We examined the cross-regulation of signaling between ACTHand platelet-activating factor (PAF)-mediated steroidogenesis in the perfused guinea pig adrenal gland. Our method of in situ perfusion using an artificial medium can evaluate whether cortisol secretion in response to ACTH and PAF is interactive. Treating adrenal glands with 100 pg/ml ACTH diminished the subsequent cortisol response to 10 nM PAF. By contrast, PAF resulted in subsequent potentiation of ACTH-induced cortisol secretion. A

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... xture of 50 mM L-a-1-oleoyl-2-acetyl-snglycerol (OAG), an activator of protein kinase C (PKC), and 3 . 3 mM calcium ionophore (A23187), or 10 mM forskolin (FRK) diminished the cortisol response to PAF, whereas that to ACTH was unaffected. Each of PAF, ACTH, or FRK eliminated the cortisol response to OAG plus A23187, whereas that to FRK was unaffected. These data show that the protein kinase A (PKA)-dependent processes activated by ACTH or FRK can interfere with PAF-induced signal transduction at receptor and post-receptor levels. In contrast, PKC-dependent processes activated by PAF promoted ACTH-signaling at receptor and post-receptor level. Cross-regulation between processes activated by PAF receptor-PKC and by ACTH receptor-PKA might function in the multifactorial regulation of adrenocortical steroidogenesis.