# Ghrelin and obestatin: energy balance and circadian rhythms

- Canonical: https://nutrifit.health/knowledge/ghrelin-obestatin-energy-homeostasis-circadian
- Language: en
- Published: 2026-10-08T18:31:00.844Z
- Updated: 2026-10-08T18:31:00.844Z
- Author: NutriFit Editorial

> GHRL peptide maturation, GOAT and GHSR, neural appetite pathways, sleep, and meal timing. Primary findings and limits of obestatin and experimental-treatment hypotheses.

Ghrelin connects the digestive system's state with growth hormone release, food seeking, and neural energy regulation. Calling it the hunger hormone is useful shorthand but does not explain its acylated and unacylated forms, sampling problems, or interactions with other signals. Cholecystokinin, PYY, GLP-1, and oxyntomodulin contribute to satiation; ghrelin participates in this network rather than determining every meal on its own.

Howard and colleagues described the growth hormone secretagogue receptor in 1996; Kojima and colleagues isolated its natural acylated ligand from the stomach in 1999. In 2005, Zhang and colleagues proposed another GHRL-derived peptide, obestatin, as an opposing regulator of food intake. Their subsequent history illustrates why reproducibility, animal species, and clinical endpoints matter alongside molecular mechanisms. Adaptation to energy shortage remains a central context for ghrelin, but this axis alone does not explain contemporary obesity.

## One precursor, distinct products

Human GHRL lies in chromosome region 3p25.3. Canonical preproghrelin contains 117 amino acids. Removing its 23-residue signal peptide leaves 94-residue proghrelin. Alternative splicing produces other transcripts, so this sequence cannot be assigned indiscriminately to every product of the locus. The signal peptide directs the nascent protein into the secretory pathway through the endoplasmic reticulum, ER.

$$
117\ \text{preproghrelin residues}-23\ \text{signal residues}=94\ \text{proghrelin residues}.
$$

The N-terminal region yields mature, 28-residue ghrelin. PC1/3, encoded by PCSK1, has direct experimental support as a processing endoprotease: PC1/3-deficient mice showed impaired production of mature ghrelin in the stomach. The same study showed that acylation did not require completed proteolytic processing (Zhu et al., 2006). An obligatory sequence of “release mature ghrelin first, then GOAT acts” is therefore misleading. PC2 and carboxypeptidase E should not be given equally established roles in every human compartment. Rat proghrelin length in that experiment also differs from the human precursor.

| Product of the canonical human precursor | Sequence and structural feature | Interpretation |
|---|---|---|
| Ghrelin, 28 residues | GSSFLSPEHQRVQQRKESKKPPAKLQPR; Ser3 carries an O-acyl group in AG | Acylation is necessary for conventional high-affinity GHSR-1a activation |
| Unacylated ghrelin, UAG or des-acyl | The same sequence without the Ser3 acyl group | Not a conventional GHSR-1a agonist, but not necessarily biologically inert |
| Obestatin, 23 residues | FNAPFDVGIKLSGVQYQQHSQAL–NH₂ | C-terminal amidation and the species-specific sequence matter experimentally |

The obestatin segment lies in the precursor's C-terminal region, commonly numbered 76–98 in human preproghrelin. Rodent sequences differ, so experiments using a synthetic mouse peptide do not test an identical human molecule. C-terminal amidation uses a glycine-extended substrate and PAM. Its sequential reactions require copper, oxygen, and reducing support, including ascorbate. This describes amidated-peptide biosynthesis; it does not establish that vitamin C supplementation increases beneficial obestatin effects. Immunoreactivity also needs to be distinguished from confirmed mature peptide and precursor fragments.

[![Human GHRL precursor maturation:117−23=94, GOAT/Ser3 before PC1/3,28-residue ghrelin and a separate C-terminal obestatin branch; schematic, not atomic structure.](https://api.nutrifit.health/api/v2/public/knowledge/files/images/nutrifit-scientific-20261002-ghrelin-obestatin-energy-homeostasis-circadian-maturation-en-v1.png)](https://api.nutrifit.health/api/v2/public/knowledge/files/images/nutrifit-scientific-20261002-ghrelin-obestatin-energy-homeostasis-circadian-maturation-en-v1.png)

The main source of circulating ghrelin is endocrine cells in the gastric oxyntic mucosa, especially the body and fundus. X/A-like cells is the usual rodent designation; P/D1 cells is used in humans. Many gastric cells are closed-type cells without direct luminal contact; open-type endocrine cells also occur in the intestine. Nutrients may therefore change secretion through metabolic, paracrine, and neural signals, rather than contacting every secretory cell directly.

