Characteristics of spermidine uptake by isolated rat enterocytes

Eukaryotic cells require polyamines for growth. The supply of polyamines to growing cells may be increased either by new synthesis or increased uptake. We have recently shown that putrescine uptake by isolated rat enterocytes is energy dependent, saturable, and ouabain insensitive. Although putrescine uptake was inhibited by putrescine and cadaverine, it was not inhibited by equal concentrations of spermine and spermidine. These data indicated that a carrier mechanism separate from that putrescine existed for spermidine and spermine. In the current study spermidine uptake by isolated enterocytes was saturable, temperature dependent, and inhibited by 1 mM KCN. Kinetic analysis resulted in a Km = 2.51 x 10(-6) M and a Vmax = 3.57 x 10(-12) mol.10(6) cells-1.15 min-1. Spermidine uptake was 70% inhibited by 1 mM ouabain. Replacement of sodium by choline, lithium, tetramethylammonium, or N-methyl-D-glucamine also inhibited spermidine uptake. Replacement of Na+ by mannitol or sucrose, however, depressed uptake but not significantly. Spermidine uptake was inhibited by 1 mM ouabain. Spermidine uptake was inhibited by relatively low concentrations of spermine and high concentrations of putrescine; while putrescine uptake was inhibited by relatively high concentrations of both spermine and spermidine. Kinetic data indicated that spermidine and spermine share a carrier that is distinct from the one mediating the uptake of putrescine. While spermidine uptake does not appear to depend on Na+ cotransport, it may be dependent on the electrical gradient established by the Na+-K+-ATPase.

Putrescine uptake and release by colon cancer cells

We have investigated the uptake and release of [3H]putrescine by a human colon adenocarcinoma cell line (LoVo) maintained on filter inserts. This culture system permits the cells to develop morphological polarity and provides separate access to the basolateral and apical surfaces of the cells. [3H]putrescine was taken up more readily by the basolateral than by the apical side of the cells. [3H]putrescine uptake could be stimulated greater than 300 times by either 10 mM asparagine or 10% fetal bovine serum. [3H]putrescine was accumulated to a concentration gradient of approximately 300-fold; uptake could be inhibited 50% by 7.5 microM unlabeled putrescine and was not dependent on Na+. The release of [3H]putrescine into the apical medium was inhibited by asparagine or fetal bovine serum. Usually, less than one-thousandth of the [3H]putrescine taken up into the cells was released into the apical medium. Release of [3H]putrescine did not correspond to the accumulation of [14C]-inulin in the apical medium. For these reasons we concluded that putrescine release was not simply passive leakage but was responsive to intracellular demand. The [3H]putrescine taken up by the cells as well as that released into the apical medium was greater than 90% unmetabolized at 4h.

Mucosal ornithine decarboxylase in the small intestine: localization and stimulation

In most tissues increases in ornithine decarboxylase (ODC) are associated with growth. Refeeding fasted rats. a potent stimulus for mucosal growth, strongly increases ODC in both small and large intestinal mucosa. In the small bowel, almost all of this increase occurs in the mature villus cells rather than the proliferative crypt cells. Nevertheless, inhibition of ODC with difluoromethylornithine blocks the growth response. Using a highly specific, polyclonal antiserum to ODC, we have determined that in the fasted rat ODC is localized almost exclusively to the villus cells. Using antiserum dilution techniques, we have shown that, within 2 h, refeeding increases the amount of immunoreactive ODC in both villus and crypt cells. Furthermore, the trophic hormone gastrin also increases ODC, but only in the crypt cells. Epidermal growth factor increased ODC to a greater extent than gastrin, but stimulation was more general, including both crypt and villus cells. Perfusing an isolated segment of small bowel in situ with glycine for 2 h also increased immunoreactive ODC but only in the villus cells. Thus in the small intestine the effect of refeeding on ODC activity appears to be mediated by different types of stimuli: luminal nutrients increase enzyme levels in the absorbing villus cells, while trophic peptides stimulate ODC synthesis in the proliferative crypt cells.

