Thyrotropin does not activate the phosphatidylinositol bisphosphate hydrolyzing phospholipase C in the dog thyroid.
The effects of thyrotropin (TSH) and carbamylcholine (Cchol) on labeling by [3H]inositol of inositol lipids (i.e. total phosphoinositides (PI)) and inositol phosphates (IP) and on diacylglycerol (DAG) generation was studied in dog thyroid slices. Both agents (TSH 1-250 mU/ml, Cchol 10(-6) to 10(-4) M) increased the incorporation of [3H]inositol into PI and IP during 4 h labeling experiments; but the [3H]IP/[3H]PI ratio as compared to the control one was not modified by TSH (10 mU/ml: 1.03 +/- 0.24) while it was increased by Cchol (10(-5) M: 6.14 +/- 1.81). Slices prelabeled in the absence of agonists were then incubated in the presence or absence of 10 mM LiCl +/- 10(-4) M inositol. With LiCl alone, Cchol increased [3H]IP generation, while no such effect of TSH could be detected. However, in the absence of LiCl or in the presence of both LiCl and 10(-4) M inositol, TSH and Cchol both increased [3H]PI and [3H]IP, but IP and PI labeling remained strictly proportional with TSH (10 mU/ml: [3H]IP/[3H]PI ratio = 1.03 +/- 0.06 vs. control), while Cchol increased this ratio (10(-5) M = 2.44 +/- 0.24) with a preferential accumulation of IP. Both agonists stimulated DAG formation with similar kinetics and maximal effects (400% of control at 60 min).(ABSTRACT TRUNCATED AT 250 WORDS)
Mockel
J
J
Department of Endocrinology, Hôpital Erasme, Brussels, Belgium.
Laurent
E
E
Lejeune
C
C
Dumont
J E
JE
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004285:Dogs; D004789:Enzyme Activation; D010716:Phosphatidylinositols / Q000378:metabolism*; D013961:Thyroid Gland / Q000201:enzymology*; D013972:Thyrotropin / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism*
D010716:Phosphatidylinositols; D002217:Carbachol; D013972:Thyrotropin; D010738:Type C Phospholipases