An autoradiographic study of the cell proliferation during involution of the rat pancreas.

After ligation of the rat pancreas, DNA synthesis in centoacinar cells and cells of the intercalary ducts, proximal and distal to the ligature, was suppressed for about 18 hr. This preceded a large increase in thymidine labelling of the nuclei of these cells. The increase in the thymidine indices was much greater and more prolonged in the distal pancreas where duct-like structures were formed that replaced the acini. DNA synthesis in acinar cells proximal to the ligature was suppressed for 36 hr preceding an increase in the thymidine indices much smaller than that in the duct cells. DNA synthesis in acinar cells distal to the ligature ceased and the acinar cells progressively died. We propose that the pancreas is composed of proliferative units, each comprising acinar cells, centroacinar cells and intercalary ducts, which react as a whole when acinar cell loss occurs in pathological processes.

Involution of the pancreas after ligation of the pancreatic ducts. I: a histological study.

A detailed histological study of pancreatic involution after ligation of the pancreatic duct is reported. Cytological evidence acinar cell damage is evident from the beginning and loss of zymogen granules occurs early. The acini diminish in size rapidly from the 36th hour to the 3rd day. The cell deletion appears to occur in 2 phases with apparently different characteristics. The first phase appears to be related to the initial cell damage. The letter phase is more general but of uncertain nature. Considerable proliferation of cells occurs in the ducts resulting, with the few remaining acinar cells, in duct-like structures which themselves undergo involution. The duct changes therefore are not passive but involve continued cell proliferation and cell death over a long period.

Mercuric chloride-induced tubulonecrosis in the rat kidney: the recovery phase.

Regeneration of the renal tubules in rats, after death of the cells of the pars recta caused by a dose of 1.5 mg HgCl2/kg, was examined by histological and radioautographic methods. The tubules regenerated from surviving squamoid cells at both ends of the necrotic segments, which often appeared to arise from epithelial cells that had cast off superficial "dead cytoplasm" to leave the basal parts containing the nucleus in a rim of cytoplasm. The tubular epithelium was reconstituted between the 2nd and 5th days by proliferation and sliding extension of the squamoid cells along the tubules and predominantly from the distal end of the necrotic segments where the cell proliferation was extremely active. Inflammation in reaction to the dead cells was insignificant. Although the majority of tubules regenerated in a regular fashion some degree of anomalous epithelial proliferation occurred in patches, predominantly in the junctional area between the pars recta and the loops of Henle and perhaps most frequently in reference to those nephrons with superficial and mid-cortical glomeruli. The exuberant proliferation led to scattered epithelial growths projecting into the lumen of the tubules, and there was evidence that these obstructed the discharge of necrotic debris. Tubular collapse and atrophy leading to the formation of small scars followed, more often affecting the short looped nephrons.

Mercuric chloride-induced renal tubular necrosis in the rat.

A light microscopic study of the renal tubulonecrotic lesion in rats given a small dose of HgCl2 is described. The changes consist of a rapidly developing vacuolation of the cytoplasm with loss of basophilic staining within 4 h that leads to cell breakdown, fragmentation and dissolution by 48 h. Nuclear changes appear to set in later. Permanent patchy fibrotic lesions were found in the kidneys at 10 days. The animals pass a large amount of urine of low osmolarity, low Na+, K+ and Cl- for a period of 3 days accompanied by an increased water intake. Nevertheless there appeared to be no water or ionic imbalance between daily inputs and outputs. Blood urea levels were greatly increased for 3 days, but did not return to normal by the 10th day.

Repeated partial hepatectomy as a promoting stimulus for carcinogenic response of liver to nitrosamines in rats.

Partial hepatectomy 24 h before a single i.p. dose of dimethylnitrosamine, diethylnitrosamine or ethylmethylnitrosamine increased the carcinogenic response in the liver of rats as determined by the number of tumours and the number of "focal proliferations" produced. Secondly, in rats given a single i.p. dose of diethylnitrosamine, 3 partial hepatectomies 5, 10 and 15 weeks after dosing the animals increased the carcinogenic response in the liver. The stimulus of repeated partial hepatectomy therefore appears to act as a "promoting agent" for liver carcinogenesis, that is if the single dose of diethylnitrosamine is regarded as an "initiating agent" in the terms of the two-stage hypothesis.

Influence of carbon tetrachloride on induction of tumours of the liver and kidneys in mice by netrosamines.

Mice were given a single dose of nitrosolimethylamine, nitrosoliethylamine or nitrosomethylethylamine and the yield of tumours and related lesions in the livers determined 12 months later. A hepatonecrotic dose of CCl4 24 or 48 h before the nitrosamines, increased the yields of hepatocellular tumours and proliferative foci in the livers, whereas when given 60 h before the nitrosamines there was no significant effect.

The binding of ethyl carbamate to DNA of mouse liver in vivo: the nature of the bound molecule and the site of binding.

Ethyl carbamate, labelled at C1 with 14C, bound in vivo to liver DNA of intact and partially hepatectomised mice. Isotope (18O) enrichment was not detected in the oxygen of liver DNA of mice injected with [18O] ethyl carbamate, C2H5--18O--CO--NH2. This suggests that it was the ethyl group and not the ethoxy group which bound to DNA. Chromatographic analysis of acid hydrolysates of liver DNA from mice treated with [1-14C] ethyl carbamate provided no evidence of alkylation or other form of binding to purine or pyrimidine bases. On relatively mild acid hydrolysis the alkyl group remained bound to the "apurinic acid" fraction, while more vigorous hydrolysis lead progressively first to its separation as highly ionisable hydrophilic non-volatile compounds and then to its loss as a volatile compound. DNAase I followed by phosphodiesterase hydrolysis also split off the 14C-containing group as a volatile compound. The volatile compound was identified as ethanol. These results suggest that the alkyl group was bound as an ester to a phosphate group in the DNA chain. Results with DNA from partially hepatectomised mice did not differ from those with DNA from intact mice.

