Some aspects of the inhibition of the action of antidiuretic hormone by lithium ions in the rat kidney and bladder of the toad Bufo marinus

Aquaporin-2 as a biomarker of distal renal tubular function using lithium as an experimental model

Aquaporin-2 protein levels can be detected in the urine of normal of subjects if measured after fluid deprivation. By contrast, in patients with nephrogenic diabetes insipidus caused by mutations in the aquaporin-2 gene, urine aquaporin-2 protein excretion cannot be detected. We propose that properly standardized measurements of urinary aquaporin-2 protein may provide a useful biomarker of distal tubular function in a variety of acquired conditions that impair concentrating ability including some nephrotoxic agents.

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.

Effects of lithium on cAMP generation in cultured rat inner medullary collecting tubule cells

The effects of lithium (Li) on the cAMP system in rat inner medullary collecting tubule cells were studied. While acute exposure to 5 mM Li was without effect, 10 mM, 25 mM and 50 mM Li significantly decreased AVP-stimulated cAMP formation. In contrast, cells grown in 5 mM Li for 72 hours which caused no morphologic changes enhanced cAMP formation (fmol/microgram protein) in response to both 10 nM AVP (114.5 +/- 9.2 vs. 71.6 +/- 7.4, P less than 0.005) and 100 nM AVP (182 +/- 14 vs. 120 +/- 8.3, P less than 0.001), N = 16. A similar enhancement was observed when cAMP formation was stimulated by a post-receptor agonist, cholera toxin. The role of eicosanoids was examined with 5 microM meclofenamate which reversed Li-enhanced cAMP formation in response to both AVP and cholera toxin. To define the eicosanoid responsible, cyclooxygenase products were measured. Prostaglandin E2 and thromboxane B2 synthesis were unchanged by Li, but the production of prostacyclin was significantly (P less than 0.02) increased. Prostacyclin (3 microM) mimicked the effect of Li to enhance the response to 10 nM AVP as cAMP levels increased from 100 +/- 11 to 173 +/- 13, P less than 0.05. The experiments suggest that acute exposure of Li at concentrations of 10 mM or greater inhibit cAMP formation but prolonged Li exposure enhances cAMP formation by increasing the formation of prostacyclin.

Prevalence, pathogenesis, and treatment of renal dysfunction associated with chronic lithium therapy

From the analysis of several studies published from 1979 to 1986 comprising 1,172 patients, we estimated that glomerular filtration rate (GFR) was normal in 85% of unselected patients on chronic lithium therapy. The remaining 15% of patients displayed only mild reduction in GFR, clustering at approximately 60 mL/min. Thus, the data available to date do not support earlier concerns that long-term lithium therapy could eventuate into renal insufficiency. The most prevalent renal effect of lithium is impairment of concentrating ability, which we estimated to be present in at least 54% of 1,105 unselected patients on chronic lithium therapy. This defect translated into overt polyuria in only 19% of unselected cases. A renal lesion confined to the collecting tubule has been described in humans who have taken lithium for short periods of time. This lesion may represent the collecting tubule's response to the intracellular accumulation of lithium, which interferes with cAMP formation and results in an early and probably reversible inhibition of antidiuretic hormone (ADH)-mediated water transport. However, long-term lithium therapy may induce a progressive and partly irreversible defect in concentrating ability. The potential risk for dehydration associated with lithium-induced polyuria, as well as the discomfort inherent to this side effect, deserves evaluation and consideration for therapeutic intervention. Amiloride has additional advantages over conventional treatment of nephrogenic diabetes insipidus using thiazide diuretics. The action of amiloride on ADH-mediated water transport seems specific in as much as it is capable of preventing the uptake of lithium in high resistance epithelia and thereby prevents the inhibitory effect of intracellular lithium on water transport. Unlike thiazides, amiloride has a weak natriuretic effect and is less likely to increase plasma lithium levels by causing volume contraction. In addition, amiloride, by conserving potassium, obviates the need for potassium supplementation that is usually required to prevent hypokalemia when thiazides are used to treat lithium-induced polyuria. Since amiloride may prevent chronic intracellular lithium accumulation in the collecting tubule, future studies should elucidate whether amiloride also has a role in preventing lithium-induced chronic tubulo-interstitial damage.