Reference values for FEV1 in Japanese-American men from 45 to 68 years of age

Pulmonary function is known to vary by racial group, yet no standards have been published for Asian-Americans. The Honolulu Heart Program, a prospective epidemiologic study of cardiovascular disease, provided an opportunity to examine pulmonary function, specifically, forced expiratory volume in one second (FEV1), in Japanese-American men 45 to 68 yr of age. Of a cohort of 6,346 men, 1,490 were identified as healthy asymptomatic nonsmokers. Prediction equations and reference values were derived from this subgroup. When the prediction equation was compared with those derived from Caucasian and black populations, mean predicted FEV1 for Japanese-Americans was intermediate to higher values for Caucasians and lower values for blacks. In addition to age and height, skinfolds, dynamometry, and biacromial diameter were found to be independent predictors of FEV1. In summary, standards derived from Japanese-American populations should be used when measuring pulmonary function in this group and additional physical measurements make a small contribution to the accuracy of prediction equations.

Correlates of FEV1 and prevalence of pulmonary conditions in Japanese-American men

Correlates of forced expiratory volume in one second (FEV1) and the prevalence of pulmonary disease and symptoms were examined in 6,346 Japanese-American men 45 to 68 yr of age. There was a significant inverse dose-response relationship between FEV1 and cigarette smoking measured as pack-years, number of cigarettes, or number of years smoked. Ex-smokers had FEV1 values that were intermediate to the higher values for nonsmokers and the lower values for current smokers. Among current smokers, inhaling and starting to smoke at a younger age were associated with lower values of FEV1, independent of pack-years. FEV1 was also correlated with a variety of other biologic and sociobehavioral variables, even after removing the effects of smoking. These variables included skinfold thickness, dynamometry, hematocrit, triglycerides, and systolic blood pressure. When compared with Caucasian populations, these Japanese-American men had low prevalence rates of airflow obstruction and pulmonary disease symptoms.

Prostaglandin-mediated trophic effects on the rat duodenum: the role of polyamines

Ornithine decarboxylase (ODC) is the initial rate-limiting enzyme in polyamine biosynthesis. The relationship between ODC and polyamines and the trophic effect of prostaglandin in the rat gastrointestinal tract are unknown. In these studies we determined whether inhibition of ODC activity and subsequent polyamine biosynthesis with the specific enzyme inhibitor difluoromethyornithine (DFMO) would attenuate prostaglandin-mediated trophic effects in the rat duodenum. Significant increases in duodenal mucosal wet weight, RNA, DNA, and protein were found following treatment with 16,16-dimethyl-PGE2 (1 mg/kg) for 1 week. This trophic response was significantly reduced (P less than 0.01) in the duodenum of rats treated concomitantly with DFMO. In addition, this prostenoid significantly increased (4X) duodenal ODC levels, 2 hr following acute administration. These results suggest that polyamines are required for the prostaglandin-stimulated growth of the rat duodenal mucosa.

Gastric mucosal ornithine decarboxylase: localization and stimulation by gastrin

Gastrin injection and refeeding fasted rats are effective trophic stimuli for the oxyntic gland mucosa of the stomach. Neither stimulus increases detectable ornithine decarboxylase (ODC) activity in the tissue. Difluoromethylornithine (DFMO), a potent inhibitor of ODC, blocks the mucosal growth response, indicating that ODC activity is necessary for growth. Elevated levels of spermidine and spermine are detectable in the mucosa after gastrin administration. Using a highly specific, polyclonal antiserum to ODC, we determined that the enzyme is present in oxyntic gland mucosa confined to a narrow band of cells at the base of the gastric pits and openings of the glands. In antral mucosa, ODC is present throughout the lower 20% of the mucosa, which consists of the necks and pyloric glands. Using antiserum dilution techniques, we show that gastrin administration increases immunoreactive ODC in the oxyntic gland area but not in the antral mucosa, where it has no trophic effect. Elevated cellular content of ODC is apparent within 2 h after injection of gastrin, peaks at 4 h, and declines to basal levels by 12 h. Gastrin-stimulated increase in ODC is confined to the narrow band of cells in which low levels of the enzyme protein were detected in control animals. The decarboxylating activity detectable in oxyntic gland mucosal extracts is not inhibited by administration of DFMO or cycloheximide, each of which inhibits ODC activity in other tissues. Addition of unlabeled lysine to the decarboxylation assay reaction of oxyntic gland mucosa extract inhibits the decarboxylation of radiolabeled ornithine substrate. Thus it is likely that the stomach possesses nonspecific decarboxylase activity, which accounts for most of the measured activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Longitudinal versus cross-sectional estimation of lung function decline--further insights

