Evening primrose oil reduces urinary calcium excretion in both normal and hypercalciuric rats

Hypercalciuria is an important risk factor in the aetiology of idiopathic urolithiasis and many treatment modalities in clinical practice are directed towards reducing urinary calcium excretion. There are no natural animal models of hypercalciuria, such as the spontaneous hypertensive rat; however, the streptozotocin-diabetic rat is accepted as a good model for studies of disordered renal function associated with diabetes mellitus. Hypercalciuria is a prominent feature of the streptozotocin-diabetic rat and the model was, therefore, used to study the influence of evening primrose oil on urinary calcium excretion. Twenty rats divided into two groups of ten rats each were maintained on either normal rat chow (group 1) or primrose oil enriched diet (group 2) for 10 weeks. At 4 weeks both groups of rats were made diabetic with streptozotocin. Urine calcium measurements were serially performed before commencement of the diet, during the pre-streptozotocin (pre-diabetic) phase and during the post streptozotocin (diabetic) phase. The urine calcium excretion was significantly less in the primrose oil fed animals during both the pre-diabetic phase and the diabetic phase compared with the rats on the normal rat chow. These results indicate that evening primrose oil, a rich source of gamma-linolenic acid, helps to reduce urine calcium excretion in normal animals as well as in the hypercalciuric streptozotocin-diabetic rat. Dietary modifications with long-chain omega-6 and omega-3 fatty acids might be a useful adjunct in the treatment of idiopathic hypercalciuric urolithiasis.