On the basis of our previous finding that prolactin (PRL) cells of the bullfrog (Rana catesbeiana) contain immunoreactive α-subunit of pituitary glycoprotein hormones, experiments were conducted to see whether the immunoreactive α-subunit is released from PRL cells. Cell immunoblot analysis revealed that approximately 10% of cells that released immunoreactive PRL also released immunoreactive α-subunit. Western blot analysis of the culture media revealed that a considerable amount of the free form of α-subunit was released from the dispersed anterior pituitary cells. Moreover, it was found that addition of α-subunit to the culture medium enhanced PRL release. The results raise the possibility that α-subunit secreted by PRL cells acts as an autocrine and/or paracrine factor.
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