Small synthetic molecules called growth-hormone secretagogues (GHSs) stimulate the release of growth hormone (GH) from the pituitary. They act through GHS-R, a G-protein-coupled receptor for which the ligand is unknown. Recent cloning of GHS-R strongly suggests that an endogenous ligand for the receptor does exist and that there is a mechanism for regulating GH release that is distinct from its regulation by hypothalamic growth-hormone-releasing hormone (GHRH). We now report the purification and identification in rat stomach of an endogenous ligand specific for GHS-R. The purified ligand is a peptide of 28 amino acids, in which the serine 3 residue is n-octanoylated. The acylated peptide specifically releases GH both in vivo and in vitro, and O-n-octanoylation at serine 3 is essential for the activity. We designate the GH-releasing peptide 'ghrelin' (ghre is the Proto-Indo-European root of the word 'grow'). Human ghrelin is homologous to rat ghrelin apart from two amino acids. The occurrence of ghrelin in both rat and human indicates that GH release from the pituitary may be regulated not only by hypothalamic GHRH, but also by ghrelin.

Ghrelin is a growth-hormone-releasing acylated peptide from stomach.

Small synthetic molecules called growth hormone secretagogues (GHSs) stimulate the release of growth hormone (GH) from the pituitary. They act through the GHS-R, a G protein-coupled receptor whose ligand has only been discovered recently. Using a reverse pharmacology paradigm with a stable cell line expressing GHS-R, we purified an endogenous ligand for GHS-R from rat stomach and named it "ghrelin," after a word root ("ghre") in Proto-Indo-European languages meaning "grow." Ghrelin is a peptide hormone in which the third amino acid, usually a serine but in some species a threonine, is modified by a fatty acid; this modification is essential for ghrelin's activity. The discovery of ghrelin indicates that the release of GH from the pituitary might be regulated not only by hypothalamic GH-releasing hormone, but also by ghrelin derived from the stomach. In addition, ghrelin stimulates appetite by acting on the hypothalamic arcuate nucleus, a region known to control food intake. Ghrelin is orexigenic; it is secreted from the stomach and circulates in the bloodstream under fasting conditions, indicating that it transmits a hunger signal from the periphery to the central nervous system. Taking into account all these activities, ghrelin plays important roles for maintaining GH release and energy homeostasis in vertebrates.

https://www.physiology.org/doi/pdf/10.1152/physrev.00012.2004

Ghrelin: Structure and Function

The family of voltage-gated sodium channels initiates action potentials in all types of excitable cells. Nine members of the voltage-gated sodium channel family have been characterized in mammals, and a 10th member has been recognized as a related protein. These distinct sodium channels have similar structural and functional properties, but they initiate action potentials in different cell types and have distinct regulatory and pharmacological properties. This article presents the molecular relationships and physiological roles of these sodium channel proteins and provides comprehensive information on their molecular, genetic, physiological, and pharmacological properties.

https://pharmrev.aspetjournals.org/content/pharmrev/57/4/411.full.pdf

International Union of Pharmacology. XLVIII. Nomenclature and Structure-Function Relationships of Voltage-Gated Calcium Channels

The structure

Ghrelin is a peptide predominantly produced by the stomach. Ghrelin displays strong GH-releasing activity. This activity is mediated by the activation of the so-called GH secretagogue receptor type 1a. This receptor had been shown to be specific for a family of synthetic, peptidyl and nonpeptidyl GH secretagogues. Apart from a potent GH-releasing action, ghrelin has other activities including stimulation of lactotroph and corticotroph function, influence on the pituitary gonadal axis, stimulation of appetite, control of energy balance, influence on sleep and behavior, control of gastric motility and acid secretion, and influence on pancreatic exocrine and endocrine function as well as on glucose metabolism. Cardiovascular actions and modulation of proliferation of neoplastic cells, as well as of the immune system, are other actions of ghrelin. Therefore, we consider ghrelin a gastrointestinal peptide contributing to the regulation of diverse functions of the gut-brain axis. So, there is indeed a possibility that ghrelin analogs, acting as either agonists or antagonists, might have clinical impact.

