Selective downregulation of rat cardiac beta 1-adrenoceptors by cyclosporine A: prevention by diltiazem or angiotensin-converting enzyme inhibitors

The calcineurin inhibitor cyclosporine A improves lipopolysaccharide-induced vascular dysfunction but does not rescue from cardiovascular collapse in endotoxemic mice

The calcineurin inhibitor cyclosporine A (CsA) improves survival in endotoxemic mice. It was hypothesized that CsA counteracts the bradycardia and hypotension characteristic of endotoxemia. Vascular reactivity was determined in lipopolysaccharide (LPS; 50 μg/mL)-treated mouse aortic rings suspended in a myograph. Arterial blood pressure and heart rate were measured continuously with indwelling catheters in conscious mice treated with CsA and a bolus injection of LPS (2 mg/kg). The α1-adrenoceptor agonist phenylephrine induced stable tension of aortic rings that were attenuated significantly by LPS. Co-incubation of rings with LPS and CsA (1 × 10(-7) mol/L-1 × 10(-5) mol/L) restored vascular reactivity to phenylephrine. Intravenous administration of CsA (20 and 40 mg/kg/day) to mice induced a significant increase (by approximately 10 mmHg) in mean arterial blood pressure (MAP), with no effect on heart rate. An LPS bolus led to significant decreases in MAP (by approximately 30 mmHg) and heart rate (to 50 % of baseline). CsA-treated LPS-mice exhibited higher MAP at some (20 mg/kg) or all (40 mg/kg) time points after LPS. The decrease in MAP (Δ pressure) was similar between vehicle- and CsA-treated groups. The 50 % decrease in heart rate was not affected by CsA. Inducible nitric oxide synthase (iNOS) mRNA and protein levels in LPS-treated mice organs and plasma NO x concentration were significantly reduced by CsA. It is concluded that in a murine model of endotoxemia, increased peripheral vascular resistance and suppression of systemic NO formation by cyclosporine A are not sufficient to prevent cardiovascular collapse, which is caused primarily by compromised cardiac function.

The cardiac beta-adrenoceptor-G-protein(s)-adenylyl cyclase system in monocrotaline-treated rats

In rats, injection of the alkaloid monocrotaline (MCT) causes right ventricular hypertrophy and cardiac failure. In order to study whether, in MCT-treated rats, changes in the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system might be comparable to those found in human primary pulmonary hypertension, we assessed in right and left ventricles from MCT-treated rats the components of the beta -adrenoceptor system: the receptor number and subtype distribution (by (-)-[(125)I]iodocyanopindolol binding), the G-proteins (by quantitative Western blotting), and the activity of adenylyl cyclase. A single injection of 60 mg/kg i.p. MCT caused in rats right ventricular hypertrophy (RVH); part of the rats developed cardiac failure (RVF). In these rats the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system was markedly changed beta -adrenoceptors were desensitized due to a decrease in receptor number, an uncoupling of the receptor from the G(s)-adenylyl cyclase system, a decrease in G(s)and a decrease in the activity of the catalytic unit of adenylyl cyclase. In general, these changes were more pronounced in right ventricles v left ventricles, and in rats with RVF v rats with RVH. On the other hand, cardiac muscarinic receptors and G(i)appeared not to be altered. We conclude that in MCT-treated rats changes in the cardiac beta -adrenoceptor-G-protein(s)-adenylyl cyclase system occur that resemble those observed in human primary pulmonary hypertension. Thus, MCT-treated rat appears to be a suitable animal model to study in more detail the pathophysiology of the development of right heart failure, and to identify new therapeutic possibilities.

Diurnal changes in cyclosporine effect on ornithine decarboxylase and noradrenergic and cholinergic activities in submaxillary lymph nodes

Diurnal changes in cyclosporine efficacy to affect ornithine decarboxylase activity, [3H]norepinephrine uptake and [3H]choline conversion into [3H]acetylcholine were examined in rat submaxillary lymph nodes. Cyclosporine (5 or 20 mg/kg) caused a dose-dependent decrease in lymph node ornithine decarboxylase, being active at 5 or 20 mg/kg in Freund's adjuvant-treated rats, and at 20 mg/kg in rats treated with the adjuvant's vehicle. In immunized rats the lower cyclosporine dose was ineffective when injected during the night. Cyclosporine increased lymph node [3H]norepinephrine uptake dose dependently, with significant differences between the 20 mg/kg dose and controls in vehicle-treated rats and between 5 or 20 mg/kg and controls in Freund's adjuvant-treated rats. In immunized rats, 5 mg/kg cyclosporine increased [3H]norepinephrine uptake when injected at 13:00 or 17:00 h. Both doses of cyclosporine augmented lymph node synthesis of [3H]acetylcholine to a similar extent. In immunized and non-immunized rats cyclosporine suppressed the diurnal rhythm of lymph node adrenergic and cholinergic activity found in controls. After unilateral sympathetic denervation (by superior cervical ganglionectomy) and/or unilateral parasympathetic decentralization (by chorda tympani section), cyclosporine (5 mg/kg) decreased Freund's adjuvant-induced activation of lymph node ornithine decarboxylase when injected at 17:00 or 01:00 h. On the sham-operated side, cyclosporine was effective when injected at 17:00 h only. Decentralization, or a combined ganglionectomy plus decentralization, decreased lymph node ornithine decarboxylase activity. The results active regulation of the effects of cyclosporine in submaxillary lymph nodes by local autonomic nerves.