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Lamberts SWJ, Macleod RM. 
“Metergoline and Other Peripheral Serotonin Antagonists Inhibit Prolactin Secretion through Mechanisms Unrelated to Serotonin”. 
Proc.Soc.Exp,Biol.Med.. 1979;162(1):75-79.
The effects of metergoline and other peripheral serotonin antagonists on prolactin secretion were investigated Blood samples and hemipoitary glands were obtained from healthy Sprague-Dawley rats (200 to 220 g) and female WistarFurth rats (200 to 220 g) with MtTW15 tumors of about 8 Ems, The hem“puitary glands were incubated with 3H-leucine for 5 hr. and then gland homogenates and incubation medium were subjected to polyacrylamide gel electrophoresis and the prolactin segments were counted for 3H, Serum and incubation medium prolactin was measured by RIA. Reserpine (2 ma, i,p,) increased the Serum prolactin of male rats by 300%, but this was inhibited by 1 mg/kg metergoline. In female rats 1 mcM metergoline inhibited 3H-prolactin secretion by 44% and RIA prolactin by 25%, Haloperidol itself had no effect. but at 10 EM it abolished the inhibition by metergoline. Serum prolactin was reduced from 10.7+4.2 to 3.97+0.59 mcg/ml in tumor bearing rats by i.p. injections of 25 mg/kg/day methysergide for 3 days. Simultaneous injection of 1 mg/kg/day haloperidol raised this level to 6.25 + 0.76 mcg/ml. In vitro Secretion of prolactin was strongly inhibited by 1 pM methergine or 0.5 mcM LSD and weakly inhibited by 2-Br-LSD. I pM LSD inhibited RIA prolactin and 3H-prolactin secretion by 53% and 80%. respectively. This inhibitionwas abolished by coincubation with 100 EM haloperidol. Conclusion The effects of metergoline and methysergide on prolactin secretion were mediated by the stimulation of a dopamine receptor in the pituitary.
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