/pdf/biological-physiological-pathophysiological-and-k7otyeslc1.pdf

Biological, physiological, pathophysiological, and pharmacological aspects of ghrelin.

The mechanism by which GH-releasing peptides elicit GH secretion has remained largely unknown. In this study, the effects of a second generation GH-releasing peptide, Ala-His-D-beta Nal-Ala-Trp-D-Phe-Lys-NH2(GHRP-1), on cAMP, intracellular Ca2+ ([Ca2+]i), and GH release were examined using rat pituitary gland static monolayer cell cultures. It was found that GHRP-1 increased GH release in a dose-dependent manner up to 3-fold, while having no effect on cAMP levels. In contrast, simultaneous elevations of cAMP and GH were observed after treatment with GHRH. To further define the underlying mechanism of GHRP-1-mediated GH release, its effect on [Ca2+]i was determined using a fluorescent Ca2+ indicator, fura-2. GHRP-1 dose dependently increased [Ca2+]i up to 45.5 nM +/- 5.6 nM. A similar elevation of [Ca2+]i was observed after GHRH treatment. Similar to GHRH, GHRP-1-induced increases in [Ca2+]i and GH release were inhibited by somatostatin. Furthermore, the GHRP-1-induced increases in [Ca2+]i and GH were also suppressed by nifedipine. The interaction between the voltage-dependent Ca2+ channels and GHRP-1 was investigated in cells maximally stimulated by KCl. The addition of GHRP-1 had no effect on the KCl-stimulated GH release. To investigate the possible interaction between the adenylyl cyclase pathway and GHRP-1, cells were maximally stimulated with forskolin or (Bu)2cAMP. Addition of GHRP-1 stimulated GH release beyond that observed using cAMP elevating agents. Similar results were obtained in the presence of a protein kinase C, 4 beta-phorbol 12-myristate 13-acetate (PMA). The GHRP-1-stimulated GH release was additive to that observed with PMA stimulation. Based on these findings, it was concluded that 1) GHRP-1 treatment leads to an increase in [Ca2+]i; 2) unlike GHRH, GHRP-1 releases GH via a Ca(2+)-dependent, cAMP-independent mechanism; 3) GHRP-1-induced increases in [Ca2+]i and GH release are sensitive to somatostatin inhibition; and 4) cAMP-elevating agents and PMA have an additive effect on the GHRP-1-stimulated GH release, indicating these agents stimulate GH release via a mechanism separate from that of GHRP-1.

Mechanisms of action of a second generation growth hormone-releasing peptide (Ala-His-D-beta Nal-Ala-Trp-D-Phe-Lys-NH2) in rat anterior pituitary cells.

Multiple receptor regulation of cyclic nucleotides in rat pinealocytes.

In this study, the effect of cGMP on the dihydropyridine-sensitive (L- type) Ca2+ current was investigated using the whole cell version of the patch-clamp technique in rat pinealocytes Dibutyryl-cGMP (1 x 10(-4) M) induced a pronounced inhibition of the L-type Ca2+ channel current The dibutyryl-cGMP effect was concentration dependent Elevation of cGMP by nitroprusside had a similar inhibitory action on the L-type Ca2+ channel current Norepinephrine, which increased cGMP in rat pinealocytes, also inhibited this current The action of cGMP was independent of cAMP elevation since the cAMP antagonist, Rp-cAMPs, had no effect on the inhibitory action of dibutyryl-cGMP The involvement of cyclic GMP-dependent protein kinase was suggested by the blocking action of two protein kinase inhibitors, (1-(5-isoquinolinesulfonyl)-2- methylpiperazine (H7) and N-(2-guanidinoethyl)-5- isoquinolinesulfonamide (HA1004), on the dibutyryl-cGMP effect on the L- type Ca2+ channel current Taken together, these results suggest that (1) cGMP modulates L-type Ca2+ channel currents in rat pinealocytes, causing inhibition of this current; (2) the action of cGMP appears to be independent of cAMP elevation; and (3) phosphorylation by cGMP- dependent protein kinase may be involved

https://www.jneurosci.org/content/jneuro/15/4/3104.full.pdf

cGMP inhibits L-type Ca2+ channel currents through protein phosphorylation in rat pinealocytes.

