The effect of hyperthyroidism and hypothyroidism on alpha 1- and alpha 2-adrenergic responsiveness in rat aortic smooth muscle.
We report the role of thyroid hormones on in vitro responsiveness of rat aortic smooth muscle to alpha-adrenergic stimulation. Four groups of rats: hypothyroid, hyperthyroid, thyroxine (0.1 mg/kg) treated hypothyroid and controls were employed. Response of alpha 1- and alpha 2-adrenoceptors was evoked with 6 incremental doses (10(-9) to 10(-4) M) of preferential alpha 1-agonist, phenylephrine and alpha 2-agonist, clonidine respectively. alpha 1-Adrenoceptors were also evoked by phenylephrine after blockade of alpha 2-adrenoceptors with 10(-7) M yohimbine. Similarly, alpha 2-adrenoceptors were stimulated with clonidine after blocking alpha 1-adrenoceptors with selective antagonists prazosin (10(-7) M). Aortic responsiveness to alpha-agonist norepinephrine was compared between the aortae of hypothyroid and euthyroid rats after blockade of alpha 2-adrenoceptors with 10(-4) M corynanthine. We report that in hypothyroid aortae, alpha 1-adrenergic response was significantly decreased, the dose response curve shifted to the right and the maximal response was 30% less than the normal; alpha 2-adrenergic response was completely inhibited in hypothyroid state; also, IP injections of 0.1 mg/kg thyroxine twice in 48 h to thyroidectomized rats reversed the effects of hypothyroidism on both alpha 1- and alpha 2-adrenergic response. Hyperthyroidism did not alter alpha 1- and alpha 2-adrenergic response. These results signify the role of thyroid hormones in the regulation of alpha-adrenergic response in rat aortae.
Rahmani
M A
MA
Division of Science and Mathematics, Bethune-Cookman College, Daytona Beach, Florida 32015.
Cheema
I R
IR
Sen
S
S
Peoples
B
B
Riley
S R
SR
D000818:Animals; D001011:Aorta / Q000378:metabolism / Q000503:physiopathology; D003000:Clonidine / Q000494:pharmacology; D006980:Hyperthyroidism / Q000378:metabolism / Q000503:physiopathology*; D007037:Hypothyroidism / Q000378:metabolism / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000503:physiopathology*; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology; D013963:Thyroid Hormones / Q000502:physiology; D013974:Thyroxine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D013963:Thyroid Hormones; D010656:Phenylephrine; D015016:Yohimbine; D003000:Clonidine; D013974:Thyroxine; D009638:Norepinephrine