GABA receptor agonists: pharmacological spectrum and therapeutic actions

From the data discussed in this review it appears that GABA receptor agonists exhibit a variety of actions in the central nervous system, some of which are therapeutically useful (Table V). GABA receptor agonists, by changing the firing rate of the corresponding neurons accelerate noradrenaline turnover without changes in postsynaptic receptor density and diminish serotonin liberation with an up-regulation of 5HT2 receptors. These effects differ from those of tricyclic antidepressants which primarily block monoamine re-uptake and cause down-regulation of beta-adrenergic and 5HT2 receptors. The GABA receptor agonist progabide has been shown to exert an antidepressant action which is indistinguishable from that of imipramine in patients with major affective disorders. The fact that: (a) GABA receptor agonists and tricyclic antidepressants affect noradrenergic and serotonergic transmission differently; and (b) tricyclic antidepressants alter GABA-related parameters challenges the classical monoamine hypothesis of depression and suggests that GABA-mediated mechanisms play a role in mood disorders. Decreases in cellular excitability produced by GABAergic stimulation leads to control of seizures in practically all animal models of epilepsy. GABA receptor agonists have a wide spectrum as they antagonize not only seizures which are dependent on decreased GABA synaptic activity but also convulsant states which are apparently independent of alterations in GABA-mediated events. These results in animals are confirmed in a wide range of human epileptic syndromes. GABA receptor agonists decrease dopamine turnover in the basal ganglia and antagonize neuroleptic-induced increase in dopamine release. On repeated treatment, progabide prevents or reverses the neuroleptic-induced up-regulation of dopamine receptors in the rat striatum and antagonizes the concomitant supersensitivity to dopaminomimetics. Behaviorally, GABA receptor agonists diminish the stereotypies induced by apomorphine or L-DOPA suggesting that GABAergic stimulation results also in an antidopaminergic action which is exerted beyond the dopamine synapse. These effects of GABA receptor agonists may represent the basis of the antidyskinetic action of these compounds which, however, remains to be fully confirmed. GABA receptor agonists reduce striatal acetylcholine turnover, an effect which occurs at doses much lower than those which affect dopamine neurons. Since hyperactivity of cholinergic neurons plays a determinant role in the pathogenesis of some parkinsonian symptoms, it is conceivable that GABAergic stimulation is effective in ameliorating Parkinson's disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Artefactual inhibition of dopamine uptake by psychotropic drugs on striatal synaptosomal preparation

On striatal synaptosomal preparations, using a double labelling test, numerous antidepressant drugs demonstrated an inhibitory effect on [3H]DA uptake at the same high concentrations producing a [14C]DA release. This releasing effect was also shared by non-antidepressant agents and was observed on synaptosomes preloaded with [3H]5HT. The imipramine-induced release of DA was not modified by increasing concentration of K+, by decreasing concentration of Na+, by deleting Ca2+ from the incubation medium, or by blocking the catecholamine uptake systems with nomifensine or cocaine. The imipramine effect was reversible and was possibly initiated by a transient physico-chemical modification of the synaptosomal membrane. It was concluded that the DA uptake carrier is probably not involved in the effect of these drugs.

Structural and functional response of toad urinary bladder to LiCl

The physiological and morphological response of toad urinary bladder was examined during mucosal exposure of LiCl both with and without vasopressin (VP). With 20 or 100 mU/ml of VP in the serosal bath there was a decrease in Jv between the first and second VP stimulation in LiCl-treated bladders (VP20, -14 +/- 6%; VP100, -16 +/- 5%) that was not different from that observed without LiCl (VP20, -8 +/- 3%, P = NS). However, with 1 mU/ml of VP, a significant decrease in Jv was evident in LiCl-treated (-30 +/- 10%) versus control sacs (+6 +/- 8%; P less than 0.02). At all VP concentrations tested, a significant decrease in SCC and PD was observed between the first stimulation without LiCl and the second stimulation with LiCl. Both osmotic (Pf) and diffusional water permeability (Pd) were increased significantly with 11 mM LiCl only, while neither basal nor VP-stimulated urea permeability (Pu) was affected. Morphological changes paralleled the physiological alterations induced by LiCl. These data demonstrate that LiCl interferes with the osmotic response of the toad bladder to low concentrations of VP, and increases both Pf and Pd while leaving Pu unaffected. These findings coupled with the cell swelling and intracellular vacuolization suggest the presence of a defect in transepithelial water movement somewhere beyond the apical membrane of the granular cell exposed to LiCl.

