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W J Krause

Publications and source records attributed to W J Krause.

At least 37 records · Page 2Linked to original sources
PubMed1996

Milk composition in the North American opossum (Didelphis virginiana).

The composition of milk samples collected from captive opossums (Didelphis virginiana) was determined at various intervals during lactation. The milk solids increased from 9% at week one to a maximum of 34% at 11 weeks post-partum. There were changes in the relative proportions of protein, lipid and carbohydrate at different stages of lactation. Lipid represented the greatest fraction of the solids except for a period at mid-lactation when there was a peak in protein concentration. The concentrations of sodium, potassium and magnesium were relatively constant, 41 +/- 4, 35 +/- 11 and 9.2 +/- 1.6 mmol respectively, although calcium increased from 13 +/- 5 mmol at week one to a peak of 112 +/- 35 mmol at 9 weeks.

Aging↗
PubMed1996

Opossum colonic mucosa contains uroguanylin and guanylin peptides.

Uroguanylin and guanylin are structurally related peptides that activate an intestinal form of membrane guanylate cyclase (GC-C). Guanylin was isolated from the intestine, but uroguanylin was isolated from urine, thus a tissue source for uroguanylin was sought. In these experiments, uroguanylin and guanylin were separated and purified independently from colonic mucosa and urine of opossums. Colonic, urinary, and synthetic forms of uroguanylin had an isoelectric point of approximately 3.0, eluted from C18 reverse-phase high-performance liquid chromatography (RP-HPLC) columns at 8-9% acetonitrile, elicited greater guanosine 3', 5'-cyclic monophosphate (cGMP) responses in T84 cells at pH 5.5 than pH 8, and were not cleaved and inactivated by pretreatment with chymotrypsin. In contrast, colonic, urinary, and synthetic guanylin had an isoelectric point of approximately 6.0, eluted at 15-16% acetonitrile on C18 RP-HPLC columns, stimulated greater cGMP responses in T84 cells at pH 8 than pH 5.5, and were inactivated by chymotrypsin, which hydrolyzed the Phe-Ala or Try-Ala bonds within guanylin. Uroguanylin joins guanylin as an intestinal peptide that may participate in an intrinsic pathway for cGMP-mediated regulation of intestinal salt and water transport. Moreover, uroguanylin and guanylin in urine may be derived from the intestinal mucosa, thus implicating these peptides in an endocrine mechanism linking the intestine with the kidney.

Amino Acid Sequence↗
PubMed1996

Prouroguanylin and proguanylin: purification from colon, structure, and modulation of bioactivity by proteases.

Uroguanylin and guanylin are peptides isolated from urine and intestinal mucosa, which regulate cyclic GMP production in enterocytes by activating an apical membrane, receptor-guanylate cyclase. This study extended our previous findings, which showed that colonic mucosa of opossums contained uroguanylin and guanylin peptides, by purifying prouroguanylin and proguanylin from this tissue. Prouroguanylin and proguanylin coeluted from Sephadex G-75 gelfiltration columns with a similar molecular size between 6 and 12 kDa. Mass spectrometry indicated that proguanylin (approximately 8.7 kDa) had a 10% lower molecular mass than prouroguanylin (approximately 9.7 kDa). Isoelectric focusing separated prouroguanylin (pI approximately 4.5) from proguanylin (pI approximately 7.5). N-terminal sequence analysis of reverse phrase-HPLC purified prohormones revealed 13 amino acids in opossum proguanylin that shared 77-85% identity with human and rat proguanylin, but only 23% identity with opossum prouroguanylin. The N-terminal 19 residues obtained for opossum prouroguanylin shared 32-42% identity with rat and human proguanylin. Prouroguanylin and proguanylin were both inactive and required pretreatment with proteases to elicit cyclic GMP responses in T84 cells. V8 protease treatment of proguanylin liberated a bioactive, 16-amino acid form of guanylin. Chymotrypsin treatment activated prouroguanylin, but inactivated the bioactive peptide domain within proguanylin. In summary, colonic mucosa contains the bioactive peptide and inactive prohormone forms of uroguanylin and guanylin. Thus, after proteolytic processing of prouroguanylin and proguanylin, bioactive uroguanylin and guanylin could both function to regulate guanylate cyclase activity by autocrine and/or paracrine actions on enterocytes. Also, these peptide hormones are implicated in an intestinal-renal axis for the endocrine regulation of salt and water homeostasis.

