Diabetes-induced rat tracheal segment supersensitivity to carbachol

Treatment with Cyclohexenonic Long-Chain Fatty Alcohol Reverses Diabetes-Induced Tracheal Dysfunction in the Rat

In this study, we tried to elucidate the effect of cyclohexenonic long-chain fatty alcohol (N-hexacosanol) on tracheal dysfunction in diabetic rats. Diabetes was induced in 8-week-old male Sprague-Dawley rats by administering an intraperitoneal injection of 50 mg/kg streptozotocin. Non-diabetic control rats received an injection of citrate-phosphate buffer alone. Four weeks after the induction of diabetes, rats were randomly divided into 5 groups: age-matched non-diabetic control rats (group A); 4-week diabetic rats without N-hexacosanol treatment (group B); diabetic rats treated with vehicle (group C), and diabetic rats treated with N-hexacosanol at a dose of 2 or 8 mg/kg i.p. every day for the following 4 weeks (group D and group E, respectively; n = 6-8 animals in each group). Serum glucose and insulin levels were determined, as were the contractile responses induced by carbachol and 100 mmol/l KCl. The participation of M(2) and M(3) receptors was investigated in the trachea by real-time polymerase chain reaction (PCR), hematoxylin and eosin (HE) and immunohistochemical staining. Hypertrophy of airway smooth muscle was observed in diabetic rats, and was ameliorated by treatment with N-hexacosanol. Treatment with either 2 or 8 mg/kg N-hexacosanol did not alter diabetic rat status, i.e., body weight, serum glucose or serum insulin levels, but it significantly reversed the decrease in tracheal wall thickness and diabetes-induced hypercontractility in the rat trachea. In the immunohistochemical studies, muscarinic M(2) and M(3) receptors were expressed in the airway smooth muscle, the elastic fibers, the fibroblast and the surface of epithelium, and these expressions were not altered by either induction of diabetes or N-hexacosanol treatment. The expression of M(3) muscarinic receptor mRNAs in the trachea tended to be increased by the induction of diabetes and normalized when treated with N-hexacosanol. Our data indicate that N-hexacosanol could reverse diabetes-induced hypercontractility in the rat trachea.

Increased function of inhibitory neuronal M2 muscarinic receptors in trachea and ileum of diabetic rats

1. Release of acetylcholine from parasympathetic nerves is inhibited by neuronal M(2) muscarinic receptors. The effects of streptozotocin-induced diabetes on prejunctional M(2) and postjunctional M(3) muscarinic receptor function in rat trachea and ileum were investigated in vitro. 2. Neuronal M(2) muscarinic receptor function was tested by measuring the ability of an agonist, pilocarpine, to inhibit and an antagonist, methoctramine, to potentiate electrical field stimulation (EFS)-induced contraction of trachea and ileum. Concentration-response curves to pilocarpine and methoctramine were shifted to the left in both to a greater degree in diabetics than controls. 3. In trachea, post-junctional M(3) muscarinic receptor function was increased since maximum contractile responses to the muscarinic agonists acetylcholine and carbachol were greater in diabetics than controls. This increase offset the increased function of the inhibitory neuronal M(2) muscarinic receptors since EFS-induced, frequency-dependent contraction was equal in control and diabetic rats. 4. In contrast, post-junctional M(3) muscarinic receptor function was unchanged by diabetes since concentration-response curves to acetylcholine and carbachol were not different between groups. Thus, EFS-induced contractions of the ileum were decreased in diabetics versus controls. 5. In conclusion, inhibitory M(2) muscarinic receptors on parasympathetic nerves in the trachea and ileum are hyperfunctional in diabetic rats. The function of post-junctional M(3) muscarinic receptors in the trachea, but not the ileum, is also increased in diabetes. 6. The dysfunction of inhibitory, neuronal M(2) muscarinic receptors in the airways may protect against hyperreactivity and in the ileum may contribute to gastrointestinal dysmotility associated with diabetes.

