Single time point studies

Circadian factors - single time-point studies adequate ... 

Single time point studies are useful when assessing current conditions of birds in a small area, and results can serve as preliminary data for long-term studies. Some birds are collected by shooting (57), thus it is important to make sure that ammunition used does not contaminate the bird. Opportunistic collection of dead birds is also used (112), When birds are shot or collected dead to examine one time point, life history information is limited. 

Modifications for efflux inhibition studies are as frequent as efflux studies and include all parts of the method (permeability time, inhibitors, determination of Papp at single time point versus several time points). 

One distinction between many of the studies of behavioral toxicity in children and adults is that while the former have tended to be primarily longitudinal in nature, following the effects of toxicant exposures to children across the course of development, most of the occupational exposure studies are cross-sectional studies that encompass only a single time point of measurement of behavioral function. 

The problem with current laboratory methods is that they only measure formaldehyde at a single time point under equilibrium conditions. In contrast, real-life use of particleboard involves climatic shocks. This was well illustrated by a study at the center for surface technology In Haarlem (3). Figure 1 shows that changes in air humidity and temperature greatly and promptly influence formaldehyde emission. Thus, while laboratory tests allow a qualitative evaluation of the emission risk, they do not permit quantitative extrapolation to real-life conditions. 

Even with satellite animals, repeated sampling within a rodent species is often not performed. Usually, each animal contributes to the data at a single time point. When the animal is sacrificed to obtain the pharmacokinetic data, these animals are said to be destructively sampled. The number of animals in such studies is large and costly since often a study has many different dose levels, are dosed in both males and females, and samples are collected at many time points. As a com-... 

The small delay time requirement is especially important in the case of rapidly changing dynamic samples. It may be waived in the case of some single time point measurements (i.e., while recording quasi-steady samples). In fact, some studies, which target qualitative detection of short-lived species rather than temporal profiles of reactants of intermediates, impose less rigorous requirements for the experimental systems. The following sections provide examples of various TRMS systems emphasizing the role of interfaces. 

The distribution of endosulfan and endosulfan sulfate was evaluated in the brains of cats given a single intravenous injection of 3 mg/kg endosulfan (Khanna et al. 1979). Peak concentrations of endosulfan in the brain were found at the earliest time point examined (15 minutes after administration) and then decreased. When tissue levels were expressed per gram of tissue, little differential was observed in distribution among the brain areas studied. However, if endosulfan levels were expressed per gram of tissue lipid, higher initial levels were observed in the cerebral cortex and cerebellum than in the spinal cord and brainstem. Loss of endosulfan was most rapid from those areas low in Upid. Endosulfan sulfate levels peaked in the brain at 1 hour postadministration. In contrast, endosulfan sulfate levels in liver peaked within 15 minutes postadministration. The time course of neurotoxic effects observed in the animals in this study corresponded most closely with endosulfan levels in the central nervous system tissues examined. 

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