This paper explores the extent to which differences in longitudinal versus cross-sectional inference may be influenced by the choice of statistical models. Using lung function data on 524 working men, we first compare the goodness-of-fit and implication for longitudinal decline of a variety of cross-sectional models. We then compare the predicted longitudinal patterns from these models with those observed over a period of four years. In general, both approaches provide qualitatively, if not quantitatively, similar messages concerning the relative effects of smoking and age on lung function decline. Nonetheless, we acknowledge the existence of real selection and cohort effects. Although we recognize the utility of cross-sectional designs, we discourage quantitative comparisons between studies, especially longitudinal versus cross-sectional.

Amiloride inhibits rat mucosal ornithine decarboxylase activity and DNA synthesis

Refeeding fasted rats induces a dramatic trophic response in gastrointestinal mucosa and is associated with elevations in both the rate of DNA synthesis and ornithine decarboxylase (ODC) activity. The signal for these increases is unknown. Amiloride prevents cell alkalinization by blocking Na+-H+ exchange at apical epithelial cell membranes. In study 1, rats were fasted 48 h, treated with amiloride (0.5 to 500 mg/kg), and refed for 4 h. Refeeding increased ODC activities in the jejunal mucosa (X8) and liver (X19) but not in the oxyntic gland mucosa. In the jejunum, but not the liver, the activation of ODC was completely abolished by 100 mg/kg amiloride. In study 2, the rate of DNA synthesis was determined by measuring the rate of [3H]thymidine incorporation 16 h after refeeding. Refeeding resulted in significantly increased rates of DNA synthesis (dpm.microgram DNA-1.30 min-1) over fasted levels, and amiloride at 100 mg/kg significantly reduced the elevations in the jejunum and liver. In conclusion, amiloride inhibits the postprandial increases in jejunal ODC activity and DNA synthesis in the jejunum and liver. The results indicate that 1) the Na+-H+ antiport is essential to the increased ODC activity in the jejunum and the stimulation of DNA synthesis in the jejunum and liver after a meal and 2) increases in DNA synthesis and their suppression by amiloride are not necessarily linked to ODC activity.

Does the single-breath N2 test identify the smoker who will develop chronic airflow limitation?

We report here the results of a 9- to 11-yr follow-up of 2 cohorts in which spirometry and the single-breath N2 test were used throughout the follow-up period to determine the usefulness of the single-breath N2 test in identifying the smoker who is experiencing a rapid decline in FEV1 and is therefore likely to be at risk of developing chronic airflow limitation. The analyses are based on 734 subjects tested from 3 to 5 times over the follow-up period; 82 smokers developed an abnormal FEV1 during the follow-up period. Of these, 71 (87%) had had an abnormal single-breath N2 test at some time prior to the FEV1 becoming abnormal. Of the single-breath N2 test variables, CC/TLC was the only one significantly associated with the rate of decline of FEV1 in both cohorts once adjustments were made for age, sex, height, and smoking. We conclude that the single-breath N2 test can be useful in identifying the smoker who is at risk of developing chronic airflow limitation. However, its usefulness is diminished by the high proportion of smokers who have mild functional abnormalities but do not progress to develop chronic airflow limitation. We also find that the single-breath N2 test does not appear to have a useful predictive value in nonsmokers.

