Effects of glycaemic variability on cardiac remodelling after reperfused myocardial infarction: Evaluation of streptozotocin-induced diabetic Wistar rats using cardiac magnetic resonance imaging

AIMS

In addition to hyperglycaemia, glycaemic variability seems to be associated with poor outcomes after acute myocardial infarction. This study explored the impact of glycaemic variability in diabetic Wistar rats subjected to myocardial ischaemia/reperfusion.

METHODS

Animals with streptozotocin-induced diabetes received insulin either to maintain stable hyperglycaemia (Dh group) or to generate glycaemic variability (Dv). After experimental myocardial ischaemia/reperfusion was surgically induced, 7T cardiac magnetic resonance imaging (CMR) was performed at weeks 1 (w1) and 3 (w3).

RESULTS

Twenty-six rats were randomized [sham group (S): n=5; control group (C): n=7; Dh group: n=6; and Dv group: n=8]. The mean amplitude of glucose reflecting glycaemic variability was higher in the Dv than in the Dh group (9.1±2.7mmol/L vs 5.9±1.9mmol/L; P<0.05). CMR assessment at w3 revealed ventricular enlargement in both Dh and Dv groups compared with the C and S groups (end-diastolic volume: 1.60±0.22 and 1.36±0.30mL/kg compared with 1.11±0.13 and 0.87±0.11mL/kg, respectively; P<0.05). Circumferential strain was altered between w1 and w3 in the remote area only in the Dv group, resulting in a lower value in this group than in the S, C and Dh groups (-0.11±0.01 vs -0.17±0.05, -0.15±0.03 and -0.16±0.03, respectively; P<0.05). In addition, at w3, oedema was also higher in the remote area in the Dv than in the C group (18.3±4.9ms vs 14.5±1.7ms, respectively; P<0.05).

CONCLUSION

In the context of experimental myocardial ischaemia/reperfusion, our results suggest that glycaemic variability might have a potentially deleterious impact on myocardial outcomes beyond the classical glucose metrics.

Remifentanil produces cross-desensitization and tolerance with morphine on the mu-opioid receptor

Remifentanil is a powerful mu-opioid (MOP) receptor agonist used in anaesthesia with a very short half-life. However, per-operative perfusion of remifentanil was shown to increase morphine consumption during post-operative period to relieve pain. In the present study, we aimed to describe the cellular mechanisms responsible for this apparent reduction of morphine efficacy. For this purpose, we first examined the pharmacological properties of both remifentanil and morphine at the MOP receptor, endogenously expressed in the human neuroblastoma SH-SY5Y cell line, to regulate adenylyl cyclase and the MAP kinase ERK1/2 pathway, their potency to promote MOP receptor phosphorylation, arrestin 3-CFP (cyan fluorescent protein) recruitment and receptor trafficking during acute and sustained exposure. In the second part of this work, we studied the effects of a prior exposure of remifentanil on morphine-induced inhibition of cAMP accumulation, activation of ERK1/2 and analgesia. We showed that sustained exposure to remifentanil promoted a rapid desensitization of opioid receptors on both signalling pathways and a pretreatment with this agonist reduced signal transduction produced by a second challenge with morphine. While both opioid agonists promoted Ser(375) phosphorylation on MOP receptor, remifentanil induced a rapid internalization of opioid receptors compared to morphine but without detectable arrestin 3-CFP translocation to the plasma membrane in our experimental conditions. Lastly, a cross-tolerance between remifentanil and morphine was observed in mice using the hot plate test. Our in vitro and in vivo data thus demonstrated that remifentanil produced a rapid desensitization and internalization of the MOP receptor that would reduce the anti-nociceptive effects of morphine.

A novel mutation 3090 G>A of the mitochondrial 16S ribosomal RNA associated with myopathy

We describe a young woman who presented with a progressive myopathy since the age of 9. Spectrophotometric analysis of the respiratory chain in muscle tissue revealed combined and profound complex I, III, II+III, and IV deficiency ranging from 60% to 95% associated with morphological and histochemical abnormalities of the muscle. An exhaustive screening of mitochondrial transfer and ribosomal RNAs showed a novel G>A substitution at nucleotide position 3090 which was detected only in urine sediment and muscle of the patient and was not found in her mother's blood cells and urine sample. We suggest that this novel de novo mutation in the 16S ribosomal RNA, a nucleotide which is highly conserved in different species, would impair mitochondrial protein synthesis and would cause a severe myopathy.

A study of PAF-induced ocular inflammation in the rat and its inhibition by the PAF antagonist, L-652,731

A significant inflammatory reaction in the rat conjunctiva followed the subconjunctival injection of synthetic platelet activating factor (PAF) in doses which ranged from 10 ng to 1 microgram, an inflammatory response being evaluated as the increase in both tissue weight and extravasation of Evans blue dye in the conjunctival tissue. Inflammation was still present 6 h after the injection of 0.1 microgram of PAF. Orally administered indomethacin or BW 755C failed to alter the response to 0.1 microgram of PAF. In contrast, the PAF-induced inflammation was blocked by the oral administration of the PAF receptor antagonist, L-652,731, a dose as low as 5 mg kg-1 eliciting a significant inhibition. The topical administration of L-652,731, (two doses of 100 micrograms as a 1% suspension), elicited a slight, but significant blockade of 23%. Its antagonistic action was more striking when it was co-injected subconjunctivally with 0.1 microgram of PAF, a dose as low as 3 micrograms evoking a significant blockade. The topical administration of 0.1 microgram of PAF did not elicit a significant inflammatory reaction and this contrasts with the results obtained after its subconjunctival injection.