Improved glucose homeostasis in male obese zucker rats coincides with enhanced baroreflexes and activation of the nucleus tractus solitarius

Parul Chaudhary, Ann M. Schreihofer

Research output: Contribution to journalArticle

Abstract

Young adult male obese Zucker rats (OZR) develop insulin resistance and hypertension with impaired baroreflex-mediated bradycardia and activation of nucleus tractus solitarius (NTS). Because type 1 diabetic rats also develop impaired baroreflex-mediated NTS activation, we hypothesized that improving glycemic control in OZR would enhance compromised baroreflexes and NTS activation. Fasting blood glucose measured by telemetry was comparable in OZR and lean Zucker rats (LZR) at 12–17 wk. However, with access to food, OZR were chronically hyperglycemic throughout this age range. By 15–17 wk of age, tail samples yielded higher glucose values than those measured by telemetry in OZR but not LZR, consistent with reports of exaggerated stress responses in OZR. Injection of glucose (1g/kg ip) produced larger rises in glucose and areas under the curve in OZR than LZR. Treatment with metformin (300 mg·kg-1·day-1) or pioglitazone (5 mg·kg-1·day-1) in drinking water for 2–3 wk normalized fed glucose levels in OZR with no effect in LZR. After metformin treatment, area under the curve for blood glucose after glucose injection was reduced in OZR and comparable to LZR. Hyperinsulinemia was slightly reduced by each treatment in OZR, but insulin was still greatly elevated compared with LZR. Neither treatment reduced hypertension in OZR, but both treatments significantly improved the blunted phenylephrine-induced bradycardia and NTS c-Fos expression in OZR with no effect in LZR. These data suggest that restoring glycemic control in OZR enhances baroreflex control of heart rate by improving the response of the NTS to raising arterial pressure, even in the presence of hyperinsulinemia and hypertension.

Original languageEnglish
Pages (from-to)R1195-R1209
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume315
Issue number6
DOIs
StatePublished - 1 Dec 2018

Fingerprint

Zucker Rats
Solitary Nucleus
Baroreflex
Homeostasis
Glucose
Telemetry
Metformin
pioglitazone
Hyperinsulinism
Bradycardia
Hypertension
Area Under Curve
Blood Glucose
Therapeutics

Keywords

  • Baroreceptor reflex
  • Hyperglycemia
  • Metabolic syndrome
  • Metformin
  • Pioglitazone

Cite this

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title = "Improved glucose homeostasis in male obese zucker rats coincides with enhanced baroreflexes and activation of the nucleus tractus solitarius",
abstract = "Young adult male obese Zucker rats (OZR) develop insulin resistance and hypertension with impaired baroreflex-mediated bradycardia and activation of nucleus tractus solitarius (NTS). Because type 1 diabetic rats also develop impaired baroreflex-mediated NTS activation, we hypothesized that improving glycemic control in OZR would enhance compromised baroreflexes and NTS activation. Fasting blood glucose measured by telemetry was comparable in OZR and lean Zucker rats (LZR) at 12–17 wk. However, with access to food, OZR were chronically hyperglycemic throughout this age range. By 15–17 wk of age, tail samples yielded higher glucose values than those measured by telemetry in OZR but not LZR, consistent with reports of exaggerated stress responses in OZR. Injection of glucose (1g/kg ip) produced larger rises in glucose and areas under the curve in OZR than LZR. Treatment with metformin (300 mg·kg-1·day-1) or pioglitazone (5 mg·kg-1·day-1) in drinking water for 2–3 wk normalized fed glucose levels in OZR with no effect in LZR. After metformin treatment, area under the curve for blood glucose after glucose injection was reduced in OZR and comparable to LZR. Hyperinsulinemia was slightly reduced by each treatment in OZR, but insulin was still greatly elevated compared with LZR. Neither treatment reduced hypertension in OZR, but both treatments significantly improved the blunted phenylephrine-induced bradycardia and NTS c-Fos expression in OZR with no effect in LZR. These data suggest that restoring glycemic control in OZR enhances baroreflex control of heart rate by improving the response of the NTS to raising arterial pressure, even in the presence of hyperinsulinemia and hypertension.",
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T1 - Improved glucose homeostasis in male obese zucker rats coincides with enhanced baroreflexes and activation of the nucleus tractus solitarius

AU - Chaudhary, Parul

AU - Schreihofer, Ann M.