Amino Acid Sequence↗
PubMed1995

Molecular anatomy of an endodermal gland: investigations on mucus glycoproteins and cell turnover in Brunner's glands of Didelphis virginiana using lectins and PCNA immunoreactivity.

Brunner's glands are located in the submucosa of the proximal duodenum and are unique to mammalian species. The North American opossum (Didelphis virginiana) is generally regarded as a prototype marsupial that closely resembles fossil didelphids which can be placed at the beginning of mammalian evolution. The current investigation provided an opportunity for the analysis of secretory products from these glands in a species thought to be more closely related to earlier evolutionary forms. Extracts of Brunner's glands were subjected to SDS-PAGE and Western blotting. The results indicate the presence of two high molecular weight PAS-positive glycoprotein bands. In addition to these two PAS-positive bands, several other glycoprotein bands were detected in the high molecular weight range that bind several lectins which typically recognize O-linked carbohydrates indicative of mucus type glycoproteins. The same lectins bind to glandular structures in tissue sections. Comparison of lectin binding sites with the pyloric glands of the stomach and duodenal goblet cells indicates that Brunner's glands carbohydrate residues resemble those of the pyloric glands more closely than those of the duodenal goblet cells. The low cell turnover rate in Brunner's glands is in contrast to the rapid turnover rate of goblet cell precursors in the duodenal crypts. The mucus composition and the cell turnover rate correlate well with embryological data and suggest that Brunner's glands of Didelphis evolved from an epithelium more closely associated with the stomach than that of the duodenum as the topography of the gland would suggest.

Animals↗
PubMed1995

Distribution of Escherichia coli heat-stable enterotoxin/guanylin/uroguanylin receptors in the avian intestinal tract.

Pathogenic strains of enteric bacteria secrete small heat-stable toxins (STs) that activate membrane guanylyl cyclase receptors found in the intestine. The intestinal peptide agonists, guanylin and uroguanylin, are structurally related to STs. Receptors for 125I-ST were found throughout the entire length of the intestinal tract of all the birds examined. These receptors were restricted to intestinal epithelial cells covering villi and forming intestinal glands and were not observed in other strata of the gut wall. The most intense labeling of receptors by 125I-ST occurred in the region of the microvillus border of individual enterocytes. There appeared to be a decrease in receptor density distally along the length of the small intestine, although labeling of receptors by 125I-ST was observed throughout the small intestine and colon. Cellular cGMP accumulation responses to Escherichia coli ST and rat guanylin in the domestic turkey and duck were greater in the proximal small intestine compared to the distal small intestine or colon. Brush border membranes (BBM) isolated from the mucosa of proximal small intestine of turkeys exhibited agonist-stimulated guanylyl cyclase activity. The rank order potency for enzyme activation was E. coli ST > uroguanylin > guanylin. Competitive radioligand binding assays using 125I-ST and turkey intestine BBM revealed a similar rank order affinity for the receptors that was exemplified by the Kd values of ST 2.5 nM, uroguanylin 80 nM and guanylin 2.6 microM. It may be concluded that functional receptors for the endogenous peptides, guanylin and uroguanylin, occur in the apical membranes of enterocytes throughout the avian intestine. The receptor-guanylyl cyclase(s) of proximal small intestine were preferentially activated by uroguanylin relative to guanylin, but both endogenous peptides were less potent than their molecular mimic, E. coli ST.

Amino Acid Sequence↗
PubMed1994

Brain growth and neocortical development in the opossum.

General brain growth and differentiation of the neocortex have been studied in the marsupial, Didelphis virginiana from the 10.5 day embryo through adulthood. Didelphis is born after a short gestation period of about 12.5 days, at a time when the telencephalic wall consists only of two layers and is considered to be at an embryonic stage of development. The cortical plate does not appear until late in the first postnatal week, thus neocortical development is totally a postnatal phenomenon in Didelphis as has been shown in other marsupial species examined to date. The general pattern of development and the establishment of the six-layered adult neocortex in Didelphis is similar to that described in eutherian mammals. Signs of cortical lamination can be seen as early as postnatal day 35 and the cytoarchitecture of a typical mammalian neocortex is well defined by postnatal day 60 in Didelphis prior to the onset of weaning.

Animals↗
PubMed1994

Distribution of heat-stable enterotoxin/guanylin receptors in the intestinal tract of man and other mammals.

