Bioactive and immunoactive prolactin levels after TRH-stimulation in the sera of normal women

The availability of an improved microbioassay for lactogenic hormone measurement has enabled comparison of basal and dynamic prolactin bioactivity (BA) and immunoactivity (IRMA) in normal human serum. Serum from 16 normal females aged 22-74 years was assayed and revealed a mean BA/IRMA prolactin ratio of 1.6 for basal and 1.8 for peak TRH-stimulated levels. Basal prolactin levels in postmenopausal women measured by bioassay were lower than in premenopausal women showing a relative and absolute decrease in prolactin bioactivity with age, but there was no significant difference in dynamic levels. There was also no significant difference in BA or IRMA levels following the stress of venepuncture. These findings indicate that, as previously described for basal levels, there is a good correlation between dynamic prolactin bioactivity and immunoactivity in human serum.