Immunoreactive dynorphin-A in bovine anterior pituitary and its in vitro release.

The anterior lobe (AL) of the bovine pituitary contained and released, during in vitro culture, a form of immunoreactive dynorphin-A (ir-DYN-A) larger than that occurring in neural tissue. Bovine AL tissue from intact females contained less ir-DYN-A than did AL tissue from castrated males. Enzymatically dispersed AL cells contained and released ir-DYN-A in vitro. Preincubation of dispersed AL cells for 18 hr, rather than 1.5 hr, increased the content and release of ir-DYN-A as well as LH. Addition of gonadotropin-releasing hormone (GnRH) to tissue slices or dispersed cells stimulated release of LH, but in contrast to published observations from rat AL, GnRH had no effect on release of ir-DYN-A. Addition of estradiol-17 beta, with or without progesterone, increased release of ir-DYN-A but not LH during 2-hr cultures. In summary, bovine AL contains and releases in vitro a large molecular weight form of ir-DYN-A. Although this ir-DYN-A was not coreleased with LH, a reproductive role was suggested by in vivo and in vitro effects of gonadal hormones on ir-DYN-A in the bovine anterior pituitary.