During GnRH-induced ovulation in hypophysec-tomized rats, both PAI-I mRNA and activity were also increased in a time-dependent fashion. These data suggest that the action of PRL on PAI-I gene expression in granulosa cells might be through a protein kinase C-dependent pathway. Buy Asthma Inhalers Online
PRL is a pituitary hormone mainly involved in stimulating milk production. However, there is abundant evidence to show that the ovary is also one of the primary target tissues for PRL. Specific PRL receptors have been found in the granulosa cells and other compartments of the ovary. Although a large body of evidence has shown that an increase in PRL dose inhibits steroidogenesis in cultured granulosa cells, McNatty et al. reported that steroid production by cultured human granulosa cells is stimulated by a low physiological dose of PRL, whereas high doses are inhibitory, suggesting that PRL may exert an effect on ovarian function depending on the stage of ovarian cell differentiation. Studies in rats and mice have indicated that PRL binding sites on granulosa cells are low before ovulation but increase in response to the preovulatory LH surge. Therefore, progesterone production induced by LH is further enhanced by PRL. A similar sequence of events appears to occur in the pig. Increases in the number of PRL receptors on granulosa cells are associated with increases in the capacity of progesterone secretion by PRL.