Publisher Summary This chapter focuses on the mechanism of action of adrenocorticotropic hormone (ACTH). The hormone stimulates steroidogenesis by a mechanism involving the synthesis of a protein with a rapid rate of turnover; the level of the protein then determines the rate of steroidogenesis. The experiments described in the chapter show that the inhibition of ACTH action by cycloheximide does not involve the inhibition of a step in the pathway prior to cholesterol but indicates that the antibiotic blocks steroidogenesis by preventing the further transformation of cholesterol in the pathway. The study presented in the chapter also demonstrates how the inhibition of protein synthesis blocked steroidogenesis by preventing the transformation of cholesterol to pregnenolone and the inhibitor had no effect on the other steps of the pathway. The injection of ACTH caused a marked decrease in adrenal cholesterol in association with its metabolism to the steroid hormones.

On the Mechanism of Action of ACTH

Acute adrenocorticotropic hormone stimulation of adrenal corticosteroidogenesis. Discovery of a rapidly induced protein.

Acute stimulation of steroidogenesis in corpus luteum and adrenal cortex by peptide hormones. Rapid induction of a similar protein in both tissues.

Publisher Summary This chapter discusses the aspects of ovarian cholesterol metabolism that appear to be subject to control, directly or indirectly, by gonadotropins. These include lipoprotein uptake, de novo sterol synthesis, intracellular cholesterol transport, mitochondrial cholesterol side chain cleavage, and the synthesis and hydrolysis of cholesteryl esters. The chapter focuses on the corpus luteum as this is the best studied component of the ovary with respect to sterol metabolism. Luteal cells have a unique life cycle; their steroidogenic activity and, therefore, their cholesterol requirements change dramatically as they differentiate from granulosa cells and undergo a period of secretory activity followed by a phase of waning function and structural demise.

Cholesterol metabolism by ovarian tissue.

Stimulation of steroid secretion by antimicrotubular agents.

In cultures of mouse adrenocortical tumor cells (Sato9s minimal deviation Y-1 clonal strain), the acceleration of steroid biosynthesis after exposure to adrenocorticotropic hormone or cyclic adenosine 39,59-monophosphate is maximum within 15 to 60 minutes and precedes any significant increase in labeling of protein with [4,5- 3 H]leucine. However, when cytosol proteins are separated by acrylamidegel electrophoresis, rapid changes in the amount and labeling of several protein fractions are evident in less than 30 minutes and are no longer evident within 60 minutes. This finding supports the proposal that the effects of tropic hormones and their intracellular mediators involve rapid selective effects on protein synthesis.

http://science.sciencemag.org/content/sci/168/3930/483.full.pdf

Adenosine 3',5'-Monophosphate, Adrenocorticotropic Hormone, and Adrenocortical Cytosol Protein Synthesis

When ( 3 H)- or ( 14 C)-labeled nucleosides or nucleotides are dried on solid supports and subsequently counted in a toluene-scintillator system, there is a greater loss of counting efficiency than is indicated by channels ratios or externally standarized quench correction. The resulting inaccuracy suggests that the efficiency of double isotope counting on solid supports is unpredictable.

Marvin F. Grower

Papers

Adenosine 3',5'-Monophosphate, Adrenocorticotropic Hormone, and Adrenocortical Cytosol Protein Synthesis

Local absorption of low energy betas by solid supports: a problem in heterogeneous counting