Characteristics of putrescine uptake in isolated rat enterocytes

Polyamines are necessary for the growth of eukaryotic cells and are supplied either by new synthesis or cellular uptake. To our knowledge, no information is available on polyamine uptake by gastrointestinal cells. In the current study, isolated villous enterocytes from the rat accumulated putrescine to an eightfold concentration gradient. Uptake was temperature dependent, saturable, and inhibited by 1 mM KCN. Kinetic analysis showed a Km of 1.23 X 10(-5) M and a Vmax of 2.60 X 10(-10) mol.10(6) cells-1.15 min-1. Enterocytes from the distal one-fourth of the gut showed the highest rate of uptake. Putrescine uptake was inhibited by cadaverine and spermine but not by the amino acids asparagine, AIB, or leucine. Sodium replacement by choline, lithium, N-methyl-D-glucamine, or tetramethylammonium significantly inhibited uptake, but replacement of Na+ by sucrose or mannitol was without effect. The inhibition observed was believed to be due to the ability of the cations to interact in some way with the carrier. Neither ouabain nor digitoxigenin had any effect on uptake. These data indicate that putrescine is accumulated by villous enterocytes by a carrier-mediated process that does not appear to involve Na+ contransport.

The role of food intake on gastric mucosal growth and gastrin receptors during pregnancy and lactation

We examined the effects of pregnancy and lactation on mucosal growth and the numbers and affinity of gastrin receptors in the oxyntic gland mucosa in rats and compared these with changes in serum gastrin levels and food consumption. Gastric mucosal DNA, RNA, and protein contents were significantly increased during lactation. These changes were not observed in either pregnant or nonlactating rats which had given birth at the same time as the lactating animals. The gastrin-binding capacity of a membrane fraction of the oxyntic mucosa was also increased at the corresponding periods in lactating rats (Days 7, 15, 20). Scatchard plot analysis revealed that the number of gastrin receptors was significantly increased without any change in affinity. Food consumption and levels of serum gastrin remained unaltered in pregnant and non-lactating rats compared to virgin controls, but were significantly increased in lactating rats. Increased serum gastrin levels and gastrin binding capacities in lactating rats (Day 15) were abolished by preventing increased food consumption by means of pair feeding. The results demonstrate that the number of gastrin receptors in the oxyntic mucosa increases during lactation in rats. This increase is probably due to hypergastrinemia caused by increased food intake. The increased number of gastrin receptors may be involved in the mechanism of hypertrophic responses of the gastric mucosa in lactating rats.

Ultrastructure of degenerative changes following ricin application to feline dental pulps

The ultrastructure of degenerative changes within the ipsilateral trigeminal ganglion, and partes caudalis and interpolaris of the spinal trigeminal nucleus in the cat is described following the application of the potent toxin ricin to the tooth pulps of unilateral maxillary and mandibular posterior teeth, including the cuspids. Survival times ranged from 6 to 10 days. Typical changes identified within the ipsilateral trigeminal ganglion included myelin fragmentation and 'compartmentalization' of the axoplasm of medium-sized myelinated axons, while small myelinated and unmyelinated axons underwent a more variable response ranging from electron-lucent to electron-dense changes. The affected cell body was characterized by the presence of swollen, electron-lucent mitochondria, a reduction of cytoplasmic ribosomes and a filamentous hyperplasia. Other changes often included an eccentric nucleus and satellite cell proliferation. Degenerative changes often occurred in isolated elements surrounded by normal profiles, suggesting specificity of ricin within the trigeminal ganglion. Changes within brainstem axons showed both an electron-dense and a lucent, fragmenting type of axonal alteration. Terminal changes ranged from electron-dense to lucent and also included filamentous hyperplasia and 'hyperglycogenesis'. The altered axonal knobs contained round synaptic vesicles that were presynaptic to dendritic profiles and postsynaptic to terminals containing flattened synaptic vesicles. The above brainstem alterations were identified specifically in the following areas: ventrolateral, medial and dorsomedial pars interpolaris; the ventrolateral and mid-dorsal to dorsomedial areas of the marginalis and outer substantia gelatinosa layers of pars caudalis; and in ventral pockets corresponding to lamina V of the medullary dorsal horn. Dense alterations within terminals containing flattened synaptic vesicles that are typically presynaptic to primary afferents in these areas were rare findings, but along with vacuolization of dendritic profiles suggest a trans-synaptic effect possibly due to the exocytosis of ricin. The results are discussed in relation to different reports of dental projections and with regards to patterns of transganglionic degeneration.

