Growth hormone (GH), produced and released from the anterior pituitary, controls body growth, carbohydrate-protein-lipid metabolism and water-electrolyte balance. GH release is stimulated by hypothalamic GH-releasing hormone (GHRH) and inhibited by somatostatin. GH secretagogues (GHSs) are synthetic compounds that are potent stimulators of GH release. Recently, GHSs, working through a novel orphan G-protein-coupled receptor (GPCR), the GHS receptor (GHS-R) have emerged as strong regulator of GH release. Until recently, the identity of an endogenous ligand for GHS-R was not known. Ghrelin ('ghre' is the Proto-Indo-European root of the word "grow") has been purified and identified from rat and human stomach as the endogenous ligand for the GHS-R. The rat and human mature Ghrelin (28-aa) are produced from 117 amino acids precursor peptides that have a signal peptide followed by the ghrelin sequence. At the C-terminus of the ghrelin sequence, processing occurs at an uncommon Pro-Arg recognition site. In rat stomach, two isoforms of mRNA for pro-ghrelin are produced from the gene by an alternative splicing. One mRNA encodes the ghrelin precursor, and another encodes a des-Gln14-ghrelin precursor. des-Gln14-ghrelin is identical to ghrelin, except for the deletion of Gln14. This deletion results from the use of the CAG codon, which encodes Gln14 as a splicing signal. The activity of both ghrelins is the same. However, des-Gln14-ghrelin is only present in low amounts in the stomach, indicating that ghrelin is the major active form. Ghrelin has an unusual modification at Ser3 residue that is n-octanoylated and it is essential for biological activity. Ghrelin is the first known example of a bioactive peptide modified by an acyl acid. Rat and human Ghrelin differs in just two amino acids.

There is no structural homology between ghrelin and peptide GHSs (GHRP-6 or hexarelin). Ghrelin has partial sequence homology with motilin. Rat ghrelin is expressed in the stomach, small and large intestines, and brain regions (hypothalamic arcuate nucleus) that are involved the regulation of food intake. Normal adult human plasma samples contain 100-120 fmol Ghrelin/ml. Both ghrelin and GHS-R expression is detected in the heart, suggesting that ghrelin might have some cardiovascular effects. Ghrelin administration stimulates GH secretion but also causes weight gain by increasing food intake and reduction in fat utilization and anti-ghrelin IgG administration suppressed feeding.

GHS-R (rat 364 aa; human 366 aa, ~90% sequence homology) is a receptor for GHRP and non-peptide, low mol wt. secreatgogues (e.g., L692, 429, MK-0677). This receptor is coupled to G-alpha-11 proteins. Two isoforms of GHS-R have been reported: isoform 1a (human 366 aa) and type 1b (289 aa and only 5 TM domains) appears not to bind the ghrelin. GHS-R displays the typical structure of GPCR with TM domains, extracellular N-terminus and intracellular C-terminus. It is expressed in not only in the pituitary and hypothalamus but also in the hippocampus, pancreas, and neuroendocrine tumors, including somatotropinomas and rat GH3 cells.

ADI has produced antibodies to Ghrelin, and GHS-R using peptide sequences specific for each protein. The appropriate control immunogenic peptides are also available to confirm specificity of antibodies. Purified ghrelins (acylated and non-acylated) as well as des-ghrelins are also available for various studies.
 

~CT=near C-terminus; h= Human; m= Mouse; r= Rat; b= Bovine, p=Pig, Ch=chicken

"Neat Antisera" are the unpurified antiserum and it is suitable for ELISA and Western.
"Affinity pure" IgG may be more suitable for immunohistochemical applications and to reduce background in most applications.
"Control peptides" cannot be used for Western as they are very short peptides. They are intended for ELISA or antibody blocking studies to establish antibody specificity.