Effects of lithium on water intake and renal concentrating ability in rats with vasopressin-deficient diabetes insipidus (Brattleboro strain)

Glucagon-like peptide-1 receptor agonist administration suppresses both water and saline intake in rats

Glucagon-like peptide-1 (GLP-1) plays an important role in energy homeostasis. Injections of GLP-1 receptor (GLP-1R) agonists suppress food intake, and endogenous GLP-1 is released when nutrients enter the gut. There is also growing evidence that the GLP-1 system is involved in the regulation of body fluid homeostasis. GLP-1R agonists suppress water intake independent of their effects on food intake. It is unknown, however, whether this suppressive effect of GLP-1R agonists extends to saline intake. Accordingly, we tested the effect of the GLP-1R agonists liraglutide (0.05 μg) and exendin-4 (0.05 μg) on water and saline intake, as stimulated either by angiotensin II (AngII) or by water deprivation with partial rehydration (WD-PR). Each agonist suppressed AngII-induced water intake; however, only exendin-4 suppressed saline intake. WD-PR-induced water and saline intakes were both attenuated by each agonist. Analysis of drinking microstructure after WD-PR found a reliable effect of the agonists on burst number. Furthermore, exendin-4 conditioned a robust taste avoidance to saccharine; however, there was no similar effect of liraglutide. To evaluate the relevance of the conditioned taste avoidance, we tested whether inducing visceral malaise by injection of lithium chloride (LiCl) suppressed fluid intake. Injection of LiCl did not suppress water or saline intakes. Overall, these results indicate that the fluid intake suppression by GLP-1R activation is not selective to water intake, is a function of post-ingestive feedback, and is not secondary to visceral malaise.

Glucagon-like peptide-1 receptor agonists suppress water intake independent of effects on food intake

Glucagon-like peptide-1 (GLP-1) is produced by and released from the small intestine following ingestion of nutrients. GLP-1 receptor (GLP-1R) agonists applied peripherally or centrally decrease food intake and increase glucose-stimulated insulin secretion. These effects make the GLP-1 system an attractive target for the treatment of type 2 diabetes mellitus and obesity. In addition to these more frequently studied effects of GLP-1R stimulation, previous reports indicate that GLP-1R agonists suppress water intake. The present experiments were designed to provide greater temporal resolution and site specificity for the effect of GLP-1 and the long-acting GLP-1R agonists, exendin-4 and liraglutide, on unstimulated water intake when food was and was not available. All three GLP-1R ligands suppressed water intake after peripheral intraperitoneal administration, both in the presence of and the absence of food; however, the magnitude and time frame of water intake suppression varied by drug. GLP-1 had an immediate, but transient, hypodipsic effect when administered peripherally, whereas the water intake suppression by IP exendin-4 and liraglutide was much more persistent. Additionally, intracerebroventricular administration of GLP-1R agonists suppressed water intake when food was absent, but the suppression of intake showed modest differences depending on whether the drug was administered to the lateral or fourth ventricle. To the best of our knowledge, this is the first demonstration of GLP-1 receptor agonists affecting unstimulated, overnight intake in the absence of food, the first test for antidipsogenic effects of hindbrain application of GLP-1 receptor agonists, and the first test of a central effect (forebrain or hindbrain) of liraglutide on water intake. Overall, these results show that GLP-1R agonists have a hypodipsic effect that is independent of GLP-1R-mediated effects on food intake, and this occurs, in part, through central nervous system GLP-1R activation.

Thermal dehydration-induced thirst in lithium-treated rats

Lithium is used as the primary treatment for bipolar disorder but has the common side effects of diuresis and thirst. In the present study, the effects of lithium on water balance responses of male Sprague-Dawley rats to thermal dehydration were examined. Rats ate either unadulterated food or food containing 2 g/kg lithium carbonate for 10 days. Then the control and lithium-treated rats were exposed to either 25 or 37.5 degrees C without food or water for 4 h. The rats were then allowed access to water for 3 h at 25 degrees C or were anesthetized and blood samples were taken. Lithium treatment caused an initial decrease in food intake, a decrease in body weight, and an increase in urine output. Heat exposure caused similar increases in evaporative water loss in control and lithium-treated rats. Heat exposure led to changes in blood indicators of body water status indicative of dehydration, whereas lithium had no effects on blood indicators of body water status. Water intake was increased by both heat exposure and by lithium treatment with the lithium-treated rats being more responsive to the thirst-inducing effects of thermal dehydration. Lithium treatment does not appear to impair water balance responses to heat exposure.

Side-effects of lithium at lower therapeutic levels: the significance of thirst

The prevalence of thirst, subjective polyuria and related side-effects was investigated in 87 patients attending a lithium clinic and in a group of 52 controls. Thirst was surprisingly common, occurring in 67% of patients, in spite of the fact that they had been maintained on relatively low levels of lithium, and was due principally to the lithium rather than to other psychotropic drugs. Urine flow and impaired renal water absorption correlated with the serum lithium level and the length of treatment in the patients, despite the fact that few were clinically polyuric. The pattern of the results confirms previous suggestions that lithium may stimulate the thirst mechanism directly as well as via an increased renal resistance to vasopressin. The possible implications in terms of clinical response are discussed.

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.