ABSTRACT
Enterostatin is a pentapeptide released from its precursor protein procolipase, which is synthesized in the exocrine pancreas and gastric mucosa. As central injection of enterostatin has potent effects on feeding, we hypothesized that the procolipase may also be expressed in the brain. We confirmed the presence of preprocolipase gene expression in amygdala by reverse transcription-polymerase chain reaction and Northern blot analysis and of protein expression by Western blots. Immunohistochemical analysis using antibodies for procolipase and enterostatin identified their immunoreactivity (IR) in rat brain. Procolipase IR was present in the cytoplasm of paraventricular, amygdala, and the dorsal thalamus nucleus. Enterostatin IR was evident in the fibers of the dorsal thalamus and arcuate nucleus. In vivo injection of enterostatin antibody into rat amygdala increased food intake. These data suggest that procolipase and enterostatin are synthesized within specific regions of the brain that function in the regulation of food intake centrally.
Subject(s)
Brain/physiology , Colipases/metabolism , Gene Expression/physiology , Protein Precursors/metabolism , Analysis of Variance , Animals , Antibodies/pharmacology , Behavior, Animal , Blotting, Northern/methods , Blotting, Western/methods , Colipases/genetics , Colipases/immunology , Eating/drug effects , Eating/physiology , Enzyme Precursors , Immunohistochemistry/methods , Male , Protein Precursors/genetics , Protein Precursors/immunology , RNA, Messenger/metabolism , Rats , Reverse Transcriptase Polymerase Chain Reaction/methodsABSTRACT
Enterostatin, a pentapeptide released from the exocrine pancreas and gastrointestinal tract, selectively inhibits fat intake through activation of an afferent vagal signaling pathway. This study investigated if the effects of enterostatin were mediated through a CCK-dependent pathway. The series of in vivo and in vitro experiments included studies of 1) the feeding effect of peripheral enterostatin on Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors, 2) the effect of CCK-8S on the intake of a two-choice high-fat (HF)/low-fat (LF) diet, 3) the effects of peripheral or central injection of the CCK-A receptor antagonist lorglumide on the feeding inhibition induced by either central or peripheral enterostatin, and 4) the ability of enterostatin to displace CCK binding in a 3T3 cell line expressing CCK-A receptor gene and in rat brain sections. The results showed that OLTEF rats did not respond to enterostatin (300 microg/kg ip) in contrast to the 23% reduction in intake of HF diet in Long Evans Tokushima Otsuka (LETO) control rats. CCK (1 microg/kg ip) decreased the intake of the HF diet in a two-choice diet regime with a compensatory increase in intake of the LF diet. Peripheral injection of lorglumide (300 microg/kg) blocked the feeding inhibition induced by either near-celiac arterial or intracerebroventricular enterostatin, whereas intracerebroventricular lorglumide (5 nmol icv) only blocked the response to intracerebroventricular enterostatin but not to arterial enterostatin. Enterostatin did not bind on CCK-A receptors because neither enterostatin nor its analogs VPDPR and beta-casomorphin displaced [3H]L-364,718 from CCK-A receptors expressed in 3T3 cells or the binding of 125I-CCK-8S from rat brain sections. The data suggest that both the peripheral and central responses to enterostatin are mediated through or dependent on peripheral and central CCK-A receptors.
