Comparison of two reference preparations for horse chorionic gonadotrophin in four in-vivo and in-vitro assays.

This research comparatively analyzes different preparations of horse chorionic gonadotrophin (CG), a hormone. It found that the most majority of the test samples produced consistent results in various tests, suggesting these preparations accurately represent the hormone in its natural state. However, the International Reference Preparation (IRP2) had significantly varying results in different tests, indicating a potential issue with its representation of the hormone.

Hormone Preparations and Assay Systems

• The study compared several preparations of horse chorionic gonadotrophin (CG), a hormone, with different purities and from different sources.
• These preparations were tested in four different assays: radioimmuno, radioreceptor, in-vitro cell culture, and in-vivo assays.
• The majority of the tested preparations demonstrated consistent activities across the four assay systems indicating that these preparations accurately represent the natural, or ‘native’, form of the hormone.

IRP2 Preparations and Discrepancies

• However, the second International Reference Preparation (IRP2) presented discrepancies in its activities across the assays.
• In particular, the relative in-vivo activity of the IRP2 was almost 50% lower than what was observed in the other three assays.
• This differing activity level could be due to the hormone undergoing denaturation during preparation or an unrepresentative selection of isoforms — different forms of the same protein.
• Although IRP2 proved to be a reliable standard for in-vivo assays, its inconsistent performance in in-vitro assays poses challenges for its standardization.

Standard Considerations and Final Thoughts

• The report suggests that for the standardization of horse CG hormone preparations using in-vitro methods, a standard that shows consistent results in both in-vivo and in-vitro assays needs to be utilized.
• According to the results, the NIH standard, unlike the IRP2, meets these requirements, showing consistent performance in different assay systems.
• This research, therefore, highlights the importance of selecting an appropriate standard for conducting assays, which can significantly impact the accuracy and reliability of the results.