In vivo effects of adrenocorticotropin on hamster adrenal steroidogenic enzymes.
The hamster, a rodent possessing adrenal 17 alpha-hydroxylase activity, was used to study the effect of ACTH on the regulation of cortisol formation in vivo. The characterization of the mRNA and protein of hamster adrenal steroidogenic enzymes revealed close similarities between this animal and other mammalian species. The hamster adrenal RNA hybridized in a single band to cDNA probes for bovine adrenal P450scc, P450(17 alpha), P450c21, to mouse adrenal P450(11 beta), and to pig testis 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in the areas of 2.2, 2.0, 2.3, 2.0, and 2.1 kilobases, respectively. Immunoblotting analyses revealed the presence of single protein bands reacting with antibodies to bovine P450scc, P450c21, porcine P450(17 alpha), or human placental 3 beta HSD in the areas of 52, 55, 51, and 41 kilodaltons, respectively, whereas two protein bands were detected at 48 and 52 kilodaltons with the antibody to bovine P450(11 beta). After stimulation with ACTH injected at 5-h intervals over 20 h, plasma cortisol levels, which were already increased 2.5 h after the first injection, remained elevated for the duration of treatment and returned to control values 15 h after the last injection. The ratios of plasma cortisol to corticosterone were 1.5, 3.9, and 7 at 0, 2.5, and 5 h after the first injection and continued to rise to a value of 11 at 15 h after multiple injections. This ratio returned to control values 15 h after cessation of either the short term (one injection) or long term (five injections) treatment, indicating a control mechanism favoring cortisol formation upon ACTH stimulation. Of the adrenal enzyme systems examined, only three were directly affected by ACTH treatment. The mRNA level of 3-hydroxy-3-methylglutaryl-coenzyme-A reductase, the key precholesterol regulatory step, increased after ACTH administration within 2.5 h and remained elevated during the entire study period. ACTH provoked a rapid and sustained increase in P450scc mRNA levels, which decreased very slowly after cessation of treatment without reaching control values 30 h after the last injection. Meanwhile, ACTH treatment caused no changes in the amount of adrenal cytochrome P450scc protein during treatment and 30 h after its cessation. Therefore, we postulate that factors other than newly synthesized P450scc protein participate in the control of this rate-limiting step. The high P450scc mRNA levels observed suggest stabilization of mRNA and posttranscriptional events affecting its catabolism.(ABSTRACT TRUNCATED AT 400 WORDS)
LeHoux
J G
JG
Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Mason
J I
JI
Ducharme
L
L
D000311:Adrenal Glands / Q000201:enzymology*; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D008297:Male; D008647:Mesocricetus; D012333:RNA, Messenger / Q000378:metabolism; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis*
D012333:RNA, Messenger; D013256:Steroids; D000324:Adrenocorticotropic Hormone; D013254:Steroid 17-alpha-Hydroxylase; D002786:Cholesterol Side-Chain Cleavage Enzyme