Abstract
Abstract Thyrotropin-releasing hormone (TRH) is a hypothalamic tripeptide with the structure l-pyroglutamyl-l-histidyl-l-prolinamide. TRH stimulates prolactin and decreases growth hormone production by GH3 cells, a clonal strain of rat pituitary cells grown in culture. TRH binds to specific receptors on GH3 cells. The activities of 26 analogs of TRH have been measured with the GH3 cell system. Both biological activity (prolactin stimulation and growth hormone depression) and affinity for the TRH receptor have been determined for each peptide. The biological activities of the analogs varied over more than a 10,000-fold range. Biological potency correlated with affinity for the TRH receptor for each peptide. The maximum activity of each active analog was the same as that of TRH. The effects of TRH and TRH analogs on prolactin and growth hormone appeared to involve binding to the same receptor. The TRH receptor on GH3 cells is highly selective, particularly for the COOH-terminal prolinamide of TRH. The prolactin-stimulating activities of analogs closely parallel their thyrotropin-releasing activities, suggesting that the TRH receptors on lactotrophs and thyrotrophs are similar or identical.
Highlights
The affinity of analogs for the Thyrotropin-releasing hormone (TRH) receptor was determined by measuring the ability of different concentrations of a peptide to inhibit the binding of 13HlTRH to GH, homogenates in experiments such as that shown in Fig. 3 and described under “Methods.” Apparent dissociation constants of analog-receptor complexes were determined from plots of these data (e.g. Fig. 3)
The prolactin-stimulating activities of the TRH analogs studied in these experiments varied over more than a lO,OOO-fold range
From the linearity of this plot it is evident that the biological potencies of the peptides correlate directly with their affinities for the TRH receptor
Summary
Causes an increase in the rate of synthesis and release of prolactin and a decrease in growth hormone production [10,11,12]. TRH stimulates prolactin and decreases analogs are of particular importance Such studies will be growth hormone production by GH, cells, a clonal strain of of value in defining and comparing the structural requirements rat pituitary cells grown in culture. Using reccphave been measured with the GHI cell system Both bio- tors for TRH from cells which produce either thyrotropin or prological activity (prolactin stimulation and growth hormone lactin, but not both hormones, binding studies of TRH analogs depression) and affinity for the TRH receptor have been will permit determination of the relationships between peptide determined for each peptide. The TRH receptor measured with GHB cells, of 26 peptides with structures related on GH3 cells is highly selective, for the COOH- to that of TRH Both biological (prolactin-stimulating) activity terminal prolinamide of TRH. Administration of TRHi causes the release of thyrotropin from the anterior pituitary gland; it has been found to stimulate
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