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ANA MARÍA PASCUAL-LEONE PASCUAL AN. R. ACAD. NAC. FARM.

access brain tissue from blood and play a crucial role in this process, leptin,
secreted by adipocytes from the white adipose tissue, and insulin, secreted by the
endocrine pancreas. The other pathway regulates the short term onset of appetite
and end of food intake and, on this pathway, the recently reported peptinergic
brain-intestines axis plays a central role.

Orexins, first reported in 1998 and secreted by the lateral hypothalamus, neu-
rons and secretory cells from intestines, stomach and pancreas, seem to play a role
in the integration of both pathway since they are involved in transferring the
intestinal responses to the brain.

Keys words: Energy balance.— Brain-intestines axis.— Orexins.

EXTENSIVE ABSTRACT

The control of feeding behaviour or, in other words, onset and ending of appe-
tite, takes place at brain level in two different pathways. One of the pathways
ensures a long term stability of the peripheric adipose tissue throughout a balance
between caloric intake and energy expenditure. There are two hormones that may
access brain tissue from blood and play a crucial role in this process, leptin,
secreted by adipocytes from the white adipose tissue, and insulin, secreted by the
endocrine pancreas. The other pathway regulates the short term onset of appetite
and end of food intake and, on this pathway, the recently reported peptinergic
brain-intestines axis plays a central role.

Orexins, first reported in 1998 and secreted by the lateral hypothalamus, neu-
rons and secretory cells from intestines, stomach and páncreas, seem to play a role
in the integration of both pathways since they are involved in transferring the
intestinal responses to the brain. These responses, both hormonal and mechanical,
are generated by the enteric nervous system to face changes in pH, peristaltism
and composition of the digestive mass. Furthermore, brain orexins seem to regu-
late important homeostatic processes such as the sleep/awake rhythm and energy
homeostasis. Orexins may exert these actions because, although they are secreted
in restricted brain areas (perifornical, lateral and dorsal hypothalamus) the proyec-
tions of the nervous axons are very extended to very different parts of the neu-
roaxis, such as olfatory bulbs, cerebral cortex, anterior and posterior hypothala-
mus, brainstem and all levels of the spinal cord. Short term control of appetite
seems to be the most primitive system conserved through evolution; orexin struc-
ture is similar in amphibian than in mammals. However, its high degree of con-
servation seems the result of their fundamental role in the integration of important
homeostatic processes for the organic balance.

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