Carcinogenesis by carbamic acid esters and their binding to DNA.

The tumor-initiating potency of three simple alkyl carbamates and mono-N-substituted ethyl carbamates was examined in Hall strain mice. The binding of 14C-labeled carbamates of DNA was measured in Crackenbush mice. Ethyl carbamate was the most potent carcinogen for the epidermis, liver, and lung, followed by its N-alkyl derivatives. Methyl carbamate was without effect but n-propyl and n-butyl were possible carcinogens. The ethyl esters bound to a greater extent to DNA in liver and skin than the methyl, n-propyl, and n-butyl esters and only this binding persisted. A preliminary application of croton oil increased the yield of skin tumors but not of liver or lung tumors. It also increased the binding of the alkyl carbamates to DNA in skin, the increase being greatest with ethyl carbamate. The binding persisted longer in treated than in non-croton oil-treated mice.

Partial hepatectomy and toxicity of dimethyl-nitrosamine and carbon tetrachloride, in relation to the carcinogenic action of dimethylnitrosamine.

The yield of tumours in the liver of rats was increased when dimethylnitrosamine was given 1, 6 or 12 h after partial hepatectomy and still further increased if it was given after an interval of 24-72 h. The increase was greater after two-thirds than after one-third hepatectomy. An increase in the number of kidney tumours was also found. Microsomal DMN-demethylase activity was depressed after partial hepatectomy for up to 6 days in mice and rats. The LD50 of DMN on the other hand was decreased for 3 days, after which it returned to normal. The extent of liver necrosis produced by DMN was increased at 6 and 24 h after partial hepatectomy but was within the usual range at longer intervals. These results suggest that prolonged exposure of the tissues to DMN after partial hepatectomy played a significant role in the development of liver tumours as well as those in the kidney, in addition to the role of regeneration of the liver, and that the relative roles were still to be elucidated.

The effect of a dose of dimethylnitrosamine on the toxicity of a subsequent dose and on the toxicity of carbon tetrachloride in mice.

Mice were given a first dose of dimethylnitrosamine (DMN) and the LD50 of a second dose determined at various times later. The total dose (sum of the 2 doses) tolerated under these conditions increased slowly as the interval between the 2 doses increased, to a maximum that was maintained until the 6th day. The LD50 of the second dose then returned slowly to normal by the 10th day. The data suggest that the biochemical lesion in DMN induced liver necrosis developed relatively slowly.

The effect of a tubercle lipid adjuvant on the distribution of injected foreign red blood cells.

Increased localization occured of injected foreign red cells in the spleen and lungs of animals treated with a tubercle bacillary lipid adjuvant given intravenously. The distribution changes varied depending upon the time interval between injections of the adjuvant and the foreign red cells. These changes offer an explanation of the augmentation of haemolysins and haemagglutinins previously shown for the lipid.

Reduction of carbon tetrachloride toxicity by prior administration of a single small dose in mice and rats.

Mice were given progressively smaller doses of carbon tetrachloride (CCl4) and at intervals later the LD50 of a second dose was determined. The LD50 was greater than in previously untreated mice as soon as 10 min after the first dose, increased to a maximum between 12 and 24 h that was maintained for about 3 or 4 days, after which the LD50 returned to normal by the 7th day. The maximum LD50 reached was dependent on the first dose, but even a minute first dose, 0-004 ml/kg, had a significant effect. The same phenomenon was confirmed in rats. Administration of promethazine before doseing with CCl4 did not have this effect, nor did an ether anaesthetic.

Protection by carbon tetrachloride against the toxic effects of dimethylnitrosamine in mice.

A single intraperitoneal dose of carbon tetrachloride (CCl4), from 0-004 to 0-5 ml/kg, protected male mice against the toxic effects of dimethylnitrosamine (DMN). The LD20 of DMN was increased by a factor of about 4-2 with the highest dose of CCl4 and by a lesser factor with lower doses. The increase in LD50 correlated with a decrease in DMN-demethylase activity in the liver of CCl4 treated mice. These effects commenced within 10 min of administration of CCl4, increased very rapidly for 12 h to a high level which was maintained for up to 60 h, after which the LD50 of DMN and the level of DMN-demethylase returned slowly to normal only in 5 or 6 days. The administration of CCl4 reduced the acute hepatonecrotic action of DMN.

Increased carcinogenic action of dimethylnitrosamine after prior administration of carbon tetrachloride.

Rats were given a single dose of dimethylnitrosamine (DMN, 20 mg/kg body weight) alone or 42 or 60 hours after a non-lethal hepatotoxic dose of carbon tetrachloride (CC1(4)) and killed 12 months later. DMN alone produced no tumours in the kidney and a few in the liver, but when given 42 hours after CC1(4), tumours formed in the kidneys and the number in the liver was increased. When given after 60 hours, the incidence of kidney tumours was less but that of liver tumours was further increased. A larger dose of DMN (40 mg/kg) was tolerated 42 hours after CC1(4) and enhanced the number of kidney and liver tumours, the latter apparently due to an increased proportion of cholangiomata. Numerous small focal proliferations of atypical liver cells and of bile duct epithelium were observed after treatment with DMN. The incidence of these lesions in the different experimental treatments varied in a similar manner to the liver tumours.