Biomedical subjects

G H Curtis

Publications and source records attributed to G H Curtis.

14 recordsLinked to original sources

PubMed1996

Latest Homo erectus of Java: potential contemporaneity with Homo sapiens in southeast Asia.

Hominid fossils from Ngandong and Sambungmacan, Central Java, are considered the most morphologically advanced representatives of Homo erectus. Electron spin resonance (ESR) and mass spectrometric U-series dating of fossil bovid teeth collected from the hominid-bearing levels at these sites gave mean ages of 27 +/- 2 to 53.3 +/- 4 thousand years ago; the range in ages reflects uncertainties in uranium migration histories. These ages are 20,000 to 400,000 years younger than previous age estimates for these hominids and indicate that H. erectus may have survived on Java at least 250,000 years longer than on the Asian mainland, and perhaps 1 million years longer than in Africa. The new ages raise the possibility that H. erectus overlapped in time with anatomically modern humans (H. sapiens) in Southeast Asia.

Africa↗

PubMed1995

Intraluminal pH modulates gastric prostaglandin synthesis.

Prostaglandins play an important role in modulating gastric mucosal integrity and in regulating gastric acid secretion, but little is known regarding regulation of prostaglandin synthesis by the stomach. We have therefore examined the effects of changes in gastric intraluminal pH on the capacity of gastric tissue to synthesize prostaglandin E2. Oral administration of solutions with a pH of 8.3 or 10 markedly reduced the capacity of the gastric tissue to synthesize prostaglandin E2, but did not affect synthesis of leukotriene B4. This phenomenon was observed in three strains of rats. Administration of the same solutions subcutaneously did not affect gastric prostaglandin synthesis. On the other hand, oral administration of a solution of pH 1 significantly increased prostaglandin synthetic capacity, while a solution with a pH of 3 had no effect. The effects observed were not attributable to differences in the osmolarity of the test solutions. These studies suggest that changes in gastric intraluminal pH result in changes in gastric prostaglandin synthesis. It is possible that this represents a physiological response aimed at maintaining gastric mucosal integrity when intraluminal pH is low, while also providing a feedback inhibition of gastric acid secretion.

Animals↗

PubMed1994

Age of the earliest known hominids in Java, Indonesia.

40Ar/39Ar laser-incremental heating of hornblende separated from pumice recovered at two hominid sites in Java, Indonesia, has yielded well-defined plateaus with weighted mean ages of 1.81 +/- 0.04 and 1.66 +/- 0.04 million years ago (Ma). The hominid fossils, a juvenile calvaria of Pithecanthropus and a partial face and cranial fragments of Meganthropus, commonly considered part of the Asian Homo erectus hypodigm, are at least 0.6 million years older than fossils referred to as Homo erectus (OH-9) from Olduvai Gorge, Tanzania, and comparable in age with the oldest Koobi Fora Homo cf. erectus (Homo ergaster) in Kenya. These ages lend further credence to the view that Homo erectus may have evolved outside of Africa. If the ancestor of Homo erectus ventured out of Africa before 1.8 Ma, the dispersal would have predated the advent of the Acheulean culture at 1.4 Ma, possibly explaining the absence of these characteristic stone cleavers and hand axes in East Asia.

Africa↗

PubMed1994

Transport of bovine serum albumin across rat jejunum: role of the enteric nervous system.

To assess the mechanisms for movement of antigenically intact macromolecules across small intestinal mucosa, transport kinetics of bovine serum albumin (BSA) uptake and the effect of neural and metabolic inhibition were examined in stripped short-circuited rat jejunum. The mucosa was exposed to BSA, and, after a 50-min equilibration, mucosal-to-serosal movement of immunologically intact BSA was determined by enzyme-linked immunosorbent assay and total BSA by radiolabeled 125I-BSA. Intact BSA uptake demonstrated saturable kinetics. Immunologically intact BSA crossed the intestinal mucosa as 4.5% of total 125I-BSA flux. Colchicine and 4 degrees C significantly reduced uptake of immunologically intact BSA. NaF significantly reduced uptake of immunologically intact BSA and 125I-BSA. Treatment with tetrodotoxin significantly reduced intact BSA uptake, but did not significantly alter total BSA uptake. The muscarinic cholinoceptor antagonist atropine also significantly inhibited transport of intact BSA, whereas the nicotinic cholinoceptor antagonist hexamethonium had no effect. These findings indicate that transport of intact macromolecules across small intestinal mucosa is a saturable energy-dependent process that utilizes the microtubular network and is regulated by the enteric nervous system primarily through cholinergic nerves acting on muscarinic receptors.

Animals↗

PubMed1993

Effect of cyclooxygenase inhibition on macromolecular transport in rat gastric mucosa.

