Effect of diabetes and elevated glucose on nitric oxide‐mediated neurotransmission in rat anococcygeus muscle

Abstract

Nitric oxide (NO)‐mediated neurotransmission is impaired in anococcygeus muscle from 8‐week streptozotocin‐induced diabetic rats. This study investigated the effects of insulin treatment, and the duration of diabetes on this impairment. In addition, the effect of in vitro exposure to elevated glucose has been investigated on NO‐mediated relaxations, in muscles from untreated rats. Relaxant responses to field stimulation (0.5‐5 Hz, 10 s train), sodium nitroprusside (SNP; 5 and 10 nM) and NO (1 and 3 μM) were significantly impaired in anococcygeus muscles from 8‐week diabetic rats, compared to responses from control rats. Insulin treatment (5 u Lente day−1, s.c.) of diabetic rats prevented the development of this impairment. Consistent with findings in 8‐week diabetic rats, relaxations induced by field stimulation, SNP and NO were attenuated in tissues from 2‐week and 4‐week diabetic rats compared to corresponding control responses, whereas relaxations to papaverine (3 and 10 μM) were not reduced. In contrast, diabetes of 3‐days duration did not affect relaxations to field stimulation, SNP or NO. Incubation of anococcygeus muscles from untreated rats in medium containing elevated glucose (44.1 mM) for 6 h, significantly impaired relaxations to field stimulation compared to responses obtained after normal glucose (11.1 mM) incubation. Relaxations to SNP and to NO were not affected by 6h exposure to elevated glucose. Similarly, incubation in hyperosmolar solutions containing mannose or sucrose for 6 h, impaired relaxations to field stimulation, but not to SNP or NO. The results indicate that the diabetes‐induced impairment of NO‐mediated neurotransmission in the rat anococcygeus muscle develops between 3 days and 2 weeks after the induction of diabetes with streptozotocin. Prevention of the impairment by insulin treatment suggests that it is specific for the diabetic state. In addition, the impairment may be related to hyperglycaemia and the consequent rise in osmolarity, since in vitro exposure to high glucose as well as to other hyperosmolar media impaired NO‐mediated relaxations to field stimulation.

Insulin Reversal of Impaired Nitrergic Transmission in the Anococcygeus Muscle from Diabetic Rats

“…The findings in the present study support our previous observations that in rats treated with STZ to induce diabetes, relaxant responses to nitrergic nerve stimulation, sodium nitroprusside and nitric oxide are attenuated in anococcygeus muscles 4 and 8 weeks after induction [17][18][19]. Together with our initial results these findings suggest that diabetes impairs smooth muscle reactivity to nitric oxide, although a concurrent prejunctional defect in nitric oxide synthesis/release cannot be excluded.…”

“…This impaired reactivity appears to be specific for nitric oxide, since relaxations to nitric oxide-independent relaxant agents such as papaverine are not altered by diabetes [17]. We have previously demonstrated that normalisation of blood glucose levels with daily insulin treatment from the time of induction can prevent these altera-tions [19]. The results of the present study now suggest that insulin treatment can also reverse established defects in nitrergic neurotransmission.…”

“…Insulin treatment of 8-week diabetic rats for the entire duration of diabetes was shown to prevent the impairment in nitrergic neurotransmission, thus confirming that this diabetes-induced defect in rat anococcygeus muscle can be prevented by improved glycaemic control [19]. An ability of insulin to also retard or reverse the advanced clinical complications of diabetes is of particular importance, as the current conventional management of the disease does not prevent the development of complications.…”

“…However, we have previously demonstrated that the in vitro exposure of anococcygeus muscles from normal rats to medium containing elevated glucose for 6 h, can reduce nitric oxide-mediated relaxations to nerve stimulation, suggesting that acute hyperglycaemia contributes to impaired nitrergic transmission [19].…”

Pathophysiology of diabetic erectile dysfunction: potential contribution of vasa nervorum and advanced glycation endproducts

“…In diabetic patients or individuals with impaired glucose tolerance, the recovery from reduced vasodilation has been shown to be delayed. 20,24 Although high glucose concentrations impair nitrergic function acutely and reversibly in vitro, 24,25 ED occurs much later in diabetic animal models. 5,13,[26][27][28] These observations have led the researchers to conclude that endothelial dysfunction precedes nitrergic dysfunction.…”