Background: Although prolactin (PRL) is produced predominantly by the anterior pituitary gland, recent studies have found PRL in normal brain tissues and in various neoplasms. Many of these studies have used immunohistochemical methods to detect PRL production, so the distinction between de novo synthesis and uptake by tissues with PRL receptors was not possible with these approaches. PRL production by various neoplasms has been designated as ectopic, since it was assumed that non-neoplastic cells were not producing this hormone.
Experimental design: The reverse transcriptase polymerase chain reaction technique (RT-PCR) was used to detect PRL mRNA in various normal rat tissues and normal and neoplastic human tissues. The sensitivity of RT-PCR to detect amplified products starting with very low amounts of total RNA was also determined. Amplified DNA was detected by ethidium bromide staining, Southern hybridization with 32P-labeled probes and with a chemiluminescent method.
Results: PRL expression was readily detected in normal rat brain and pituitary. One fg of starting total pituitary RNA was sufficient to detect PRL expression with RT-PCR. PRL was detected in human hypothalamus, cerebellum, and normal breast tissues (3/4 cases) as well as in breast carcinomas (5/7 cases). A lung, an endometrial and a medullary thyroid carcinoma also expressed PRL. The chemiluminescent detection system was as sensitive as 32P-labeled probes in detecting the amplified PCR product.
Conclusions: These results indicate that PRL gene expression is present in normal and neoplastic mammary and other tissues and can be readily detected by RT-PCR.