The human intestinal tract, as well as that of several eutherian and metatherian mammals, was examined for the distribution of heat-stable enterotoxin (ST)/guanylin receptors. These receptors were confined to the intestinal epithelium lining the lumen and forming the intestinal glands throughout the length of both the small intestine and colon of all species examined. In man and most other mammalian species, there appeared to be a decrease in receptor density distally along the longitudinal axis of the small intestine. ST/guanylin receptors were not observed in other strata forming the gut wall. Along the vertical axis of the human small intestine (villus/crypt unit), as well as that of most other mammals, receptor density was greatest in enterocytes located near the base of villi and in those forming the proximal portion of the intestinal glands. ST/guanylin receptors were for the most part confined to the region of the plasmalemma forming the microvillus border. In the colon of man and the other species examined, receptor density was greatest in enterocytes forming the proximal region of the intestinal glands. Receptors were present in the intestinal epithelium lining the lumen of the colon, but generally were fewer in number. The distribution of cellular cGMP accumulation responses to E. coli ST and guanylin in the opossum (Didelphis virginiana) and raccoon (Procyon lotor) revealed that proximal small intestine had greater magnitudes of cGMP responses than did the distal small intestine. Proximal colon had greater cGMP responses than distal colon, which had no significant cGMP responses to either ST or guanylin.

Animals↗
PubMed1993

Uroguanylin: structure and activity of a second endogenous peptide that stimulates intestinal guanylate cyclase.

The intestinal hormone guanylin and bacterial heat-stable enterotoxins (STs) are members of a peptide family that activates intestinal membrane guanylate cyclase. Two different peptides that activate the human intestinal T84 cell guanylate cyclase have been purified from urine and intestinal mucosa of opossums (Didelphis virginiana). The highly acidic peptide, QEDCELCINVACTGC, was named uroguanylin because it was isolated from urine and shares 53% identity with guanylin. A second peptide, SHTCEICAFAACAGC, was purified from urine and intestinal mucosa. This alanine-rich peptide was 47% identical to uroguanylin and 73% identical to human guanylin, suggesting that it may be an opossum homologue of guanylin. Synthetic uroguanylin-(2-15) (i.e., EDCELCINVACTGC) was 10-fold more potent than synthetic rat guanylin, but both peptides were less potent than Escherichia coli ST in the T84 cell cGMP bioassay. Uroguanylin-(2-15) and guanylin inhibited 125I-ST binding to T84 cell receptors in competitive radioligand binding assays. Transepithelial Cl- secretion was stimulated by 1 microM uroguanylin, indicated by an increase in the short circuit current of T84 cells. Thus, uroguanylin is another paracrine hormone in the emerging peptide family that activates intestinal membrane guanylate cyclase. The second peptide may be the opossum form of guanylin, or perhaps, it is still another member of this peptide family. The presence of uroguanylin and guanylin in urine and receptors in proximal tubules suggests that these peptides may also originate from renal tissue and may regulate kidney function.

Amino Acid Sequence↗
PubMed1993

Morphological observations on the unique paired capillaries of the opossum retina.

Light-microscopic and ultrastructural analysis of the ocular tissues of the North American opossum (Didelphis virginiana) revealed that the arterial and venous segments of retinal vessels, including capillaries of the smallest calibre, occur in pairs. They do not form anastomotic networks, the common pattern in mammals with vascularised retinae, but instead the two segments of the pair join to form hairpin end loops. The paired vessels, with the arteriolar limb usually on the vitread aspect, penetrate the retina and branch to form three distinct layers of capillaries. The most superficial lies in the nerve fiber layer, the middle is situated in the inner nuclear layer and the deepest extends to the external limiting membrane, which is considerably deeper than in normal mammalian holangiotic retinae. The paired capillaries display classical morphological features of central nervous system capillaries, i.e., they are lined by continuous endothelial cells united by tight junctions. The lining endothelium is supported by a distinct basal lamina that splits to envelop pericytes. The latter, although abundant, are invariably interposed between the two vessels that form each vascular unit. Phylogenetic and functional aspects of this unique form of retinal vascularisation are discussed.

Animals↗
PubMed1993

Development of the eye in the North American opossum (Didelphis virginiana).

