Pyridoxine (B6)-Induced Inhibition of Prolactin Release in the Female Rat*

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Abstract
Adult female rats were injected with 50 mg B6 [pyridoxine] of diluent (C) i.p. at 1200 h on proestrus. B6 prevented the increase in PRL [prolactin] secretion normally observed at 1300 h and this inhibition was prolonged until at least 1500 h by a 2nd injection of B6 at 1400 h. All B6-treated and control animals had normal proestrous LH [luteinizing hormone] surges and ovulated the next day. To determine whether the inhibitory effect of B6 on PRL release was due to enhanced dopamine synthesis or to a direct effect on the pituitary, ovariectomized rats were treated with a potent inhibitor of dopamine synthesis, .alpha.-methyl-p-tyrosine (.alpha.-MPT). The administration of B6 either with or 4 h after .alpha.-AMT significantly decreased the PRL rise observed in animals treated with .alpha.-MPT alone. B6 also significantly suppressed the TRH[thyrotropin releasing hormone]-induced PRL rise in both .alpha.-MPT-treated and normal rats, but had no effect on the TRH-induced rise in plasma TSH [thyrotropin] concentration. These studies demonstrate that pharmacological doses of B6 reduce the proestrous PRL surge and that this reduction may be at least partially due to a direct effect on the pituitary, inasmuch as B6 decreased the PRL rise after .alpha.-MPT and/or TRH administration.