Penfluridol Decreases Secretagogue-Induced TSH, GH, and LH Secretion in vitro:A Possible Role for Calcium-Calmodulin

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Abstract
This study was designed to investigate the effects of penfluridol, a potent neuroleptic calmodulin inhibitor, on basal and secretagogue-stimulated secretion of thyroid-stimulating hormone (TSH), growth hormone (GH), and luteinizing hormone (LH). The drug had no effect on basal TSH or LH release, but decreased GH release in a dose-related manner. TSH, LH, and GH secretion stimulated by calcium ionophore A23187 or 50 mM K+ was decreased by penfluridol as was TSH and GH release stimulated by dibutyryl-cAMP (dbcAMP). Penfluridol reversibly abolished the stimulatory effect of thyrotropin-releasing hormone (TRH) on TSH release in perifused dispersed pituitary cells. The compound inhibited hormonal release without affecting hormonal synthesis and cellular morphology (trypan blue exclusion test). Penfluridol appears to inhibit hormonal secretion by interfering with the calcium-calmodulin system in the anterior pituitary; therefore calmodulin may be an important link in the stimulus-secretion coupling of adenohypophyseal hormones.