Effects of variations in the extracellular osmolality on the permeability to nonelectrolytes of vascular smooth muscle

Erythritol: an interpretive summary of biochemical, metabolic, toxicological and clinical data

A critical and comprehensive review of the safety information on erythritol was undertaken. Numerous toxicity and metabolic studies have been conducted on erythritol in rats, mice and dogs. The toxicity studies consist of long-term feeding studies conducted to determine carcinogenic potential, intravenous and oral teratogenicity studies to determine the potential for effects on the foetus, oral studies in which erythritol was administered over one or two generations to determine the potential for reproductive effects, and studies in bacterial and mammalian systems to determine mutagenic potential. The majority of the safety studies conducted were feeding studies in which erythritol was mixed into the diet at concentrations as high as 20%. The metabolic studies in animals have shown that erythritol is almost completely absorbed, not metabolized systemically and is excreted unchanged in the urine. The safety studies have demonstrated that erythritol is well tolerated and elicits no toxicological effects. The clinical program for erythritol involved a series of single-dose and repeat-dose, short-duration studies which have been used to investigate the human correlates to the physiological responses seen in the preclinical studies. The clinical studies showed erythritol to be well tolerated and not to cause any toxicologically relevant effects, even following high-dose exposure. Erythritol administered orally to humans was rapidly absorbed from the gastrointestinal tract and quantitatively excreted in the urine without undergoing metabolic change. At high oral doses, urinary excretion accounted for approximately 90% of the administered dose with minimal amounts appearing in the faeces. A comparison of the human and animal data indicated a high degree of similarity in the metabolism of erythritol and this finding supports the use of the animal species used to evaluate the safety of erythritol for human consumption. It can be concluded, based on the available studies that erythritol did not produce evidence of toxicity.

Differential effects of alcohols on intracerebral arterioles. Ethanol alone causes vasoconstriction

We compared the effect of the acute application of ethanol, methanol, 1-propanol, 1-butanol, urea, and mannitol (1-100 mM) on the basal tone of isolated-cannulated rat intracerebral arterioles to determine if the response of these arterioles to ethanol could be attributed to alteration of membrane fluidity or changes in osmolality. These arterioles spontaneously developed tone to 62.0 +/- 8.4% of passive diameter (44.2 +/- 11.9 vs. 70.9 +/- 14.7 microns). Ethanol caused a dose-dependent reduction in arteriolar diameter starting at 3 mM (p = 0.03), reaching a diameter of 81.4 +/- 3.0% of basal tone at 100 mM. In comparison, all other agents tested caused the arterioles to dilate, with the exception of 1-propanol, which produced inconsistent vessel responses. At 100 mM concentration, methanol, 1-butanol, urea, and mannitol dilated intracerebral arterioles by 116.1 +/- 12.7, 151.5 +/- 12.4, 131.1 +/- 17.0, and 149.8 +/- 6.6%, respectively. Thus, in a concentration range associated with acute intoxication, ethanol causes constriction of isolated intracerebral arterioles. The mechanism of action of ethanol cannot be accounted for solely based upon its physicochemical characteristics of osmolality or lipid solubility, but rather may reflect a more specific action on one or more cellular mechanisms responsible for determining basal intracerebral arteriolar tone. The characterization of the response of intracerebral arterioles to ethanol is important in view of epidemiologic links between ethanol consumption and cerebrovascular disease.

Evidence for uneven alpha-receptor distribution in the rat portal vein

The smooth muscle of the rat portal vein which supports propagation becomes supersensitive to exogenous l -norepinephrine after elimination of the vessel's intramural neuronal uptake mechanism. Such supersensitivity is generally associated with intimate neuromuscular connections. Since the adrenergic vasomotor fibers in the portal vein do not enter the muscle tissue, it has been proposed that muscle cells close to the nerve terminals must determine the response to norepinephrine. With the aim of elucidating the mechanism behind the prejunctional supersensitivity, the total uptake of labeled norepinephrine in the portal vein was analyzed and its distribution within the vessel wall was evaluated directly using isotopically labeled frozen sections. The total uptake of the portal vein, related to its endogenous norepinephrine content, was comparable with that in other vascular and nonvascular tissues. The 3 H-uptake profile of the vessel wall showed that the neurogenic uptake was confined to the narrow adrenergic plexus between the longitudinal and the circular muscle layers. The neuronal uptake mechanism therefore could only influence the concentration of exogenous norepinephrine at muscle cells close to the nerve terminals. These results support the hypothesis that the prejunctional supersenstivity in the rat portal vein indicates that the alpha receptors are located on muscle cells in the vicinity of the adrenergic nerve terminals.