Analyses for susceptibility of rat anterior pituitary cells to prolactin-releasing peptide

We validated the effect of prolactin-releasing peptide (PrRP) on prolactin (PRL) secretion from rat anterior pituitary cells in in vitro culture, We f ound that culture conditions considerably influenced the response of the an terior pituitary cells to PrRP, Longer culture term (4d) was required to ob tain better responses of the anterior pituitary cells to PrRP in comparison to thyrotropin-releasing hormone (TRH), Under the culture conditions emplo yed here, PrRP was comparable to TRH in the potency promoting PRL secretion , and the action of PrRP was very specific for PRL secretion, The susceptib ility of the anterior pituitary cells to PrRP varied in female rats dependi ng on the process of reproduction: the cells prepared from lactating rats w ere the most sensitive to PrRP compared with those from random-cycle and pr egnant rats. Because the expression levels of PrRP receptor mRNA in the pit uitary varied during the reproductive process, we speculated that the susce ptibility of the anterior pituitary cells would reflect cellular changes in cluding the expression level of PrRP receptors. In addition, treatment with estrogen in vivo enhanced the susceptibility of the cultured anterior pitu itary cells in male rats. Our results indicate that the susceptibility of t he rat anterior pituitary cells to PrRP is regulated by physiological mecha nisms.