Prenatal and postnatal development of the small intestine in the insectivore Suncus murinus

Contractile effect of tachykinins on Suncus murinus (house musk shrew) isolated ileum

Recent studies used Suncus murinus to investigate the anti-emetic potential of NK(1) tachykinin receptor antagonists. However, the pharmacology of tachykinin receptors in this species has not been fully characterized. In the present studies, therefore, we examined a range of tachykinin receptor agonists for a capacity to induce contractions of the isolated ileum. The tachykinin NK1 receptor preferring agonists substance P, septide and [Sar9Met(O2)11] substance P, and the tachykinin NK2 preferring agonists neurokinin A and GR 64349 (Lys-Asp-Ser-Phe-Val-Gly-R-gamma-lactam-Leu-Met-NH2) caused concentration dependent contractions with EC50 values in the nanomolar range. However, the tachykinin NK3 preferring agonists neurokinin B and senktide (1nM-1microM) induced only weak contractions. The action of senktide, but not [Sar9Met(O2)11] substance P, septide, or GR 64349, was antagonized significantly by atropine (P<0.05); tetrodotoxin and hexamethonium were inactive. The tachykinin NK1 receptor antagonist CP-99,994 ((+)-[(2S,3S)-3-(2-methoxy-benzyl-amino)-2-phenylpiperidine]) (10-100nM) inhibited substance P- and septide-induced contractions non-competitively. The pA2 value estimated for CP-99,994 against septide was 7.3+/-0.1. It also non-competitively antagonized the contractile responses induced by [Sar9Met(O2)11] substance P with a pA2 of 7.4+/-0.1. CP-99,994 also had a slight inhibitory action on neurokinin A-induced contractions, but did not modify the action of GR 64349. Conversely, the tachykinin NK2 receptor antagonist, saredutant, competitively antagonized GR 64349-induced contractions with a pA2 of 7.34+/-0.02. On the other hand, the presence of both CP-99,994 and saredutant competitively antagonized substance P-induced contraction. The present studies indicate that tachykininNK1 and NK2 receptors exist in the ileum of S. murinus and are involved in mediating contractions directly on smooth muscle, whereas tachykinin NK3 receptors may play a minor role involving a release of acetylcholine.

Action of GLP-1 (7-36) amide and exendin-4 on Suncus murinus (house musk shrew) isolated ileum

Glucagon-like peptide-1 (GLP-1) receptor agonists have been reported to modulate gastrointestinal motility but the mechanism is essentially unknown. In the present studies, we investigated the potency and mechanism of action of GLP-1 receptor ligands on the isolated ileum of Suncus murinus, an insectivore used in anti-emetic research. Ileal segments were mounted in organ baths containing Kreb's solution. Cumulative concentration-response curves to GLP-1 (7-36) amide (0.1-300 nM) and exendin-4 (0.1-100 nM) were constructed in the absence and presence of exendin (9-39) amide (0.3-3 nM). GLP-1 (7-36) amide and exendin-4 induced concentration-dependent contractions yielding pEC50 values of 8.4+/-0.2 and 8.4+/-0.4, respectively. Exendin (9-39) antagonized the action of both agonists in a non-competitive reversible manner, with apparent pKB values of 9.5 and 9.7, respectively. Tetrodotoxin (1 microM), atropine (1 microM) and hexamethonium (500 microM) were used to determine the contractile mechanism of action of exendin-4. Tetrodotoxin and atropine significantly antagonized (P<0.01) the contractile action of exendin-4 (10 nM); hexamethonium (500 microM) had no action. These studies suggest that GLP-1 receptor agonists contract the ileum indirectly via postganglionic enteric neurones and an involvement of muscarinic receptors. These studies provide information relevant to the use of this species to estimate the therapeutic indexes of GLP-1 receptor agonists.

[Early fetal development of the small intestine mucosa in cattle (Bos primigenius taurus)]

The development of the bovine small intestine was examined in 24 embryos and fetuses by light microscopic, scanning and transmission electron microscopic methods. Special reference was paid to the genesis of the epithelium and particularly of the villi intestinales. The primitive intestine consists of one layer of epithelial cells surrounded by mesenchym and tunica serosa. The fetal intestine (up to the 24th week of gestation) shows all the morphologic structures of the adult. In small intestine the development of cryptae and villi intestinales starts before the 7th week of gestation and progresses with a proximo-distal gradient. Epithelial proliferation that gives rise to primary epithelial villi makes epithelium become temporarily stratified. Finger-like secondary villi develop by proliferation of the mesenchym. In addition to this process mucosal folds occur in duodenum giving rise to villi by segmentation. At the same time the differentiation of epithelium starts. The fetal small intestine, like many other fetal tissues displays masses of glycogen.

Prenatal and postnatal development of the large intestine in the insectivore Suncus murinus, the laboratory shrew

Development of the large intestine in the insectivore Suncus murinus (the laboratory shrew) was investigated from day 21 to 30 of gestation and from birth to 20 days of age. Two days before birth, the stratified epithelium in the large intestine changed into a single layer. Although neither villi nor villus-like structures were ever present, fissures, corresponding to openings of the crypts, appeared on the mucosal surface before birth. These increased in number as well as in width and depth, connected with each other, and gave the mucosal surface a ridge-like appearance by 20 days of age. An elevation containing submucosae appeared shortly after birth and formed a large circular fold during the neonatal period. Goblet cells were the predominant epithelial cell type. Individual epithelial cells were mature-looking a few days before birth; goblet cells contained numerous mucous globules and absorptive cells possessed well-developed organelles. However, although goblet cells increased in number and exhibited active mucous-releasing forms after birth, absorptive cells never showed morphologic evidence of active endocytosis, such as apical endocytotic complexes and large supranuclear vacuoles. Each epithelial cell was similar in ultrastructure to that of the adult shortly after birth.

Existence of an endothelio-endothelial placenta in the insectivore, Suncus murinus

The interhemal membrane of the chorioallantoic placenta in the insectivore Suncus murinus was investigated by means of electron microscopy. In the interhemal membrane the syncytiotrophoblast clearly intervened between the hypertrophied maternal endothelium and the fetal endothelium by day 20 of pregnancy. Although the syncytiotrophoblast showed a sieve-like feature from day 20 to 24, it was distinctly continuous. The syncytiotrophoblast, however, became discontinous in most areas of the labyrinthine zone after day 24, and finally both projections of the maternal and the fetal endothelium contacted each other. These findings indicate the focal existence of an endothelio-endothelial condition within an otherwise endothelio-chorial placenta.