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      Dissociation of Thyrotropin and Prolactin Responsiveness to Thyrotropin Releasing Hormone Stimulation in L -Dopa Treated Parkinsonian Patients

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      Hormone Research in Paediatrics

      S. Karger AG

      hTSH, hPRL, TRH, <italic>L</italic>-Dopa treatment, Parkinsonians

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          The hPRL, hTSH and T<sub>3</sub> response to thyrotropin releasing hormone (TRH) stimulation (200 µg i.v.) were studied in 8 parkinsonian patients under chronic L-dopa-carbidopa therapy. In 6 out of the 8 patients studied, treatment was stopped for a period of 2 weeks and the TRH stimulation test was repeated under similar experimental conditions. In the L-dopa-carbidopa treated patients basal hTSH levels and the hTSH response to TRH were significantly suppressed. By contrast, in the 6 patients 2 weeks after cessation of treatment, although basal hTSH levels were still suppressed, a normal hTSH response to TRH was observed. Neither the basal T3 and T4 concentrations, nor the T3 response to TRH were affected by the L-dopa-carbidopa treatment. In addition, basal hPRL levels as well as the hPRL response to TRH were within the normal range in the two groups of patients studied. Our study provides further support for a dopaminergic inhibitory action on the hypothalamo-hypophyseal-thyroidal axis (HHTA). The inhibition of basal hTSH secretion and the hTSH response to TRH by L-dopa, suggest that the blocking action of dopamine is exerted at the hypothalamic as well as at the pituitary level. In our hands, chronic administration of L-dopa did not affect either tonic hPRL secretion or the hPRL response to TRH. The dissociation or response to TRH under the same inhibitory action of dopaminergic stimulation can be interpreted as demonstrating a greater sensitivity of the pituitary thyrotrophs, than the prolactin secreting cells, to the blocking effect of dopamine.

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          Author and article information

          Horm Res Paediatr
          Hormone Research in Paediatrics
          S. Karger AG
          25 November 2008
          : 15
          : 2
          : 78-87
          Department of Neurology, Institute of Reproductive Endocrinology, Municipal Governmental Medical Center, University of Tel-Aviv, Israel
          179437 Horm Res 1981;15:78–87
          © 1981 S. Karger AG, Basel

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          Pages: 10
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