Mechanisms of insulin inhibition of ACTH-stimulated steroid secretion by cultured bovine adrenocortical cells.
Results of previous studies indicated that insulin at levels comparable to those in humans during hyperinsulinemia decreased ACTH-stimulated cortisol and androstenedione secretion by bovine adrenal fasciculata-reticularis cells in primary culture. In the present studies this inhibitory action was examined further by comparing the effects of insulin on ACTH-stimulated corticosteroid secretion with its effects on 8-(4-chlorophenylthio)-cAMP (cpt-cAMP), forskolin- and [5val]angiotensin II (Ang II)-stimulated corticosteroid secretion. Effects on corticosteroid secretion were correlated with effects on cAMP accumulation and rates of cAMP production. Monolayers were incubated for 24 h in the absence or presence of each agonist alone or in combination with insulin. Insulin (1.7 x 10(-9) or 17.5 x 10(-9) M) caused about a 50% decrease in cortisol and androstenedione secretion in response to ACTH (10(-11) or 10(-8) M). Insulin also decreased ACTH-stimulated aldosterone secretion by cultured glomerulosa cells. Cpt-cAMP (10(-4) or 10(-3) M)-stimulated increases in cortisol and androstenedione secretion were inhibited by insulin, but to a lesser extent than those in response to ACTH. The inhibition of cpt-cAMP-stimulated steroid secretion was not related to increased degradation of the cyclic nucleotide. Increases in cortisol and androstenedione secretion caused by a submaximal concentration (10(-6) M) of forskolin were decreased 50-70% by insulin. In contrast, insulin failed to significantly affect cortisol or androstenedione secretion caused by a maximal concentration (10(-5) M) of forskolin. The secretory responses to Ang II (10(-8) M) were also unaffected by insulin. The effect of insulin to inhibit ACTH-stimulated steroid secretion was accompanied by a reduction in cAMP accumulation as well as an apparent inhibition of adenylate cyclase activation. These data indicate that the effect of insulin to attenuate ACTH-stimulated corticosteroid secretion results from both an inhibition of ACTH-stimulated adenylate cyclase activity and an antagonism of the intracellular actions of cAMP.
Department of Obstetrics and Gynecology, University of Tennessee, Memphis 38163.
N A
NA
Klein
R N
RN
Andersen
P R
PR
Casson
J E
JE
Buster
R E
RE
Kramer
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000302:Adrenal Cortex / Q000187:drug effects / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000735:Androstenedione / Q000378:metabolism*; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006854:Hydrocortisone / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D013873:Thionucleotides / Q000378:metabolism
D007328:Insulin; D013873:Thionucleotides; D000804:Angiotensin II; D005576:Colforsin; D000735:Androstenedione; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000324:Adrenocorticotropic Hormone; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine; D006854:Hydrocortisone