Differential changes of adrenoceptor- and muscarinic receptor-linked prostacyclin synthesis by the aorta and urinary bladder of the diabetic rat

Effects of aminoguanidine and N(G)-nitro-L-arginine methyl ester on vascular responses of aortae and lungs from streptozotocin-diabetic rats

Aminoguanidine (AG) treatment can prevent the development of some functional anomalies in experimentally diabetic rats, possibly via the prevention of a diabetes-induced vascular dysfunction. The acute effects of AG on endothelium-dependent relaxation of aortae in the presence of indomethacin and on pressor responses and prostacyclin release in isolated perfused lungs, were therefore investigated using tissues from control and streptozotocin-diabetic rats. Endothelium-dependent relaxations of aortae were reduced by aminoguanidine (control 20%, and diabetic 25%). For lungs, angiotensin II-induced pressor responses were unaffected by AG, whereas the nitric oxide synthase inhibitor L-NAME caused integrated pressor responses to be increased in lungs from control and diabetic rats (2.0 and 1.8 fold respectively). Individually, AG (1 mM) and L-NAME (10 microM) did not affect total cumulative prostacyclin release by control lungs, whereas significant increases for both were observed for diabetic lungs. In summary, these studies firstly provide evidence that AG can increase prostacyclin release from tissues in vitro, with little effect upon endothelium-dependent vasodilatation, and secondly, that the regulation of vasodilator prostanoid release by the pulmonary circulation of the rat may be altered in experimental diabetes.

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 35 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 compared 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 PGE1-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 vasculature to generate cAMP and cGMP may constitute an adaptive response to counteract the reduction in receptor-linked NO release. Impaired adenylate or guanylate cyclase activity does not contribute to erectile dysfunction in diabetic rats.