenous AVP in rats treated with lithium. CPZ had no influence on plasma-Li levels in rats treated with lithium. It is suggested that CPZ by unknown mechanisms interferes with the effects of lithium on the water permeability response to AVP.

Renal pathology associated with lithium therapy

Renal biopsies have been examined in patients either currently (50 patients) or previously (5 patients) on maintenance lithium therapy for severe affective disorders. In patients currently taking lithium, a distinctive lesion of the distal convoluted tubules and collecting ducts was identified. This lesion consisted of vacuolation and swelling of the cytoplasm with accumulations of PAS positive material; this material was confirmed to be particulate glycogen by light and ultrastructural techniques. This 'lithium-associated' lesion was not present in patients who had discontinued lithium therapy. Prospective studies showed that the accumulation of glycogen occurs in distal tubules and collecting ducts within days of commencing lithium treatment. The relationship of this distinctive lesion to the patchy focal cortical interstitial fibrosis seen in these biopsies remains to be elucidated.

Plasma levels of antidiuretic hormone in patients receiving prolonged lithium therapy

Among 18 patients receiving prophylactic, long-term lithium treatment for manic-depressive psychosis, a high incidence of increased thirst and frequency of micturition (60-70 per cent) was noted on direct questioning. Symptoms arose at varying times after the start of lithium therapy; in no patient did symptoms antedate the use of the drug. Plasma levels of antidiuretic hormone were found, on average, to be higher than in normal control subjects for a given level of plasma osmolality, although the scatter of results was wide. It is suggested that elevation of antidiuretic hormone occurs as a compensatory mechansims for the polyuria which is a common feature of long-term lithium treatment. The more florid form of nephrogenic diabetes insipidus occasionally seen in lithium takers seems likely to be due to a different mechanism from the more common mild polyuria.