Sympathetic β₁-adrenergic input, somatostatin, insulin, and substrate availability participate in regulation, with response direction and magnitude depending on the model. Ghrelin is also detected in intestine and pancreatic ε-cells, particularly during development. Reports from other tissues require attention to methods and low concentrations. Central ghrelin synthesis remains disputed: receptor expression in the brain does not demonstrate abundant local production. A fixed gastric contribution such as 70–80% is not transferable to every state and assay.

## GOAT: an acyl group changes recognition

In 2008, independent studies by Yang and Gutierrez identified MBOAT4, ghrelin O-acyltransferase, GOAT. This integral membrane MBOAT-family enzyme operates within the secretory pathway. It transfers an acyl group from acyl-CoA onto the Ser3 hydroxyl, forming an ester bond. The principal recognized human acyl-ghrelin species carries octanoyl, C8; other acyl variants have also been described.

$$
\mathrm{Ghrelin\!-!Ser3\!-!OH+octanoyl\!-!CoA}
\xrightarrow{\mathrm{GOAT}}
\mathrm{Ghrelin\!-!Ser3\!-!O\!-!CO\!-!(CH_2)_6\!-!CH_3+CoA\!-!SH}.
$$

This equation represents group transfer, not an obligatory reaction on an already released 28-residue peptide. Precursor modification can precede completed maturation. Octanoic acid must be available in an activated form. Dietary medium-chain lipids can affect substrate availability, but this does not establish MCT as a universal appetite-control method. An obligatory, specific role for ACSF2 is not established here. Comparing C6, C8, and C10 depends on substrate and assay conditions: C8 predominance in blood does not prove that GOAT always has its lowest Km for C8 in vitro.

Taylor and colleagues' 2013 topology work supports 11 transmembrane helices and one reentrant loop. In that model, conserved His338 is on the luminal side, whereas Asn307 is on the cytoplasmic side. Placing both together in the ER lumen as a demonstrated simple catalytic dyad is incorrect. How the enzyme connects acyl-CoA and peptide availability through its membrane architecture is investigated using topology, mutagenesis, and structural models. A schematic is not an experimentally resolved atomic structure.

Acyl-ghrelin, AG, effectively activates GHSR-1a. UAG lacks the same conventional agonist activity, but studies describe GHSR-independent effects on metabolism, cell survival, and vascular responses. Their receptor basis and physiological significance remain incompletely understood. “Inactive waste” is as misleading as declaring UAG a proven therapeutic antagonist of AG.

Unacylated immunoreactivity often predominates in plasma, but 10–20% AG and 80–90% UAG are not immutable physiological constants. The ester linkage is unstable: temperature, processing delay, acidification, esterase inhibitors, and antibody specificity affect results. Butyrylcholinesterase and other hydrolases have been studied in deacylation. One fixed decay rate or half-life across methods, doses, and physiological states is unjustified. Comparisons require consistently handled samples and explicit identification of AG, UAG, or total ghrelin.

## GHSR: structure, basal activity, and signaling

GHSR lies in region 3q26.31. Full-length GHSR-1a contains 366 amino acids and seven transmembrane helices. The approximately 289-residue splice variant GHSR-1b retains five helices and is not a conventional independently functioning ghrelin receptor. Coexpression can alter GHSR-1a trafficking or signaling in model systems; describing it as a universal dominant inhibitor in every tissue goes beyond that evidence.

Structures explain how the peptide and lipid portions participate in recognition. 6KO5 represents an antagonist-bound receptor (Shiimura et al., 2020); 7NA7 a ghrelin–receptor–Gi complex (Liu et al., 2021); and 7F9Y a ghrelin-bound Gq complex (Wang et al., 2021). The latter paper's correct DOI ends in 25364-2, rather than 25368-2. Prepared and stabilized complexes reveal important states, but are not snapshots of every natural receptor configuration inside a living neuron.

