Page 61 - Anatomy and Physiology of Farm Animals, 8th Edition

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Lipophilic hormone
VetBooks.ir Diffusion Extracellular fluid

Nucleus Target cell

Proteins
DNA
Nuclear
receptor

Ribosome
Cytoplasmic mRNA
receptor Hormone
receptor Hormone mRNA
complex response
element Nuclear envelope

Nuclear pore

Figure 2-19. Lipophilic ligands, such as steroid hormones, interact with intracellular receptors in
target cells. After the hormone binds to the receptor in either the cytoplasm or the nucleus it often dimerizes
(not shown) and the hormone receptor complex (HRC) binds to the hormone response element (HRE) in
the promoter region of the DNA. The HRC–HRE interaction can activate or inhibit gene transcription.
In this figure, it has activated gene transcription, formation of mRNA, and protein synthesis. Source:
adapted from Guyton and Hall, 2006. Reproduced with permission from Elsevier.

G protein subunits with the GPCR will activation is a common sequela of both Gα ‐
s
determine the biological effect of ligand bind­ and Gα ‐associated receptor‐ligand bind­
q
ing on second messengers. If the receptor is ing. Protein kinase A (PKA) is the cAMP
associated with a Gα subunit, the effect dependent kinase whose activity follows
i
will be a decrease in adenylyl cycle activity; cAMP availability within the cell, and protein
conversely, a Gα ‐associated GPCR will kinase C (PKC) is activated by DAG. Kinase
s
increase adenylyl cyclase activity, thus either activity after LR binding is responsible for
increasing or decreasing the formation of much of the diversity in signal transduction
cAMP within the cell (Fig. 2‐18). Alternatively, within the cell, as well as terminating the
GPCRs that interact with Gα ‐associated G signal. Examples of hormones that utilize
q
proteins will initiate the activation of phos­ GPCRs include all protein and peptide hor­
pholipase C (PLC) on the interior of the plasma mones (excluding parathyroid hormone,
membrane. PLC hydrolyzes phosphatidy­ glucagon, and luteinizing hormone), modi­
linositol 4,5‐bisphosphate (PIP ) into two fied fatty acid derived hormones (excluding
2
second messengers: inositol 1,4,5‐trisphos- prostaglandins), and some amino acid
phate (IP ) and diacylglycerol (DAG). IP derived hormones (excluding epinephrine)
3
3
will result in the release of calcium from These hormones are reviewed in depth in
the smooth endoplasmic reticulum. Kinase Chapter 13.