VARIATIONS IX SENSITIVITY OF OVARIECTOMIZED GUINEA PIGS TO RELAXIN1

Abstract

A characteristic pattern of changing sensitivity was exhibited by guinea pigs being used for relaxin assay. A rapid increase in sensitivity to relaxin during the 1st 2-3 test doses is followed by a period of relative constancy, after which the sensitivity gradually diminishes until a completely refractory condition is reached. Under the conditions of our experiments, the refractory state is reached within 3-6 months. The decreased sensitivity to relaxin is not reversed by increasing the amount of estrogen used for priming. Although the development of a relaxin-specific antibody as a possible cause has not been ruled out, experiments designed to test this possibility gave negative results. Some qualifications have been introduced into the accepted relaxin assay procedure in order to circumvent the additional variable of diminished sensitivity. The need for a standard relaxin preparation is emphasized, and a method proposed for its standardization.