In Liu and colleagues' structure, the E124³·³³–R283⁶·⁵⁵ salt bridge separates two pocket regions: the N-terminal peptide occupies one, and the octanoyl chain the other. Hydrophobic contacts near I178⁴·⁶⁰, L181⁴·⁶³, and F286⁶·⁵⁸ explain the lipid group's contribution. Activation-related rearrangements of an aromatic cluster and TM6 open the intracellular region for G-protein engagement. Superscript positions use a common GPCR numbering system and must not be confused with human sequence positions. Not every part of the flexible peptide has equally precise coordinates; a helix displacement measured in one complex is not a universal distance for all states.

GHSR-1a has substantial constitutive activity: signaling can occur without added ghrelin. In overexpression systems it can reach a sizeable fraction of maximal response, sometimes around half, but this does not measure “50% hunger” in humans. Receptor density, coupling, and cellular environment influence basal signaling. A neutral antagonist limits agonist action without necessarily suppressing constitutive activity. An inverse agonist reduces basal activity relative to a specified assay. Neither term means that every receptor function is completely switched off. The endogenous peptide LEAP2 also interacts with the axis as an antagonist and inverse agonist in investigated systems.

Pantel and colleagues described A204E in two families. It lies in the second extracellular loop, rather than TM5. Reduced cell-surface expression and loss of constitutive signaling with preserved ghrelin responsiveness were associated with short stature and incomplete penetrance. This does not establish a severe growth-and-puberty syndrome in every carrier. An unsupported additional F279L example should not be presented as an equally established familial diagnosis.

Gq/11 activates phospholipase Cβ, which hydrolyzes membrane PIP₂ to IP₃ and DAG:

$$
\mathrm{PIP_2+H_2O}\xrightarrow{\mathrm{PLC\beta}}\mathrm{IP_3+DAG}.
$$

IP₃ opens its ER channels and increases cytosolic Ca²⁺; DAG and calcium participate in PKC activation. Calcium-dependent kinases, altered ion currents, and secretion can follow. GHSR can also couple to Gi/o, affect cAMP, recruit β-arrestins, and redistribute internally. ERK and Akt responses depend on cellular context; every branch need not activate simultaneously in every tissue. Studies of GHSR–DRD2, GHSR–MC3R, and GHSR–CB1 heteromers reveal additional interactions in specific cellular and animal models (Kern, 2012; Rediger, 2011; Lillo, 2021), rather than a universal receptor mechanism for food addiction.

## From stomach to hypothalamus, pituitary, and reward circuits

Access of peripheral signals to the brain depends on the blood–brain barrier, specialized vascular regions, and neural routes. The median eminence next to the arcuate nucleus contains fenestrated capillaries; tanycytes and nutritional state can affect local access. Vagal afferents may contribute. AG should not be depicted as freely crossing the entire barrier, nor UAG as always having the opposite transport pattern. Species, direction of transport, and experimental models matter.

An important arcuate target is the orexigenic NPY/AgRP population, many of whose neurons release GABA. Ghrelin increases activity and changes synaptic organization (Cowley et al., 2003). NPY acts through receptors including Y1/Y5. AgRP opposes melanocortin signaling, including antagonism and inverse agonism at MC4R. GABA can inhibit POMC neurons. POMC yields α-MSH, which activates melanocortin receptors and contributes to satiation. Synaptic inhibition must not be portrayed as an immediate cessation of all POMC synthesis and processing.

[![Acyl-ghrelin/GHSR/NPY-AgRP-GABA pathways, separate inhibition of POMC and MC4R, food seeking,VTA/NAc and GH; sleep, circadian phase and meals as context.](https://api.nutrifit.health/api/v2/public/knowledge/files/images/nutrifit-scientific-20261002-ghrelin-obestatin-energy-homeostasis-circadian-integration-en-v1.png)](https://api.nutrifit.health/api/v2/public/knowledge/files/images/nutrifit-scientific-20261002-ghrelin-obestatin-energy-homeostasis-circadian-integration-en-v1.png)

A metabolic mechanism involving CaMKKβ, AMPK, ACC, malonyl-CoA, CPT1, and UCP2 has been investigated in NPY/AgRP neurons. AMPK activation promotes phosphorylation that reduces ACC activity. Lower malonyl-CoA relieves CPT1 inhibition and favors fatty-acid oxidation. UCP2 participates in mitochondrial redox control and sustained neuronal activation in Andrews and colleagues' 2008 experimental model:

$$
\mathrm{AMPK}\uparrow\ \Rightarrow\ \mathrm{ACC\ activity}\downarrow\ \Rightarrow\ \mathrm{malonyl\!-!CoA}\downarrow\ \Rightarrow\ \mathrm{CPT1\ inhibition}\downarrow.
$$