Effect of experimental diabetes on GABA-mediated inhibition of neurally induced contractions in rat isolated trachea

1. In the present study, we investigated the effect of GABA and selective GABA agonists and antagonists on neurally induced tracheal contractions in streptozotocin (STZ) diabetic rats. 2. Contractile responses to electrical field stimulation (EFS) in rat tracheal rings were completely abolished by atropine and tetrodotoxin, but were unaffected by the ganglion blocker hexamethonium, indicating that they were mediated via neuronal release of acetylcholine (ACh). 3. Contractions induced by EFS, but not by exogenous ACh, were inhibited by GABA and the selective GABA(B) receptor agonist baclofen, but not by the selective GABA(A) receptor agonist 3-aminopropane sulphonic acid. The inhibitory effects of GABA or baclofen were not affected by the GABA(A) antagonist bicuculline, but were significantly reversed by the GABA(B) antagonist phaclofen. 4. The inhibitory effects of both GABA and baclofen were found to be significantly greater in trachea from control rats compared with tissues from diabetic rats. 5. Non-adrenergic, non-cholinergic relaxation responses elicited by EFS in precontracted tracheal rings from diabetic and control rats were similar in magnitude and were unaffected by GABA or GABA analogues. 6. These results suggest that GABA decreases the response to EFS by directly inhibiting the evoked release of ACh through GABA(B) receptors in rat trachea and that STZ-induced diabetes causes an impairment in the inhibitory effect of GABA on neurally induced contractions in this tissue.

The effect of experimental diabetes on cholinergic neurotransmission in rat trachea: role of nitric oxide

We investigated the effect of nitric oxide (NO) on the responses of isolated tracheas to acetylcholine and to electrical field stimulation in streptozotocin-diabetic and controls rats. The contractile responses to acetylcholine were neither different nor affected by the NO synthase blocker, N(omega)-nitro-L-arginine methyl ester (L-NAME), in the two groups. Diabetic rat tracheas were supersensitive to field stimulation. L-NAME enhanced field stimulation-induced contractions at low frequencies in control rat tracheas, but had no effect in diabetic rat tracheas. After L-NAME treatment, there was no difference in sensitivity to field stimulation between the groups. The relaxation responses to sodium nitroprusside in acetylcholine-precontracted tracheas were not different between the groups. However, diabetic rat trachea was supersensitive to the relaxant effect of sodium nitroprusside on contractile responses to field stimulation. These results suggested that the increase in sensitivity to field stimulation in tracheas from diabetic rats might be due to impairment in the production and/or release of an endogenous NO-like factor.

The effects of acetylcholine on insulin-dependent and non-insulin-dependent diabetic rat tracheal segments

1. In the present study, the contractile effects of acetylcholine (Ach) were investigated in isolated tracheal strips obtained from insulin-dependent (ID) and non-insulin-dependent (NID) diabetic rats. 2. The maximum responses to Ach were significantly decreased in 5-6 week ID diabetic rat tracheal segments compared with those from controls but, the sensitivity (pD2 values) of ID diabetic tracheas to Ach were not significantly altered relative to corresponding controls. 3. Tracheas isolated from 11-12 week NID diabetic rats exhibited reduced maximal contractile effect of Ach and also sensitivity (pD2 values) of NID diabetic tracheas to Ach were significantly decreased when compared to control rat tracheas. 4. Insulin treatment of both group of diabetic rats for 10 days corrected the changes observed in diabetic tracheas.

The effect of oral vanadyl treatment on the reactivity of tracheal smooth muscle obtained from insulin-dependent diabetic rats

1. In this study, we investigated the contractile effects of acetylcholine (ACh) and KCl in tracheas obtained from 12-13 wk insulin-dependent (ID)-diabetic rats. 2. The maximum contractile responses to ACh and KCl were significantly increased in ID-diabetic rat tracheas compared with those from controls. But the sensitivity (pD2 values) of ID-diabetic tracheas to these agents were not significantly altered relative to controls. 3. The alterations which occurred in ID-diabetic rats were prevented with oral vanadyl treatment during a 10 wk period.