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The rates of active transport of calcium in vitro by everted gut-sacs prepared from the proximal small intestine of the rat have been quantified and expressed in absolute units. A maximal rate of transport has been measured. The bulk of the calcium transferred to the serosal surface of the gut-sac is ionized calcium, suggesting that the process is an active cation transport mechanism. The active transfer is relatively specific for Ca++, and no significant accumulation of Mg++, Sr++, Ba++ or K+ in the fluid bathing the serosal surface could be demonstrated. The active transport of calcium in vitro is greater with gut-sacs from growing than from older rats, and it is greater with gut-sacs from pregnant than from nonpregnant rats. The results suggest that the active transport mechanism can increase the intestinal absorption of calcium facultatively to meet the needs of the organism.

1.Thin-layer chromatography of porphyrin methyl esters provides a useful and rapid technique for resolving mixtures of porphyrins from biological samples.2. Application of this technique to urinary, faecal and hepatic porphyrins from patients with symptomatic porphyria revealed five porphyrins of interest which could be identified by mass spectrometry as the methyl esters of porphyrins with 8-, 7-, 6-, 5-and 4-carboxyl groups. Millimolar extinction coefficients at the Soret absorption maxima for these porphyrin methyl esters in chloroform solution were measured.3. A consistent pattern of urinary porphyrin excretion in symptomatic porphyria was seen with 8-, 7-, 6-, 5-and 4-carboxyl porphyrins constituting approximately 60%, 25%, 3%, 3% and 9% of the total respectively. Uroporphyrin (73%), heptacarboxylic porphyrin (26%) and hexa-carboxylic porphyrin (I %) were the only porphyrins detected in the liver of one patient.4. Isomer analysis of excreted and hepatic porphyrins revealed that uroporphyrin was approximately 35% isomer I11 , hepta-and hexa-carboxylic porphyrins almost all isomer I11 and penta-carboxylic and coproporphyrin approximately 50% isomer 111. 5. To explain these findings it is suggested that there are two metabolic pathways for the handling of 6-aminolaevulic acid (ALA) in the liver.Symptomatic porphyria (porphyria cutanea tarda) is a well defined syndrome characterized clinically by increased mechanical fragility, blistering, pigmentation and superficial ulceration of the sun-exposed skin. A history of alcohol abuse and evidence of chronic parenchymatous liver disease can usually be elicited. The serum iron concentration is frequently raised and siderosis of the liver of varying degree is invariably present. Unlike inherited forms of hepatic porphyria, a positive family history of the disorder is exceptional and acute attacks are unknown.The disease is distinguished biochemically by a characteristic pattern of haem precursor

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