Adrenocorticotropin-induced changes in ovine pituitary gonadotropin secretion in vitro

In vitro pituitary perifusion experiments were conducted to examine the effect of ACTH and related peptides on basal and GnRH-stimulated gonadotropin release. Treatments of 5 X 10(-7) M ACTH-(1-39), ACTH-(1-24), or ACTH-(18-39) were examined for their ability to influence basal gonadotropin secretion and the subsequent response to a 10(-9)- or 10(-8) M GnRH challenge. Administration of the 1-39 or 18-39 peptide sequences of ACTH similarly stimulated the release of LH and FSH (P less than 0.01). ACTH-(1-24) had no effect on basal gonadotropin secretion. Pretreatment with ACTH-(1-39) inhibited the LH and FSH responses to 10(-9) and 10(-8) M GnRH (P less than 0.05). Suppression of the LH response to 10(-8) M GnRH (P less than 0.05) and the FSH response to 10(-9) M GnRH (P less than 0.05) was observed after ACTH-(1-24) treatment. The administration of ACTH-(18-39) had no significant effect on GnRH-induced gonadotropin release. PRL concentrations were not affected by any of the ACTH peptides. Exposure to 10(-10) M GnRH or 5 X 10(-7) M synthetic ACTH-(1-39) produced an equivalent stimulation of LH secretion. GnRH pretreatment enhanced (P less than 0.05), while ACTH-(1-39) diminished (P less than 0.05), the subsequent response to GnRH. The GnRH receptor antagonist [D-pGlu1, D-Phe2, D-Trp3,6]GnRH attenuated the LH and FSH responses to GnRH and ACTH-(1-39) (P less than 0.05). The results obtained in this study indicate that certain portions of the ACTH molecule may affect gonadotropin secretion, perhaps by interacting with the GnRH receptor.