III.5.E. Inhibition of food intake

Food intake is inhibited by complex effects:

1. a feeling of stomach fullness through mechanoreceptors;
2. a feeling of small intestine fullness through mechanoreceptors;
3. chemical and hormonal factors.

The chemical and hormonal effects are listed below:

a) Serotonergic tractus

Serotonin (5-HT, 5-hydroxytryptamine)

Its main effect is exerted on the hypothalamus.

It inhibits the appetite for carbohydrates.

b) Dopaminergic tractus

Here there is a double effect:

1. 1. in the area of the ARC and HT-LH it inhibits food intake;
   2. in the VMH area, it increases food intake (leptin is an inhibitor here).

It has effects mainly on the fat intake.

It is part of “award”-regulating network.

c) Glycogen peptide-1 (GLP-1)

This is the most effective appetite suppressant.

When administered into the brain in fasting rats, it causes a 95% decrease in food intake.

It inhibits NPY and gastric emptying.

It increases insulin synthesis and secretion.

It decreases glucagon production.

d) Leptin

This is released from the adipose tissue.

It inhibits food intake by NPY inhibition.

e) CCK

This decreases food intake by NPY inhibition.

It slows down gastric emptying.

f) insulin

This inhibits food intake by NPY inhibition.  

It stimulates AGRP and POMC neurons.

g) Cytokines (TNF-α and IL-6)

These suppress the appetite during inflammation and infection.

h) α-MSH (α-melanocyte-stimulating hormone )

This moderates food intake by NPY inhibition.

i) CRH

This inhibits food intake and decreases the body weight.

Its production is stimulated by leptin.                      

In anorexia nervosa, ACTH has no effect and CRH production is therefore increased.

j) Pro-opiomelanocortin (POMC)

Various hormones are produced from this (e.g. ACTH, α-MSH and endorphins). It inhibits food intake and increases energy consumption.

Its receptor agonists are tested as drug targets.

k) Cocaine- and amphetamine-regulated transcript (CART)

This inhibits food intake.

Its production is stimulated by GLP-1.

l) Bombesin

This decreases food intake by NPY inhibition.

m) Estrogens

These stimulate leptin release, and hence decrease food intake.

n)  Peptide tyrosine tyrosine (PYY)

This is produced mainly in the intestines.

It inhibits food intake.  

o) TRH

This decreases food and drink intake,

inhibits leptin release and

increases the BP.

It is inhibited by NPY, AGRP and α-MSH.

Its production is stimulated by leptin.

p) Ciliary neurotrophic factor (CNTF)

This is produced by various motoric neurons. It is similar structurally to IL-6.

It decreases food intake by NPY inhibition.

It decreases the body weight in humans, but has a side-effect (vomiting). 

q) GHRH

GHRH in a large dose inhibits food intake, but in a small dose increases protein intake. Its level is decreased in obese, but increased in anorexia nervosa patients.

Table 6 overviews food intake-inhibiting hormones.

Table 6. Food intake-inhibiting hormones
(E = epinephrine, Ach = acetylcholine, ACTH = adrenocorticotropic hormone, AA =amino acid, Arg = arginine, CCK = cholecystokinin, CRH = corticotropin releasing hormone, G = gastrin, GH = growth hormone,
GIP = Glucose-dependent insulinotropic polypeptide, gastrin inhibitory peptide, gastrointestinal polypeptide,
GLP = Glucagon-like peptide, Glu = glucose, GRH = GH releasing hormone, Leu = leucine, Lys = lysine, MCH = melanin-concentrating hormone , AGC = adrenal gland cortex, AGM = adrenal gland medulla, N = norepinephrine, NPY = neuropeptide Y, OXA = orexin, OXM = enteroglucagon, glicentin, oxyntomodulin, PP = pancreas polypeptide, T₄ = thyroxine, TSH = thyroid-stimulating hormone, VIP = vasoactive intestinal polypeptide, glycogenolysis = glycogen breakdown, lypolysis = fat breakdown, glycolysis = glucose breakdown, gluconeogenesis= glucose production)

Regulation of eating

Eating is regulated by various hormonal and neuronal co-effects, as outlined in Fig. 17.

Figure 17. Regulation of eating  

(GLP=glucagon-like peptide, HT=hypothalamus, POMC/CART=pro-opiomelanocortin/cocaine- and amphetamine-regulated transcript, TNF-α=tumor necrosis factor alpha,
NPY/AGRP=neuropeptide Y/Agouti-related peptide – AGRP, GH= growth hormone, GHRH/GRF= GH-releasing factor, DA=dopamine, α-MSH=α-melanocyte-stimulating hormone, N= norepinephrine, GABA= gamma-aminobutyric acid, PYY=peptide tyrosine tyrosine,  CRH= corticotropin-releasing hormone, TRH= thyrotropin-releasing hormone,  MCH= melanin-concentrating hormone;
red arrow = inhibition, green arrow = stimulation)