Potential estrogenic and antiestrogenic activity of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and the linear siloxane hexamethyldisiloxane (HMDS) in immature rats using the uterotrophic assay.

The cyclic siloxane octamethylcyclotetrasiloxane (D4) and the linear siloxane hexamethyldisiloxane (HMDS) have numerous industrial and consumer applications and thus have the potential for human exposure. The present study was undertaken to examine potential estrogenic and antiestrogenic activities of D4 and HMDS. To address potential differences in sensitivity between rat strains the study used both Sprague-Dawley (SD) and Fischer 344 (F-344) rats. Estrogenicity of the test compounds was determined by measuring absolute and relative uterine weights in immature rats and by monitoring uterine epithelial cell height. In order to place the data obtained for D4 into perspective relative to strong and weak estrogenic compounds, the response produced by D4 at 0, 10, 50, 100, 250, 500, and 1000 mg/kg/day was compared to responses produced by ethinyl estradiol (EE) (1, 3, 10, or 30 microg/kg/day), diethylstilbestrol dipropionate (DES-DP) (0.5, 1.5, 5, 15 microg/kg/day), and coumestrol (CE) (10, 35, 75, 150 mg/kg/day). Antiestrogenic effects were evaluated by co-administering D4 (500 mg/kg/day) with EE at 1, 3, 10, and 30 microg /kg/day. All compounds were administered in sesame oil at a volume of 5 mL/kg by oral gavage. Beginning on postnatal day 18 (SD) or 21 (F-344) each pup (12 per group) received a single dose of test compound once a day for 4 consecutive days. The pups were euthanized the morning after the last treatment and their uteri removed, weighed, and processed for histological examination. EE and DES-DP produced a significant dose-dependent increase in absolute and relative uterine weights and uterine cell height. The maximum increase in uterine weight following EE exposure was approximately 350% relative to controls in both strains. The weak phytoestrogen CE also produced a dose-related increase in absolute and relative uterine weight and epithelial cell height, but the response occurred over a much higher range of doses. At the highest dose of CE, uterine weight was increased approximately 230% relative to controls. Following exposure to D4, absolute and relative uterine weights and uterine epithelial cell height were statistically significantly increased in both strains of rats at doses above 100 mg/kg/day. In terms of uterine weight, D4 was approximately 0.6 million times less potent than EE or DES-DP in SD pups and 3.8 million times less potent than EE or DES-DP in F-344 pups. The maximal increase in uterine weight, relative to controls, produced by D4 at 1000 mg/kg/day was approximately 160% in SD rats, while the maximum increase produced by D4 in F-344 rats was 86%. D4 co-administered over a wide range of EE doses, resulted in a significant reduction in uterine weight compared to EE alone. HMDS was evaluated in SD rats only. The response produced by HMDS (600 and 1200 mg/kg/day) was compared to EE (3 microg/kg/day). Antiestrogenic effects were evaluated by co-administering HMDS (1200 mg/kg/day) with EE at 3 microg/kg/day. HMDS had no measurable effect on uterine weight under the experimental conditions described here. However, HMDS coadministered with EE did produce a small, but statistically significant reduction in uterine weight compared to EE alone. In conclusion, D4 showed weak estrogenic and antiestrogenic activity that was several orders of magnitude less potent than EE, and many times less potent than the weak phytoestrogen CE.

Repeated inhalation exposure to octamethylcyclotetrasiloxane produces hepatomegaly, transient hepatic hyperplasia, and sustained hypertrophy in female Fischer 344 rats in a manner similar to phenobarbital.

