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Food Lipids: Chemistry, Nutrition, and Biotechnology

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4. Effects of Hormones <strong>and</strong> Pharmacological Agents<br />

Use of hormones <strong>and</strong> pharmacological agents has further illuminated factors that<br />

may play a role in the effect of dietary fat on food intake. Pancreatic procolipase is<br />

a cofactor for lipase, an enzyme necessary for proper fat digestion. A pentapeptide<br />

produced by the cleavage of procolipase, Val-Pro-Asp-Pro-Arg, or enterostatin, has<br />

been shown to reduce food intake in rats (99), especially when consuming a highfat<br />

diet (100). Peripheral injection or intracarotid injection (101), or injection into<br />

the lateral ventricle (102), suppresses fat intake in fat-adapted rats, suggesting both<br />

a gastrointestinal site <strong>and</strong> a central site of action. Also, high-fat feeding <strong>and</strong> cholecystokinin-8<br />

(CCK-8) increase intestinal enterostatin levels (103). Lin et al. (104)<br />

report that �-casomorphin 1–7 stimulates intake of a high-fat diet in rats <strong>and</strong> this<br />

effect is inhibited by enterostatin or naloxone.<br />

Much research has been focused on CCK <strong>and</strong> its effects on satiety [for review,<br />

see Smith <strong>and</strong> Gibbs (105)]. It has been well documented that consumption of fat<br />

stimulates the release of CCK, activating receptors in the stomach. This signal is<br />

transmitted along the vagus to the nucleus of the solitary tract, where it is forwarded<br />

to the hypothalamus. Vagotomy can block these effects of systematically administered<br />

CCK (106), as can CCK-A receptor antagonists (107).<br />

Morphine has also been shown to have specific effects on intake of dietary fat.<br />

Rats given morphine injections subsequently increase fat intake while suppressing<br />

carbohydrate intake when given separate sources of macronutrients (108–110) or<br />

mixed diets (111). Continuous infusion of morphine also stimulates fat intake (112).<br />

An opioid agonist, butorphanol, also increases consumption of a high-fat diet (54).<br />

Administration of opioid antagonists suppresses fat intake with little effects on protein<br />

or carbohydrate intake (113,114). In humans, opioids also appear to play a role<br />

in regulating fat intake. Opiate antagonists cause a decrease in intake of fat calories<br />

with less effect on carbohydrate consumption (115–117).<br />

Corticosterone has also been implicated in the regulation of fat intake. Castonguay<br />

et al. (118,119) reported that adrenalectomy reduces total caloric intake in rats,<br />

particularly fat intake, <strong>and</strong> that corticosterone can restore the fat consumption. Others<br />

(120) have reported that the type 1 adrenocorticoid receptor mediates corticosterone’s<br />

effect on fat appetite. However, others (121) have suggested that corticosterone acts<br />

to enhance carbohydrate rather than fat intake. It has been suggested (122) that the<br />

differing levels of micronutrients added to the diets in these studies may account for<br />

these disparate findings.<br />

Investigators have also reported that the peptide galanin influences appetite for<br />

fat. Leibowitz (123) first demonstrated that galanin stimulates fat intake, especially<br />

at the end of the nocturnal cycle. Galanin is thought to work in concert with norepinephrine,<br />

which is colocalized with galanin in paraventricular neurons (124).<br />

Smith et al. (125) report that centrally injected galanin induces fat intake only in fatpreferring<br />

rats, i.e., baseline feeding preferences are important in determining the<br />

feeding response to galanin.<br />

Leptin, the gene product of ob gene, is shown to regulate body fat in mice <strong>and</strong><br />

is produced in human adipose tissue as well [for review, see Harris (126)]. Reports<br />

as to its relationship with fat intake in humans indicate that it is negatively associated<br />

with fat intake. Havel et al. (127) report that in women, high-fat/low-carbohydrate<br />

meals result in a lowering of 24-hour circulating leptin concentration. Other research<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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