methylatropine and Cardiovascular-Diseases

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

Earlier studies from the authors' laboratory showed that malnourishment induces alterations in the cardiovascular homeostasis increasing the basal mean arterial pressure and heart rate. In this study, the authors evaluated whether the sympathetic and parasympathetic efferent activities contribute to changes in the cardiovascular homeostasis through altered modulation of the arterial baroreflex of malnourished rats. After weaning, male Fischer rats were given 15% (Normal Protein--NP) or 6% (Low Protein--LP) protein diet for 35 d. The baroreflex gain and latency were evaluated before and after selective autonomic blockades in control and malnourished rats. It was observed that malnourishment affected the baroreflex gain in response to activation and deactivation of the arterial baroreflex. Moreover, malnourished rats showed increased baroreflex latency as compared to that of control rats. Regarding the autonomic efferent activity directed to the heart, the data showed increased sympathetic and decreased parasympathetic efferent activities in malnourished rats, and such alterations could be related to the observed changes in the arterial baroreflex gain as well as in the basal mean arterial pressure and heart rate.

Topics: Animals; Arteries; Atropine Derivatives; Baroreflex; Body Weight; Cardiovascular Diseases; Gene Expression Regulation; Male; Metoprolol; Pressure; Proteins; Rats; Rats, Inbred F344