Hormonal control of glucose production and pyruvate kinase activity in isolated rat liver cells: influence of hypothyroidism.
Hormonal control of glucose production and of L-pyruvate kinase activity has been measured in isolated liver cells from fed control and thyroidectomized rats. In hypothyroid rats, sensitivity to isoproterenol as measured by these parameters was increased: the apparent K0.5 for isoproterenol-induced stimulation of glucose production decreased from 8.0 +/- 3 X 10(-6) M in control rats to 2.0 +/- 0.2 X 10(-8) M in hypothyroid rats (P less than 0.001) and the apparent K0.5 for inhibition of L-pyruvate kinase was 5 +/- 2 X 10(-7) M vs. 7 +/- 2 X 10(-9) M (P less than 0.001) in control and thyroidectomized rats, respectively. Utilisation of specific adrenergic antagonists confirmed increased beta-adrenergic responsiveness in hypothyroid rats. This phenomenon was not reversed by 3 days of T3 treatment (10 micrograms/100 g body weight). Sensitivity to the alpha-agonist was unchanged by thyroid status. Stimulation of glucose production and inhibition of L-pyruvate kinase activity by glucagon and their reversal by insulin were not affected by hypothyroidism. The dose-response curve to vasopressin and its maximal effect measured on stimulation of glucose production were unchanged in thyroidectomized rats. Thus, hypothyroidism produces a specific enhancement of liver beta-adrenergic responsiveness without affecting sensitivity to glucagon, insulin and vasopressin.
D000818:Animals; D002395:Catecholamines / Q000494:pharmacology; D005947:Glucose / Q000096:biosynthesis*; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D010187:Pancreatic Hormones / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000378:metabolism*; D051381:Rats; D013963:Thyroid Hormones / Q000502:physiology*; D013965:Thyroidectomy; D014284:Triiodothyronine / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D002395:Catecholamines; D010187:Pancreatic Hormones; D013963:Thyroid Hormones; D014284:Triiodothyronine; D014667:Vasopressins; D011433:Propranolol; D011770:Pyruvate Kinase; D005947:Glucose; D010646:Phentolamine