Age-related changes in the cell kinetics of rat foot epidermis

Abstract. The durations of the cell cycle and its component phases have been determined for the basal layer of the epidermis of the skin from the upper surface of the hind foot of the rat using single pulse [³H]-thymidine labelling and the percent labelled mitosis (PLM) technique. Rats of three age groups were used, namely 7, 14 and 52 weeks. The duration of DNA synthesis (T_s) and the G₂ plus M phase (Tg₂± m) were comparable in 7-week and 52-week-old rats ( P > 0–1). The major difference between 7-week and 52-week-old rats was in the duration of the G₁ phase (Tg₁). In 7-week-old rats Tg₁ was 15.0 ± 0.8 h and in 52-week-old rats Tg₁ was 31.2 ± 3.5 h. A consequence of this variation was that the overall duration of the cell cycle was longer in 52-week-old rats (53.9 ± 5.3 h) than in 7-week-old rats (30.1 ± 1.3 h).
Difficulties were found in fitting a simple curve to the PLM data for 14-week-old rats. This suggests that the proliferative cell population of the epidermis of rats of this age group may be heterogeneous. A satisfactory fit to the data was obtained using a computer model which assumed that the proliferative population of the epidermis of 14-week-old rats was a mixture of cells with cell cycle parameters the same as those of the 7-week and the 52-week-old rats. These two sub-populations of relatively slowly and rapidly proliferating cells were present in the ratio of 2:1.     

Role of nitric oxide in the airway response to exercise in healthy and asthmatic subjects.

A role of nitric oxide (NO) has been suggested in the airway response to exercise. However, it is unclear whether NO may act as a protective or a stimulatory factor. Therefore, we examined the role of NO in the airway response to exercise by using N-monomethyl-L-arginine (L-NMMA, an NO synthase inhibitor), L-arginine (the NO synthase substrate), or placebo as pretreatment to exercise challenge in 12 healthy nonsmoking, nonatopic subjects and 12 nonsmoking, atopic asthmatic patients in a double-blind, crossover study. Fifteen minutes after inhalation of L-NMMA (10 mg), L-arginine (375 mg), or placebo, standardized bicycle ergometry was performed for 6 min using dry air, while ventilation was kept constant. The forced expiratory volume in 1-s response was expressed as area under the time-response curve (AUC) over 30 min. In healthy subjects, there was no significant change in AUC between L-NMMA and placebo treatment [28.6 +/- 17.0 and 1.3 +/- 20.4 (SE) for placebo and L-NMMA, respectively, P = 0.2]. In the asthmatic group, L-NMMA and L-arginine induced significant changes in exhaled NO (P < 0.01) but had no significant effect on AUC compared with placebo (geometric mean +/- SE: -204.3 +/- 1.5, -186.9 +/- 1.4, and -318.1 +/- 1.2%. h for placebo, L-NMMA, and L-arginine, respectively, P > 0.2). However, there was a borderline significant difference in AUC between L-NMMA and L-arginine treatment (P = 0.052). We conclude that modulation of NO synthesis has no effect on the airway response to exercise in healthy subjects but that NO synthesis inhibition slightly attenuates exercise-induced bronchoconstriction compared with NO synthase substrate supplementation in asthma. These data suggest that the net effect of endogenous NO is not inhibitory during exercise-induced bronchoconstriction in asthma.     

Leukocytosis and Enhanced Susceptibility to Endotoxemia but Not Atherosclerosis in Adrenalectomized APOE Knockout Mice

Hyperlipidemic apolipoprotein E (APOE) knockout mice show an enhanced level of adrenal-derived anti-inflammatory glucocorticoids. Here we determined in APOE knockout mice the impact of total removal of adrenal function through adrenalectomy (ADX) on two inflammation-associated pathologies, endotoxemia and atherosclerosis. ADX mice exhibited 91% decreased corticosterone levels (P<0.001), leukocytosis (WBC count: 10.0 ± 0.4 x 10E9/L vs 6.5 ± 0.5 x 10E9/L; P<0.001) and an increased spleen weight (P<0.01). FACS analysis on blood leukocytes revealed increased B-lymphocyte numbers (55 ± 2% vs 46 ± 1%; P<0.01). T-cell populations in blood appeared to be more immature (CD62L+: 26 ± 2% vs 19 ± 1% for CD4+ T-cells, P<0.001 and 58 ± 7% vs 47 ± 4% for CD8+ T-cells, P<0.05), which coincided with immature CD4/CD8 double positive thymocyte enrichment. Exposure to lipopolysaccharide failed to increase corticosterone levels in ADX mice and was associated with a 3-fold higher (P<0.05) TNF-alpha response. In contrast, the development of initial fatty streak lesions and progression to advanced collagen-containing atherosclerotic lesions was unaffected. Plasma cholesterol levels were decreased by 35% (P<0.001) in ADX mice. This could be attributed to a decrease in pro-atherogenic very-low-density lipoproteins (VLDL) as a result of a diminished hepatic VLDL secretion rate (-24%; P<0.05). In conclusion, our studies show that adrenalectomy induces leukocytosis and enhances the susceptibility for endotoxemia in APOE knockout mice. The adrenalectomy-associated rise in white blood cells, however, does not alter atherosclerotic lesion development probably due to the parallel decrease in plasma levels of pro-atherogenic lipoproteins.     

