During fetal development of the sheep lung, elastin content continually increases. For examination of the processes controlling this elastin accumulation, an explant culture system was characterized with respect to changes in tropoelastin production in sheep lung during fetal and early postnatal development. Relative tropoelastin production in cultured lung explants, quantitated by immunoprecipitation, was about 0.3% of total [14C] valine incorporation during the period from 55 to 104 days after conception. This percentage began to increase by 112 days after conception, reached a maximum value of about 1.0% by 135 days after conception, and then declined to 0.5% soon after birth. The absolute rate of tropoelastin production paralleled these changes in relative tropoelastin production. For evaluation of the processes controlling tropoelastin production in the developing sheep lung, total cellular RNA prepared from 68-day-old fetal, 107-day-old fetal, and 147-day-old fetal lung was translated in a rabbit reticulocyte lysate system. Elastin mRNA activity, expressed as the amount of elastin precursor translated per microgram per microgram of DNA, increased about 3-fold during fetal lung development, and elastin precursor synthesis, expressed as a proportion of total translational activity, increased in parallel. It appears, therefore, that elastin production in developing fetal lung is modulated, at least in part, by the amount of available translatable elastin mRNA present in the tissue.

SummaryReasons for performing study: Exposure of horses to airborne particulates during stable confinement has been linked with airway inflammation in these animals. Understanding that link requires accurate measures of exposures and greater understanding of the sources of variability in these exposures. Objectives: Area and breathing zone particulate concentrations were measured over time in order to determine the relative variability introduced by daily, monthly or between horse variations. Additionally, the relationship between area and breathing zone respirable particulate concentrations was examined. Methods: The study was conducted in a Thoroughbred training stable. Breathing zone and area respirable particulate concentrations were measured over a 30-month period. Mixed-model analysis of variance was used to determine effect of month and year at the time of sampling and the daily variance upon area particulate concentrations. The effects of hay feeding method and horse variance on breathing zone measures were included in the model. Real-time concentrations of particulate matter with an aerodynamic diameter of 10 mm or smaller (PM10) were measured to determine the effect of barn door position. Significance was set at P<0.05. Results: Average area particulate concentration varied with month and year of sampling but daily variation was not significant. Maximum area respirable particulate concentrations were significantly affected by daily variation. Opening barn doors resulted in lower PM10 levels. Horses fed from hay nets were exposed to significantly higher concentrations of respirable particulates in their breathing zone than when fed hay on the ground. Horse-to-horse variability was significant. Breathing zone concentrations were significantly greater than area concentrations and the 2 measurements were not correlated. Conclusions: While area respirable particulate concentrations reflected seasonal changes, these measures are poor predictors of individual horse exposure. Instead, methods of feeding and individual horse behaviour are important determinants of exposure. Potential relevance: Studies investigating the effect of natural exposures on lung health in horses should consider the effects of individual behaviour and management practices on breathing zone exposure.

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Egg weight, hatching time, and hatchability of young pullet eggs were measured in lines selected for fast and slow hatching times and a control. Eggs were collected from three hatches four weeks apart and from four age groups of pullets each differing from the next age by three weeks. Line effects were significant for hatching time and the fast line had significantly smaller egg weight. No difference was observed between lines for hatchability. Significant linear effects of the age groups of the pullets were observed for all three traits and significant quadratic effects were noted for hatching time. As age of pullet increased, hatching time declined and egg weight and hatchability increased. There were significant linear by linear interactions between hatch and age for all traits, because the youngest age groups changed at a faster rate over hatches than did the older age groups.The interaction between selected lines and age groups was not significant for any trait. This result indicates that the genetic differences in hatch time obtained in these lines by selection are genetically uncorrelated with the hatch time differences resulting from age differences, and neither are related to early hatchability. Selection for hatching time reduced the hatching time of the eggs laid by young pullets, but did not increase the hatchability of their eggs.

The regulation of elastin production has been evaluated and compared in two systems in the developing sheep: nuchal ligament and lung. Absolute rates of production in explant culture were estimated by immunoprecipitation of newly synthesized elastin and determination of precursor pool specific activities. Lung elastin production increased about 2.5-fold while nuchal ligament production increased about 9-fold during the latter half of gestation. In comparison, the activities of elastin messenger RNA(mRNAE) of these tissues were determined in a cell-free system by immunoprecipitation. The increases in mRNAE activity largely paralleled the rises in elastin production, suggesting that elastin synthesis in these tissues is regulated, at least in part, by the availability of translationally active mRNAE.