To examine the role of 11 beta-hydroxysteroid dehydrogenase 1 (11 beta-HSD1) in the control of glucocorticoid actions in the ovine pituitary during development, we have sought developmental changes in the distribution and the level of 11 beta-HSD1 mRNA by in situ hybridization. In the pars distalis, 11 beta-HSD1 mRNA was present by day 60; its amount did not change significantly until term (days 145-147) when it increased dramatically. The level of 11 beta-HSD1 mRNA increased further during the postnatal period. In contrast, 11 beta-HSD1 mRNA in the pars intermedia was not detectable until day 135; it increased in amount at days 140-143, but did not change significantly thereafter through to adulthood. We have also measured levels of both dehydrogenase and reductase activities of 11 beta-HSD1 in the pars distalis of fetal sheep at day 140 and term, and of postnatal sheep at 1-2 months of age, to determine whether changes in 11 beta-HSD1 mRNA are reflected in the levels of enzyme activities. There were progressive increases in both dehydrogenase and reductase activities from day 140 to 1-2 months postnatally, although dehydrogenase activity was consistently higher than reductase activity. Finally, we have determined the effect of short-term intrafetal cortisol infusion (5 micrograms/min for 12 h) on levels of pituitary 11 beta-HSD1 mRNA by in situ hybridization. There was no effect of cortisol infusion on 11 beta-HSD1 mRNA expression.(ABSTRACT TRUNCATED AT 250 WORDS)