Another low-dose vs. high-dose biological response

[Muckerheide <muckerheide@MEDIAONE.NET>]

Title: Another low-dose vs. high-dose biological response

Friends,

Note again that responses to low dose (0.5 Gy) are opposite to high dose(5 Gy):
"The daily average cAMP/cGMP ratio in cells of SCN, pineal, serum and lymphocyte changed according to the dose of irradiation at which the mice were exposed. The high dose of 5 Gy increased the ratio, and the low dose of 0.5 Gy decreased the ratio. ... the peak phases of the cAMP/cGMP ratio at the low-dose groups appeared in advance from about 2 to 8 hours, whereas those at the high-dose groups were delayed from about 3 to 6 hours in comparison to that of the normal mice."

Regards, Jim Muckerheide
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Chin Med J (Engl) 1999 Feb;112(2):146-8

Dose-related effect of irradiation on circadian rhythm of cellular messengers in neural and immune system of mouse.

Tong J, Qin L, Geng M.

Department of Radiation Medicine, Suzhou Medical College, Suzhou 215007, China.

OBJECTIVE: To explore toxic effect of gamma-irradiation on circadian rhythms of cAMP and cGMP in signal pathway between the central nuclei and peripheral lymphocyte. METHODS: 60Co gamma-ray of 0.5 Gy and 5.0 Gy was applied to groups of mice at each circadian timepoint of a day. 24 hours after the irradiation, the pineal and suprachiasmatic nuclei (SCN) were removed, and the T lymphocytes in blood were separated by a step-centrifugal and nylon-filter treatment, for measurements of cAMP and cGMP by using the RIA procedure. The results were expressed as circadian rhythms of the cAMP/cGMP ratio derived from the Cosinor analysis. RESULTS: The daily average cAMP/cGMP ratio in cells of SCN, pineal, serum and lymphocyte changed according to the dose of irradiation at which the mice were exposed. The high dose of 5 Gy increased the ratio, and the low dose of 0.5 Gy decreased the ratio. There was a significant difference of cAMP/cGMP levels between the irradiated and the control groups, as well as between CT00:00 and CT12:00 of a day. In addition, the peak phases of the cAMP/cGMP ratio at the low-dose groups appeared in advance from about 2 to 8 hours, whereas those at the high-dose groups were delayed from about 3 to 6 hours in comparison to that of the normal mice. CONCLUSION: Toxic effect of gamma-irradiation on the cAMP/cGMP circadian rhythm in the central nuclei and peripheral lymphocyte could be characterized by a low-dose hormesis.