Octamethylcyclotetrasiloxane (D4) has been described as a phenobarbital-like inducer of hepatic enzymes. Phenobarbital (PB) and phenobarbital-like chemicals induce transient hepatic and thyroid hyperplasia and sustained hypertrophy in rats and mice. The extent to which these processes are involved with D4-induced hepatomegaly is not known. The present study has evaluated the effects of repeated inhalation exposure to D4 vapors on hepatic and thyroid cell proliferation and hypertrophy with respect to time and exposure concentration. Female Fischer 344 rats were exposed via whole body inhalation to 0 ppm D4, 700 ppm D4 vapors (6 h/day; 5 days/week), or 0.05% PB in drinking water over a 4-week period. Incorporation of 5'-bromo-2-deoxyuridine (BrdU) and the abundance of proliferating cell nuclear antigen were used as indicators of cell proliferation. Designated animals from each treatment group were euthanized on study days 6, 13, and 27. The effect of D4 exposure concentration on hepatic cell proliferation was evaluated at 0, 7, 30, 70, 150, 300, or 700 ppm. Liver-to-body weight ratios in animals exposed to 700 ppm D4 were increased 18, 20, and 22% over controls while PB-treated animals showed increases of 33, 27, and 27% over controls on days 6, 13, and 27 respectively. Hepatic incorporation of BrdU following exposure to D4 was highest on day 6 (labeling index = 15-22%) and was at or below control values by day 27. This pattern of transient hyperplasia was observed in all hepatic lobes examined and was similar to the pattern observed following treatment with PB.

Physiological modeling reveals novel pharmacokinetic behavior for inhaled octamethylcyclotetrasiloxane in rats.

Octamethylcyclotetrasiloxane (D4) is an ingredient in selected consumer and precision cleaning products. Workplace inhalation exposures may occur in some D4 production operations. In this study, we analyzed tissue, plasma, and excreta time-course data following D4 inhalation in Fischer 344 rats (K. Plotzke et al., 2000, Drug Metab. Dispos. 28, 192-204) to assess the degree to which the disposition of D4 is similar to or different from that of volatile hydrocarbons that lack silicone substitution. We first applied a basic physiologically based pharmacokinetic (PBPK) model (J. C. Ramsey and M. E. Andersen, 1984, Toxicol. Appl. Pharmacol. 73, 159-175) to characterize the biological determinants of D4 kinetics. Parameter estimation techniques indicated an unusual set of characteristics, i.e., a low blood:air (P(b:a) congruent with 0.9) and a high fat:blood partition coefficient (P(f:b) congruent with 550). These parameters were then determined experimentally by equilibrating tissue or liquid samples with saturated atmospheres of D4. Consistent with the estimates from the time-course data, blood:air partition coefficients were small, ranging from 1.9 to 6.9 in six samples. Perirenal fat:air partition coefficients were large, from 1400 to 2500. The average P(f:b) was determined to be 485. This combination of partitioning characteristics leads to rapid exhalation of free D4 at the cessation of the inhalation exposure followed by a much slower redistribution of D4 from fat and tissue storage compartments. The basic PK model failed to describe D4 tissue kinetics in the postexposure period and had to be expanded by adding deep-tissue compartments in liver and lung, a mobile chylomicron-like lipid transport pool in blood, and a second fat compartment. Model parameters for the refined model were optimized using single-exposure data in male and female rats exposed at three concentrations: 7, 70, and 700 ppm. With inclusion of induction of D4 metabolism at 700 ppm (3-fold in males, 1-fold in females), the parameter set from the single exposures successfully predicted PK results from 14-day multiple exposures at 7 and 700 ppm. A common parameter set worked for both genders. Despite its very high lipophilicity, D4 does not show prolonged retention because of high hepatic and exhalation clearance. The high lipid solubility, low blood:air partition coefficient, and plasma lipid storage with D4 led to novel distributional characteristics not previously noted for inhaled organic hydrocarbons. These novel characteristics were only made apparent by analysis of the time-course data with PBPK modeling techniques.

Interpreting the toxicologic significance of alterations in anogenital distance: potential for confounding effects of progeny body weights.

