Toxicological potential of 2-alkylcyclobutanones--specific radiolytic products in irradiated fat-containing food--in bacteria and human cell lines.

Food irradiation has been considered as a safe processing technology to improve food safety and preservation, eliminating efficiently bacterial pathogens, parasites and insects. This study aims to characterize the toxicological potential of 2-alkylcyclobutanones (2-ACBs), radiolytic derivatives of triglycerides, formed uniquely upon irradiation of fat-containing food. In irradiated food they are generated proportionally to fat content and absorbed radiation dose. The cyto- and genotoxic potentials of various highly pure synthetic 2-ACBs were studied in bacteria and human cell lines. While pronounced cytotoxicity was evident in bacteria, no mutagenic activity has been revealed by the Ames test in Salmonella strains TA 97, TA 98 and TA 100. In mammalian cells genotoxicity was demonstrated mainly by the induction of DNA base lesions recognized by the Fpg protein as determined by both the Comet Assay and the Alkaline Unwinding procedure. Formation of DNA strand breaks was observed by the Alkaline Unwinding procedure but not by the Comet Assay. The extent of cytotoxicity and genotoxicity were dependent on chain length and degree of unsaturation of the fatty acid chain. Further studies will have to clarify mechanisms of action and potential relevance for human exposure situation.

Relationship between substance P, intestinal wall compliance and vascular resistance in the canine ileum.

Substance P (SP) is one of many vasoactive peptides found within the gastrointestinal tract with actions on intestinal smooth muscle. Thus, its vasodilatory action could be attenuated through its stimulatory effect on intestinal smooth muscle producing subsequent elevations in extravascular pressure and thus, passively opposing the vasodilation. The aim of this study was to examine for such a possibility for SP by simultaneously assessing ileal perfusion pressure and intestinal wall compliance in the canine ileum during intra-arterial infusion of SP. Infusion of SP at either 0.74 or 7.4 pmol/min significantly decreased ileal perfusion pressure by 8 and 30%, respectively, without affecting wall compliance. During SP infusion at 74 pmol/min, perfusion pressure fell by 49% while wall compliance decreased by 43%, reflecting a significant increase in ileal wall tension. During SP infusion at 7.4 and 74 pmol/min, a 'two-phase' reduction in perfusion pressure was observed. These data suggest that although SP markedly increases ileal wall tension, the elevation in extravascular pressure produced is not strong enough to overcome its potent vasodilatory action in the canine ileum. The potential of a physiologic role for blood-borne SP is discussed.

O-(beta-hydroxyethyl)-rutoside (Venoruton) fails to block histamine or bradykinin-induced edema formation in the canine forelimb perfused at constant arterial inflow.

O-(beta-hydroxyethyl)-rutoside (Venoruton) has been reported to alleviate edema formation in chronic venous insufficiency. In an attempt to elucidate Venoruton's potential as an antiinflammatory agent, we infused Venoruton (20 mg/minute) intraarterially into the canine forelimb perfused at constant flow during the simultaneous intraarterial infusion of histamine (4 micrograms base/minute) or bradykinin (2 micrograms/minute). The infusion of Venoruton alone for forty minutes resulted in a small but significant increase in forelimb arterial pressures but no change in systemic pressure or forelimb skin lymph flow, protein concentration or protein transport. Subsequent infusion of either histamine or bradykinin resulted in a significant decrease in forelimb arterial pressures and a marked increase in skin lymph flow, lymph total protein concentration and lymph total protein transport. The changes in forelimb vascular pressures and skin lymph parameters were similar to those seen during the infusion of either histamine or bradykinin alone. These data indicate that the intraarterial infusion of Venoruton at this dosage does not inhibit the ability of simultaneously infused histamine or bradykinin to increase transvascular fluid and macromolecular efflux in the canine forelimb perfused at constant arterial inflow.

Evidence for constriction of canine prenodal lymphatic vessels by vasoactive agents and carotid occlusion.

