Effect of storage on the bioactivity of two international reference preparations of human pituitary luteinizing hormone in vitro.

There was no loss of biological activity in vitro when the 1st International Reference Preparation (IRP) for human pituitary gonadotrophins [FSH and LH/interstitial cell stimulating hormone (ICSH) for bioassay] code no. 69/104 and the 1st IRP for human pituitary LH/ICSH [for immunoassay] code no. 68/40 were stored for 1 year at -70 degrees C in a buffered 0.8% saline solution containing 1% bovine plasma albumin (BPA). However, storage of the 69/104 preparation at -20 degrees C in either 0.1 or 1% BPA, or at -70 degrees C in the presence of 0.1% BPA showed a small but significant decrease (approximately 10%) in activity over the same period. It is, therefore, advantageous to store these reference preparations at -70 degrees C in the presence of 1% BPA.