Biomedical subjects
A R Stebbing
Publications and source records attributed to A R Stebbing.
Growth hormesis: a by-product of control.
Data from experiments, in which colonies of a hydroid, Laomedea flexuosa, were exposed to a range of Cu2+ concentrations and a marine yeast, Rhodotorula rubra, was exposed to a range of Cd2+ concentrations, not only exhibit hormesis, but also suggest how its occurrence in growth experiments might be explained. When growth data are considered as normalized specific rates against a time base, their oscillatory form indicates the output of a growth regulatory mechanism whose behaviour can be used to interpret the typical concentration-response curve exhibiting hormesis. Advantages may be conferred upon organisms whose growth control mechanisms overcorrect in response to low levels of inhibitory loading by toxic agents (stimulus), while at higher concentrations it is the overloading of such control mechanisms that results in the threshold in concentration-response curves (inhibition). It is suggested that if different examples of hormesis share a common explanation, it lies in the behaviour of homeostatic and homeorhetic feedback mechanisms, which respond to perturbation non-specifically and may overcorrect for adaptive reasons to low levels of inhibitory challenge.
Hormesis--the stimulation of growth by low levels of inhibitors.
Hormesis is the name given to the stimulatory effects caused by low levels of potentially toxic agents. When this phenomenon was first identified it was called the Arndt-Schulz Law or Hueppe's Rule because it was thought to occur generally. Although this generalisation is not accepted today, there has never been more evidence in its support, justifying a re-examination of the phenomenon. Evidence from the literature shows that not only has growth hormesis been observed in a range of taxa after exposure to a variety of agents, but also that the dose-response data have a consistent form. While there are a number of separate hypotheses to explain specific instances of hormesis, the evidence presented here suggests that different examples might have a common explanation, and the possibility of a general theory is considered.
An experimental approach to the determinants of biological water quality.
A case is presented for the use of experimental bioassay techniques to detect and measure variations in water quality in the marine environment by exposing suitable organisms in the laboratory to water samples collected in the field. A technique is described which was developed for this purpose with the use of a clonal hydroid; preliminary results from Swansea Bay show that it is sensitive to the variations in water quality that occur there. Chemical techniques are being developed for use in conjunction with such bioassays to identify the kinds of contaminants responsible for a detected effect, and some preliminary experiments suggest that divalent metals and the volatile constituents of hydrocarbons can be removed selectively from sea water.
Hormesis: interpreting the beta-curve using control theory.
Data from experiments exposing colonial hydroids to toxic growth inhibitors have provided evidence of growth control mechanisms that respond adaptively to counter toxic inhibition. Analysis of growth data and the development of simulation models provide an interpretation of both alpha- and beta-curves. The hypothesis also suggests that hormesis is related to adaptation by growth control mechanisms that confer tolerance to subsequent exposure.