Yutaka Kasuya

Impairment of endothelium-dependent relaxation and changes in levels of cyclic GMP in aorta from streptozotocin-induced diabetic rats

1 Acetylcholine (ACh)‐induced relaxation of aortic strips with endothelium and production of cyclic GMP between streptozotocin‐induced diabetic and age‐matched control rats were compared. 2 The concentration‐response curve for ACh‐induced relaxation was shifted to the right in diabetic rats. IC50 values for ACh were 4.57 ± 0.67 × 10−8 m and 1.00 ± 0.87 × 10−7 m in aortic strips from age‐matched control and diabetic rats, respectively (n = 6, P < 0.05). 3 Relaxations produced by atrial natriuretic peptide (ANP) in diabetic aortae were similar to those in age‐matched vessels. 4 Relaxations produced by sodium nitroprusside (SNP) in diabetic aortae were similar to those in age‐matched vessels. 5 Basal levels of cyclic GMP and ACh‐induced production of cyclic GMP were significantly decreased in diabetic rats. 6 These results suggest that functional changes in endothelium but not in guanylate cyclase activity in the aorta may occur in diabetes, and, thus, spontaneous and ACh‐induced formation of cyclic GMP may be decreased. This decrease in production of cyclic GMP may be responsible for the decreased response of the aorta to the relaxant effect of ACh.

Streptozotocin-induced diabetes selectively alters the potency of analgesia produced by μ-opioid agonists, but not by δ- and κ-opioid agonists

Abstract To investigate the possible mechanisms of the alterations in morphine-induced analgesia observed in diabetic mice, we examined the influence of streptozotocin-induced (STZ-induced) diabetes on analgesia mediated by the different opioid receptors. The antinociceptive potency of morphine (10 mg/kg), administered s.c., as determined by both the tail-pinch and the tail-flick test, was significantly reduced in diabetic mice as compared to that in controls. Mice with STZ-induced diabetes had significantly decreased sensitivity to intracerebroventricularly (i.c.v.) administered μ-opioid agonists, such as morphine (10 μg) and [ d -Ala2, N-Me Phe4,Gly-ol5]enkephalin (DAMGO, 0.5 μg). However, i.c.v. administration of [ d -Pen2,5]enkephalin (DPDPE, 5 μg), a δ-opioid agonist, and U-50,488H (50 μg), a κ-opioid agonist, produced pronounced antinociception in both control and diabetic mice. Furthermore, there were no significant differences in antinociceptive potency between diabetic and control mice when morphine (1 μg), DAMGO (10 μg), DPDPE (0.5 μg) or U-50,488H (50 μg) was administered intrathecally. In conclusion, mice with STZ-induced diabetes are selectively hyporesponsive to supraspinal μ-opioid receptor-mediated antinociception, but they are normally responsive to activation of δ- and κ-opioid receptors.

Functional changes in vascular smooth muscle and endothelium of arteries during diabetes mellitus

To investigate the influence of diabetes mellitus on the responsiveness of the vascular smooth muscle, the effects of various vasoactive agents on the reactivity of the vascular smooth muscle from diabetic animals have been undertaken, focusing on the functional changes in the endothelium, alpha-adrenoceptors, beta-adrenoceptors, voltage-dependent Ca(2+)-channels, receptor-operated Ca(2+)-channels, phosphatidylinositol turnover and potassium channels. Among the functional changes, it is a common phenomenon that decreases in acetylcholine-induced production of cyclic GMP are due to the attenuation of release of endothelium-derived relaxing factor through an impairment of endothelium; this observation was found in both rats and rabbits with diabetes mellitus. These functional changes in diabetes may be responsible for the vascular complications such as coronary heart disease, cerebrovascular disease, and an acceleration in atherosclerosis.

Antinociceptive effects of the selective non-peptidic δ-opioid receptor agonist TAN-67 in diabetic mice

The antinociceptive potencies of 2-methyl-4 alpha alpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12 alpha alpha-octahydro-quinolino[2,3,3-g]isoquinoline (TAN-67), a non-peptidic delta-opioid receptor agonist, were examined using the acetic acid abdominal constriction test and the tail-flick test in diabetic mice. TAN-67, at doses of 3-100 mg/kg, s.c. [corrected], produced a marked and dose-dependent inhibition of the number of acetic acid-induced abdominal constrictions in both non-diabetic and diabetic mice. The antinociceptive effect of TAN-67 in the acetic acid abdominal constriction test in diabetic mice was greater than that in non-diabetic mice. Indeed, the ED50 (95% confidence limits) value of TAN-67 for the inhibition of acetic acid-induced abdominal constrictions in diabetic mice (6.0 (3.5-10.5) mg/kg) was significantly lower than that in non-diabetic mice (31.4 (14.2-69.4) mg/kg). The antinociceptive effect of TAN-67 was not antagonized by pretreatment with either beta-funaltrexamine, a selective mu-opioid receptor antagonist, or nor-binaltorphimine, a selective kappa-opioid receptor antagonist. When 7-benzylidenenaltrexone (0.3 mg/kg, s.c.), a selective delta 1-opioid receptor antagonist, was administered 10 min before treatment with TAN-67, the antinociceptive effect of TAN-67 was significantly antagonized. However, naltriben, a selective delta 2-opioid receptor antagonist, had no significant effect on the antinociceptive effect of TAN-67. Furthermore, in the tail-flick test, TAN-67 at doses of 3-30 mg/kg, s.c. [corrected], also produced a marked and dose-dependent antinociceptive effect in diabetic mice, but not in non-diabetic mice. In conclusion, TAN-67 produced an antinociceptive effect through the activation of delta 1-opioid receptors. Furthermore, the results of this study support our hypothesis that mice with diabetes are selectively hyperresponsive to delta 1-opioid receptor-mediated antinociception.

