methylatropine and Protein-Energy-Malnutrition

1. In the present study, we evaluated the autonomic balance of the heart in protein/energy-undernourished rats. 2. Rats were divided into two groups according to the diet they received after weaning: (i) the control group (n=16), given a 15% protein diet, and (ii) the malnourished group (n=14), fed a 6% protein diet. Cardiovascular recordings were made and, through selective autonomic blockade, the tonic autonomic balance, cardiac autonomic index and the power spectrum of heart rate (HR) variability were determined. 3. Muscarinic receptor blockade with methylatropine (5.0 mg/kg, i.v.) increased HR in the control group (371 ± 6 vs 427 ± 15 b.p.m. before and after drug administration, respectively), but not the malnourished group (438 ± 24 vs 472 ± 38 b.p.m. before and after drug administration, respectively). Inhibition of β(1)-adrenoceptors with metoprolol (2.0 mg/kg, i.v.) reduced HR in malnourished rats (428 ± 24 vs 355 ± 16 b.p.m. before and after drug administration, respectively), but had no effect on the HR of the control group (363 ± 8 vs 362 ± 7 b.p.m. before and after drug administration, respectively). Double autonomic blockade by inhibiting both muscarinic cholinoceptors and β(1)-adrenoceptors reduced HR in the malnourished group (428 ± 24 vs 342 ± 14 b.p.m.) but had no effect on HR in the control group (371 ± 6 vs 382 ± 6 b.p.m.). 4. Sympathetic tone was augmented in malnourished compared with control rats (131 ± 17 vs 41 ± 11 b.p.m., respectively), whereas parasympathetic tone was reduced in malnourished compared with control rats (-4 ± 4 vs 22 ± 9 b.p.m., respectively). 5. The ratio of oscillations in HR induced by sympathetic and parasympathetic activity was higher in malnourished compared with control rats (0.43 ± 0.03 vs 0.34 ± 0.02, respectively). 6. The results of the present study indicate that protein malnutrition after weaning increases sympathetic activity and reduces vagal activity to the heart in rats. These data provide a new perspective on the pathophysiology of metabolic and cardiovascular diseases associated with protein malnutrition, especially with regard to autonomic modulation.

Topics: Animals; Atropine Derivatives; Autonomic Nervous System; Cardiovascular Diseases; Diet, Protein-Restricted; Electrocardiography; Heart; Heart Rate; Male; Metoprolol; Parasympatholytics; Protein-Energy Malnutrition; Rats; Rats, Inbred F344; Sympatholytics; Weaning

In this study we assessed the role of Bezold-Jarisch reflex (BJR) in the regulation of blood pressure (BP) of malnourished (MN) and control rats (CN) with sino-aortic denervation (SAD). Fischer rats were fed diets containing either 6% (MN) or 15% (CN) protein for 35 days after weaning. These rats underwent sham or SAD and catheterization of femoral artery and vein for BP measurements and drug injection. Phenylbiguanide (PBG 5 μg/kg, i.v.) for activation BJR, produced bradycardia (-317±22 bpm for CN vs. -372±16 bpm for MN) and hypotension (-57±4 mm Hg for CN vs. -54±6 mm Hg for MN. After SAD, MN rats had reduced hypotensive (-37±7 mm Hg for MN vs. -82±6 mm Hg for CN) and bradycardic (-124±17 for MN vs. -414±20 bpm CN) responses to BJR activation. To evaluate the contribution of the parasympathetic component due to BJR for the fall in BP, methyl atropine bromide, was given between two injections of PBG (5 μg/kg) separated by 10 min each other. Both bradycardic (-216±21 bpm before and -4±3 bpm after for CN -226±43 bpm before and -9±20 bpm after for MN) and hypotensive (-42±4 mm Hg before and -6±1 mm Hg after for CN -33±9 mm Hg before and -5±2 mm Hg after for MN) responses were abolished in CN and MN groups. These data indicate that dietary protein malnutrition changes the relation between baroreflex and BJR required for maintenance of the BP during malnourishment.

Topics: Animals; Atropine Derivatives; Biguanides; Blood Pressure; Body Weight; Denervation; Dose-Response Relationship, Drug; Heart Rate; Male; Malnutrition; Muscarinic Antagonists; Nitroprusside; Phenylephrine; Protein-Energy Malnutrition; Rats; Rats, Inbred F344; Reflex; Serotonin Receptor Agonists; Sinoatrial Node; Vasoconstrictor Agents; Vasodilator Agents