Anogenital distance (AGD) is an endpoint that was recently added to the U.S. EPA testing guidelines for reproductive toxicity studies. This endpoint is sensitive to hormonal effects of test chemicals. It is possible that apparent alterations in AGD might occur after treatment with agents that affect overall pup body size. In such cases, hormonal activity might be associated incorrectly with the test treatment. The analyses in this report evaluated statistical correlations between pup body weight and AGD in control litters. AGDs were measured on postnatal day 1 in 1501 pups derived from 113 untreated female Sprague-Dawley rats in two independent two-generation reproductive toxicity studies. Significant correlations were detected between AGD and body weight and between AGD and the cube root of body weight. In males, AGD increased 0.26 mm for each 1 g increase in body weight. In females, AGD increased 0.13 mm per 1 g increase in body weight. Although there were essentially no differences between the regression models developed to predict AGD in either males or females using body weight as a covariate and those based on the cube root of body weight, such similarities in predictivity might not occur in larger animals with broader weight ranges than those encountered in this analysis. Normalization of AGD by dividing by body weight significantly overcompensated for differences in body size. Normalizing with the cube root of body weight resulted in an AGD/cube root of body weight ratio that was constant across the range of body weights observed in this study. In conclusion, as a preferred method to account for body size effects on AGD, analysis of covariance is recommended. If a normalization is done directly, the ratio of AGD to the cube root of body weight is the more appropriate metric.

Induction of hepatic xenobiotic metabolizing enzymes in female Fischer-344 rats following repeated inhalation exposure to decamethylcyclopentasiloxane (D5).

Decamethylcyclopentasiloxane (D5) is a cyclic siloxane with a wide range of commercial applications. The present study was designed to investigate the effects of D5 on the expression and activity of selected rat hepatic phase I and phase II metabolizing enzymes. Female Fischer-344 rats were exposed to 160 ppm D5 vapors (6 h/day, 7 days/week, for 28 days) by whole-body inhalation. Changes in the activity and relative abundance of hepatic microsomal cytochromes P450 (CYP1A, CYP2B, CYP3A, and CYP4A), epoxide hydrolase, and UDP-glucuronosyltransferase (UDPGT) were measured. Repeated inhalation exposure of rats to D5 increased liver size by 16% relative to controls by day 28. During a 14-day post-exposure period, liver size in D5-exposed animals showed significant recovery. Exposure to D5 did not change total hepatic P450, but increased the activity of hepatic NADPH-cytochrome c reductase by 1.4-fold. An evaluation of cytochrome P450 (CYP) enzymes in hepatic microsomes prepared from D5-exposed rats revealed a slight (1.8-fold) increase in 7-ethoxyresorufin O-deethylase (EROD) activity, but no change in immunoreactive CYP1A1/2 protein. A moderate increase (4.2-fold) in both 7-pentoxyresorufin O-depentylase (PROD) activity and immunoreactive CYP2B1/2 protein (3.3-fold) was observed. Testosterone 6beta-hydroxylase activity was also increased (2.4-fold) as was CYP3A1/2 immunoreactive protein. Although a small increase in 11- and 12-hydroxylation of lauric acid was detected, no change in immunoreactive CYP4A levels was measured. Liver microsomal epoxide hydrolase activity and immunoreactive protein increased 1.7- and 1.4-fold, respectively, in the D5-exposed group. UDPGT activity toward chloramphenicol was induced 1.8-fold, while no change in UDPGT activity toward 4-nitrophenol was seen. These results suggest that the profile for enzyme induction following inhalation exposure of female Fischer-344 rats to D5 vapors is similar to that reported for phenobarbital, and therefore D5 may be described as a weak "phenobarbital-like" inducer.

Racial differences in scleroderma among women in Michigan.

OBJECTIVE: To examine racial differences in disease onset, extent, manifestations, and survival among women with scleroderma. METHODS: A retrospective cohort study of women with scleroderma, diagnosed in Michigan between 1980 and 1991, was conducted. Clinical, laboratory, and demographic data were abstracted from the patients' medical records. RESULTS: A total of 514 women with scleroderma were identified: 117 (23%) were black and 397 (77%) were white. Among black women, the mean age at diagnosis was lower (44.5 years versus 51.5 years; P < 0.001) and diffuse disease was more common (49.6% versus 24.9%; P < 0.001) than among white women. The overall incidence of scleroderma was 14.1 per million per year: 22.5 per million per year in black women versus 12.8 per million per year in white women (P < 0.001). Pericarditis (P = 0.009), pulmonary hypertension (P < 0.001), pleural effusions (P = 0.01), myositis (P = 0.02), and an erythrocyte sedimentation rate >40 mm/hour (P < 0.001) were more frequent among black women, while white women were more likely to have digital infarctions (P < 0.001). Survival at 7 years from diagnosis was 72.5% among black women and 77.6% among white women. Age-adjusted survival was significantly reduced among black women (P = 0.033), most likely because of increased diffuse involvement. Survival among those with renal or pulmonary involvement was also significantly reduced. CONCLUSION: Black women with scleroderma were significantly more likely than white women to develop diffuse disease, be diagnosed at a younger age, have a higher incidence of inflammatory features, and have a worse age-adjusted survival rate.

