Norvaline2-TRH : binding to TRH receptors in rat brain homogenates

Norvaline2-thyrotropin-releasing hormone ([Nva2]TRH) has been described as a thyrotropin-releasing hormone (TRH) analog with no thyrotropin (TSH)-releasing capacity but enhanced analeptic activity compared with TRH, as shown by the reversal of haloperidol-induced catalepsy. We have evaluated the rec...

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Veröffentlicht in:European journal of pharmacology 1990-05, Vol.180 (1), p.1-12
Hauptverfasser: VONHOF, S, FEUERSTEIN, G. Z, COHEN, L. A, LABROO, V. M
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Sprache:eng
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Zusammenfassung:Norvaline2-thyrotropin-releasing hormone ([Nva2]TRH) has been described as a thyrotropin-releasing hormone (TRH) analog with no thyrotropin (TSH)-releasing capacity but enhanced analeptic activity compared with TRH, as shown by the reversal of haloperidol-induced catalepsy. We have evaluated the receptor-binding properties of [Nva2]TRH in homogenates of rat anterior pituitary, hypothalamus, brainstem and cortex tissue, using [3H]TRH and [3H][3-Me-His2]TRH as radioligands. Apparent Ki values at high affinity TRH-binding sites, labelled predominantly by [3H][3-Me-His2]TRH, ranged from 17.0 to 36.9 microM in all tested regions. Additionally, [Nva2]TRH was shown to compete with [3H]TRH at low affinity TRH-binding sites with similar affinities. It is concluded that the loss of TSH-releasing activity of [Nva2]TRH appears to be due to a drastic reduction in binding affinity to the high affinity TRH receptor subtype. Its analeptic activity, however, may be mediated by low affinity TRH binding sites which are predominantly labelled by [3H]TRH or by yet unidentified mechanisms.
ISSN:0014-2999
1879-0712
DOI:10.1016/0014-2999(90)90586-U