Unoccupied prolactin binding components of the benign and malignant human prostate in a subclinical and clinical...

Optimal conditions for the quantitation of free prolactin binding components of human prostatic tissue obtained by TURP were studied by applying gamma receptor assay. The radioligand used was 125I-prolactin. Significantly greater heat stability of the prostate membrane prolactin binding sites, when compared to that of androgen cytoplasmic receptors, was confirmed. The saturability and specificity of the prolactin binding components was demonstrated by the results of both Scatchard plot analysis and displacement studies. Free prolactin receptors were found in none of the poorly differentiated (G3) prostatic tumors examined, and only in 62.5% of medium differentiated (G2) prostatic malignancies. The majority of tissue specimens coming from patients with either BPH or well differentiated prostatic tumor (G1) contain measureable amounts of free prolactin membrane binding components. In the present study we report also the case in which the change in tumor differentiation toward a higher grade (G2 to G1, provoked by the successful chemohormonal treatment) is accompanied with the appearance of previously absent free prolactin binding components. In histologically proven BPH tissue specimens free prolactin receptor negative status has been found in most patients with a slight increase in serum PAP values, while receptor rich status was detected in the majority of those with elevated PSA concentrations. We believe therefore that the prolactin receptor values, when used as part of the multivariable analysis, may participate in further delineation of the role of prolactin in the development of prostate cancer, but may also play a role in a subclinical prediction related to the conversion of either an adenoma or a latent adenocarcinoma to the clinically manifest prostatic malignancy.