We measured pressure in a prenodal lymphatic in the canine forelimb during constant flow pump-perfusion of the brachial artery. We made bolus i.a. injections of 1.0 micrograms angiotensin II, norepinephrine, bombesin, or bradykinin, 20 micrograms 5-hydroxytryptamine (5HT), or occluded the carotid arteries. Norepinephrine, 5HT, or carotid occlusion produced regular rises in forelimb perfusion pressure and in lymphatic pressure. Angiotensin II increased forelimb arterial pressures but increased lymphatic pressure in only four experiments. Bombesin increased artery pressures but did not affect lymphatic pressure. Small vein pressure was increased by carotid occlusion, 5HT and norepinephrine. Increases in lymphatic pressure were coincident with increases in vein pressure but no related in magnitude. Bradykinin decreased forelimb arterial and venous pressures but did not affect lymphatic pressure. Either active constriction of lymphatic vessels or passive compression by movements of adjacent blood vessels could increase lymphatic pressure. These data do not preclude a passive component of pressure rise in the lymphatics nor do they support the concept. We conclude that active constriction of prenodal lymphatic vessels in the dog forelimb can occur in response to circulating vasoactive agents and bilateral carotid occlusion.

Anti-inflammatory actions of enprofylline, a modified xanthine, in the canine forelimb.

It has been previously reported that enprofylline (3-propyl xanthine) prevents histamine-mediated edema formation in the guinea pig lung. To further assess the potential anti-inflammatory effects of enprofylline, we infused it intra-arterially into the canine forelimb before and during a local intra-arterial infusion of histamine (4 micrograms/min) while monitoring forelimb skin lymph parameters. Infusion of enprofylline at 2 mg/min significantly decreased forelimb arterial pressures and increased heart rate and pulse pressure. Subsequent infusion of histamine caused a further reduction in forelimb arterial pressures and an increase in lymph flow, protein concentration, and protein transport similar to that seen with the infusion of histamine alone. Infusion of enprofylline at 5 mg/min decreased forelimb arterial pressures and systemic pressure. Subsequent histamine infusion further reduced forelimb arterial pressures, but the increase in lymph parameters was markedly attenuated. Enprofylline infused at 10 mg/min also decreased forelimb arterial and systemic pressures, but subsequent histamine infusion was essentially without effect on lymph parameters. To assess the role of catecholamines in enprofylline-mediated attenuation of histamine edema formation, we infused enprofylline at 5 mg/min in the presence of a beta 2-receptor blockade produced by the intra-arterial infusion of ICI 118551. The effects of enprofylline and histamine on vascular pressures were similar to those seen in the absence of beta 2-receptor blockade, but lymph flow, protein concentration, and protein transport increased similar to that seen with histamine alone. These data indicate that enprofylline is capable of attenuating histamine-induced increases in microvascular permeability, but this action of enprofylline is of an indirect nature, mediated through the release of catecholamines.

Aminophylline attenuates the edemogenic actions of histamine in the canine forelimb.

Xanthines have been employed clinically to treat asthma and related pulmonary conditions because of their bronchodilator properties. In addition, xanthines have been reported to block and/or attenuate the increase in microvascular permeability to macromolecules produced by some putative inflammatory mediators. In order to more completely assess the anti-inflammatory capabilities of xanthines, we have infused aminophylline intra-arterially in the canine forelimb prior to and during a local intra-arterial infusion of histamine. Forelimb prenodal lymph flow, protein concentration and protein transport were used as indices of transvascular fluid and protein flux. Infusion of histamine (4 micrograms/min) significantly decreased forelimb arterial pressures and increased lymph flow, protein concentration and protein transport. Aminophylline infusion (10 mg/min) decreased forelimb arterial pressures but did not affect lymph parameters. Histamine infusion during infusion of aminophylline increased lymph parameters but the increases were markedly less than with histamine infusion alone. Infusion of aminophylline (20 mg/min) decreased forelimb arterial pressures and systemic pressure. Subsequent histamine infusion resulted in small but significant increases in lymph parameters. These data indicate that aminophylline infusion can blunt the ability of subsequently administered histamine to increase microvascular permeability as evidenced by the attenuation of the increases in lymph flow, protein concentration and protein transport.

Histamine-induced fluid efflux in the canine forelimb as affected by carotid occlusion or hemorrhage.

Infusion of catecholamines concurrently with histamine into the forelimb of the dog prevents histamine-induced increases in lymph flow, protein concentration and forelimb weight. This study tested whether the sympathoadrenal discharge of catecholamines induced by carotid occlusion or hemorrhage would similarly prevent histamine's actions in the canine forelimb. Carotid occlusion or hemorrhage, begun after 30 minutes of histamine infusion (4 micrograms base/min), resulted in a reduction in lymph flow but lymph protein concentration was not changed. Infusion of histamine into the forelimb for 30 minutes in control studies caused the forelimb to gain weight. In experimental studies hemorrhage, begun at one minute after the start of histamine significantly reduced this weight gain but occlusion of the carotid arteries at one minute after the start of histamine did not significantly affect weight gain. These results show that sympathetic nerve activity can lower elevated lymph flow and that sympathetic activity due to hemorrhage reduces the accumulation of interstitial fluid caused by histamine. It seems probable that endogenous catecholamines act directly on filtering vessels to lessen histamine-induced increases in permeability. However, a constriction of lymphatic vessels could have contributed to the reduction in lymph flow and we have no evidence against this possibility.

