Pituitary changes of desacetyl-alpha-melanocyte-stimulating hormone throughout development.

Adrenocorticotropin (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH) and desacetyl-alpha-MSH (des-alpha-MSH) concentrations were evaluated in 4 embryos and 18 fetal pituitaries collected after spontaneous (n = 9) and prostaglandin-induced abortion (n = 9) at 13-25 weeks of gestation. The peptides were measured by radioimmunoassays after a high-performance liquid chromatographic separation of the homogenates. In both embryonic and fetal pituitaries, des-alpha-MSH concentrations were 2-4 times higher than those of alpha-MSH and 1- to 50-fold increased in comparison to those of ACTH. Either melanotropin showed the highest pituitary content in the first part of the second trimester, while the ACTH content remained constant. In the oldest fetuses (over 20th week), the pituitaries collected after prostaglandin-induced abortion showed markedly increased values of both des-alpha-MSH and alpha-MSH in comparison to samples collected after spontaneous abortion. In conclusion, des-alpha-MSH, the typical melanotropic hormone of fetal pituitary, undergoes important changes during development. Des-alpha-MSH seems to be the end product of proopiomelanocortin cleavage and its pituitary content increases in concomitance with the fetal adrenal sprout. Moreover, these data indicate that the intermediate pituitary lobe could be activated by the stress of labor after the 20th week of pregnancy.