Silage or limit-fed grain growing diets for steers: I. Growth and carcass quality.

The influence of energy source (silage- [S] or grain- [G] based) on organ growth, carcass quality, and meat acceptability independent of rate of gain was examined. Sixty-four Angus steers were allotted to one of the two treatments and given ad libitum access to silage or limit-fed grain for 145 d. All steers were then given ad libitum access to a grain diet for 45, 75, or 105 d. Eight steers from each treatment were slaughtered at the end of the growing phase and at each of the termination dates. The silage-based growing diet consisted (DM basis) of 55% sorghum silage (averaged 23.6% dry matter), 22% alfalfa hay, 10.8% ground shelled corn, and 10.8% soybean meal and contained 12.8% CP. Dry matter in the grain-based diet, composed of 76.5% ground shelled corn, 5% soybean meal, 13.6% cottonseed hulls, 3.5% molasses, and .4% salt and 1% limestone, contained 12.1% CP. It was limit-fed to produce rates of gain similar to the silage diet eaten ad libitum, using net energy for gain of each diet calculated from organic matter digestibility determined in digestion trials. The finishing diet was similar to the grain growing diet except that alfalfa hay replaced the cottonseed hulls. No implants or ionophores were used. High silage moisture decreased ADG the first 45 d, so steers fed grain gained faster, but thereafter gains were similar. At the end of the growing phase, steers fed grain had heavier shrunk and empty body weights and larger livers. However, liver size was not different when adjusted for growing ADG. By 45 d with ad libitum access to the finishing diet, 75% of the carcasses from steers fed both diets graded Choice. Steers fed silage had tougher (P < .05) steaks with less flavor intensity (P < .05) at the end of the growing phase; these differences diminished after 75 d on feed. These results suggest that choice beef can be produced in only 45 d in the feedlot, but tenderness and flavor among Choice carcasses remained inferior for steers fed silage for at least 75 d on a high-grain diet.

Silage or limit-fed grain growing diets for steers: II. Empty body and carcass composition.

The influence of energy source (silage- or grain-based) on empty body and carcass composition and adipocyte cellularity independent of rate of gain was tested. Sixty-four Angus steers were allotted to either a forage (ad libitum) or grain (limit-fed) diet for a growing phase (145 d) followed by 45, 75, or 105 d of ad libitum access to a grain-based diet. Eight steers were slaughtered initially and eight from each treatment were slaughtered at the end of the growing phase, and at each of the termination dates. The silage growing diet consisted (DM basis) of 55% sorghum silage (approximately 24% dry matter), 22% alfalfa hay, 11% ground shelled corn, and 11% soybean meal. The grain-based growing diet was composed of 77% ground shelled corn, 5% soybean meal, 14% cottonseed hulls, 3% molasses, and 1% salt and mineral; it was limit-fed to produce the same rate of gain as the silage diet. No implants or ionophores were used. At the end of the growing phase, the steers fed grain were heavier and had a higher percentage of fat in the empty body (24 vs 19% fat) and the carcass (26 vs 21% fat) than did steers fed forage. Rate of gain during the growth phase was related positively to percentage of carcass fat; when corrected for fill, data for both diets fit one regression line for fat vs rate of gain. When adjusted for gain during the growing phase, fat content was not different in empty body or carcass, but internal fat was higher (P < .10) for steers fed grain. After 45 d on the finishing diet, carcass fat remained low (23%), but after 75 and 105 d, fat content reached 27%. Source of energy did not detectably affect carcass composition independent of rate of gain. Cell size of adipocytes from four adipose depots increased with time on feed but were not affected by diet during the growing phase. Lean Choice beef can be produced in only 45 d in the feedlot with medium-framed Angus cattle.

