Expression of short and long forms of prolactin receptor in the rat

The expression of the prolactin receptor gene has been visualized in various rat tissue types by in situ hybridization. Probes specific to the intracellular domains of the short and long forms of receptor were prepared. Sex differences in the expression of prolactin receptors were seen in a number of tissue types, for example the liver, the adrenal gland and the pituitary. The expression of mRNA specific to the long form of the prolactin receptor was predominant in the adrenal gland, pituitary, thymus, spleen, skin, heart skeletal muscle, testis, epididymis, prostate, seminal vesicle, pancreas and esophagus, whereas mRNA specific to the short form was more strongly expressed in the liver, kidney and lung. Prolactin receptor mRNA was absent from the dermis, rectum, penis, vagina, adrenal medulla, the posterior lobe of pituitary and the olfactory bulb (< 5 arbitrary units). The highest level of mRNA was in the ileum (> 100 arbitrary units), followed by the intermediate lobe of the pituitary, digestive tract, female liver, adrenal cortex and the ovaries. The advantage of in situ hybridization is that it permits the identification of specific regions or cells expressing mRNA. Whether actual receptor proteins encoded by these transcripts are expressed in all such tissue types remains to be determined. Prolactin actions has not been found in all tissues expressing prolactin receptor transcripts, nor has any definite correlation been found between the expression of the short and long forms of prolactin receptor and their specific functions.