Intracrine

Intracrine refers to a hormone that acts inside a cell. Steroid hormones act through intracellular (mostly nuclear) receptors and, thus, are considered to be intracrines. In contrast, peptide or protein hormones, in general, act as endocrines, autocrines, or paracrines by binding to their receptors present on the cell surface. Several peptide/protein hormones or their isoforms also act inside the cell through different mechanisms. These peptide/protein hormones, which have intracellular functions, are also called intracrines. The term 'intracrine' is thought to have been coined to represent peptide/protein hormones that also have intracellular actions.

The biological effects produced by intracellular actions are referred as intracrine effects, whereas those produced by binding to cell surface receptors are called endocrine, autocrine, or paracrine effects, depending on the origin of the hormone. The intracrine effect of some of the peptide/protein hormones are similar to their endocrine, autocrine, or paracrine effects; however, these effects are different for some other hormones.

References

Re RN. The intracrine hypothesis and intracellular peptide hormone action. Bioessays. 2003 Apr;25(4):401-9. PMID 12655647.
Re RN. The origins of intracrine hormone action. Am J Med Sci. 2002 Jan;323(1):43-8. PMID 11814142
Kumar R, Singh VP, Baker KM. The intracellular renin-angiotensin system: a new paradigm. Trends Endocrinol Metab. 2007 May 15. doi:10.1016/j.tem.2007.05.001 PMID 17509892.
Fiaschi-Taesch NM, Stewart AF. Minireview: parathyroid hormone-related protein as an intracrine factor--trafficking mechanisms and functional consequences. Endocrinology. 2003 Feb;144(2):407-11. doi:10.1210/en.2002-220818 PMID 12538599.
Sorensen V, Nilsen T, Wiedlocha A. Functional diversity of FGF-2 isoforms by intracellular sorting. Bioessays. 2006 May;28(5):504-14. PMID 16615083.

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