Decreased bioactivity of circulating prolactin in patients with rheumatoid arthritis

Growth hormone and prolactin (PRL) were measured by radio-immunoassay in sera of 36 patients with rheumatoid arthritis (24 females and 12 males) and of 50 normal blood donors (25 males and 25 females). The bioactivity of PRL was also determined for both groups, using the Nb2 rat lymphoma proliferation assay. Although no significant difference was found between serum PRL values of patients and controls when determined by radio-immunoassay, the bioactivity of PRL was significantly decreased in patients' sera, when compared to values obtained in age and sex-matched controls. This decreased PRL bioactivity could not be attributed to drug treatments administered to the patients examined.