This is a qualitative directional scheme, not a rate equation or proof that ghrelin accelerates whole-body fat burning. Neuronal metabolism can support feeding, while chronic ghrelin administration increases fat mass in animal experiments. [CPT1 and fatty-acid transport](/knowledge/carnitine-palmitoyltransferase-cpt1-fatty-acid-oxidation) clarify malonyl-CoA's role and why tissue consequences differ. CREB and FoxO1 participate in expression regulation but cannot be collapsed into one immutable linear cascade. A universal voltage shift from −55 to −40 mV, a 90% neuronal response, and an obligatory TRPC5 role should not be imported from different systems without direct verification.

Ghrelin and leptin, with broadly opposing energy signals, converge on several neuronal populations. [Leptin, hypothalamic inflammation, and POMC](/knowledge/leptin-resistance-hypothalamic-inflammation-pomc) explain why receptor availability and energy balance cannot be inferred from one ghrelin measurement. Pituitary somatotrophs respond with increased GH secretion, interacting with GHRH and somatostatin. During energy shortage the axis helps regulate fuel and glucose availability; it does not guarantee muscle preservation under every fasting condition.

GHSR in the ventral tegmental area links the signal with dopamine circuits and projections to the nucleus accumbens. Abizaid and colleagues (2006) demonstrated altered dopamine-neuron activity and synaptic inputs experimentally. This helps explain a motivational component of food seeking but does not make ghrelin the sole cause of sweet cravings or addiction. Imaging and animal models examine different levels of response, and an enhanced reward signal does not make behavior inevitable.

## What remains of the obestatin hypothesis

Zhang and colleagues' initial 2005 report linked obestatin with reduced food intake, slower motility, and GPR39. Subsequent experiments did not consistently reproduce the combined findings. Holst and colleagues (2007) demonstrated GPR39 activation by zinc ions, but not obestatin, in the tested systems. Depicting two equally established, opposing hormones from one gene is therefore misleading. Nevertheless, uncertainty about the receptor and anorexigenic effect does not establish that the peptide has no biological activity.

Granata and colleagues (2008) reported survival effects in β-cells and human islets, Akt/ERK changes, and expression of genes related to β-cell mass and function. Findings involving PDX1, GLP-1R, and transporter programs belong to their particular systems. GLUT2 should not be declared the universal main glucose transporter of human β-cells by analogy with rodents. Cell-culture protection does not establish restoration of β-cell mass or diabetes treatment in patients.

Muscle-regeneration studies examined satellite cells, proliferation, differentiation, Pax7, MyoD, myogenin, and ERK, Akt, and p38 pathways (Gurriarán-Rodríguez et al., 2012). Their obestatin/GPR39 model must be described alongside the disputed identification of the direct receptor. It is inconsistent to declare the ligand relationship definitively disproven while presenting the same receptor as settled in muscle. Changes in injured animal muscle do not supply a clinical obestatin-administration protocol.

Endothelial models have investigated NO-dependent responses, angiogenesis, and inflammatory or adhesion markers. These are preclinical directions rather than established atherosclerosis prevention. Circulating ghrelin/obestatin ratios have been discussed in obesity and fatty liver disease, but depend on assays, ghrelin form, and feeding state. No universally validated ratio diagnoses MASLD, selects treatment, or determines “metabolic age.”

## Premeal peaks and internal clocks are distinct

Cummings and colleagues' 2001 human study found total ghrelin rising before meals and falling afterwards. This supports a relationship with meal initiation; it does not establish that every AG peak appears 60–90 minutes beforehand or that ghrelin must initiate every meal. Learned schedules, anticipation, fasting, and the previous meal's size interact. Meal-induced suppression involves more than filling the stomach.

Daily organization includes the suprachiasmatic nucleus, light input, and peripheral clocks. CLOCK/BMAL1 and PER/CRY feedback loops participate in cellular rhythms, while feeding also synchronizes peripheral processes. Food-anticipatory rhythms in animals do not require a single identified “hunger clock”; distributed oscillators are discussed. They cannot be equated completely with the SCN or one gastric gene.

