Failure of short-term γ-linolenic acid treatment to reduce urinary calcium loss of diabetic rats

Calcium re-absorption in the kidney is impaired in streptozotocin (STZ) diabetic rats, thereby causing hypercalciuria. Increased calcium loss starts within 1–2 days after induction of diabetes and reaches a plateau after 2 weeks. The excessive calcium excretion was previously shown to be reduced by treatment with γ-linolenic acid (GLA) or evening primrose oil rich in GLA. However, in these studies, the animals were pre-treated for several weeks before injection of STZ. In the present study we investigated whether GLA can reduce calcium excretion when treatment starts at the same time as induction of diabetes. Rats were made diabetic with 60 mg/kg STZ and at the same time food was fortified with 0.4% GLA for the treatment group. A control group was treated with vehicle alone and given standard feed only. Urine was collected from animals in metabolism cages every 3rd day for a period of 26 days. The diabetic group increased their food and water consumption, and urine and faeces production as compared to the control group. The urinary loss of Ca, Mg, Zn, Na, K and creatinine was markedly increased in the diabetic group as compared to the control. GLA treatment, however, did not affect any of these variables. Analysis of fatty acids in kidneys of the rats showed an increased concentration of GLA in the treated group as compared to the two non-treated groups. We conclude that GLA treatment must commence before STZ injection in order to attenuate diabetes-induced hypercalciuria.