Hormonal effects on development of the secretory apparatus of chief cells

We used light microscopy, transmission electron microscopy, and stereological point-counting methods to investigate the response of rat gastric chief cells to corticosterone and thyroxine during postnatal development. Administration of corticosterone or thyroxine to normal animals in the first two postnatal weeks increased relative numbers of chief cells in the fundic mucosa but did not change the absolute number of total cells in each gland. The chief cells displayed more rough endoplasmic reticulum, zymogen granules, and Golgi saccules in corticosterone- or thyroxine-injected rats than in normal control rats. When rats were either adrenalectomized or made hypothyroid using propylthiouracil, the number of chief cells dramatically decreased. Ultrastructural studies of chief cells from adrenalectomized or hypothyroid rats showed retarded differentiation as indicated by increased free ribosomes, less rough endoplasmic reticulum, fewer zymogen granules, and poorly developed Golgi apparatuses. In adrenalectomized animals, thyroxine replacement alone failed to induce the histological maturation of chief cells, but addition of corticosterone stimulated chief cell differentiation. In hypothyroid animals, either thyroxine or corticosterone replacement restored the differentiation of chief cells to normal levels. Our data indicate that 1) corticosterone is necessary for gastric chief cell maturation during postnatal development, 2) a decrease or loss in either corticosterone and/or thyroxine results in retarded chief cell differentiation and functional activity, and 3) the effect of thyroxine on chief cell development is secondary to an accompanying increase in serum corticosterone.

Dual fluorometric/colorimetric detection system for an automated random-access instrument utilizing standard polystyrene test tubes as precision cuvettes

To attain the optical precision necessary to precisely quantify fluorescent or colorimetric signals, analytical systems have typically included quality-controlled cuvettes, flow cells, or dual-beam reference systems. We describe a system where a fluorescence or transmittance signal is quantified in single, standard, 12-mm-diameter polystyrene test tubes. Tube-to-tube variation is minimized by referencing the primary signal to a second reference signal. The tube is carefully oriented within a positioner that allows for the precise placement of the tube within a light path 7.6 mm in diameter. The detection system allows for use of either four pairs of fluorescence excitation/emission wavelengths or eight transmittance wavelengths, which are selected by using specific interference filters. The impact of temperature, tube imperfections, surface flaws, and distortions is minimized by using a reference ratio. Fluorescence is measured with an orthogonal photomultiplier tube, and transmittance with a photodiode; both are illuminated with an ordinary long-life tungsten-halogen lamp. This system is used with the Becton Dickinson AFFINITY system, an automated random-access analyzer with analyte-specific unit-package reagents. The polystyrene tube of the reagent package, which has an antibody-absorbed surface, serves as both the cuvette and the separation medium. Use of the reference ratio method reduces intertube imprecision of fluorometric or transmittance signals, for more precise quantification of various analytes.

Dual fluorometric/colorimetric detection system for an automated random-access instrument utilizing standard polystyrene test tubes as precision cuvettes

To attain the optical precision necessary to precisely quantify fluorescent or colorimetric signals, analytical systems have typically included quality-controlled cuvettes, flow cells, or dual-beam reference systems. We describe a system where a fluorescence or transmittance signal is quantified in single, standard, 12-mm-diameter polystyrene test tubes. Tube-to-tube variation is minimized by referencing the primary signal to a second reference signal. The tube is carefully oriented within a positioner that allows for the precise placement of the tube within a light path 7.6 mm in diameter. The detection system allows for use of either four pairs of fluorescence excitation/emission wavelengths or eight transmittance wavelengths, which are selected by using specific interference filters. The impact of temperature, tube imperfections, surface flaws, and distortions is minimized by using a reference ratio. Fluorescence is measured with an orthogonal photomultiplier tube, and transmittance with a photodiode; both are illuminated with an ordinary long-life tungsten-halogen lamp. This system is used with the Becton Dickinson AFFINITY system, an automated random-access analyzer with analyte-specific unit-package reagents. The polystyrene tube of the reagent package, which has an antibody-absorbed surface, serves as both the cuvette and the separation medium. Use of the reference ratio method reduces intertube imprecision of fluorometric or transmittance signals, for more precise quantification of various analytes.

