Prostaglandin D2 diminishes transmucosal potential difference in rat colonic mucosa in vitro in contrast to the increasing effect of prostaglandin E1

The effect of Prostaglandin D2 (PGD2) on ion transport was investigated in the rat colon in vitro. Ion transport across the intestinal mucosa was estimated by transmucosal potential difference (PD) and short circuit current (Isc) in the Ussing chamber. PGD2 added to the serosal reservoir induced a sustained reduction in PD and Isc at the concentration of higher than 10(-7)M, producing the maximal decrease at 10(-5)M. PGD2 at 10(-5)M completely blocked the increase in PD elicited by prostaglandin E1 (PGE1), theophylline, dibutyryl cAMP or serotonin. Adenylate cyclase activity was determined in the colonic mucosal homogenates after addition of PGD2 and PGE1. Treatment with PGD2 or PGE1 caused a significant increase in the enzyme activity. Combined treatment with both prostaglandins induced no more increase than that elicited by PGE1 alone. These results suggest that PGD2 has an anti-secretory effect on the rat colon and it may regulate the ion transport process through other mechanism than the modification of cyclic AMP concentration in mucosal cells.     

Marked increase in gastric histidine decarboxylase activity in patients with hypergastrinemia.

Histidine decarboxylase (HDC) activity and histamine content were measured in endoscopic gastric biopsy specimens of 19 control subjects with normogastrinemia and 6 patients with hypergastrinemia. In controls, the HDC activity was 3 fold higher in fundic mucosa (120 +/- 13 fmol/min/mg protein, mean +/- S.E.) than in antral mucosa (39 +/- 5 fmol/min/mg protein). In patients with hypergastrinemia, an extremely high HDC activity (713 +/- 181 fmol/min/mg protein) was observed in fundic mucosa, although the HDC activity in antral mucosa was not significantly different from that of controls. The histamine content in fundic mucosa was also significantly higher in patients with hypergastrinemia than in controls but no significant difference was seen in histamine content in antral mucosa between the two groups. These results are compatible with the hypothesis that in man, as well as in rat, histamine synthesis in fundic mucosa is enhanced by gastrin.     

The core molecule from type H proteoglycan. Release of mannose-containing oligosaccharides by digestion with N-oligosaccharide glycopeptidase.

Chick-embryo cartilage contains a unique set of proteoglycans. Type H proteoglycan (PG-H) is the most abundant, constituting over 90% of the total cartilage hexuronate. We previously showed that treatment of PG-H with chondroitinase ACII and keratanase yields a protein-enriched core molecule [PG(-CS,KS)] with enzymically modified linkage oligosaccharides of the chondroitin sulphate and keratan sulphate chains. We report here that further treatment of PG(-CS,KS) with pepsin and N-oligosaccharide glycopeptidase (almond glycopeptidase) released four distinct types of mannose-containing oligosaccharide. Two of them were shown to be: (Formula: see text). Of the mannose-containing glycopeptides formed by pepsin digestion, about 40% (as mannose) were resistant to N-oligosaccharide glycopeptidase. Since the resistant fraction was enriched in keratan sulphate remnants, it is suggest that the mannose-containing oligosaccharides in this fraction represent those located in a keratan sulphate-enriched region of PG-H.     

Isolation and characterization of a third proteoglycan (PG-Lt) from chick embryo cartilage which contains disulfide-bonded collagenous polypeptide

Chick embryo epiphyseal cartilage has been shown to contain three different proteoglycan species (PG-H, PG-Lb, and PG-Lt). This report is concerned with the purification and characterization of the third proteoglycan, PG-Lt. The proteoglycan can be separated from the other two by virtue of its low buoyant density in a CsCl density gradient and further purified by consecutive ion exchange and gel chromatography. The final preparation is composed of PG-Lt monomer and PG-Lt oligomer. The amino acid composition of PG-Lt is quite different from that of PG-H and PG-Lb and rather resembles that of collagens with respect to high content of glycine and high degrees of hydroxylation of proline and lysine. PG-Lt monomer is composed of disulfide-bonded subunits of Mr congruent to 120,000 and 190,000 as demonstrated by its gel electrophoretic behavior after reduction with 2-mercaptoethanol. The latter, but not the former, contains dermatan sulfate chains with glucuronic acid/iduronic acid residues and yields a protein-enriched core molecule of Mr congruent to 100,000 after digestion with chondroitinase ABC. Both of the protein subunits are completely digestible with bacterial collagenase. Immunofluorescence microscopic examination of cartilage tissues, using an antibody against PG-Lt, shows that this proteoglycan exists in both the cartilage matrix and perichondrial noncartilagenous region. When chondrocytes are plated onto tissue culture dishes, the antibody stains strands found on the cell surfaces and in the intercellular space of substrate-attached cell layers, suggesting that PG-Lt mediates cell-to-cell and cell-to-substrate contacts.     

