Differential Regulation of Anterior Pituitary Corticotrope Function is Observed in Vivo but not in Vitro in Two Lines of Ethanol‐Sensitive Mice

Anterior pituitary corticotrope function was analyzed in the long sleep (LS) and short sleep (SS) lines of mice selectively bred for differences in sensitivity to ethanol. In vivo challenge with acute ethanol or CRH administration or the stress of novel handling resulted in a more pronounced increase in serum corticosterone levels in LS mice compared with SS mice. Likewise, in vivo administration of ethanol resulted in 3‐fold higher levels of anterior pituitary pro‐ACTH/endorphin mRNA in LS mice compared with SS mice. However, this differential regulation of the HPA axis during in vivo analysis was not observed during in vitro studies of anterior pituitary corticotrope function. Primary cultures of LS and SS anterior pituicytes responded appropriately but equivalently to a variety of secretagogues known to stimulate anterior pituitary ACTH secretion. These secretagogues included CRH (10 nm), dibutyryl‐cAMP (1 mm), vasopressin (100 nm), and phorbol 12‐myristate 13‐acetate (10 nm). Ethanol had no direct stimulatory effect on pituitary ACTH secretion. Quantitation of anterior pituitary corticotrope peptide biosynthesis was determined by immunoprecipitation and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of extracts from [³⁵S]methionine‐labeled anterior pituitary explants and from [³⁵S]methionine‐labeled primary cultures of anterior pituitary cells. LS mice pro‐ACTH/endorphin biosynthesis in pituitary explants was 2‐fold greater than pro‐ACTH/endorphin biosynthesis in SS mice pituitary explants. However, in culture, isolated from hypothalamic and adrenal factors, the LS anterior pituitary pro‐ACTH/endorphin biosynthetic rate became eguivalent to the SS anterior pituitary pro‐ACTH/endorphin biosynthetic rate. The results suggest that the differential regulation of LS and SS anterior pituitary corticotropes observed in vivo is not due to genetic differences in LS and SS anterior pituitary corticotrope function.