Marsupials are unique models for developmental biology-oriented research because of the immature state of their development at birth. The North American opossum (Didelphis virginiana) has several advantages over other marsupials, including large litter size, short prenatal period (12.5 d), an extended postnatal period while accessible in the pouch, and its ability to reproduce reliably in captivity. Studies of ocular development in this species have not been reported previously. The aim of the present investigation was therefore to document the major landmarks in prenatal and postnatal development of the cornea, lens, iris, ciliary body and retina. Fifteen embryos (10.5, 10.7 and 11 d postconception and 6 h after birth [12 d]) were studied by paraffin histology. Eyes of pouch young at 8 d, 2, 6, 9 and 13 wk were studied by transmission electron microscopy and light microscopy. The study revealed a similar pattern of ocular development in Didelphis to other metatherian and eutherian mammals. Differentiation of the eye is particularly rapid in the 2 d before birth. For example, although the lens vesicle separates from the surface ectoderm on d 10, by birth (2.5 d later) a primitive cornea and fused eyelids have formed, presumably to protect the eye during migration to the pouch. At birth the retinal pigment epithelium (RPE) contains melanin; however, the inner layer of the optic cup does not differentiate into an inner and outer neuroblastic layer until 8 d after birth. Around 6 wk after birth most components of the adult eye are identifiable, albeit in an immature form. These include the corneal layers, the iris (including the sphincter pupillae), ciliary processes, RPE tapetum, and a fully laminated retina with immature photoreceptors. A knowledge of the timing of major events in eye development in Didelphis and their comparison with equivalent events in human eye development should allow the appropriate choice of stages for any future experimental studies utilising this marsupial species.

Animals↗
PubMed1992

Morphological observations on the harderian gland of the North American opossum (Didelphis virginiana).

The Harderian gland of the North American opossum (Didelphis virginiana) is large and well developed, despite the absence of a nictitating membrane in the adult of this species. The elongate glands are surrounded by a delicate connective tissue capsule from which thin septae extend, subdividing the gland into numerous lobules. The secretory units of the opossum Harderian gland are drained by a well defined but not extensive intralobular and interlobular duct system. Most of the secretory end pieces consist of tubulo-alveolar units with widely dilated lumina filled with secretory product. Numerous intact lipid vesicles suspended within an amorphous material constitute the luminal contents. Cells lining the tubulo-alveolar secretory end-pieces are usually columnar in shape, and characterized by numerous lipid-containing secretory vesicles and aggregations of poly-tubular complexes 40-60 nm in diameter. In addition, these cells contain numerous large irregularly shaped mitochondria, whose matrix is of considerable electron density. Intralobular and interlobular ducts are lined by electron-lucent epithelial cells that lack both the lipid-containing vesicles and the large mitochondria, although typical smaller mitochondria are found scattered within the cytoplasm. Both secretory end-pieces and ductal elements are invested by an abundance of myoepithelial cells. A second, smaller serous type of secretory unit may occur near the centre of some Harderian gland lobules. In these units secretory tubules and acini are compactly arranged surrounding a narrow lumen. Serous cells are pyramidal in shape and the cytoplasm is characterized by numerous electron-dense secretory granules and scattered profiles of rough endoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A scanning electron microscopic study of the opossum nasal cavity prior to and shortly after birth.

The nasal cavities of opossums prior to and shortly after birth were examined by scanning electron microscopy. Numerous morphologically mature olfactory receptor neurons are observed in the dorso-rostral-most extent of the olfactory epithelium positioned adjacent to the opening of the nares in all prenatal stages and newborn animals examined. The remainder of the olfactory epithelium, occupying a more dorso-caudal position within the nasal cavity, is undifferentiated, and lacks morphologically mature receptor neurons. A short transition zone of stratified squamous epithelium lies between the epithelium lining the nares and olfactory epithelium. It forms an abrupt junction with the latter. The remainder of the nasal cavity in this group of animals is lined by a non-ciliated pseudostratified type (undifferentiated respiratory) of epithelium. By the end of the second postnatal week the morphologically mature olfactory epithelium is no longer observed in the vestibular area of the nasal cavity, which is lined by stratified squamous epithelium at this time. Mature receptor neurons are now observed within the olfactory epithelium lining the roof of the nasal cavity and covering the turbinates. The greater part of the nasal cavity is lined by a ciliated respiratory epithelium. It is proposed that the precocious differentiation of mature olfactory receptor neurons within the rostral-most extent of the olfactory epithelium just prior to birth is important in guiding the newborn young to the pouch.

