| Summary: | The effects of adrenergic agonists in the heart were investigated in isolated cardiac
tissues and in the whole heart in 8 week diabetic and age-matched control rats by measuring
contractile force following administration of PE in presence of timolol, or ISO. Plasma
thyroid hormones as well as insulin, glucose and triglyceride was measured. The contractile
force of the isolated cardiac tissues was measured in tissue baths under physiological
conditions and results expressed by construction of concentration response curves to
adrenoceptors agonists, 10⁻⁹ to 10⁻⁴ M for ISO and 10⁻⁷ to 10⁻³ M for PE. The contractile
force of the whole heart was measured as left ventricular systolic pressure, without
pharmacological intervention and following administration of 10⁻⁶ M PE or 10⁻⁵ M ISO in the
perfusate. The hearts were clamp-frozen at 0, 15 and 30 seconds, and 1, 4 minutes following
adrenoceptor agonists for measurement of cAMP levels. Cardiac cAMP was measured in the
frozen ventricles by employing Amersham commercial SPA kit while protein was measured
by using Bio-Rad Dye method. The tissue content of cAMP was expressed as pmol
cAMP/mg protein.
It was found that the contractile response to PE was increased whereas that to ISO
was decreased significantly in diabetic papillary muscle but not the left atria from the same
group of animals. The chronotropic effect of PE was increased and that of ISO was
decreased significantly in diabetic right atria. The contractile force of the whole heart
preparation was increased in diabetic hearts following both adrenoceptor agonists and the
increased positive inotropic effect of ISO was accompanied by an increase in cAMP levels.
In all of the diabetic animals, the thyroid hormone levels were significantly lower than those
of the controls. These findings confirmed that the cardiac alterations and the low thyroid
state in ALX-induced diabetic rats are similar to those that occur in STZ-induced diabetic rats
although further studies would be needed to reveal the interrelation between the diabetesassociated
low thyroid state and diabetic cardiomyopathy.
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