Radiation-induced rectal complications are not influenced by age: a dose fractionation study in the rat

Radiation-induced complications of the rectum are an important dose-limiting factor in radiotherapy of pelvic malignancies. In general, animal studies demonstrated no differences in acute and late normal tissue toxicity with age, but little is known about rectal complications in relation to age. For this purpose, an extensive histological and dose fractionation study was carried out on the rectum of young (12 weeks) and older (77-80 weeks) rats. In this paper, the results of dose fractionation are presented in relation to age at the time of irradiation. Young and older animals were irradiated with single and fractionated doses. After irradiation, rectal complications could lead to occlusion and stenosis, eventually resulting in the clinical symptoms of a megacolon and a possible fistula. For each dose group, cumulative survival rates were obtained with Kaplan-Meier analysis, from which dose-effect curves and the associated LD(50) values for a megacolon/fistula were calculated. The majority of responders died between 8 and 24 weeks after irradiation, irrespective of age. For both age groups, only the fractionation data showed a reduction in the mean latency with increasing dose. In the older age group, 39% of the responders developed a fistula compared to 26% for the younger animals. The LD(50) values increased from around 30 Gy after single doses to nearly 65 Gy after 10 fractions. The increases in LD(50) values with the number of fractions were independent of the age of the rats. For each of the dose fractionation schedules, log-rank testing indicated no significant differences in cumulative survival rates between younger and older animals (P > 0.10). The high alpha/beta ratios obtained for both the young and older animals strongly suggested that the late rectal complications were a consequence of early epithelial injury. Associated histological findings indicated that blood vessel damage, which was already evident at a high incidence at 4 weeks after irradiation, could also play a significant role in the occurrence of consequential late injuries. In conclusion, data obtained for the latent period of rectal occlusion, for the dose-effect curves, for the log-rank testing of cumulative survival rates, and for the alpha/beta ratios strongly support the hypothesis that the incidence of radiation-induced rectal complications is independent of age. Late rectal complications could be a consequence of radiation-induced acute injury.     

Repetitive apneas induce periodic hypertension in normal subjects through hypoxia.

Periodic increases in blood pressure (BP) can occur in the sleep apnea syndrome (SAS) during recurrent apneas. To investigate the mechanisms causing this periodic hypertension, we simulated SAS by imposing a matching breathing pattern on seven healthy awake male volunteers. Continuous finger arterial BP, electrocardiogram, arterial O2 saturation (SaO2), end-tidal CO2, and tidal volume were measured. The role of hypoxia was studied by comparing apneas during depletion of O2 in the spirometer with those during 100% O2 breathing. In all subjects, BP periodically reached values greater than 150/95 mmHg in the hypoxic series. During the hyperoxic apnea series, however, BP remained stable. End-apneic mean BP was shown to be inversely correlated to SaO2 in six subjects in the SaO2 range from 60 to 100%. Although the hypoxic BP pattern closely mimicked that in SAS, the heart rate pattern in four of our subjects remained distinct from that in patients. Atropine could not prevent large BP swings in the hypoxic series. We conclude that SaO2 is a major determinant of periodic hypertension in recurrent apneas. Its effect probably results from chemoreflex modulation of peripheral resistance.     

Schistosoma mansoni: Demonstration of two circulating antigens in infected hamsters

In this study the presence of two circulating schistosome derived antigens, probably both polysaccharides, was demonstrated in hamsters heavily infected with Schistosoma mansoni. One antigen was an anodic, heat-stable, high molecular weight substance; it was demonstrated in serum, adult worm antigen and in the excretory and secretory products of adult worms. The antigen was demonstrated in the epithelial cells of the schistosome gut. A second antigen, cathodic, heat-stable and a low-molecular weight substance (MW < 30,000), was demonstrated in hamster serum, hamster urine, adult worm antigen, and in the excretory and secretory products of adult worms. Two additional schistosome derived antigens, both heat-labile, were demonstrated in hamster urine.     

A comparison of the radiation response of the epidermis in two strains of pig

The response of the epidermis was compared in two strains of pig, the English Large White and the G?ttinger Miniature, after irradiation with 90Sr beta rays. The effects of two types of anesthesia were also tested in pigs of each strain, a volatile gas mixture of approximately 70% oxygen, approximately 30% nitrous oxide, and 2% halothane, and an intravenously administered narcotic azaperon/etimodat with the animals breathing air. Strain- and anesthetic-related changes were compared on the basis of dose-effect curves for the incidence of moist desquamation from which ED50 values (+/- SE) were determined, i.e., the dose required to produce this effect in 50% of the fields irradiated. For English Large White pigs anesthetized with the volatile gas mixture, an ED50 of 27.32 +/- 0.52 Gy was obtained for moist desquamation. Irradiation with the azaperon/etomidat anesthesia in this strain of pig produced a significantly higher ED50 of 33.36 +/- 0.76 Gy (P less than 0.001). This appeared to be related to the fact that the animals were breathing air, i.e., a lower oxygen concentration (approximately 21%), at the time of irradiation. For the G?ttinger Miniature pig the ED50 values for moist desquamation were 38.93 +/- 3.12 Gy and 43.36 +/- 1.34 Gy while using the gaseous anesthetic mixture and the azaperon/etomidat anesthesia with the animals breathing air, respectively. These ED50 values are 10-11 Gy higher than those obtained for the English Large White pig under identical conditions of anesthesia, which resulted in a strain difference ratio of approximately 1.35. Radiation under the volatile gas mixture anesthesia resulted in a uniform irradiation response over the skin of the flank in both strains of pig. Radiation under azaperon/etomidat anesthesia resulted in a nonuniform skin response over the flank. The ED50 for moist desquamation was significantly higher in dorsal sites on the flank compared with the ventral area of English Large White pigs; a similar trend was seen in G?ttinger Miniature pigs. This difference in the radiosensitivity over the flank skin while the animals are under azaperon/etomidat anesthesia at the time of irradiation was associated with the animals breathing air and is in agreement with findings published previously for animals under halothane anesthesia and breathing air.