Influence of triiodothyronine injections on calf immune response to an infectious bovine rhinotracheitis virus challenge and nitrogen balance of lambs.

Three experiments were conducted to determine the influence of triiodothyronine (T3) or propylthiouracil (PTU) on the humoral immune response of calves challenged with infectious bovine rhinotracheitis virus (IBRV) and on nitrogen depletion and repletion of lambs deprived of feed and water for 3 d. In Exp. 1, 18 steer calves (BW 284 +/- 6 kg) challenged with IBRV were limit-fed (1.5% BW) a 60% concentrate diet and injected (s.c.) daily with alkaline saline, .4 mg of T3, or .8 mg of T3. Injections of T3 did not affect serum antibody titers to IBRV, blood leukocyte counts, or plasma free fatty acid, ceruloplasmin, and cholesterol concentrations but increased (P < .05) plasma glucose concentrations and decreased (P < .05) plasma urea N concentrations. In Exp. 2, 36 IBRV-challenged steers (BW 266 +/- 8 kg) were given ad libitum access to a 60% concentrate diet and injected (s.c.) daily with alkaline saline, .2 mg of T3, or .4 mg of T3. In contrast to Exp. 1, injections of T3 did not affect plasma glucose or urea N concentrations and reduced (P < .05) serum antibody titers to IBRV. In Exp. 3, eight wether lambs were limit-fed (600 g/d) a 36% concentrate pelleted diet and assigned to one of four treatments in a replicated 4 x 4 Latin square designed nutrient balance experiment involving periods of nutrient depletion and repletion. Treatments were as follows: 1) alkaline saline injection (s.c.), 2) 4 mg of PTU/kg BW in water, 3) .15 mg of T3 s.c. daily for 15 d, and 4) .15 mg of T3 s.c. daily for 7 d after the 3-d feed and water deprivation period. Thyroid status affected (P < .05) predeprivation N balance but did not affect N losses during the feed and water deprivation period. Retention of N during realimentation was affected (P < .05) by T3 treatment. Results of these experiments indicate that there is a complex interrelationship among stress, nutrient status, and thyroidal status and that the effects of T3 injections on immune and metabolic responses may be dependent on the nutritional status of the animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of micellar oleic acid on canine jejunal blood flow and neurotensin release.

The purpose of this study was to evaluate the role of neurotensin in the local regulation of the lipid-induced jejunal hyperemia. Total blood flow and the arteriovenous hormone concentration difference were measured in isolated jejunal loops of anesthetized dogs with either saline, bile (10% in normal saline), oleic acid (40 mM in normal saline), or oleic acid and bile in the lumen. The bile-oleic acid mixture produced a sustained increase (+25 +/- 3%) in jejunal blood flow, whereas neurotensin release reached a maximum (1.14 +/- 0.34 pmol X min-1 X 100 g-1) 2 min after initiation of the response and then returned to control. Venous neurotensin concentrations also reached a maximum (51 +/- 17 pmol/l) at 2 min. There were no significant changes in either blood flow or neurotensin release in response to the other test solutions. Intra-arterial infusion of neurotensin did not significantly decrease jejunal vascular resistance (-12 +/- 3%) until venous concentrations of 478 +/- 101 pmol/l were attained. It seems unlikely, then, that neurotensin plays any role in the regulation of the lipid-induced jejunal hyperemia.

The effects of mefenamic acid on postprandial intestinal carbohydrate metabolism.

The effects of mefenamic acid on the food-induced changes in intestinal carbohydrate metabolism were determined in an attempt to elucidate the mechanism(s) by which inhibition of prostaglandin synthesis enhances the postprandial increases in intestinal blood flow and oxygen consumption. The data show that when the luminal perfusate was changed from saline to a nutrient/bile solution, there was an increase in carbohydrate utilization, which was offset by absorption of glucose from the lumen. Intravenous administration of mefenamic acid significantly increased both carbohydrate absorption and metabolism when food was placed in the lumen. Changes in carbohydrate absorption and metabolism have been shown to play and important role in determining the magnitude of glucose induced changes in intestinal blood flow and oxygen consumption. Therefore, it is possible that the ability of mefenamic acid to enhance significantly the food-induced increases in blood flow and oxygen consumption may be due in part to its effects on intestinal carbohydrate absorption and utilization.