Laminin A, B1, and B2 Chain Gene Expression in Transected and Regenerating Nerves: Regulation by Axonal Signals

Abstract: Laminin A, B1, and B2 chain mRNA levels in degenerating and regenerating mouse sciatic nerves were examined using northern blot analysis. In normal intact nerves, B1 and B2 mRNA steady-state levels were high, but when the nerves were crushed, the steady-state levels of B1 and B2 mRNA per milligram wet tissue weight of the distal segments of the nerves increased five- to eightfold over that of control levels as the total RNA and β-actin mRNA levels increased, suggesting that these increases were the consequence of Schwann cell proliferation after axotomy. When the steady-state levels of B1 and B2 mRNA were normalized as the ratio to total RNA or β-actin mRNA levels, however, they drastically decreased to about 20% of the normal nerve levels in the nerve segments distal to both the crush and transaction sites 1 day after injury. In the crushed nerves, B1 and B2 mRNA levels gradually increased as the regenerating nerves arrived at the distal segments and reestablished normal axon–Schwann cell contact, and then returned to normal levels on the 21 st day. In the transected nerves, where Schwann cells continued to be disconnected from axons, both B1 and B2 mRNA levels remained low. Cultured Schwann cells expressed detectable levels of B1 and B2 chain mRNA which significantly increased when the cells were cocultured with sensory neurons. However, mRNA for A chain was not detectable in the normal, axotomized nerves or in cultured Schwann cells. These data indicate that Schwann cells express laminin B1 and B2 chain mRNA that are up-regulated by axonal or neuronal contact, but they do not express A chain mRNA.     

Immunoreactive glucagons purified from dog pancreas, stomach and ileum

Previous studies have shown that pig intestine contains a 69 amino acid glucagon (glicentin) as well as a 37 amino acid glucagon (oxyntomodulin). In pig pancreas the 29 amino acid glucagon predominates. Since glucagon is thought to be expressed from a single gene in mammals, these differences in molecular forms indicate differential posttranslational processing of the glucagon precursor by different tissues. In the current study glucagon immunoreactivity (IR) was separately purified from dog pancreas, stomach mucosa and ileum mucosa. Purification and sequence analysis of the different tissue glucagons show that dog pancreas and stomach mucosa contain glucagon-29 while ileum mucosa contains glucagon-37 and glucagon-69. The latter is the major form present with glucagon-37 accounting for only 10-20% of the total ileum glucagon content. The N-terminal 32 amino acid portion of dog glucagon-69 differs at 6 sites from pig glucagon-69: RSLQDTEEKSRSFSAPQTEPLNDLDQMNEDKR... The C-terminal glucagon-37 is identical to pig oxyntomodulin.     

Similarities and differences between phytochrome-mediated growth inhibition of coleoptiles and seminal roots in rice seedlings

In rice, light is known to inhibit the growth of coleoptiles and seminal roots of seedlings through phytochrome. Here we investigated the light-induced growth inhibition of seminal roots and compared the results with those recently determined for coleoptiles. Although three rice phytochromes, phyA, phyB and phyC functioned in a similar manner in coleoptile and seminal root, the Bunsen-Roscoe law of reciprocity was not observed in the growth inhibition of seminal root. We also found coiling of the seminal root at the root tip which appeared to be associated with the photoinhibition of seminal root growth. This could be a new light-induced phenomenon in certain cultivars of rice.Key words: growth, hypocotyl, Oryza sativa, phytochrome, seminal rootPhytochrome-mediated growth inhibition was reported for both coleoptiles and seminal roots of rice seedlings in the same year by two research groups in Nagoya and Tohoku University in Japan, respectively.^1,2 Forty years after the findings, a detailed photobiological study was carried out for the coleoptile growth inhibition.³ In this study, we examined photoinhibition of seminal root growth, and found similarities and differences between light-induced growth inhibition of the two organs in rice seedlings. Although coleoptile growth was inhibited by pulses of light, growth inhibition of seminal roots required light irradiation longer than 6 h. The Bunsen-Roscoe law of reciprocity was not observed in the growth inhibition of seminal root. Action spectra were determined for the growth inhibition of coleoptiles, and the mode of inhibition was found to depend on the age of the coleoptiles. At the early stage of development [40 h after inducing germination (AIG)], photoinhibition was predominantly due to the phyB-mediated low-fluence response (LFR), but at the late developmental stage (80 h AIG), it consisted of the phyA-mediated very low-fluence response (VLFR) as well as the phyB-mediated LFR.^3,4 In the case of root growth, the sensitivity of photoinhibition also depended on age, and was most sensitive in the period of 48–96 h AIG when seedlings were irradiated for 24 h. Using rice phytochrome mutants,⁵ we found that far-red light for root growth inhibition was perceived exclusively by phyA, that red light was perceived by both phyA and phyB, and that phyC had little or no role in growth inhibition. Furthermore, the fluence rate required for phyB-mediated inhibition was more than 10,000-fold greater than that required for phyA-mediated inhibition. These characteristics of photoinhibition in seminal roots are similar to those found in coleoptiles at the late stage of development.³ In seminal roots, photoinhibition appeared to be mediated by photoreceptors in the root itself.Interestingly, coiling of the root tips always occurred when root growth was inhibited under the light condition (Fig. 1B). Under continuous light irradiation, rice seeds germinated ∼30 h AIG. Seminal roots formed a coil at the root tips during the 48–96 h period AIG, and stopped growing. When they were irradiated for only 24 h on the 3rd day AIG, coils started to form just after the end of irradiation. The roots continued to coil for ∼28 h and then began growing straight again (Fig. 1C). The coils were larger and looser than those formed under continuous light condition (Fig. 1, Open in a separate windowFigure 1Light irradiation induces coiling of root tips in rice seedlings (Oryza sativa cv. Nipponbare). A rice seedling was grown in the dark (A), or in continuous white light (55 µole m⁻² s⁻¹) (B) for 7 d at 28°C. In (C), it was irradiated by white light for 24 h during the 48–72 h period after inducing germination, and kept in the dark again until the 7th day. Arrows and arrowheads indicate the seminal and crown roots, respectively. Seedlings were grown in glass tubes of 3-cm diameter.

Table 1

The size of coil of root tips formed after white light irradiation