Hypercalciuria and hyperphosphaturia are present in long term and high dose regimens of glucocorticoid therapy. This study aims to evaluate the effect of niacin at its pharmacological dose on calcium and phosphate disturbances due to methylprednisolone administration in growing rats. Twenty one rats were randomly divided into three equal groups and treated as follows for 4 weeks: 1-Normal saline (Control); 2-Methyl Prednisolone (MP) acetate, 3.5 mg kg −1 five days a week, SC and 3-MP acetate, 3.5 mg kg −1 five days a week, SC + niacin 200 mg kg −1 daily by oral gavages. At the end of the experiment, serum and urinary calcium and phosphate assays were performed and calcium content of forth lumbar vertebrate and tibia-fibula bone was determined by atomic absorption method. No significant difference observed in serum calcium or phosphate levels among different groups (p>0.05), however an obvious hypercalciuria associated with hyperphosphaturia was present in MP group as compared to control (p<0.001). Niacin significantly decreased urinary calcium (p<0.001) and phosphate (p = 0.005) concentrations as compared to MP group. Calcium level was still significantly higher than control (p<0.001), while phosphate decreased even to a lower level than control (p = 0.005). Calcium content of forth lumbar vertebrate or tibia-fibula bone of rats remained statistically the same among different groups (p>0.05). Niacin at its pharmacological dose can ameliorate hypercalciuria and hyperphosphaturia due to long term and high dose glucocorticoid administration in growing rats without affecting bone calcium content. The possible clinical importance of this effect needs to be clarified in future studies.

Problem statement: Glucocorticoid-induced ob gene over-expression and resulted hyperleptinemia may lead to adverse consequences especially on cardiovascular system; therefore, the present study was conducted to evaluate the effects of niacin on hyperleptinemia and ob gene overexpression due to dexamethasone administration in rats. Approach: Twenty four adult male rats divided randomly into four equal groups: 1-normal saline (control), 2-dexamathasone 0.125 mg kg −1 day −1 , I.M. 3dexamathasone 0.125 mg kg −1 day −1 , I.M. + niacin 200 mg kg −1 day −1 , by oral gavages and 4-niacin 200 mg kg −1 day −1 , by oral gavages. After two weeks, blood samples were collected from all animals and leptin level assayed in harvested sera by ELISA method. Moreover, inguinal adipose tissue was excised to be examined for ob gene expression using quantitative real-time PCR. Results: Dexamethasone treatment (group 2) increased serum leptin along with its mRNA expression more than 3 folds as compared to control (p<0.001 and p = 0.001 respectively). Although leptin level in rats treated with dexamethasone+niacin was 17.8% lower than group 2; however this decrease was not significant (p>0.05). Concomitant administration of niacin with dexamethasone significantly decreased leptin gene mRNA expression compared to dexamethasone treated rats (p<0.001) and even reversed it to the control level (p>0.05). Niacin alone (group 4) had no effect on serum leptin concentration as well as leptin gene expression in comparison with control group (p>0.05). Conclusion: Niacin slightly ameliorates hyperleptinemia and reverses ob gene mRNA over-expression in adipose tissue of dexamethasone treated rats.