By experimentally separating behavior and circadian phase, Scheer and colleagues (2013) identified an endogenous evening maximum in subjective hunger. That is not a demonstrated universal ghrelin curve with a nighttime minimum. Ghrelin can rise during sleep, and meal timing and sampling alter the profile. [Melatonin and circadian organization](/knowledge/melatonin-mitochondria-circadian-receptors) explain light-related synchronization; melatonin is not a direct ghrelin substitute or guaranteed appetite suppressant.

## Nutrients, sleep, and altered-appetite states

Foster-Schubert and colleagues (2008) measured acyl and total ghrelin separately after nutrient loads. Protein produced strong suppression, lipids weaker suppression, and carbohydrates a biphasic response. Blom and colleagues (2006) also studied a high-protein breakfast. These findings inform discussion of meal composition, but do not promise 70–80% AG suppression for 3–5 hours with every protein food. Liquid loads, mixed meals, energy content, age, and glucose regulation alter applicability.

Specific nutrient-load experiments do not support a simple ranking in which complex carbohydrate always suppresses ghrelin better than fat. A rapid hormonal decline does not necessarily indicate lasting satiation; recovery of the value does not mean a diet has failed. GLP-1, CCK, PYY, mechanoreception, taste, and overall energy balance have their own contributions.

Spiegel and colleagues' small controlled 2004 experiment compared short periods of sleep restriction and extension in 12 young men. Restriction was followed by increased ghrelin, decreased leptin, and greater hunger. Taheri and colleagues' 2004 work examined population associations rather than the same intervention. These findings cannot become a rule that every night shorter than six hours raises AG by 25% and adds 350–500 kcal. Later results depend on food access, energy balance, sex, intervention duration, and assay. Sleep loss can increase intake without a reproducible mandatory change in one hormone.

In that crossover experiment, average ghrelin rose 28%, leptin fell 18%, subjective hunger rose 24%, and appetite 23%. If G and L denote the corresponding ghrelin and leptin levels, a hypothetical ratio of changes in averages gives the arithmetic below. It is not the mean of individual ratios, a validated index, or a prediction for each person:

$$
\frac{1.28G/(0.82L)}{G/L}-1=\frac{1.28}{0.82}-1\approx0.561\quad(56.1\%).
$$

In common obesity, fasting total ghrelin is often lower, even though appetite is not necessarily reduced. This exposes the limits of a single-factor model. Postmeal suppression, AG/UAG balance, and responses to weight loss vary. Ghrelin resistance in a particular animal model is not automatically an established human diagnosis. After diet-induced weight loss, levels may increase as part of adaptation favoring regain (Cummings et al., 2002).

Prader–Willi syndrome involves loss of paternal gene expression in 15q11–q13. Early studies found elevated circulating ghrelin (Cummings, 2002; DelParigi, 2002), and high levels can precede marked hyperphagia. This is a distinctive genetic setting with multifactorial impaired satiation. A fixed three-to-fivefold AG increase should not be called the sole cause, nor has neutralizing ghrelin already been proven to eliminate clinical hyperphagia.

| Observation | Supported interpretation | Unsupported leap |
|---|---|---|
| Rise before habitual meals | Ghrelin participates in anticipation and meal initiation | All hunger has one hormonal cause |
| Protein changes postmeal profiles | Nutrient composition affects response | One preload guarantees the same calorie reduction |
| Short sleep changes hormones experimentally | Sleep and energy signals interact | The same percentage applies to every person and night |
| High ghrelin in Prader–Willi syndrome | The axis warrants investigation in this genetic condition | Causality and effective treatment are established |
| Obestatin acts in culture | A cellular hypothesis merits further study | Tissue restoration in patients is demonstrated |

## Surgery and experimental interventions

Sleeve gastrectomy removes much of the fundus and body, which contain many ghrelin cells, and often reduces circulating ghrelin. It does not guarantee a 70–85% reduction in each patient, complete disappearance of peaks, or loss of food pleasure. Roux-en-Y creates a small proximal gastric pouch while leaving an excluded gastric remnant. The fundus is not simply removed or represented by one small “blind pouch.” Ghrelin changes after bypass vary; GLP-1, PYY, bile acids, neural signals, anatomy, and eating behavior also contribute (Cummings, 2002; Karamanakos, 2008).

