Sex-Independent Synthesis of a2u-Globulin and Its Messenger Ribonucleic Acid in the Rat Preputial Gland: Biochemical and Immunocytochemical Analyses*

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Abstract
α2u-Globulin is the principal urinary protein of the mature male rat. The major urinary source of this protein is the liver where it is synthesized and secreted by hepatocytes under hormonal regulation. High levels of α2u-globulin and its messenger RNA (mRNA) are also present in the preputial gland of both male and female rats, and neither castration nor ovariectomy significantly alters the preputial concentration of this protein and its mRNA. Per unit mass of RNA and protein, the preputial gland as compared to liver contains about 3-fold higher level of α2u-globulin mRNA and about 300-fold higher level of α2u-globulin. Despite a 3-fold (300%) difference in the content of α2u-globulin mRNA, nuclear run-off experiments show only a 30% higher rate of α2u-globulin gene transcription in the preputial gland than in the liver. Immunocytochemical analyses reveal that the liver possesses two α2u-globulin cell populations, one showing higher immunoreactivity than the other. In contrast, the preputial gland contains only one type of α2u-globulin containing acinar cells, and a large amount of α2u-globulin accumulates in the ductal lumen. From these results we conclude that the 300% higher level of α2u-globulin mRNA in the preputial gland is not due to a corresponding difference in the rate of transcription of α2u-globulin gene. Such a difference may represent tissue-specific regulation at a posttranscriptional level of mRNA metabolism. Furthermore, the huge difference in the α2u-globulin content of the preputial gland and the liver is primarily due to the cellular and ductal accumulation of this protein in the preputial gland us. its rapid secretion by the liver. (Endocrinology121: 1000–1005,1987)

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