ABSTRACT
<p><b>OBJECTIVE</b>To study the changes in the activities of carbon monoxide (CO) and heme oxygenase 2 (HO-2) in ED rats with hyperhomocysteinemia (HHcy).</p><p><b>METHODS</b>This study included 40 male Wistar rats weighing 280 - 310 g, 10 as normal controls (group A). HHcy models were made in the other 30 by giving 3% methionine for 4 weeks, and then divided into groups B, C and D. The rats in group B continued to be fed with 3% methionine, those in group C were treated with betaine hydrochloride, and those in group D were given zinc porphyrin IX at 45 micromol per kg per d. Penile erections of the rats were recorded, and 4 weeks later, all were killed for determination of the levels of homocysteine (Hcy) in the blood plasma and the activities of CO and HO-2 in the corpus cavernosum of the penis.</p><p><b>RESULTS</b>The level of plasma Hcy, penile erection frequency and the content of CO in the corpus cavernosum were (12.55 +/- 0.82) micromol/L, (1.88 +/- 0.05) times and (10.55 +/- 1.73) micromol/L in group A, the Hcy level significantly higher while the penile erection frequency and CO content remarkably lower than in group B ([25.01 +/- 0.94] micromol/L, [0.70 +/- 0.05] times and [9.51 +/- 1.52] micromol/L, P < 0.05 or P < 0.01), with a negative correlation between the level of Hcy and that of CO and HO-2 (P < 0.01). Compared with group B, the three parameters were all significantly increased in C ([14.37 +/- 0.47] micromol/L, [1.18 +/- 0.08] times and [10.36 +/- 1.56] micromol/L, all P < 0.05 or P < 0.01).</p><p><b>CONCLUSION</b>Decreased expressions of CO and HO-2 in the corpus cavernosum of the penis may result in ED in HHcy rats. Betaine can reduce the Hcy level in the blood plasma and CO content in the corpus cavernosum, which might be one of the mechanisms of its action on ED with HHcy.</p>