Absorption and metabolism of oral progesterone.

The absorption, metabolism, and clearance of progesterone from the peripheral circulation were investigated in five postmenopausal women after oral administration of 100 mg daily for five consecutive days. Maximal plasma concentrations of progesterone were observed within four hours after ingestion of the last dose, when the range (22.11-34.18 nmol/l; 696-1077 ng/100 ml) was comparable with that observed during the mid-luteal phase of the ovarian cycle. The surge in values lasted six hours, and progesterone concentrations remained raised for at least 96 hours. Of the three metabolites studied, the plasma concentrations of pregnanediol-3 alpha-glucuronide were most raised by treatment, the peak values ranging from 1097 nmol/l (54.9 microgram/100 ml) to over 2000 nmol/l (100 microgram/100 ml), which was the upper limit of the assay used. Concentrations of 17-hydroxyprogesterone were least raised, and the peak values ranged from 4.32 to 9.68 nmol/l (143-319 ng/100 ml). The plasma profile of 20 alpha-dihydroprogesterone most closely approximated that of progesterone, although the range of maximal values was lower (7.11-16.06 nmol/l; 228-514 ng/100 ml). Plasma concentrations of oestradiol were unchanged by giving progesterone. It is concluded that the increases in circulating concentrations of progesterone and the biologically active metabolite 20 alpha-dihydroprogesterone, and the duration of these increases, were sufficient to modulate the biochemistry of responsive tissues. Oral progesterone may thus have a therapeutic role, and this route of administration merits further investigation.     

大孔吸附树脂对苦瓜皂甙的吸附研究

试验通过静态吸附对几种树脂进行筛选,结果表明D-101对苦瓜皂甙有较大的吸附率和解吸率,适合用来提取纯化苦瓜皂甙.进一步对D-101进行动态吸附研究,结果表明,浓度为95%的乙醇,3个柱体积可以洗脱几乎所有的苦瓜皂甙.苦瓜皂甙粗提物的上样浓度为2.8～5.6 ms/mL之间.     

Absorption and metabolism of nicotine from cigarettes.

Eight men volunteers each smoked a single cirgarette containing 14C-nicotine and gave arterial blood samples during and for 50 minutes after smoking. The maximum concentration of nicotine in the arterial blood ranged from 31 to 41 mug/l in four regular cigarette smokers who inhaled. Two non-smokers achieved maximum levels of 2 and 4 mug/l. On a separate occasion two of the inhalers received 1 mg. 14C-nicotine in 10 divided doses injected intravenously. In both cases the peak arterial nicotine concentrations bore a similar relationship to the intravenous dose, as did the peak nicotine concentrations to the retained doses during smoking.     

Absorption and metabolism of fructose by rat jejunum.

The absorption and metabolism of fructose was investigated in the vascularly perfused jejunum of fructose-fed rats. With 10 mM-glutamate and 10 mM-fructose in the lumen, the viability of the tissue is maintained and fructose is absorbed and utilized at high rates. With 28 mM-fructose in the lumen, glucose appears in the vascular bed. With 10 mM- or 28 mM-fructose in the presence of 10 mM- or mM-glucose in the lumen, the fructose absorption is decreased. From 10 mM- or 28 mM-sucrose in the lumen, fructose uptake is also less than from the equivalent concentration of free fructose. The rate of appearance of fructose in the vascular bed is independent of the source of fructose from which it is derived. In the presence of glucose, either free or as sucrose, there is a marked decrease in the utilization of fructose, defined as the difference between that absorbed by the jejunum and that transported unchanged into the vascular bed. In all cases about half of the carbohydrate absorbed from the lumen is converted into lactate, most of which is secreted into the blood. The absorption of glucose and the rate of vascular appearance of glucose from glucose in the lumen are about 1.5 times greater than those of fructose from fructose in the lumen. It is concluded: firstly, that fructose uptake from the lumen of rat jejunum is determined by its concentration and by the demand for it as a fuel for the intestine, a demand that is severely decreased in the presence of glucose; secondly, that in the vascularly perfused jejunum there is no evident kinetic advantage for uptake of fructose or glucose from sucrose rather than from free monosaccharide in the lumen; thirdly, that some fructose can be converted into glucose.     

