Urocortin mRNA is expressed in the enteric nervous system of the rat

Urocortin and corticotropin-releasing factor receptor expression in the human colonic mucosa

Urocortin is a newly identified member of the CRF neuropeptide family. Urocortin has been found to bind with high affinity to CRF receptors. The present study investigated urocortin and CRF receptor expression in human colonic mucosa. Non-pathologic sections of adult colorectal tissues were obtained from patients with colorectal cancer at surgery. Urocortin expression was examined using immunohistochemistry and messenger (m) RNA in situ hybridization. Isolated lamina propria mononuclear cells (LPMC) and epithelial cells were also analyzed by flow cytometry for the characterization of urocortin-positive cells, and by RT-PCR for detection of urocortin, CRF, and CRF receptor mRNA. Urocortin peptide distribution at various stages of human development (n = 35, from 11 weeks of gestation to 6 years of age) was examined by immunohistochemistry using surgical and autopsy specimens. Immunoreactive urocortin and urocortin mRNA were predominantly detected in lamina propria macrophages. Urocortin peptide expression was detected from as early as three months of age, but not before birth or in neonates. Urocortin, CRF receptor type 1 and type 2 alpha mRNA were detected in LPMC. CRF receptor type 2 beta mRNA, a minor isoform in human tissues, was also detected in LPMC, but at lower levels. Urocortin is locally synthesized in lamina propria macrophages and may act on lamina propria inflammatory cells as an autocrine/paracrine regulator of the mucosal immune system. The appearance of urocortin after birth indicates that the exposure to dietary intake and/or luminal bacteria after birth may contribute to the initiation of urocortin expression in human gastrointestinal tract mucosa.

Peripheral corticotropin-releasing factor and stress-stimulated colonic motor activity involve type 1 receptor in rats

BACKGROUND & AIMS

Corticotropin-releasing factor (CRF) exerts its action through CRF receptors 1 and 2 (CRF-R1 and CRF-R2). CRF has preferential affinity for CRF-R1, whereas urocortin displays high affinity for both. We investigated changes in colonic motor function after intraperitoneal (IP) injection of CRF-related peptides.

METHODS

Colonic motility was recorded in vivo in conscious rats equipped with electrodes chronically implanted in the cecum and proximal colon or in vitro in distal colon; fecal output was monitored in naive rats.

RESULTS

Rat CRF, rat urocortin, and amphibian sauvagine (10 microg/kg, IP) induced a new pattern of cecocolonic myoelectric activity characterized by clustered spike bursts of long duration; the percentage of occurrence was highest after CRF. The rank order of potency to increase fecal pellet output after IP peptide injection (0.3-10 microg/kg, IP) was CRF > urocortin = sauvagine. The CRF-R1/R2 antagonist astressin (33 microg/kg, IP) and the CRF-R1 antagonist CP-154,526 (20 mg/kg, subcutaneously) inhibited IP CRF-induced changes in cecocolonic myoelectric activity and IP CRF- and water avoidance stress-induced fecal output. In vitro, CRF injected into the inferior mesenteric artery increased distal colonic myoelectric activity compared with saline injection.

CONCLUSIONS

These results demonstrate that CRF acts peripherally to stimulate colonic motility and that CRF-R1 is primarily involved in mediating IP CRF/urocortin- and water avoidance stress-induced colonic motor response.

Identification of urocortin mRNA antisense transcripts in rat tissue

Urocortin (UCN) has 45% sequence homology with corticotropin releasing factor (CRF) and binds to CRF receptors. We used reverse-transcriptase-polymerase chain reaction to demonstrate the presence of UCN RNA in various brain regions and in peripheral tissues. Ribonuclease protection assay (RPA) using sense and antisense riboprobes demonstrated the presence of a naturally occurring antisense UCN RNA transcript in a number of tissues. Northern blot indicated that the antisense transcript was the same size as sense UCN. RPA, using probes that covered bases 1 to 560 of 579 bp sequence of rat UCN, indicated that the antisense sequence was complementary to sense UCN but did not contain an open reading frame. Sense and antisense UCN RNA were co-expressed in all tissues that contained levels of either transcript detectable by RPA. Sense RNA expression was greater than antisense in the midbrain, the two transcripts were expressed equally in the hypothalamus and antisense was expressed at higher levels than sense in the liver, heart, and skeletal muscle. Antisense RNA expression was stress responsive, suggesting that it may play a role in regulating transcription or translation of UCN mRNA.

Genomic organization and tissue-specific expression of rat urocortin

The genomic organization of rat urocortin was determined using both cDNA and liver genomic DNA as templates for polymerase chain reactions. A single intron of 261 bp was found upstream to the ATG start codon, and the whole urocortin coding sequence was shown to be contained in a single exon. Relying on these results, oligonucleotide primers were designed, which can differentiate genomic DNA contamination from cDNA-derived signals in a reverse transcription-polymerase chain reaction. Tissue screening for urocortin expression revealed that the mid-brain is the major site of urocortin mRNA expression, and that other peripheral organs, including lymphoid tissues and peripheral blood lymphocytes, do not produce urocortin.