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The characteristics of the iodide-induced inhibition of cyclic AMP accumulation in dog thyroid slices have been previously described [Van Sande, J., Cochaux, P. and Dumont, J. E. (1985) Mol. Cell. Endocrinol. 40, 181-192]. In the present study we investigated the characteristics of the iodide-induced inhibition of adenylate cyclase activity in dog and horse thyroid. The inhibition of cyclic AMP accumulation by iodide in stimulated horse thyroid slices was similar to that observed in dog thyroid slices. The inhibition was observed in slices stimulated by thyroid-stimulating hormone, cholera toxin and forskolin. Increasing the concentration of the stimulators did not overcome the iodide-induced inhibition. Adenylate cyclase activity, assayed in crude homogenates or in plasma-membrane-containing particulates (100,000 x g pellets), was lower in homogenates or in particulates prepared from iodide-treated slices than from control slices. This inhibition was observed on the cyclase activity stimulated by forskolin, fluoride or guanosine 5'-[beta, gamma-imino]triphosphate, but also on the basal activity. It was relieved when the homogenate was prepared from slices incubated with iodide and methimazole. Similar results were obtained with dog thyroid. The inhibition persisted when the particulate fraction was washed three times during 1 h at 100,000 x g, in the presence of bovine serum albumin or increasing concentration of KCl. It was similar whatever the duration of the cyclase assay, in a large range of protein concentration. These results indicate that a stable modification of adenylate cyclase activity, closely related to the plasma membrane, was induced when slices were incubated with iodide. Iodide inhibition did not modify the affinity of adenylate cyclase for its substrate (MgATP), but induced a decrease of the maximal velocity of the enzyme. The percentage inhibition was slightly decreased when Mg2+ concentration increased, and markedly decreased when Mn2+ concentration increased. A detectable adenylate cyclase activity was demonstrated when intact slices were incubated in the presence of [alpha-32P]ATP, probably because of the presence of broken cells produced during the slicing. Iodide had no direct effect on this cyclase system, which confirms that iodide needs the integrity of the cell to induce the inhibition and suggests that the inhibition is not transmitted between cells.
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
November 1977,
FEBS letters,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
March 1984,
Biochimica et biophysica acta,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
August 1994,
The British journal of psychiatry : the journal of mental science,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
February 1978,
The Journal of pharmacy and pharmacology,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
December 1979,
Acta endocrinologica,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
January 1985,
Advances in cyclic nucleotide and protein phosphorylation research,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
May 1988,
Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
May 1974,
Biochemical and biophysical research communications,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
September 1986,
Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme,
P Cochaux, and
J Van Sande, and
S Swillens, and
J E Dumont
May 1985,
Surgery,
