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Summary Determinations of mercury in urine were made in samples collected from workers that were: (a) exposed prior to sampling urine has been sampled over 3 weeks'post-exposure period; (b) currently exposed sampling on consecutive days of the working week; (c) currently exposedurine sampled over 24 hrs, during working shift (morning or afternoon) and off work. Regardless of exposure time pattern in all groups studied, a diurnal variation of urinary concentrations of mercury was observed with a maximum at night and morning hours, and minimal values in the afternoon The great variability in Hgconcentrations could have been related to the time of day at which the sampling took place, and partly to variation of urine excretion rate, the 2 factors being interrelated Only a moderate variability in urinary concentrations of mercury was found when the sampling was instituted at a constant time of day, and when the results were standardized for specific gravity of urine.

Rats treated with DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine], a selective noradrenergic neurotoxin, showed no differences compared to control rats in the number of head dips, a measure of exploratory behavior. Since a previous neurochemical investigation had demonstrated that DSP-4 rats have supersensitive alpha 2- and beta-adrenergic receptors in certain regions of the central nervous system, the behavior of these animals was also examined after the injection of clonidine, an alpha 2 agonist, and clenbuterol, a beta agonist. These drugs reduced, in a dose-dependent manner, the head-dipping of both control and DSP-4 rats. However, this effect was of greater magnitude in DSP-4 animals. Control experiments suggested that the response to clonidine and clenbuterol was mediated centrally by alpha 2 and beta receptors, respectively. Other behavioral experiments with agonists of the dopaminergic and serotoninergic systems indicated that these neurotransmitter systems were unchanged in DSP-4 animals. The results are discussed in terms of the selective action of DSP-4 and the responsiveness of DSP-4 rats to adrenergic agonists. The DSP-4-treated rat may constitute a new model of functional supersensitivity to adrenergic agonists.