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N2 - Young adult male obese Zucker rats (OZR) develop insulin resistance and hypertension with impaired baroreflex-mediated bradycardia and activation of nucleus tractus solitarius (NTS). Because type 1 diabetic rats also develop impaired baroreflex-mediated NTS activation, we hypothesized that improving glycemic control in OZR would enhance compromised baroreflexes and NTS activation. Fasting blood glucose measured by telemetry was comparable in OZR and lean Zucker rats (LZR) at 12–17 wk. However, with access to food, OZR were chronically hyperglycemic throughout this age range. By 15–17 wk of age, tail samples yielded higher glucose values than those measured by telemetry in OZR but not LZR, consistent with reports of exaggerated stress responses in OZR. Injection of glucose (1g/kg ip) produced larger rises in glucose and areas under the curve in OZR than LZR. Treatment with metformin (300 mg·kg-1·day-1) or pioglitazone (5 mg·kg-1·day-1) in drinking water for 2–3 wk normalized fed glucose levels in OZR with no effect in LZR. After metformin treatment, area under the curve for blood glucose after glucose injection was reduced in OZR and comparable to LZR. Hyperinsulinemia was slightly reduced by each treatment in OZR, but insulin was still greatly elevated compared with LZR. Neither treatment reduced hypertension in OZR, but both treatments significantly improved the blunted phenylephrine-induced bradycardia and NTS c-Fos expression in OZR with no effect in LZR. These data suggest that restoring glycemic control in OZR enhances baroreflex control of heart rate by improving the response of the NTS to raising arterial pressure, even in the presence of hyperinsulinemia and hypertension.

AB - Young adult male obese Zucker rats (OZR) develop insulin resistance and hypertension with impaired baroreflex-mediated bradycardia and activation of nucleus tractus solitarius (NTS). Because type 1 diabetic rats also develop impaired baroreflex-mediated NTS activation, we hypothesized that improving glycemic control in OZR would enhance compromised baroreflexes and NTS activation. Fasting blood glucose measured by telemetry was comparable in OZR and lean Zucker rats (LZR) at 12–17 wk. However, with access to food, OZR were chronically hyperglycemic throughout this age range. By 15–17 wk of age, tail samples yielded higher glucose values than those measured by telemetry in OZR but not LZR, consistent with reports of exaggerated stress responses in OZR. Injection of glucose (1g/kg ip) produced larger rises in glucose and areas under the curve in OZR than LZR. Treatment with metformin (300 mg·kg-1·day-1) or pioglitazone (5 mg·kg-1·day-1) in drinking water for 2–3 wk normalized fed glucose levels in OZR with no effect in LZR. After metformin treatment, area under the curve for blood glucose after glucose injection was reduced in OZR and comparable to LZR. Hyperinsulinemia was slightly reduced by each treatment in OZR, but insulin was still greatly elevated compared with LZR. Neither treatment reduced hypertension in OZR, but both treatments significantly improved the blunted phenylephrine-induced bradycardia and NTS c-Fos expression in OZR with no effect in LZR. These data suggest that restoring glycemic control in OZR enhances baroreflex control of heart rate by improving the response of the NTS to raising arterial pressure, even in the presence of hyperinsulinemia and hypertension.

KW - Baroreceptor reflex

KW - Hyperglycemia

KW - Metabolic syndrome

KW - Metformin

KW - Pioglitazone

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SN - 0363-6119

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