Effects of histamine-receptor agonists on transvascular fluid and macromolecular efflux in the canine forelimb.

Histamine increases transvascular fluid and protein efflux in the canine forelimb resulting in edema formation. To clarify the receptor mechanisms of histamine edema, we infused H1 and H2-receptor agonists into the forelimb perfused at constant flow while measuring skin lymph parameters or forelimb weight. The H1-receptor agonist 2(2-pyridyl) ethylamine [PEA] or the H2-receptor agonist 4-methyl histamine (8-40 micrograms/min) singly or in combination fails to increase lymph flow, protein concentration or protein transport. PEA in a dose of 80-400 micrograms/min increases lymph flow, protein concentration and protein transport. 4-Methyl histamine in a dose of 40-200 micrograms/min produces a small but significant decrease in lymph flow and protein transport subsequent to a fall in systemic pressure. 4-Methyl histamine at 40 and 80 micrograms/min produces a progressive and sustained increase in forelimb weight PEA at 40 micrograms/min produces a small increase in forelimb weight which quickly plateaus much like the response seen with acetylcholine (10 micrograms base/min). However, infusion of PEA at 80 micrograms/min progressively increases forelimb weight, similar to that seen with 4-methyl histamine or histamine (1.4 microgram base/min). These data indicate that either H1 or H2-receptor agonists can cause edema formation in the canine forelimb, and imply that histamine edema involves both H1 and H2-receptor interaction.

Forelimb vascular pressures, skin lymph flow and lymph protein concentration as affected by vasoactive intestinal polypeptide and bombesin.

Vasoactive intestinal polypeptide (VIP) and bombesin are peptides that have been identified in several mammalian tissues including skin. In this study, we have examined the actions of these peptides on forelimb vascular pressures, skin lymph flow, lymph total protein concentration and lymph total protein transport in the canine forelimb perfused at constant arterial inflow. Local intraarterial infusion of sequentially increasing infusion rates of VIP of 300, 600, and 1500 ng/min for twenty minutes at each infusion rate resulted in dose-dependent decreases in forelimb arterial pressures but no change in skin small vein pressure. At the two higher infusion rates, systemic pressure was significantly decreased whereas heart rate significantly increased. Skin lymph parameters were not a significantly altered with the exception of a small but significant decrease in lymph flow at the highest infusion rate of VIP. Infusion of bombesin at 500 ng/min for sixty minutes resulted in significant increases in forelimb arterial and systemic pressures, no change in skin small vein pressure and a significant bradycardia. Skin lymph flow, protein concentration and protein transport were not significantly changed during the infusion of bombesin. These data indicate that while VIP and bombesin possess potent vasodilator and vasoconstrictor effects respectively, they do not significantly affect transmicrovascular fluid and macromolecular efflux in the canine forelimb perfused at constant flow, as assessed by changes in lymph flow and protein concentration.

Effects of gastrointestinal hormones on ileal vascular and visceral smooth muscle.

Blood levels of gastrin, secretin, gastric inhibitory polypeptide (GIP), and cholecystokinin octapeptide (CCK-8) increase after a meal and may affect vascular and/or visceral smooth muscle. To study this possibility, we measured the effects of local intra-arterial infusion of these hormones on ileal perfusion pressure and intestinal wall compliance. In pentobarbital sodium-anesthetized dogs, a segment of ileum was exteriorized and vascularly perfused at constant flow with arterial blood. Wall compliance was calculated from the pressure generated by incremental changes in intraluminal volume (delta V/delta P). Postprandial blood levels of these hormones did not affect ileal perfusion pressure. However, higher blood levels of secretin and GIP did significantly lower perfusion pressure. Wall compliance was significantly increased by postprandial blood levels of secretin and GIP, while postprandial blood levels of CCK-8 decreased compliance. Gastrin was without effect on compliance. These data suggest these hormones do not contribute to postprandial ileal hyperemia. However, secretin, GIP, and CCK-8 do affect the postprandial activity of ileal visceral smooth muscle.