Regulation of jejunal blood flow and oxygenation during glucose and oleic acid absorption.

To differentiate the mechanisms whereby actively absorbed glucose and passively absorbed oleic acid increase blood flow and oxygen uptake during their absorption, the effects of these two nutrients on jejunal blood flow, arteriovenous oxygen difference [(a-v)O2], O2 uptake, absorption, rubidium extraction, and capillary permeability-surface area product (PS) were compared in anesthetized dogs. Oleic acid (37 mM) produced significantly greater hyperemia (+28.2%) than glucose (270 mM) did (+12.5%). As estimated by (a-v)O2, tissue oxygen extraction was decreased by oleic acid (-12%) but increased by glucose (+6.5%); the increases in O2 uptake by these two nutrients did not differ significantly. Glucose absorption was accompanied by an increase in rubidium extraction and capillary PS (+11.3%), whereas oleic acid absorption was not. Unlike glucose, intra-arterial infusion of oleic acid decreased vascular resistance and increased blood flow equally to the mucosa and muscularis layers. A significant relation existed between oleic acid absorption and blood flow but not between glucose absorption and blood flow. The enhancement of glucose-induced hyperemia by bile was not related to glucose absorption. Unmasking of oleic acid-induced hyperemia by bile is unrelated to oleic acid absorption but is related to solubility of oleic acid in aqueous solution. The above findings suggest that glucose absorption affects both resistance and exchange vessels, whereas oleic acid absorption affects primarily resistance vessels.

Possible mechanisms for the initiation and maintenance of postprandial intestinal hyperemia.

Postprandial intestinal hyperemia is a locally mediated vascular response to the presence of nutrients in the lumen. In this review we discuss the role of various constituents of chyme in the development of the hyperemia and possible mechanisms of action. The luminal contents that produce the hyperemia are digested products of food; undigested food or pancreatic enzymes have no effect. Micellar fatty acids are the most potent vasodilators, whereas amino acids at physiological concentrations have little effect on intestinal blood flow. However, by-products of protein digestion are as potent as those of carbohydrates in increasing the blood flow. Bile increases ileal but does not alter jejunal blood flow. In addition, bile enhances the glucose-induced hyperemia and renders fatty and amino acids vasoactive. The mechanisms by which bile exerts its effect on the vasoactivity of these nutrients are poorly understood. The intestinal hyperemic response to the presence of nutrients in the lumen is mediated by a variety of regulatory pathways that vary with the nutrient. Factors involved include tissue metabolic rate, metabolites, nutrient absorption, tissue osmolality, tissue oxygen tension, intestinal peptides such as neurotensin and vasoactive intestinal polypeptide, and paracrine substances such as prostaglandins and histamine. It is likely that the hyperemia results from the complex interplay of all these factors on the intestinal vascular smooth muscle. Extrinsic and intrinsic nerves play a minor role in nutrient-induced hyperemia.

Vasoactive intestinal polypeptide, cholecystokinin, glucagon, and bile-oleate-induced jejunal hyperemia.

The purpose of this study was to evaluate the roles of vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), and glucagon in the local regulation of the lipid-induced intestinal hyperemia. Total blood flow and the arteriovenous hormone concentration gradient were measured in isolated jejunal loops of anesthetized dogs with either saline, bile (10% in normal saline), oleic acid (40 mM in normal saline), or oleic acid and bile in the lumen. The bile-oleic acid mixture increased both blood flow (+21 +/- 7%) and VIP release (+118 +/- 7%), while CCK release was considerably less. There was a transient rise in glucagonlike immunoreactivity but no change in pancreatic glucagon release. Neither bile nor oleic acid alone altered either local blood flow or hormone release. Infusion of VIP into the arterial circulation of the jejunum significantly reduced vascular resistance (-11 +/- 4%) but at a dose (150 ng . min-1 X 100 g-1) 10 times that released in response to the bile-oleic acid mixture. This study indicates that oleic acid increases both blood flow and intestinal hormone production only when present in the lumen in micellar form and suggests that VIP could play a role in the jejunal vascular response to fat.

