No abstract

Objective To clarify the effects of androgens (testosterone and dihydrotestosterone, DHT) and ageing on gene expression of vasoactive intestinal polypeptide (VIP), assessed as the expression of VIP mRNA, in rat corpus cavernosum. Materials and methods The study comprised 160 male Sprague Dawley rats divided into group A (56 rats, 5 weeks old), group B (50 rats, 10 weeks old) and group C (54 rats, 58 weeks old). Groups A±C were subdivided, respectively, into subgroups 1 (intact controls), 2 (castrated), 3 (castrated but given testosterone undecanoate 25 mg/kg per month by intramuscular injection), 4 (castrated with testosterone undecanoate 50 mg/kg per month) and 5 (treated with ®nasteride 4.5 mg/kg per day, orally). At 4 and 10 weeks after these treatments half the rats were killed. Serum samples were taken for the measurement of total and free testosterone and DHT, using a radioimmunoassay. Penile samples (corpus cavernosum) were frozen in liquid nitrogen and stored at x80uC. VIP mRNA was estimated using a semiquantitative reverse-transcription polymerase chain reaction. Results There was no signi®cant difference in VIP mRNA in rat corpus cavernosum between intact control and castrated subgroups, or subgroups treated with ®nasteride, in groups A±C, including both the 4-and 10-week old animals (P>0.05). Penile VIP mRNA was unchanged at any dose of testosterone in the castrated subgroups in all groups (P>0.05). There was no signi®cant relationship between penile VIP mRNA and ageing (P>0.05). Conclusions The gene expression of VIP in rat corpus cavernosum is independent of androgens (testosterone and DHT) and ageing. Androgens probably induce penile erection by pathways other than VIP; ageing may have little effect on penile VIP mRNA.