Effects of N-methyl-D-aspartate antagonists on the cough reflex

The effects of antagonists of N-methyl-D-aspartate (NMDA) on the capsaicin-induced cough reflex in rats were studied. Intracisternal (i. cist.) injection of MK-801, a non-competitive antagonist of NMDA, significantly decreased the number of coughs in a dose-dependent manner. The competitive antagonists of NMDA, 2-DL-amino-5-phosphonovalerate and 2-DL-amino-7-phosphonoheptanoate, also decreased the number of coughs after i. cist. injection. The antitussive potencies of both the competitive and non-competitive antagonists were similar to that of dextromethorphan. Intraperitoneal injection of MK-801 also decreased the number of coughs in a dose-dependent manner. These data suggest that excitatory amino acid neurotransmitters and NMDA receptors may be involved in the regulation of the cough reflex.

Nonspecific denervation supersensitivity in the rat vas deferens ‘in vitro’

Abstract A new method for the chronic denervation of the rat vas deferens was developed. The time course of norepinephrine content was investigated both chemically and histochemically and histochemically and correlated with the development supersensitivity of the vas denervated by this method to some stimulants in vitro. The content decreased rapidly and finally reached 1.7% of the initial level 4 days after the denervation. The disappearance of fluorescence observed in the control vas paralleled the fall in norepinephrine content determined chemically. Specific supersensitivity to norepinephrine appeared quite rapidly during the 2 days following denervation and attained a maximum within 4 days. The dose-response curve to norepinephrine was shifted to the left by a factor of about 50, and the maximum response was augmented about 3 fold. These two effects of denervation on the dose-response curve were assumed to result from pre- and postsynaptic mechanisms, respectively. Supersensitivity to acetylcholine, angiotensin, K+ and Ba++, which could be regarded as nonspecific and postsynaptic also developed rapidly. Their respective supersensitivities developed in parallel with the decrease in sympathetic transmitters in the vas deferens. The mechanism of the postsynaptic nonspecific supersensitivity after denervation in the rat vas deferens is discussed in relation to nonspecific supersensitivity caused by cocaine in the vas on which we reported previously.

Streptozotocin-induced diabetes in mice reduces the nociceptive threshold, as recognized after application of noxious mechanical stimuli but not of thermal stimuli

We report herein that streptozotocin (STZ)-induced diabetes selectively alters the nociceptive threshold with respect to noxious mechanical stimuli. Mice were rendered diabetic by an injection of STZ (200 mg/kg, IV). In the tail-pinch test, the latency of the biting response to forceps was significantly decreased in animals with diabetes of 2 weeks and 8 weeks duration as compared to that in age-matched controls. However, the nociceptive threshold, as determined by the tail-flick test, was not significantly altered. The level of substance P in the spinal cord was significantly increased in mice that has been diabetic for 2 weeks, while, there was a significant decrease, as compared to control levels, in level of substance P in mice diabetic for 8 weeks. However, the level of somatostatin was not significantly altered in mice diabetic for either 2 weeks or 8 weeks. These data suggest that STZ-induced diabetes selectively alters a neuronal system that involves substance P but not somatostatin in the spinal cord.

Restoration of endothelium-dependent relaxation in both hypercholesterolemia and diabetes by chronic taurine

We examined the effects of taurine on levels of low-density lipoprotein (LDL) cholesterol and glucose, and an endothelium-dependent relaxation in response to acetylcholine in cholesterol-fed or streptozotocin-induced diabetic mice. The acetylcholine-induced concentration-dependent relaxation was significantly attenuated in aortic rings from cholesterol-fed and streptozotocin-induced diabetic mice. The attenuated vasodilation in both cholesterol-fed and streptozotocin-induced diabetic mice was normalized by the chronic administration of taurine. The endothelium-independent relaxation of aortic rings induced by sodium nitroprusside was not significantly different between control, cholesterol-fed and streptozotocin-induced diabetic mice. The increased serum levels of LDL cholesterol in cholesterol-fed and diabetic mice were returned to normal by the chronic administration of taurine. The chronic administration of taurine had no effects on serum glucose levels. These results suggest that the impaired endothelium-dependent vasodilation seen in both cholesterol-fed and streptozotocin-diabetic mice can be normalized by the chronic administration of taurine and this effect may be, at least in part, due to lowering of serum LDL levels.

Functional changes in potassium channels in aortas from rats with streptozotocin-induced diabetes

The effects of K+ activators on aortas from control and diabetic rats were examined. The concentration-response curves for the relaxant effects of cromakalim were shifted to the right in diabetic rats. The relaxation responses of diabetic aortas to nicorandil did not differ from those of the controls. Treatment with oxyhemoglobin significantly reduced the relaxation responses to nicorandil in aortas from diabetic rats. It appears that the activity of aortic potassium channels is reduced in diabetic rats.

Role of spleen or spleen products in the deficiency in morphine-induced analgesia in diabetic mice

We examined the possibility that the spleen or factor(s) derived from spleen mononuclear cells are involved in the deficient mu-opioid receptor-mediated analgesia encountered in diabetic mice. Splenectomized diabetic mice had a significantly higher sensitivity to morphine analgesia than untreated or sham-operated diabetic mice. Naive recipient mice injected with mononuclear spleen cells from diabetic mice exhibited a lower sensitivity to morphine analgesia than vehicle-treated naive mice. These results suggest that some factor(s) derived from spleen mononuclear cells may play an important, direct or indirect role in the selective reduction in mu-agonist-mediated analgesia in diabetic mice.