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Chronotropic function in spontaneously diabetic BB rats.

S Ramanadham1, G M McGrath, J H McNeill

  • 1Division of Pharmacology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.

Canadian Journal of Physiology and Pharmacology
|May 1, 1989
PubMed
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Spontaneously diabetic rats showed normal heart rates but reduced response to isoproterenol, suggesting diabetes impacts heart function independently of thyroid hormones. This research offers insights into diabetic cardiovascular complications.

Area of Science:

  • Cardiovascular Physiology
  • Endocrinology
  • Diabetology

Background:

  • Diabetes mellitus can affect cardiac function, but the specific impact on atrial function and chronotropic responses in spontaneously diabetic models is not fully understood.
  • Previous studies in streptozotocin-induced diabetes suggested bradycardia and hypothyroidism, but these findings may not apply to all diabetic models.

Purpose of the Study:

  • To investigate isolated atrial function in spontaneously diabetic BB Wistar rats under different insulin dosages.
  • To examine the chronotropic response to isoproterenol and plasma thyroid hormone levels in these diabetic models.
  • To differentiate the cardiac effects of spontaneous diabetes from those observed in chemically induced diabetes.

Main Methods:

  • Assessment of basal atrial rates and isoproterenol-induced chronotropic responses in BB Wistar rats (nondiabetic, spontaneously diabetic with low insulin dose [BB-LI], and spontaneously diabetic with high insulin dose [BB-HI]).

Related Experiment Videos

  • Measurement of plasma thyroid hormone levels in all experimental groups.
  • Comparison of atrial function and hormonal status between diabetic and nondiabetic control groups.

    • Main Results:

    • Basal atrial rates were similar across nondiabetic (ND-BB) and spontaneously diabetic (BB-LI, BB-HI) rats.
    • Hyperglycemic BB-LI rats exhibited a blunted chronotropic response to isoproterenol compared to euglycemic BB-HI rats and controls.
    • Plasma thyroid hormone levels remained unchanged in all BB-diabetic rats, irrespective of insulin dosage.

    Conclusions:

    • Spontaneously diabetic BB rats do not develop bradycardia or hypothyroidism, contrasting with findings in streptozotocin-induced diabetes.
    • The reduced chronotropic response to isoproterenol in hyperglycemic BB-LI rats suggests a diabetes-specific effect on cardiac adrenergic signaling.
    • Altered thyroid status is unlikely to be the primary cause of decreased positive chronotropic effect of isoproterenol in diabetes.