| Experimental intervention point | What was investigated | What it does not establish |
|---|---|---|
| GOAT | GO-CoA-Tat, a bisubstrate analogue with a cell-penetrating component; glucose and weight effects in mice (Barnett, 2010) | A safe, ready-to-use oral protocol for humans |
| GHSR | Antagonists including JMV2959 and inverse agonists; food and alcohol responses in models (Jerlhag, 2009) | Treatment of every addiction, complete elimination of hunger, or superiority of every inverse agonist |
| Circulating ghrelin | L-RNA Spiegelmer NOX-B11 and derivatives; neutralization of administered ghrelin in animals (Kobelt, 2006) | Successful human gastroparesis treatment with this compound |

JMV2959 should be described as an investigated antagonist, not assumed neutral in every functional assay or arbitrarily classified as a peptide. Jerlhag's study examined alcohol reward; other substances require their own evidence. The unverified designation K-8794 does not establish a recognized drug. Structural work and experimental compounds instead help distinguish affinity, functional efficacy, tissue access, and clinical outcomes.

A particularly consequential error concerns aptamer identity. Lexaptepid pegol is NOX-H94 and targets hepcidin, as the official NCI dictionary confirms. It is not NOX-B11-2 and does not neutralize ghrelin under that name. Anti-ghrelin NOX-B11 blocked certain responses to administered ghrelin in rats; this does not demonstrate treatment of diabetic gastroparesis. Ghrelin-receptor agonists and blockers act in different directions, so trials of motility stimulation cannot validate an antagonist's efficacy.

## Practical interpretation and evidence limits

Protein-containing meals can support satiation, but a universal 25–35 g preload 25–35 minutes before eating, guaranteeing 20–30% lower subsequent intake, is not established. Added energy, tolerance, the whole diet, and clinical context matter. Ghrelin suppression is an intermediate measurement that cannot substitute for actual intake and weight outcomes.

Viscous fiber alters consistency, distension, emptying, and nutrient availability. Vagal afferents and the nucleus tractus solitarius participate in mechanosensory integration, but this does not prove a universal direct inhibitory chain to gastric ghrelin cells. Karhunen and colleagues' 2010 psyllium-enriched meal attenuated several postmeal peptide responses; the study cannot support invariably deeper and longer ghrelin suppression. Fixed water-binding capacity depends on product and method. Water and tolerance matter when using these fibers, rather than an invented hormonal dose.

Jakubowicz and colleagues (2013) compared energy allocation between breakfast and dinner in a specific group of women with metabolic syndrome. Garaulet and colleagues (2013) investigated meal timing and weight-loss effectiveness observationally. These distinct designs do not establish that everyone needs 60–70% of energy before midday, that skipping breakfast causes night-eating syndrome, or that morning meals eliminate evening hunger. Schedules should be assessed alongside sleep, shift work, medications, and sustainability.

Adequate, regular sleep supports overall health. Roughly 7–9 hours suits many adults, but individual needs and sleep disorders deserve separate attention. Darkness or increased slow-wave sleep cannot be promised to normalize ghrelin through a single β₁-adrenergic pathway. Ghrelin testing is also not a routine independent explanation for overeating: timing, molecular fraction, and specimen handling strongly limit interpretation.

This is a narrative scientific examination of the source text with targeted checks of disputed mechanisms, receptor structures, and drug identities on 8 October 2026. Accessible primary papers, abstracts, and official structure and substance records were used. Some PubMed, PMC, and DOI pages returned errors or browser checks; access was not bypassed, and reading every full text is not claimed. No systematic search, independent GRADE assessment, external peer review, or clinical validation was performed. Cellular findings, animal models, short human experiments, and clinical treatment evidence are evaluated separately.

## FAQ

### Does ghrelin always mean hunger?

No. It participates in a complex network affected by meals, sleep, energy state, and measurement methods.

### Is obestatin an established satiety hormone?

The initial hypothesis was inconsistently reproduced; cellular and animal effects do not establish clinical treatment.

### Does ghrelin blockade treat gastroparesis?

Anti-ghrelin Spiegelmers were investigated preclinically. Motility agonists and blockers act in different directions; NOX-H94 targets hepcidin.

### Can total and acyl-ghrelin be compared directly?

They are different measurements. The unstable ester linkage and sample handling affect results; identify the molecular fraction and method.

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