Effects of pituitary adenylate cyclase-activating polypeptide on gonadotropin secretion and subunit messenger ribonucleic acids in perifused rat pituitary cells.

Abstract

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) is a neuropeptide related to vasoactive intestinal peptide-secretin-glucagon which stimulates adenylate cyclase in cultured rat pituitary cells and stimulates LH and FSH release in vitro and in vivo. Because the cAMP-protein kinase-A pathway regulates the gonadotropin subunit messenger RNAs (mRNAs) and modulates GnRH-stimulated gonadotropin secretion in vitro, we examined the effects of PACAP38 on gonadotropin secretion and subunit mRNA levels. Anterior pituitary cells were prepared from 7-week-old male rats castrated at 5 weeks of age. In monolayer cultures stimulated with GnRH, 0.1-10 nM PACAP38 decreased (P < 0.05) the EC50 for GnRH dose-dependently without affecting the maximum LH secretory response. Cells were next stimulated with 1-min pulses of 2.5 nM GnRH every hour for 9 h in the absence or presence of 10 nM PACAP38, which was perifused continuously. The amplitude of GnRH-induced LH, FSH, and alpha-subunit secretory episodes from PACAP38-treated cells rose (P < 0.01) gradually to 233 +/- 54%, 197 +/- 44%, and 378 +/- 104%, respectively (mean +/- SEM; n = 5 experiments), of the value for control cells lacking PACAP38. This enhancement was sustained for at least 3 h after PACAP38 was removed from the perifusion medium. With PACAP treatment, interpulse secretion of LH and alpha-subunit increased gradually (P < 0.01) to 174 +/- 21% and 212 +/- 64% of the value for chambers stimulated with GnRH alone (control), respectively, whereas interpulse secretion of FSH declined (P < 0.001) to 75 +/- 7% of the control value. In contrast to the gradual effect of PACAP38 to enhance GnRH-induced hormone secretion, PACAP38 alone produced a transient burst of gonadotropin secretion. At the completion of the perifusions, total RNA was extracted and gonadotropin subunit mRNA levels were determined by Northern analysis. GnRH increased (P < 0.01) FSH beta mRNA to 438 +/- 52% of the level in cells stimulated with medium alone (control). Adding PACAP38 to the perifusion medium partially blocked (P < 0.01) the effect of GnRH (178 +/- 20% of the control value), and PACAP38 alone reduced (P < 0.01) FSH beta mRNA levels to 31 +/- 3% of the control value. By contrast, alpha-subunit mRNA levels were increased by both PACAP38 (143 +/- 4% of the control value; P < 0.01) and GnRH (121 +/- 2% of the control value; P < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of extracellular signal-regulated kinase by pituitary adenylate cyclase-activating polypeptide in alpha T3-1 gonadotrophs

“…These effects include stimulation of glycoprotein hormone -subunit ( GSU) gene transcription (Burrin et al 1998, Tsujii et al 1994 and gonadotroph cell proliferation (Schomerus et al 1994). PACAP receptors are members of the seven transmembrane G-protein-coupled receptor (GPCR) superfamily, but the intracellular signalling pathways that mediate the stimulatory and synergistic actions of PACAP on GSU transcription or gonadotroph cell proliferation are poorly understood.…”

Pituitary Adenylate Cyclase-activating Polypeptide Stimulates Nitric-oxide Synthase Type I Expression and Potentiates the cGMP Response to Gonadotropin-releasing Hormone of Rat Pituitary Gonadotrophs

“…Complementary to this, we have isolated a pituitary-specific promoter of NOS I that conferred responsiveness to GnRH as well as cAMP (34). The effect of PACAP on the GnRH signaling pathway (12,14,35), its role during proestrus in gonadotrope/GnRH responsiveness (36,37), and its ability to act through cAMP and Ca 2ϩ prompted us to analyze the effect of PACAP on NOS I in the pituitary. We show that, like GnRH, PACAP augments pituitary levels of NOS I in vitro, via the cAMP/PKA-dependent transduction pathway, and that this NOS I is restricted to the gonadotrope cells.…”

A Role of Pituitary Adenylate Cyclase Activating Polypeptide(PACAP) as a Regulator of Paracrine Interactions between Folliculo-Stellate Cells and Gonadotropes through the Control of Activin-Follistatin Interactions.

“…In contrast, those using perfusion systems have demonstrated consistent stimulatory effects of PACAP on gonadotropin secretion [26,36]. Since perfusion systems generally exclude the influence of internally produced substances and reflect the net action of externally added materials, it was possible that PACAP might affect the secretion of unknown substances from pituitary cells that had an ability to interfere with the hormone secreting activity of gonadotropes.…”