Defense Date

1976

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Pharmacology & Toxicology

First Advisor

Ronald P. Rubin

Abstract

Studies were carried out on the feline adrenal gland to ascertain the role of prostaglandins in the mechanism of action of ACTH. Using tritiated arachidonic acid as a prostaglandin (PG) precursor , it was demonstrated by column and thin layer chromatography techniques that isolated trypsinized adrenocortical cells possess an active PG synthetase capable of synthesizing radiolabeled PGE, PGF, and PGA/B-like substances. Concentrations of ACTH (125 - 250 μU) which stimulate steroidogenesis enhanced the conversion of radiolabeled arachidonic acid to PGE, PGF and the PGA/B products extracted from cortical cells and incubation media.

PG biosynthesis by isolated cortical cells was studied by radio immunoassay (RIA) using antisera generated against conjugates of PGE2 , PGF and PGF. PGF and PGE2 were identified as the primary PGs released by feline cortical cells, and steroidogenic concentrations of ACTH (50-250 μU) enhanced their release in a dose related manner. Indomethacin (10-5 M) inhibited PG and steroid release, whereas low indomethacin concentrations (10-9 M) potentiated ACTH-evoked PG and steroid release. The steroidogenic response to exogenous PGE2 was not markedly altered by indomethacin. 5 , 8, 11, 14- Eicosatetraynoic acid (ETA) inhibited PGE and PGF release , and elicited a concentration-dependent inhibition of ACTH-induced steroid release. Therefore, there appears to be a functional relationship between PG and steroid release. Such a relationship was further supported by studies on the perfused adrenal gland, which demonstrated that maximal PGF release in response to ACTH preceded the maximal steroidogenic response. Moreover, pregnenolone (3 μM) elicited a 30-fold increase in steroid release from isolated cortical cells but failed to augment PGF and PGE2 release; this study further supports the concept that PG synthesis occurs prior to the steroidogenic response to ACTH.

Cycloheximide did not block the steroidogenic response to pregnenolone, but completely blocked the steroidogenic effects of ACTH. Cycloheximide also depressed basal PGF and PGE2 release , while ACTH-facilitated PG release was not significantly impaired. Thus, the enzymes responsible for increasing PG synthesis are activated rather than formed de novo in response to ACTH.

Three steroidogenic agents, ACTH, an ACTH analogue NPS-ACTH, and monobutyryl cyclic AMP (BCAMP), increased PGF and PGE2 release from isolated adrenocortical cells. Calcium deprivation blocked PG and steroid release evoked by ACTH and NPS-ACTH, but only inhibited PG release elicited by BCAMP without affecting steroid release. These studies suggest a functional role for PGs in the mechanism of action of ACTH. Although the nature of this role remains to be elucidated, it appears to involve some complex interaction with calcium and cyclic nucleotides.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-27-2016

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