Micropuncture study on the effects of lithium on proximal and distal tubule function in the rat kidney

Micropuncture studies were performed in rats infused with LiCl to induce stable plasma lithium concentrations of 2--3 mEq/l, or with an equivalent amount of NaCl. In free flow experiments LiCl reduced proximal tubule fractional reabsorption of sodium and potassium. Reduced reabsorption of bicarbonate, as reflected by a decrease in TF/PCl, was also observed. Proximal fractional reabsorption of chloride, however, was not affected. The TF/PIn at the end proximal tubule was 2.6 +/- 0.2 (mean +/- SEM) in controls and 2.1 +/- 0.1 in the experimental animals (P less than 0.025). In the distal portions of the nephron lithium treatment caused a fall in fractional reabsorption of water and sodium, while potassium secretion was stimulated in the distal tubule. Previous studies have indicated that lithium influences antidiuretic hormone stimulated water transport in the collecting duct. These experiments demonstrate that lithium also affects the transport of water and electrolytes in multiple nephron segments, including the proximal and distal convolution.

Diuretics and the renal adenylate cyclase system

1 The relationship between the diuretic effectiveness and the effect on the renal adenylate cyclase of three diuretics, acetazolamide, frusemide and ethacrynic acid, was examined. The hypothesis that acetazolamide and parathyroid hormone (PTH), inhibit renal carbonic anhydrase by a cyclic adenosine 3',5'-monophosphate (cyclic AMP)-dependent mechanism was also tested.2In vitro, acetazolamide, frusemide and ethacrynic acid at high concentrations (10(-3)M) all produced some inhibition of basal and stimulated rat kidney plasma membrane adenylate cyclase. The effect of acetazolamide was much less than that of frusemide and ethacrynic acid. These plasma membrane effects were reproduced in studies of cyclic AMP formation in isolated kidney tubules of rats.3 Intravenous injections of acetazolamide did not change the total cyclic AMP content of the kidneys of rats killed by microwave irradiation.4 Acetazolamide produced a diuresis in the rat and a slight inhibition of the antidiuretic effect of Pitressin. Frusemide produced a diuresis and greatly reduced the antidiuretic response to Pitressin. Ethacrynic acid was ineffective as a diuretic in the rat and actually enhanced the antidiuretic response to Pitressin.5 In investigating the possible influence of diuretics and PTH on the activity and state of phosphorylation of carbonic anhydrase it was found that: there was no correlation between the ability of diuretics to inhibit carbonic anhydrase activity and to inhibit carbonic anhydrase phosphorylation; neither PTH nor cyclic AMP (in the presence of adenosine triphosphate, Mg(2+), K(+) and incubation at 37 degrees C) inhibited rat cortex homogenate carbonic anhydrase activity.6 It seems unlikely that any of the tested diuretics exerts its pharmacological effect by means of changes in kidney cyclic AMP metabolism.

Time course of lithium-induced alterations in renal and endocrine function in normal and Brattleboro rats with hypothalamic diabetes insipidus

