DOPAMINE INHIBITS³²P_iINCORPORATION INTO PHOSPHATIDYLINOSITOL IN THE ANTERIOR PITUITARY GLAND OF THE RAT

Abstract

The in vitro effect of dopamine, haloperidol and pimozide on 32Pi incorporation into phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine by anterior pituitary glands was studied. Dopamine decreased the incorporation of 32Pi into phosphatidylinositol in a dose-related manner without affecting phosphatidylcholine and phosphatidylethanolamine. Haloperidol and pimozide did not modify 32Pi incorporation into these phospholipids by themselves but completely reversed the inhibitory effect of dopamine on phosphatidylinositol. The inhibition of 32Pi incorporation into phosphatidylinositol synthesis in the presence of 500 nM dopamine was significant at 20 min of incubation and maximal at 30 min. The possibility that a decrease in phosphatidylinositol cleavage and turnover may be involved in the inhibitory regulation of prolactin secretion by DA is suggested.

Modulation of secretion by dopamine involves decreases in calcium and nicotinic currents in bovine chromaffin cells.

“…Dopamine interacts with the phosphatidylinositol/Ca2+ mobilization pathway in lactotrophs (Canonico, Valdenegro & Macleod, 1982;Enjalbert et al 1986) and consequently may modulate protein kinase C activity. Since in some cases, the activity of voltage-gated Ca2+ channels and nicotinic ion channels appears to be regulated by protein kinase C-mediated phosphorylation (Levitan, 1985), it is tempting to speculate that the mechanism of action of dopaminergic modulation of adrenomedullary catecholamine secretion might also involve protein kinase C. Apomorphine inhibition was unaltered by PTX pre-treatment, although it is possible in chromaffin cells that PTX-insensitive pathways of phosphatidylinositol hydrolysis exist, as described in other systems (Ashkenazi, Peralta, Winslow, Ramachandran & Capon, 1989).…”

D2‐dopamine receptor‐mediated inhibition of intracellular Ca2+ mobilization and release of acetylcholine from guinea‐pig neostriatal slices

“…In the case of prolactin release from the pituitary gland, the role of intracellular cyclic AMP has not been elucidated. Canonico et al (1982) showed that stimulation of the D2-dopamine receptor inhibits 32p incorporation into phosphatidylinositol in the rat anterior pituitary gland. They suggested that a decrease in phosphatidylinositol cleavage and turnover may be involved in the inhibitory regulation of prolactin release by dopamine.…”

Effect of 17 β-Estradiol on Phosphoinositide Metabolism and Prolactin Secretion in Anterior Pituitary Cells

“…Increases in phosphoinositide hydrolysis due to the stimu lation of a specific phospholipase C cause an increase in diacylglycerol, InsP, and phosphatidic acid -an increase that initiates a cascade of reactions culminating in Ca2 + mobilization and a biological cellular response [9,10]. Our laboratory has investi gated whether several factors that affect PRL release from the anterior pituitary gland have related effects on phosphoinosi tide metabolism.We reported that incorporation of [32P]orthophosphate into the total pituitary gland 'phosphatidylinositol fraction' was greater in tissue obtained from female rats, which had higher levels of serum estradiol, than from male rats [11,12]. Bonnetti et at.…”

“…Changes in phospholipid metabolism, in certain specific instances, repre sent an important intracellular event and function as a second messenger from activated receptor sites to processes that direct ly facilitate the release of hormones [10], Earlier reports from our laboratory showed that the incorporation of [32P]orthophosphate into pituitary gland phosphoinositides is greater in tissue obtained from female than from male rats, which raises the possibiliy that estradiol levels may play a role [11,12], It was also reported that marked changes in the incorporation of [32P]orthophosphate into pituitary gland phosphoinositide lipids occur following the injection of a-methyl-a-tyrosine, an inhib itor of dopamine synthesis and enhancer of PRL release. Con…”