#5852 EFFECT OF DIET ON THE COLLECTOR DUCT BEHAVIOUR: RELEVANCE IN PRECLINICAL DRUG DEVELOPMENT

Abstract

Abstract Background and Aims Drug induced syndrome of inadequate antidiuretic hormone secretion (SIADH) is a common problem in clinical practice. Early detection of this side effect at a preclinical level would improve safety and efficiency. We investigate the role of different diets in preclinical detection of SIADH. Method Animals were divided into two groups (n = 4 each), one receiving standard pellet based diet, and the other one a diluted hyposodic gelified liquid diet. After one week, both groups were administered daily intraperitoneal (i.p.) injections of desmopressin acetate (ddAVP; 0.4 μg/kg) and a volume of distilled water equivalent to 2.5% of body weight for 7 days. Animals were placed in metabolic cages for 24h at the end of each period to collect and analyse the urine, and a blood sample from the tail vein was obtained. Weight, water and food intake were measured on a daily basis. Results Differences in water and electrolyte balance are shown in Table 1. Pellet fed animals presented an increased water intake and produced a more concentrated urine compared to those on a hyposodic diet. When analysed in detail, urinary osmolality was mainly driven by ionic osmoles in pellet fed animals (42,25 ± 4,72 vs 266,30 ± 17,32 mOsm/kg, p<0,005). Of note, there seems to be an occult osmole, especially prominent in the pellet group (osmol gap 20,40 ± 3,18 vs 99,89 ± 9,81 mOsm/kg, p = 0,017). All of the above suggest there is a net retention of water, sodium and potassium in those animals fed with a conventional pellet diet. Daily administration of ddAVP/water induced a mild transient hyponatremia that was recovered 24h later in both groups; this situation was repeated over a 7 day period. Pellet fed animals did not modify water intake, diuresis, free water clearance or urinary osmolality after ddAVP/water treatment, suggesting that hyperosmolar diets significantly increase urinary osmolality fixating urinary water losses and impairing further urinary concentration. On the contrary, animals on a hyposodic diet did present antiaquaresis, as shown by an increase in water intake, a decrease in diuresis and free water clearance and an increase in urinary osmolality. Animals fed with hyposodic diet progressively lost weight, while pellet fed animals did not. However, this trend was reversed after 4 days of treatment with ddAVP/water, again suggesting a degree of water retention. It is remarkable that we have found signs of water retention despite the fact that the induced hyponatremia is mild and transient. Conclusion The antiaquaretic effect of ddAVP is overridden by the amount of urinary osmoles excreted when on a pellet diet, which seem to fixate the amount of water in the urine. Therefore, the use of hyposodic diets in preclinical drug development is essential when SIADH is likely to be expected, as its effects will be unnoticed if a standard diet is used.