Animals↗
PubMed1992

Immunohistochemical evidence for the presence of oxytocin in the opossum corpus luteum.

Corpora lutea from opossums late in pregnancy were examined by immunohistochemistry for the presence of oxytocin. Oxytocin-immunoreactivity was observed in all corpora lutea examined but not elsewhere in ovarian tissue. The immunoreactive staining observed was confined primarily to the perinuclear cytoplasm of reactive luteal cells. Not all luteal cells showed oxytocin-immunoreactivity. The immunohistochemical localization of oxytocin in the pregnant opossum corpus luteum demonstrates for the first time this peptide in a metatherian ovary. Its presence in this primitive species suggests that oxytocin has a fundamental role in the physiology of the mammalian ovary.

Animals↗
PubMed1992

Immunohistochemical localization of relaxin in the reproductive system of the female opossum (Didelphis virginiana).

Relaxin-immunoreactivity was demonstrated in the cytoplasm in the luteal cells from pregnant and lactating opossums. Immunoreactivity for relaxin was not demonstrated elsewhere in the ovary, in the reproductive tract or in the placenta. The corpus luteum is thought to be the primary source of relaxin in Didelphis and in this regard is similar to several eutherian mammals including man.

Animals↗
PubMed1992

Prostaglandin but not cimetidine reduces spontaneous degeneration of isolated gastric gland cells.

We studied the effect of either placebo, 16,16-dimethyl-prostaglandin E2 (16,16-dimethyl-PGE2), or cimetidine on spontaneous degeneration of isolated rat gastric glands maintained in vitro in a basic oxygenated medium for 24 h. We assessed the viability of gland cells with fast green exclusion, measured release of lactate dehydrogenase (LDH) into the medium, and assessed the cell ultrastructure using a scanning electron microscope. Gastric glands incubated in medium for 6, 12, and 24 h underwent spontaneous degeneration reflected by a decrease in cell viability, increase in LDH release into the medium, and ultrastructural cell damage. 16,16-Dimethyl-PGE2 either at 0.1, 1, or 10 micrograms/ml significantly reduced the decrease in cell viability, increasing cell survival; reduced LDH release into the medium; and ultrastructural damage. Incubation with cimetidine at 1 or 10 micrograms/ml did not affect cell viability at 6, 12, or 24 h, whereas 100 micrograms/ml reduced cell viability (vs. placebo) at 12 and 24 h. LDH release and ultrastructural damage were not affected (not reduced) by cimetidine. Our study indicates that 16,16-dimethyl-PGE2, but not cimetidine, directly protects isolated gastric gland cells against degeneration in vitro, under conditions independent of systemic, neural, and hormonal factors.

Animals↗
PubMed1992

Stimulation of intestinal Cl- transport by heat-stable enterotoxin: activation of cAMP-dependent protein kinase by cGMP.

Heat-stable enterotoxins activate guanylate cyclase, whereas heat-labile enterotoxins stimulate adenylate cyclase. Both classes of toxins cause secretory diarrhea at least in part by stimulating Cl- secretion in the intestine. The mechanism for regulation of Cl- secretion by guanosine 3',5'-cyclic monophosphate (cGMP) was investigated using cultured T84 intestinal cells as a model for intestinal crypt cells. Escherichia coli heat-stable enterotoxin (ST) markedly stimulated cGMP production in T84 cells. Cl- secretion across T84 cell monolayers cultured on permeable filters was stimulated by E. coli ST, cholera toxin, or 8-BrcAMP, but 8-BrcGMP was ineffective. cGMP analogues that are known to be potent and specific activators of cGMP-dependent protein kinase (cG-kinase) also had little effect on 36Cl- uptake by T84 cells cultured in plastic dishes. E. coli ST, forskolin, cholera toxin, or membrane-permeant cAMP analogues markedly increased 36Cl- uptake into T84 cells. The general protein kinase inhibitor, staurosporine, inhibited the stimulation of Cl- permeability elicited by E. coli ST, vasoactive intestinal peptide (VIP), or 8-BrcAMP. DEAE-Sephacel chromatography revealed a predominant type II isoform of cAMP-dependent protein kinase (cA-kinase) in T84 cells, whereas little or no cytosolic cG-kinase activity was found. Treatment of T84 cells with E. coli ST or VIP resulted in an increase in the cA-kinase activity ratio (-cAMP/+cAMP) if the cytosolic enzyme was assayed at reduced temperature (on ice).(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