Hormonal effects on development of the secretory apparatus of parietal cells

The effect of corticosterone and thyroxine on the development of parietal cells was studied in 20-day-old rats. Either corticosterone or thyroxine injection significantly increased the amount of mitochondria, tubulovesicles, and intracellular canaliculi in normal rat pup parietal cells. However, the ultrastructure of parietal cells did not change when rats were adrenalectomized or made hypothyroid by propylthiouracil (PTU) during the first week of life. Corticosterone had the same effect in hypothyroid rats as in normal rats, increasing the volume fraction of mitochondria and the surface density of tubulovesicles and intracellular canaliculi in the parietal cell. However, thyroxine failed to do so in adrenalectomized animals. When 20-day-old adrenalectomized or hypothyroid rats were challenged with secretagogues, there was no increase in maximal acid output over the basal secretory rate, while normal rats showed a 40-50% increase. We conclude that 1) normal parietal cells respond to additional thyroxine or corticosterone with increases in volume fraction of mitochondria and surface density of tubulovesicles and intracellular canaliculi; 2) the dramatic decreases in acid secretion observed in adrenalectomized or PTU-treated rats are not explained by the morphology of parietal cells that remains normal; 3) the effect of thyroxine on the development of acid secretion is mediated by corticosterone; and 4) unlike chief cells the morphological development of parietal cells does not appear to depend on corticosterone or thyroxine after postnatal day 7.

Stimulation of ornithine decarboxylase activity in digestive tract mucosa

Refeeding fasted rats with normal rat food and with a variety of amino acids increases ornithine decarboxylase (ODC) activity considerably. The time course of that increase, the areas of the digestive tract directly affected, and the effective concentrations of stimulants are unknown. By use of isolated 5-cm segments of rat jejunum, we determined that maximal activation of ODC occurred after a 2-h exposure to 0.6 M glycine. Increased activity was first apparent after a 1-h exposure to glycine and was significant after a 2-h exposure to 0.05 M glycine. ODC activity increased the most in segments of jejunum, followed by segments of ileum and then duodenum. Glycine (0.4 M) failed to increase ODC activity in gastric and colonic mucosa. Interestingly, D-alanine was more effective than L-alanine in stimulating ODC activity in the jejunum. Enzyme activity was not dependent on osmotic activity of the test substances. Glucose increased enzyme activity, but mannitol and fructose were without effect. The effects of glycine were significantly greater than those of glucose. In summary, ODC of the small intestinal mucosa is increased by direct contact with amino acids and glucose within 2 h after exposure. Increased enzyme activity depends on the nature of the stimulant rather than the osmotic activity of the solution in contact with the mucosa.

Effect of putrescine on oxyntic gland and colonic mucosal growth in rats

The effect of putrescine on oxyntic gland and colonic mucosal growth was studied by measuring the rate of [3H]-thymidine incorporation into mucosal DNA in vitro (DNA synthesis) and DNA, RNA and protein content of the mucosa following intramuscular injections of the compound (50 mumoles/100g). Saline injected animals served as controls. Multiple injections of putrescine during a 2-day fast produced a significant enhancement of mucosal DNA synthesis in oxyntic gland and colonic mucosa, with no apparent change in DNA, RNA or protein content in either of the tissues, compared to the corresponding saline-controls, when measurements were made 12-24 h after the last injection. However, when the animals were killed after 4 days, DNA, RNA and protein content of oxyntic gland mucosa, and DNA and protein content of colonic mucosa were found to be significantly higher than in the respective saline-controls. We conclude that putrescine, taken up from the blood, can stimulate growth of gastrointestinal mucosa.

