L-Dopa as a Stimulus for LH Release in the Proestrous Rat: Blockade of its Action by Pentobarbital Anesthesia

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Abstract
Intra-arterial injections (8–75 mg/kg) of L-3,4, dihydroxyphenylalanine (L-dopa) at 1 p.m. on the afternoon of proestrus produced a rapid increase in serum LH in unanesthetized female rats. Maximum responses were observed following doses of 25 mg/kg although the smallest (2.7 mg/kg) and largest (225 mg/kg) doses were ineffective in stimulating LH release. Pentobarbital anesthesia (40 mg/kg, i.p.) at 12.30 p.m. on proestrous prevented the responses to L-dopa. The 25 mg/kg dose of L-dopa, which produced maximum effects in the unanesthetized proestrous rat, caused no detectable LH release in unanesthetized diestrous rats. These results support the concept that dopaminergic mechanisms are involved in the pre-ovulatory release of LH and indicate that two of the conditions which prevent spontaneous pre-ovulatory LH release (pentobarbital anesthesia or a lack of circulating estrogens) may similarly inhibit L-dopa-mediated LH release.

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