Yin and Yang

the two opposite conditions

form the basic theory of Chinese traditional medicine

and Yang xu（weakness in vital function） and Yinxu （dificiency in vital energy）are the clinical expressions of Yang and Yin deficiencies. The authors found that the cAMP

cGMP and cAMP/cGMP ratio could reflect the Yangxu and Yinxu conditions in genaral.In this paper the nature of Yin and Yang and the cyclic nucleotides in 9 patients with hyperthyroidism and 17 patients with hypothyroidism were studied. It was found that the clinical picture of hypothyroidism conforms with the syndrome of weakness in Yang and that of hyperthyroidism with deficiency in Yin. The plasma cAMP in hyperthyroidism hypothyroidism and control group were 29.9±4.1

16.0±1.3 and 23.9±5.3 pmol/ml

respectively. The plasma cGMP in the above conditions were 4.7±0.66

7.4±0.73 and 6.6±2.2 pmol/ml

respectively. The cAMP/cGMP ratio was 7.1±1.25 in hyperthyroidism

2.6±0.32 in hypothyroidism and 4.95±0.04 in control group.In conclusion

the authors pointed out that there was a predominance of cAMP in Yin deficiency （hyperthyroidism） and a predominance of cGMP in Yang weaknss （hypothyroidism）. As the modifications of plasma cyclic nucleotides are under the influence of multiple factors

especially neuro-endocrine regulation

the reverse changes of cAMP/cGMP ratio in Yangxu and Yinxu as well as in hypo-and hyperthyroidism make the authors believe that the cyclic nucleotides changes may be related with the pathophysiological nature of Yin and Yang andmay serve as a diagnostic criteria for the Yinxu and Yangxu cenditions.