methylatropine and Diabetes-Mellitus

The Wistar fatty (WF) rat is a model of obese Type 2 diabetes mellitus (DM). These rats were bred by crossing Zucker fatty (ZF) and Wistar-Kyoto (WKY) rats. A homo-allelic leptin receptor gene mutation has been reported in ZF rats. We report here how these genetic factors contribute to plasma insulin regulation. The fasting plasma insulin levels were higher in WKY and Wistar lean (WL) rats than in Zucker lean (ZL) rats (p<0.05). The levels in WF and ZF rats were higher than in their respective lean littermates, WL and ZL rats (p<0.05). After intragastric glucose load, the plasma insulin increase was reduced upon pretreatment by intracerebroventricular (i. c.v.) methylatropine (an antagonist of the cholinergic receptor) injection in WL rats (p<0.05) but not in WF rats. Plasma glucagon-like peptide-1 (GLP-1) response to intragastric glucose load was not affected by methylatropine. After selective hepatic-vagotomy, plasma insulin levels increased in wild-type ZL rats (p<0.05). This increase was not observed in heterozygote ZL rats. Surprisingly, this response of plasma insulin was not shown in wild-type WL and WKY rats. ZF and WF rats did show a prominent decrease in insulin response (p<0.05). These results indicate that the genetic factor in ZF rats is associated with impaired vagal nerve-mediated control of insulin secretion. The genetic factor in WKY rats may diminish sensitivity to the vagal information of insulin release and contribute to insulin resistance. Therefore, we conclude that the presence of both genetic factors in a homo-allelic state is important to the development of DM in WF rats.

Topics: Animals; Atropine Derivatives; Blood Glucose; Carrier Proteins; Crosses, Genetic; Diabetes Mellitus; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Disease Models, Animal; Glucagon; Glucagon-Like Peptide 1; Glucose Tolerance Test; Injections, Intraventricular; Insulin; Insulin Resistance; Insulin Secretion; Mutation; Obesity; Peptide Fragments; Protein Precursors; Rats; Rats, Inbred WKY; Rats, Zucker; Receptors, Cell Surface; Receptors, Leptin; Vagotomy; Vagus Nerve

Spontaneously diabetic BB/W rats were compared with age-matched regular Wistar and nondiabetic BB/W rats to determine whether the presence of diabetes would alter cardiovascular regulation appreciably. Systolic and mean blood pressures measured with the tail-cuff method from 12 to 26 wk of age tended to be slightly higher in diabetic than nondiabetic BB/W rats, but the differences were not significant. Mean pressures recorded from indwelling catheters in the same rats at 28 wk of age also did not differ significantly, thereby verifying that the diabetic rats were not hypertensive. To measure baroreflex sensitivity, heart-rate responses were elicited reflexly by elevating blood pressure with phenylephrine or lowering it with sodium nitroprusside. Although reflex bradycardia elicited with phenylephrine was the same, reflex tachycardia elicited with sodium nitroprusside was more pronounced in diabetic BB/W than other rats. Underlying autonomic mechanisms were then assessed by repeating the baroreflex tests after either cholinergic blockade with methylatropine or beta-adrenergic blockade with propranolol. Magnitude of reflex bradycardia after inhibition by either cholinergic or beta-adrenergic blockade still did not differ between rat groups but that of reflex tachycardia remained significantly stronger in diabetic BB/W than other rats. These results collectively show that, although diabetic BB/W rats remained normotensive, they had enhanced reflex tachycardia that persisted even after efferent autonomic blockade. The failure to develop higher pressures with time further indicates that without additional manipulation, these rats cannot be used experimentally to simulate the simultaneous presence of hypertension in diabetic patients.

Topics: Adrenergic beta-Antagonists; Animals; Atropine Derivatives; Blood Pressure; Diabetes Mellitus; Heart Rate; Male; Nitroprusside; Parasympatholytics; Phenylephrine; Propranolol; Rats; Rats, Inbred BB; Rats, Inbred Strains; Tachycardia