OBJECTIVETo study the correlation of homocysteine (Hcy) in plasma with nitric oxide synthetase (NOS) and endogenous carbon monoxide (CO) in the penile corpus cavernosum of type 2 diabetic rats.

METHODSThis study included 40 male Wistar rats, 10 as controls (Group A) and the other 30 as diabetes mellitus (DM) models. Four weeks after the model establishment, the model rats were divided into a DM group (Group B, n = 10), an insulin treated group (Group C, n = 10), and a folic acid and vitamin B12 treated group (Group D, n = 10). All the rats were injected with apomorphine and observed for penile erection at 8 and 12 weeks, and the levels of total plasma Hcy (tHcy), NOS and CO in the penile corpus cavernosum were measured at 12 weeks.

RESULTSCompared with Group A, the level of tHcy was significantly increased, while NOS and CO activities in the penile cavernous tis-sue and erectile function remarkably decreased in Group B (P < 0.01). The incidence rate of high Hcy was 55% in the DM rats. In comparison, the level of tHcy was obviously decreased, and the NOS activity and erectile function markedly increased in Groups C and D (P < 0.01). The Hcy level showed a significant negative correlation with NOS activity (rA = -0.89, rB = -0.76, rc = -0.91, rD = -0.91) and CO content (TA = -0.82, r, = -0.77, rc = -0.93, rD = -0.81).

CONCLUSIONHigh plasma Hcy can decrease NOS and CO activities in the penile corpus cavernosum, and consequently induce erectile dysfunction in DM rats, while insulin, folic acid and vitamin B12 can improve their penile erectile function by increasing NOS and CO activities.