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Re: What is hormesis?
>Date: Tue, 24 Mar 1998 23:41:20 +0530
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
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>From: "Dr.K.S. Parthasarathy" <aerb@SOOCHAK.NCST.ERNET.IN>
>Subject: Re: What is hormesis?
>X-cc: Gautham Parthasarathy <parthga@Eng.Auburn.EDU>
>To: Multiple recipients of list MEDPHYS <MEDPHYS@LISTS.WAYNE.EDU>
>
>
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> Dear Dr Willcut,
>
>I wrote a note on Radiation Hormesis a few months ago in the Quarterly
>Newsletter published by the Indian Atomic Energy Regulatory Board. This
>may be of interest
> Issues in Perspective
>
> Radiation Hormesis
>
> K.S. Parthasarathy
>
>
> Exposure to high levels of ionizing radiation can harm
>the tissues of the human body. This has been demonstrated
>unequivocally. Many who handled X-ray Units carelessly,suffered
>extensive skin damage and became marteers. They suffered
>clinically identifiable effects. Long term studies of exposed
>populations such as the survivors of the atomic bombings at
>Hiroshima and Nagasaki demonstrated that radiation exposure has a
>potential for inducing cancers in the exposed populations.
>These can be inferred from epidemiological studies. But there
>is a group of scientists who firmly believe that low doses of
>radiation can be beneficial. Dr. T. Luckey is an eloquent
>proponent of this theory. He wrote a very interesting Book
>titled "Radiation Hormesis"
>
> In 1987, Dr. Marshall Brucer wrote an eminently
>readable feature article titled "Radiation Hormesis after 85
>years" in the American Health Physics Society's New letter.
>
> Brucer introduces the topic by citing the developments
>chronologically. Our pancreas secretes only when food passes
>through the stomach. In 1902, E. Starling, an English
>Physiologist discovered that an acid extract of duodenum
>contained 'secretin' that when discharged into blood, stimulated
>the pancreas to secrete. In 1904 Starling was the first to coin
>the term "hormone" (hormo in Greek mean to excite) to designate
>any substance produced in small amounts but carried in blood to
>influence some other organ.
>
> "Weak stimulus might stimulate what the same, but
>stronger stimulus inhibits". Based on this pharmaceutical
>principle practiced by ancients, Brucer argues that toxicity is a
>matter of dose. A peg of whiskey, a whiff of nicotine from a
>cigarette, caffeine in a cup of coffee all these stimulate. A
>single intake of few liters of alcohol, half a gram of nicotine
>or caffeine will kill. They stimulate at low doses and kill at
>high doses.
> Brucer pointed out that the word "hormesis" was coined
>by C Southam and J Ehrlich. They found that concentrations of
>oak bark extract inhibited fungal growth while in low dose,
>stimulated fungal growth. According to Brucer Starling's
>'hormone' was modified to "hormesis" (phytopathology 33:517,1943)
>
> During the 1950s, some Agricultural Chemists fed
>antibiotics to live stock. They thought that suppression of
>flora in the gut would decrease growth. But poultry, pigs and
>cattle fattened enormously on a diet containing low doses of
>antibiotics. T. Luckey who was engaged in such studies surveyed
>the literature later. In 1981, Luckey revived the term
>'hormesis' with reference to ionizing radiation backing it up
>with over 1250 articles. The effects observed include growth of
>algae under X irradiation (1898), growth of peas (1908), increase
>in life span of invertebrates (1918) and insects (1919), and
>seedling stimulation by X-rays (1927).
>
> Brucer observed that before World War I and continuing
>into 1930s about ten articles a year referred to a hormetic
>effect. After World War II, twenty articles per year mentioned
>a hormetic effect. He implied that hormesis theory did not
>thrive because all new paper head lines highlighted negative
>effects!!. For instance, H. Muller who demonstrated genetic
>effects by irradiating fruitflies in 1927, predicted a genetic
>catastrophe from atomic bomb explosiion. This lead to feverish
>publicity. Brucer bemoans the fact that no publicity was given
>the disproof 35 years later. The story of double headed babies
>in Hiroshima & Nagasaki was fiction; but it made good copy.
>According to Brucer "Health Physics and Genetics were supported
>lavishly by radiation hysteria and radiation biology became the
>]most intensely researched science in history."
>
> If the interaction of radiation with tissue is a purely
>physical mechanism, the probability for initiation of an effect
>in tissue will be is proportional to the number of initiating
>particles and hence to dose. But this picture is too simple as
>it ignores the profound biological defence mechanisms.B.L Cohen
>(Risk Analysis,1995) reviewed the evidence that biological
>defence mechanisms are stimulated by low level radiations. When
>radiation interacts with cells they may induce chromosome
>aberrations. Several studies have shown that frequency of
>chromosome aberrations induced by a high dose of radiation is
>substantially reduced if the cells are pre-exposed to low level
>dose.
>
> Cohen cites a few cases of protection afforded by pre-
>exposure to low doses. Low level radiation enhances production
>of repair enzymes. Linear no threshold concept is a simple
>theory. When the dose is low, the time interval between
>irradiation and appearance of tumor is observed to be large.In
>view of the latency period, an exposed person may die of other
>causes before cancer can develop. Cohen argues that there is a
>"practical threshold" for radiation induced cancer. Based on the
>radon-lung cancer relationship, Cohen demonstrated that the
>linear no threshold theory fails very badly in the low dose, low
>dose rate region.
>
> The International Commission on Radiological Protection in
>its publication no 60 stated thus: " There is some experimental
>evidence that radiation can act to stimulate a variety of
>cellular functions including proliferation and repair. Such
>simulation is not necessarily beneficial. In some
>circumstances,radiation appears also to enhance immunological
>responses and to modify balance of hormones in the body. In
>particular radiation may be able to stimulate the repair of prior
>radiation damage, thus decreasing its consequences. or may be
>able to improve immunological surveillance, thus strenghthening
>the body's natural mechanisms" .ICRP went on to suggest that the
>experimental data on such effects have been inconclusive, mainly
>because of statistical difficulties at low doses. The Commission
>unequivocally stated that the available data on hormesis are not
>sufficient to take them into account in radiological protection
>
> Since this report was published, some more work has been
>completed. Whether these will make any impact to force
>rethinking of ICRP's conclusions will have to be seen. The
>answers to the important questions will have to probably come
>from molecular biologists. They have also to find explanations to
>the new findings of 'genomic instability'. The debate on effects
>of low level radiation appears to generate more heat than light.
>In many m]eetings, the debates generate lot of sound and fury
>signifying nothing. Living tissue with DNA packed with genetic
>information will continue to be an enigma at least for a few more
>decades.
>
>Dr.K.S.Parthasarathy
>
>
>
>
>========================================================================
>Atomic Energy Regulatory Board,
>Niyamak Bhavan, Anushaktinagar,
>Bombay - 400 094. INDIA
>
>Tel : 5572989/90/91/93/94 FAX : 5562344 / 5565717
>email : aerb@soochak.ncst.ernet.in
>========================================================================
>
>
>On Fri, 20 Mar 1998, Virgil M. Willcut wrote:
>
>>
>> ** Mail from Medphys Listserver **
>> If you reply to this message, it will be posted on Medphys for all the
>> subscribers to review ...
>>
>>
>> I have seen the term hormesis used several times on the listserver.
>> Could someone explain, in lay terms for the non-radiobioligist, what
>> this phenomenon is?
>>
>> Thanks
>>
>> Virgil Willcut
>> virgil.willcut@sih.net
>>
>