In response to stress, adrenocorticotropin (ACTH) is secreted from anterior pituitary corticotropes. Corticotropin-releasing hormone (CRH) is a potent stimulator of ACTH secretion. The CRH stimulation of secretion is mediated by cAMP and is largely dependent on Ca2+ influx through voltage-gated L-type Ca2+ channels. This study was designed to investigate whether the expression of L-type Ca2+ channels in the rat anterior pituitary and in corticotropes is regulated by acute stress and CRH. RNase protection assays were used to quantify α1C mRNA of the L-type Ca2+ channel. The α1C mRNA levels from stressed rats increased by 31% in anterior pituitaries of rats after 30 min of exposure to cold stress. Neither 60 min cold stress nor 30 min restraint stress had an effect on α1C mRNA levels. When α1C mRNA was detected by in situ hybridization in a population of corticotropes enriched to 90%, 0.5 nM CRH (3 h) stimulated a 36% increase in the average area of label/cell and a 10% increase in the average density of label. Our results suggest that (1) the expression of α1C subunit mRNA of L-type Ca2+ channels is increased in the rat anterior pituitary with a stress-specific response that might reflect an increase both in thyrotropes and corticotropes (both are known to be stimulated by cold stress), and (2) the CRH-mediated increase in α1C mRNA expression in individual rat corticotropes, in vitro, supports the hypothesis that some of the increase in vivo is due to changes in corticotropes.

Keywords:
Ca2+ channels, Corticotropin, Corticotropin-releasing hormone, Corticotropes, Stress, Molecular neuroendocrinology, In situ hybridization, Immunocytochemistry
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