While studying the role of certain metals and chelating agents in controlling tissue injury, we found that zinc salts stabilize lysosomal membranes in vitro (1, 2) : the rupture of these particles with the resulting release of their enzymes was decreased roughly 50% by low (millimolar) concentrations of zinc. The lysis of cells or subcellular structures is frequently attributed to peroxidation of the lipid components of their membranes (3-5). Thus, one possible explanation of this effect of zinc is that it interferes in some way with peroxidation of unsaturated fatty acids in the lysosomal membrane. This hypothesis was evaluated in in vivo and in vitro experiments using carbon tetrachloride to induce lipid peroxidation.The toxic effects of CC14 in vivo are due to the metabolism of this agent by the liver microsomal drug oxidizing system to the trichloromethyl radical CC13 (6). This free radical attacks unsaturated lipids in intracel-Iular membranes, oxidizing them and causing membrane distortion. This process terminates in cell necrosis (7). Lipid peroxidation can also be induced in vitro by incubating isolated liver microsomes with CC14 in the presence of NADPH or a NADPHgenerating system (8). We have found that zinc prevents or significantly reduces the CCL-induced formation of lipid peroxides both in vEvo and in vitro.Methods. Male rats (Simonson, 200 t 15 g) fed standard Purina lab chow diet were injected sc twice weekly with CC14 at the dose 0.1 m1/100 g. Zinc acetate ( 5 my/100 g) was administered daily by intragastric gavage. Control rats were gavaged accordingly with saline. Rats were sacrificed by decapita-14047 and ES 00790. lThk work was supported by NIH grants AM-tion after 20 and 34 days. The livers were perfused in situ with 20 ml of ice cold saline and homogenized by hand with all-glass homogenizers in three volumes of Tris-KC1 buffer (0.05 M , pH 7.4). The homogenates were fractionated into mitochondria and microsomes by centrifugation: material sedimenting between 800 and 15,OOOg (20 min-mitochondria-and between 15,000 and 105,OOOg (60 min)-microsomes-was collected and resuspended in TrisKCl, 1.5 or 1 .O ml/g liver. The mitochondrial fraction thus obtained includes both mitochondria and lysosomes, although the latter are present in relatively minor amounts. However, for convenience we will refer to the fraction as a crude mitochondrial preparation. Lipid peroxides were measured in both fractions by the formation of malonaldehyde using the thiobarbituric acid (TBA) method (9). The activity of p-glucuronidase was determined (10) in aliquots of the mitochondri-a1 pellet (bound) and supernatant (free enzyme) as a measure of lysosomal membrane stability. For in vitro studies, mitochondria and microsomes were prepared from rat liver and incubated under the conditions described in the Tables. The content of thiol groups was determined according to Elman (1 1) ? and the activity of cytochrome c oxidase by the method of Wharton and Tzagoloff ( 12).Results. The in vivo administration of CCll to rats for 20...

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1. The earlier observation (Woessner, 1969) of oestradiol inhibition of collagen breakdown is confirmed and extended. Administration of 100mug of oestradiol-17beta/day to parturient rats strongly inhibits the loss of collagen from the involuting uterus. Three experiments show that this effect is due to an inhibition of collagen degradation rather than to a stimulation of collagen synthesis. 2. Uterine collagen was labelled with hydroxy[(14)C]-proline by the administration of [(14)C]proline near the end of pregnancy. By 3 days post partum, control uteri lost 83% of their collagen and 90% of their hydroxy[(14)C]proline. Uteri from oestradiol-treated rats lost only 50% of both total and labelled hydroxyproline, with no decrease in the specific radioactivity of the hydroxyproline. 3. Incorporation of [(14)C]proline into uterine collagen hydroxyproline in vivo was not affected by oestradiol treatment. 4. Urinary excretion of hydroxyproline was increased in post-partum control rats and decreased in oestradiol-treated rats. 5. An enzyme capable of cleaving 4-phenylazobenzyloxycarbonyl-l-prolyl-l-leucylglycyl- l-prolyl-d-arginine (a substrate for clostridial collagenase) increased in activity in the post-partum uterus and was unaffected by oestradiol treatment. 6. Uterine homogenates digested uterine collagen extensively at pH3.2. This digestion was unaffected by the oestradiol treatment. 7. Lysosomal fractions prepared by density-gradient centrifugation of uterine homogenates contained coincident peaks of cathepsin D activity and peptide-bound hydroxyproline. The cathepsin D and hydroxyproline contents of this peak were unaffected by oestradiol treatment.