OCCURRENCE OF STEROIDOGENIC ENZYMES IN THE BOVINE MAMMARY-GLAND AT DIFFERENT FUNCTIONAL STAGES

After the incubation of minced mammary tissues from non-lactating/non- pregnant (NL/NP), nonlactating/pregnant (NL/P), fully lactating (FL) a nd late-lactating (LL) cows with [C-14]-labelled pregnenolone or proge sterone and dehydroepiandrosterone (DHEA), the following metabolites w ere identified at all stages: 20 alpha-dihydropregnenolone, progestero ne (from pregnenolone), 5 alpha-pregnanedione, 5 alpha-pregnan-3 beta- ol-20-one, 20 alpha- and 20 beta-dihydroprogesterone (from progesteron e), 5-androstene-3 beta,17 beta-diol, 5 alpha-androstanedione, 5 alpha -androstan-3 beta-ol-17-one, androstenedione, testosterone and DHEA ac yl ester (from DHEA). These products indicate the occurrence of 3 beta -hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase, 17 beta-hyd roxysteroid oxidoreductase (17 beta-HOR), 20 alpha- and 20 beta-hydrox ysteroid dehydrogenases, steroid 5 alpha-reductase and acyl transferas e activities. Incubation of mammary tissue homogenates with [1,2,6,7-H -3]androstenedione and testosterone confirmed the presence of a 17 bet a-HOR acting prevalently in a reductive way but failed to show evidenc e of any aromatase activity beyond background level. When total RNA fr om mammary tissues of NL/NP and LL cows was reverse-transcribed and am plified by polymerase chain reaction (PCR) with three sets of primers specific for bovine P450scc, P450c17 and P450arom cDNAs, no fragment o f the expected size could be detected on gel. Southern analysis with c orresponding digoxigenin-labelled ovarian probes, however, gave a posi tive signal for P450arom cDNA in five out of eight samples of LL mamma ry tissue. These data indicate that the bovine mammary gland has very limited steroidogenic capabilities that are essentially compatible wit h the terminal activation of circulating steroids from steroidogenic e ndocrines. It is uncertain, however, whether this conclusion applies t o anestrous or ovariectomized lactating cows as well. Copyright (C) 19 96 Published by Elsevier Science Ltd.