1. A lithium chloride (1.1 g/kg) supplemented diet was given to Long Evans (LE) and Brattleboro (DI) rats to investigate its actions in the presence (LE) and absence (DI) of vasopressin. 2. During the first 24 h, Li-supplemented LE rats displayed an initial water deficit (drinking less than renal output), increased plasma antidiuretic (ADH) titres and slightly increased plasma renin activities (PRA) and plasma osmolarities. Such changes were qualitatively similar to those seen in rats fed a normal diet, but deprived of water for 24 hours. After 12 days, the Li-supplemented rats had elevated plasma ADH titres, but reduced pituitary oxytocic and antidiuretic activities. 3. The urinary losses of Na, K and Cl exceeded dietary intakes in LE rats on the introduction of the Li-supplement, and the urinary osmolarity fell by 50%. Electrolyte balances were gradually re-established, although drinking and urine production increased in parallel to reach twice the control values by day 12 of the supplement. 4. Aldosterone and corticosterone secretory rates and their peripheral plasma concentrations were unchanged both after 24 h and 28 days of the Li-supplement. 5. Li elicited no water deficit or saluresis in DI rats, and although the polyuria and polydipsia were exacerbated, urinary osmolarity did not change over the 12 day observation period. 6. Li increased Ca excretion in both rat types; after 12 days the PRA of DI but not LE animals were increased. 7. It is concluded that the overall renal actions of Li are tempered by vasopressin rather than adrenocorticosteroids.

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.

Lithium and the antidiuretic hormone

The effect of lithium on the urine concentrating response to antidiuretic hormone (ADH) and the excretion of ADH has been studied in rats and man. The maximum urine osmolarity following 18 h dehydration and Pitressin (5 u) was decreased in three out of four patients during lithium treatment compared to their response to the same test in the absence of lithium. In a fifth patient, tested only during lithium treatment, the urine remained hypotonic to plasma throughout this test. Lithium increased the excretion of ADH in non-polyuric patients from 9-22 mu/24 h in the absence of lithium to 36-202 mu/24 - during lithium treatment. In four patients with lithium-induced polyuria, a diuretic acting on the distal tubules, clorexolone, reduced the polyuria. Lithium increased urine volume and the excretion of ADH in four rats receiving lithium in their diet. The response to exogenous ADH was decreased during lithium administration.

The effects of lithium ions on the antidiuretic action of vasopressin in the rat

1 The effect of intravenous infusion of lithium, 2.56 mumol/min on the antidiuretic responses to antidiuretic hormone (ADH), adenosine triphosphate (ATP), 3'-5' adenosine cylic monophosphate (cyclic AMP) and theophyline was studied in water-loaded, alcohol-anaesthetized rats. 2 Lithium reversibly inhibits the antidiuretic response to all concentrations of ADH, depressing the maximum response but not changing the amount required for half maximal response. 3 The rate of increase of serum lithium relates more clearly to the inhibitory effect than does the serum concentration. 4 Sodium concentrations in the renal papilla seem to fall when serum lithium levels are rising. 5 Lithium inhibits the antidiuretic response to ATP and cyclic AMP but does not inhibit the response to theophyline.

The renal pathology in a case of lithium-induced diabetes insipidus

A case of lithium-induced diabetes insipidus is reported. At necropsy microscopy shoed unique and extensive damage to cells lining the distal nephron. It is suggested that these changes represent a specific toxic effect of lithium, reported here for the first time in man.

Medical research council unit for metabolic studies in psychiatry, Sheffield

The Medical Research Council Unit for Metabolic Studies in Psychiatry was set up at Middle-wood Hospital, Sheffield, in 1967. It was to a considerable extent a continuation of the Medical Research Council Unit for the Chemical Pathology of Mental Disorders which had been associated with the Department of Physiology in the University of Birmingham under the direction of Professor I. E. Bush. The latter unit had in its turn largely corne from a group headed by Sir George Pickering at Oxford.

The distribution of lithium and its effects on the distribution and excretion of other ions in the rat

1. In rats, lithium (ca 1 mEquiv/kg body weight) decreased brain sodium and magnesium, bone sodium and calcium and increased muscle calcium, plasma magnesium, urinary calcium and urine volume.2. Lithium was particularly concentrated in bone.

The effect of lithium salts on the urinary excretion of -oxoglutarate in man

1. Lithium ions in therapeutic doses cause an increase in the renal excretion of alpha-oxoglutarate and glutaric acid.2. The excretion is probably due to reduced renal tubular reabsorption.3. Neither citrate, lactate nor pyruvate excretion rises.