Biochemistry of nonheme iron in man. II. Absorption of iron

The currently accepted concept of iron absorption proposes first the entry of iron into the intestinal mucosal cell through the brush border membrane. It is a relatively slow process. In the cell, the iron may be transferred to plasma or become sequestered by ferritin. The latter becomes unavailable for transfer to plasma and is exfoliated and excreted. In iron deficiency and idiopathic hemochromatosis, the rate of iron uptake into the intestinal mucosal cell is increased and entry into ferritin is decreased, whereas the rate of transfer to plasma remains constant. The reverse occurs in case of secondary iron overload. It is currently accepted that a transferrin, whose levels increase in iron deficiency, enters the intestinal lumen from the liver via bile, where it may sequester iron and bring it into the cells by the process of endocytosis. Iron presented as inorganic ferric or ferrous salts may also be absorbed, though the more soluble ferrous salts are adsorbed much more rapidly. Heme iron is absorbed very effectively, though it is not subject to regulation by the individual's iron status to the same extent as is inorganic iron absorption. Brush border membranes apparently contain saturable iron receptors for inorganic iron, but whether or not the absorption process requires energy is an open question. Absorption of iron may also be affected by its availability; different food components affect iron absorbability to a different extent.     

Amitrole Absorption by Bean (Phaseolus vulgaris L. cv ;Red Kidney') Roots : Mechanism of Absorption

The mechanism of transport of the herbicide 3-amino-1,2,4-triazole (amitrole) into Phaseolus vulgaris roots appears to be passive, as judged by the effect of temperature (Q₁₀ = 1.3 between 15 and 25°C) and the lack of sensitivity to metabolic inhibition afforded by 2,4-dinitrophenol and NaN₃. Amitrole absorption is a linear function of external concentration over several orders of magnitude and, thus, is not facilitated by a carrier mechanism. The absorption of amitrole is sensitive to external pH, being stimulated under acid conditions. This stimulation of amitrole absorption is seen at low (≤1 millimolar) amitrole concentrations, but not at high (50 millimolar) amitrole levels. While the apparent octanol-water partition coefficient varies with the pH of the aqueous phase, there is no clear correspondence between absorption and the apparent partition coefficient. Roots do not accumulate amitrole above concentration equilibrium; however, at a time when the net amitrole content of the root tissue begins to saturate, amitrole can be detected in the xylem stream. On a fresh-weight basis, amitrole absorption by roots is equal to that accomplished by trifoliate-leaf tissue. An estimate of the permeability coefficient (according to the analysis of Tyree et al. 1979 Plant Physiol 63: 367-374) suggests that amitrole possesses near-optimal permeability for an ambimobile solute, on the order of 2.12 (± 0.47) × 10⁻⁹ meters per second.     

Studies on Inhibition of Intestinal Absorption of Radioactive Strontium: I. Prevention of Absorption from Ligated Intestinal Segments

A method is reported which permits selective suppression of absorption of radioactive strontium from ingested food material, permitting the calcium to be available to the body. Studies were carried out in vivo by injection of Sr⁸⁹ and Ca⁴⁵ in the presence of inert carrier into ligated intestinal segments in rats, and the amount of absorption was measured by standard monitoring techniques. The pattern of absorption of both ions is very similar but the rate of absorption is different. It was found that the polyelectrolyte, sodium alginate, obtained from brown algae (Phaeophyceae), injected simultaneously with radiostrontium effectively reduces the absortion of Sr⁸⁹ from all segments of the intestine by as much as 50-80% of the control values. No significant reduction in absorption of Ca⁴⁵ was observed in equivalent concentrations. The reduction in blood levels of Sr⁸⁹ and in bone uptake corresponded to the absorption pattern. The difference in the effect on strontium and calcium absorption may be due to differences in the binding capacity of sodium alginate from the two metal ions under the conditions present in vivo.     

Absorption of borate ionic species by Saccharum officinarum L.

The correlation between the effect of pH on H₃BO₃ ionizationand on borate absorption, and the effect of poly-OH compoundson absorption, suggest that B(OH)₄^– is absorbed by sugarcaneleaf tissue, rather than H₃BO₃. Diol-borate complexes have noeffect on mechanism 2 uptake, but competitively inhibit mechanism3. ¹Published with the approval of the Director of the Hawaii AgriculturalExperiment Station as Technical Paper No. 985. (Received September 2, 1968; )