Phytoconstituents and herbal extracts are known to act through multiple complex pathways, there may be some phytoconstituents which can act through HPA axis leading to down-regulation of corresponding gene/protein.
Toxicol Appl Pharmacol. 2014 Mar 1;275(2):163-75. doi: 10.1016/j.taap.2013.12.015. Epub 2013 Dec 29. Inhibitory effects of herbal constituents on P-glycoprotein in vitro and in vivo: herb-drug interactions mediated via P-gp. Li X1, Hu J2, Wang B3, Sheng L4, Liu Z5, Yang S6, Li Y7.
Drug Metab Rev. 2004 Feb;36(1):57-104. Herbal modulation of P-glycoprotein. Zhou S1, Lim LY, Chowbay B.
HPA (Hypothalamo-pituitary adernal cortex) axis in the body is some thing like akash ganga in the universe of human body. As the name suggests , It starts from bottom of the body means adernal cortex controlling corticosteroids, mineralocorticoids, etc through cortisone-cortisol interconversion system and return back from top hypothalamus-pituitary glands in a negative-positive feedback system..... anyways let me tell you one important thing about herbals....... select polyphenolic compounds with similarity to cortisol and cortisone...they will 100% have the interactions through hydrogen bondings at any receptor or ion channel level in tha HPA axis...... this is the key to HPA system...... Read Bhagyashree's PhD. Thesis for HPA and its inhibitors/activators... all the best!!!!