We have shown that the rat gastric mucosa takes up antigenically intact protein in vitro. The present study investigated the effect of two cyclooxygenase inhibitors, indomethacin and piroxicam, on gastric transport of BSA. Fasted rats were given indomethacin, piroxicam, or vehicle. After 30 min, the stomach was removed, stripped, and mounted in a Ussing chamber. Each side was bathed with Krebs buffer. Bovine serum albumin (BSA), 125I-labeled BSA (125I-BSA), and 51Cr-labeled EDTA (51Cr-EDTA) were added to the mucosal fluid and equilibrated for 30 min. Serosal fluids were sampled for two subsequent 30-min periods, and mean fluxes for immunologically intact BSA (enzyme-linked immunoabsorbent assay), total BSA (125I-BSA), and 51Cr-EDTA were calculated. Cyclooxygenase inhibition significantly (P < 0.01) reduced tissue prostaglandin E2 synthetic capacity (indomethacin, 97%; piroxicam, 92%) but did not cause either macroscopic or microscopic mucosal injury. Both inhibitors significantly (P < 0.05) decreased uptake of immunologically intact BSA (indomethacin, 91%; piroxicam, 81%) and 51Cr-EDTA. In contrast, the movement of degraded BSA was not altered by indomethacin. These findings suggest that a selective pathway exists for the uptake of intact proteins in gastric mucosa and that the pathway is modulated by cyclooxygenase metabolites.

Animals↗

PubMed1992

Macromolecular transport by rat gastric mucosa.

We previously demonstrated that the stomach is capable of mounting a type I hypersensitivity reaction to luminal antigen challenge. These findings imply that antigenically intact macromolecules cross the gastric mucosa. To test this hypothesis, rat gastric mucosa was mounted in Ussing chambers, and bovine serum albumin (BSA, 0.5 mg/ml) and 125I-labeled BSA (10 microCi) were added to mucosal fluids. After equilibration, serosal fluids were sampled for two 30-min periods, and fluxes of immunologically intact BSA (determined by an enzyme-linked immunosorbent assay) and total BSA (125I-BSA) were calculated under basal conditions and in the presence of NaF and colchicine, and at 4 degrees C. Additional experiments examined macromolecular permeability in sensitized-challenged tissues. Immunologically intact BSA (21.3 +/- 4.5 ng.30 min-1.cm-2) crossed the gastric mucosa as approximately one-fourth of the total BSA flux (78.2 +/- 7.5 ng.30 min-1.cm-2). The uptake of immunologically intact BSA was significantly reduced by NaF, an inhibitor of ATP production and endocytosis; colchicine, which inhibits polymerization of cytoskeletal microtubules; and at 4 degrees C, a general metabolic inhibitor. The transmural passage of antigen was not significantly altered by immunoglobulin E-mediated anaphylaxis. These findings indicate that intact protein antigens cross the gastric mucosa by an active, energy-dependent mechanism that uses the microtubular network.

Anaphylaxis↗

PubMed1990

Effect of acute Yersinia enterocolitica infection on small intestinal ultrastructure.

The purpose of this study was to assess the jejunal and ileal brush border injury caused by Yersinia enterocolitica and to correlate these alterations with functional abnormalities. Weanling rabbits infected with 10(10) organisms of a human pathogenic Y. enterocolitica strain were compared with control and pair-fed, sham-treated animals. On day 6, infection resulted in a diffuse decrease in brush border enzyme activities in the small intestine and villus atrophy and crypt hyperplasia in the ileum. By day 14, ileal architecture and jejunal disaccharidases had returned to normal, but enzyme abnormalities persisted in the ileum. Ultrastructural studies showed decreased brush border surface area in the jejunum and ileum on day 6 and in the ileum on day 14 of infection. Abnormalities of brush border function caused by infection correlated with the changes in microvillus surface area. In pair-fed animals on day 6, brush border surface area was slightly decreased in the ileum but increased in the jejunum, suggesting that the brush border injury resulted from infection rather than from malnutrition alone. The findings indicate that Y. enterocolitica inflicts a diffuse brush border injury that is in keeping with the generalized defect in brush border enzyme activity and transport function.

Abscess↗

PubMed1990

Intestinal anaphylaxis in the rat. Effect of chronic antigen exposure.

The effect of chronic dietary antigen challenge on the intestine was examined in sensitized rats. Three groups of Hooded-Lister rats were studied: animals sensitized to egg albumin; sham-sensitized animals; and unmanipulated controls. In sensitized rats, serum immunoglobulin E titers to egg albumin were greater than or equal to 1:64, whereas control and pair-fed rats showed no response. Sensitized rats received egg albumin 1 mg/ml in drinking water and rat chow ad libitum. Pair-fed animals also received egg albumin but were pair-fed with sensitized animals. Controls received water and rat chow ad libitum. Chronic antigen challenge resulted in reduced food intake and weight gain in sensitized animals. When the rats were killed after 9 days of antigen exposure, proximal intestine from experimental animals showed decreased disaccharidase activity, brush-border microvillus surface, area, and villus height. Crypt depth and enterocyte migration rate were increased. Mucosal mast cell involvement was suggested by mast cell proliferation, evidence of mast cell degranulation, and increased serum rat mast cell protease II levels. At the time of death, only sensitized jejunum demonstrated an increase in short-circuit current in Ussing chambers in response to antigen challenge. The findings indicate that chronic antigen exposure leads to intestinal injury, reduced food intake, and diminished weight gain.

Anaphylaxis↗

PubMed1976