Action of diltiazem on canine mesenteric artery smooth muscle.

We studied the effects of the Ca++ antagonist diltiazem on the contractile response of isolated first order branches of canine superior mesenteric artery. Maximum contraction induced by 60mM KCl was significantly reduced by 10(-9)M diltiazem and the ED50 concentration of KCl was increased by approximately 30% by the antagonist. Increasing concentrations of diltiazem produced dose-dependent reductions in the maximum contraction and increased the ED50 to KCl indicating mixed competitive and noncompetitive inhibition. Norepinephrine-induced contractions reached a maximum with 10(-5)M of the amine. This response was not altered by 10(-9)M diltiazem; however, the ED50 concentration of norepinephrine was nearly doubled when this concentration of antagonist was used, suggestive of competitive inhibition. Higher concentrations of diltiazem altered both the maximum response and the ED50 of norepinephrine, i.e., the mixed inhibition pattern. However, diltiazem did not alter the response to norepinephrine in Ca++-free medium. These data demonstrate that diltiazem causes relaxation of mesenteric arterial smooth muscle by suppressing Ca++ flux at cell membrane sites but is not influencing intracellular mechanisms of Ca++ release.

Glucagon, secretin and vasoactive intestinal polypeptide immunoreactivities in rat gut after jejuno-ileal bypass and resection.

Jejuno-ileal bypass (JIB) and resection are associated with hyperplastic and other changes in residual functional gut. In studies on endocrine changes, circulating hormone levels are usually measured. In this study with Sprague-Dawley rats, glucagon, secretin and vasoactive intestinal polypeptide (VIP), immunoreactivities were measured in extracts of gut tissues including formerly adjacent segments of functional and bypassed jejunum and ileum. Young adult (200-220 g) and mature (404-440 g) rats received greater than 90% JIB. Though slight differences were observed in the response of the young and old rats to the operations, and between the effects of JIB and resection, the results do not indicate major involvement of secretin, VIP or gut glucagon-like immunoreactivity in the effects of surgery. Changes include increased immunoreactivity of secretin in the upper and of VIP in the lower functional gut following JIB. N-terminal-to central glucagon immunoreactivity in the functional ileum did not change substantially after operations, but was significantly lower in the non-functional than functional ileum after bypass. Plasma levels of this immunoreactivity were higher following operations and highest following resection.

Effects of nicotine on canine intestinal blood flow and oxygen consumption.

The purpose of this study was to determine the effects of nicotine on intestinal blood flow and oxygen consumption. The intravenous infusion of nicotine at doses corresponding to those experienced by smokers produced a transient increase in systemic arterial blood pressure and mesenteric blood flow. Subsequently a steady-state response developed that consisted of a reduction in mesenteric blood flow due to both a decrease in blood pressure and an increase in intestinal vascular resistance. This increase in resistance was probably due to increased levels of circulating catecholamines. The intra-arterial infusion of nicotine into the intestinal circulation at doses experienced by the average smoker had no effect on either intestinal blood flow or oxygen consumption. Similarly, under in vitro conditions nicotine had no direct effect on intestinal vascular smooth muscle tension. Thus, nicotine appears to reduce intestinal blood flow indirectly as a result of its systemic effects.

Intestinal blood flow and oxygen consumption.

In this study, we examined the effects of both pharmacologically and mechanically induced increases in intestinal blood flow on intestinal oxygen consumption. Intraarterial infusions of prostacyclin (1-20 ng X kg-1 X min-1) significantly increased both blood flow and oxygen consumption under free flow conditions. However, the increase in oxygen consumption appears to be due to the corresponding increase in blood flow rather than a direct effect of prostacyclin on intestinal metabolism. This conclusion is supported by the finding that a mechanically induced increase in intestinal blood flow (60%) can also produce an increase in intestinal oxygen consumption (24%). These findings support the hypothesis that intestinal oxygen consumption is flow-dependent over a wide range of blood flows.