alpha 1-Adrenergic agonists have recently been found to potentiate vasoactive intestinal peptide (VIP) stimulation of rat pinealocyte cAMP and cGMP. alpha 1-Adrenergic agonists also elevate pineal intracellular Ca2+ [( Ca2+]i) and activate protein kinase-C. In the present study, the possible involvement of Ca2+ and protein kinase-C in the alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP accumulation was examined with agents that alter [Ca2+]i or activate protein kinase-C. It was found that treatment with a Ca2+ chelator or with inorganic Ca2+ channel blockers inhibited alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP responses. Increasing [Ca2+]i by treatment with A23187, ouabain, or K+ potentiated VIP stimulation of cAMP and cGMP response. These observations indicate that Ca2+ mediates the alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP accumulation, as is true for the alpha 1-adrenergic potentiation of beta-adrenergic stimulated cAMP and cGMP accumulation. Activators of protein kinase-C mimicked the large effect alpha 1-adrenergic agonists have on cAMP accumulation in VIP-treated pinealocytes and had a small effect on cGMP accumulation in VIP-treated cells. These effects were not blocked by the Ca2+ chelator EGTA. However, the effects of a protein kinase-C activator on the cGMP response in VIP-stimulated cells were amplified by K+ (15 mM) or ouabain (1 microM), presumably through an action causing an increase in [Ca2+]i. These results suggest protein kinase-C is involved in the alpha 1-adrenergic potentiation of VIP-stimulated cAMP accumulation, as is the case for the alpha 1-adrenergic potentiation of beta-adrenergic stimulated cAMP. Protein kinase-C is also involved in cGMP accumulation, provided that there is a modest increase in [Ca2+]i.

α1-Adrenergic Potentiation of Vasoactive Intestinal Peptide Stimulation of Rat Pinealocyte Adenosine 3′,5′-Monophosphate and Guanosine 3′,5′- Monophosphate: Evidence for a Role of Calcium and Protein Kinase-C

The effect of pituitary adenylate cyclase activating polypeptide (PACAP) on the L-type Ca2+ channel current (L-channel current) was studied in smooth muscle cells prepared from the rat tail artery. PACAP caused an increase in the amplitude of the L-channel current. The maximal increase (56%) occurred at a PACAP concentration of 1 x 10(-8) M; higher concentrations resulted in a smaller increase. Investigation into the intracellular mechanisms of PACAP action revealed that the increase in L-channel currents was blocked by calphostin C and bisindolylmaleimide IV [protein kinase C (PKC) inhibitors] and mimicked by 4 beta-phorbol 12-myristate 13-acetate (PMA), an activator of PKC. PACAP was also found to cause translocation of PKC, suggesting that the increase in the current by PACAP was due to PKC. In contrast, activation of cAMP-dependent protein kinase (PKA) by 8-bromo-cAMP caused an inhibition of the L-channel current. A high concentration of PACAP (1 x 10(-6) M) had no effect on the L-channel current. The...

Anthony K. Ho

Papers

Mechanisms of action of a second generation growth hormone-releasing peptide (Ala-His-D-beta Nal-Ala-Trp-D-Phe-Lys-NH2) in rat anterior pituitary cells.

Multiple receptor regulation of cyclic nucleotides in rat pinealocytes.

cGMP inhibits L-type Ca2+ channel currents through protein phosphorylation in rat pinealocytes.

α1-Adrenergic Potentiation of Vasoactive Intestinal Peptide Stimulation of Rat Pinealocyte Adenosine 3′,5′-Monophosphate and Guanosine 3′,5′- Monophosphate: Evidence for a Role of Calcium and Protein Kinase-C

PACAP modulates L-type Ca2+ channel currents in vascular smooth muscle cells: involvement of PKC and PKA.