Relationship between ornithine decarboxylase activity and gastric damage

Hypertonic NaCl increases the activity of gastric mucosal ornithine decarboxylase (ODC). Intragastric administration of concentrated NaCl solution also induces ulcers in the glandular gastric mucosa. The relationship between ODC activity and gastric mucosal damage and the significance of ODC increases in hypertonic NaCl-treated rats are unknown. Rats were fasted 24 h before being given 1.0 ml of 3.4 M NaCl, 120 mM aspirin in 100 mM HCl or 50% ethanol intragastrically. The oxyntic gland mucosa was removed and assayed for ODC and in some experiments DNA, RNA, and protein content. DNA, RNA, and protein content were decreased by 3.4 M NaCl, and these decreases were much greater if ODC was inhibited by pretreatment with alpha-difluoromethylornithine (DFMO). Both aspirin and 3.4 M NaCl induced ODC activity 6 h later. However, DFMO increased the lesion index only in NaCl-treated rats. Although ethanol produced damage, it had no effect on ODC levels, and DFMO did not alter the severity of ethanol lesions. When different concentrations (0.4, 0.8, 1.6, 2.5, and 3.4 M) of NaCl were administered, ODC activities were increased 6 h later in rats receiving 1.6, 2.5, and 3.4 M NaCl but not lower concentrations. Gross lesions appeared in response to the 2.5 M dose and increased with increasing NaCl concentration. However, microscopic damage of the gastric mucosa occurred at all the concentrations tested. These data show that 1) ODC activation is not necessarily produced by damage, 2) in the case of NaCl, increasing damage increases ODC, and 3) ODC appears to have a role in the prevention of a recovery to damage caused by NaCl.

Role of ornithine decarboxylase in functional development of rat gastric mucosa

The effects of inhibiting polyamine synthesis on the functional development of the gastric mucosa were studied in rats from 5 to 40 days old. They were treated from day 14 after birth with alpha-difluoromethylornithine (DFMO) at a concentration of 2% in the drinking water of mothers and pups. The rats were weaned on day 18. Basal acid and pepsin secretion, oxyntic gland mucosal pepsinogen content, and antral gastrin content followed similar developmental patterns in control animals. Levels of these parameters remained measurable but low until around the time of weaning, when dramatic log linear rises were observed. DFMO failed to delay the onset of the rises in any of these maturational indices. Ornithine decarboxylase (ODC) activity in the oxyntic gland mucosa was low but discernible in rats of every age studied. DFMO significantly reduced ODC activity at every age except 40 days, where there was no difference from control values. Our results suggest that ODC activity in the rat gastric mucosa does not change appreciably during neonatal development and that inhibiting putrescine synthesis from its precursor ornithine by DFMO treatment does not prevent or delay gastric mucosal maturation.

Effect of epidermal growth factor on polyamine-synthesizing enzymes in rat enterocytes

A number of peptides having trophic activity on gastrointestinal mucosa and growth factors are known to induce small intestinal ornithine decarboxylase (ODC) activity. The effect of peptides on ODC and S-adenosylmethionine (SAMDC) activities (key enzymes in polyamine biosynthesis) in isolated enterocytes is unknown. Male Sprague-Dawley rats were fasted for 72 h and injected intraperitoneally with epidermal growth factor (EGF), pentagastrin, or glucagon, or intragastrically with EGF. A similar volume of water served as a control. Villus tip, midvillus, and crypt cell fractions were collected and identified. ODC and SAMDC activities were determined in these cells 4 h after peptide injection. EGF given intraperitoneally, but not intragastrically, stimulated ODC activity along the cryptvillus column. Pentagastrin and glucagon did not induce polyamine biosynthetic enzyme activity. ODC and SAMDC activities in intestinal mucosal scrapings from fasted animals also were increased 2-4 h after intraperitoneal EGF treatment. It is possible that EGF binding at the serosal surface of the crypt enterocyte and subsequent ODC induction is important in initiating the cellular proliferation that is known to occur after treatment with this peptide.

Methodologic issues in the analysis of lung function data

The forced expiratory volume in one second (FEV1) is routinely used in epidemiologic studies of lung function to assess the presence and severity of obstructive airways disease. Normative prediction equations developed using data from healthy, asymptomatic individuals may then be used both in a clinical setting and to adjust comparisons among risk subgroups for known demographic differences. Unfortunately no concensus has yet developed as to how best to model lung function data. This paper addresses this issue in a systematic manner using data derived from two cohorts followed over a period of 9-11 years. We compare a variety of cross-sectional and longitudinal models for FEV1, show how they may be expressed as members of a larger class of general linear models, and discuss goodness-of-fit procedures for comparing them. We found little objective evidence for discriminating among these models; only those fit to FEV1/ht3 performed poorly. We argue on subjective grounds for the use of models based on FEV1 as a function of age, height and their interactions.