Adenylate and guanylate cyclase activity in the penis and aorta of the diabetic rat: an in vitro study



Objective To investigate the role of adenylate and guanylate cyclases in the mediation of erection in diabetic rats.

Materials and methods Hyperglycaemic diabetes mellitus was induced in 3 5 rats using streptozotocin. Two months later the penises and aortae of these rats were excised and cut into rings or segments before being treated with varying concentrations of acetylcholine (Ach). sodium nitroprusside (NaNP), prostaglandin E1 (PGE1) and adrenaline (AD). The levels of adenosine 3'5′-cyclic monophosphate (cAMP) and guanosine 3'5′-cyclic monophosphate (cGMP) so generated were measured by radioimmunoassay and the results com- pared with those from seven age-matched control rats that had not been given streptozotocin.

Results Ach-stimulated cGMP synthesis was impaired in the aortae in diabetic rats. Ach-stimulated cGMP synthesis was undetectable in the penis. NaNP-stimulated cGMP and PGE,-stimulated cAMP synthesis was enhanced in both the penises and aortae in diabetic rats compared with controls. AD-stimulated cAMP synthesis was enhanced in the aorta in diabetic rats compared with controls, but AD had no effect on CAMP synthesis in the penis.

Conclusion Ach-stimulated nitric oxide (NO) synthesis is impaired in the vasculature of diabetic rats and an Ach-NO axis may not be present in the penis of the rat. The enhanced capacity of the penis and vasculat- ure to generate cAMP and cGMP may constitute an adaptive response to counteract the reduction in recep- tor-linked NO release. Impaired adenylate or guanylate cyclase activity does not contribute to erectile dysfunc- tion in diabetic rats.