Comparative aspects of brain TRH inactivation in different vertebrate species

Griffiths, E.C.; Visser, Theo J.; Klootwijk, W.; McDermott, J.R.; Smith, A. Ian

doi:10.1016/0016-6480(82)90130-7

Cited by 8 publications

(3 citation statements)

References 20 publications

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“…Thyrotrophin-releasing hormone (TRH) has been located in the chicken hypothalamus (Jackson & Reichlin, 1974;Jackson, 1978), and TRH-degrading enzymes have been demonstrated in the plasma, hy¬ pothalamus and pituitary glands of domestic fowl (Griffiths, Visser, Klootwyk et al 1982;Scanes, Harvey & Bolafh, 1985;. Synthetic TRH has multiple effects on pituitary function in birds, not only stimulating thyrotrophin (TSH) release (Scanes, 1974;Almeida & Thomas, 1981) but also the secretion of luteiniz¬ ing hormone (LH) (Wentworth, Burke & Birrenkott, 1976;Bonney & Cunningham, 1977;Harvey, Sterling & Klandorf, 1983), prolactin (Harvey, Scanes, Chadwick & Bolton, 1978a;Hall, Harvey & Scanes, 1986) and growth hormone (GH) (Harvey et al 1978a;Harvey, 1983a).…”

Section: Introductionmentioning

confidence: 99%

Thyrotrophin-releasing hormone (TRH)-induced growth hormone secretion in fowl: binding of TRH to pituitary membranes

Harvey

Baidwan²

1989

Journal of Molecular Endocrinology

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Heat-labile specific binding sites for [3H]3-methylhistidine2-TRH [( 3H]Me-TRH) were demonstrated on chicken adenohypophysial membranes. These binding sites were of both high affinity (dissociation constant, Kd = 15.53 nM) and low capacity (maximum binding capacity, Bmax = 8.73 pmol/g tissue) and of low affinity (Kd = 104.5 nM) and high capacity (Bmax = 32.41 pmol/g). Binding of [3H]Me-TRH to the pituitary membranes was greater at 4 degrees C than at 39 degrees C and occurred with rate constants (k1) of 1.6 x 10(6) and 3.39 x 10(6) M-1 min-1 respectively. Dissociation of [3H]Me-TRH binding at 4 degrees C occurred with a rate constant (k-1) of 0.125 min-1. Binding sites for [3H]Me-TRH were found in the cephalic lobe of the pituitary gland (the location of most lactotrophs and thyrotrophs) and in the caudal lobe (the location of most somatotrophs). The number of binding sites was greater in the caudal lobe than in the cephalic lobe, although the affinity of [3H]Me-TRH binding did not differ. The binding of [3H]Me-TRH to caudal lobe membranes was displaced by Me-TRH, TRH, pGlu-His-Pro-Gly-NH2 and [Glu1]-TRH, with half-maximal effective doses of 33 nM, 70.7 nM, 1.23 microM and 22 microM respectively, but not by [Phe2]-TRH, TRH free acid or His-Pro-diketopiperazine. The number of caudal lobe binding sites for [3H]Me-TRH in old birds was less than that in young ones, and the number of binding sites was increased in birds deprived of food for 48 h. TRH-induced GH secretion in birds would thus appear to be mediated by specific receptors on caudal lobe somatotrophs, and these results suggest that physiological changes in GH secretion (during growth and periods of fasting) are causally related to the abundance of TRH-binding sites.

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Section: Introductionmentioning

confidence: 99%

Thyrotrophin-releasing hormone (TRH)-induced growth hormone secretion in fowl: binding of TRH to pituitary membranes

Harvey

Baidwan²

1989

Journal of Molecular Endocrinology

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“…In immature domestic fowl and other birds TRH is a potent stimulator of GH release in vivo and to a lesser extent in vitro [12, 16, 30, 32]. The in vivo effects of TRH might therefore be aug mented by the TRH degradation products, TRH-OH or HPD, which have both endocrine and central actions re lated to those of TRH [4,9,11, 29]. This possibility has therefore been determined in the present study.…”

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confidence: 86%

“…2, 18, 25, 38], The degradation rate, as in rats [1,[25][26][27]34], was also age-related, in that it was fastest in adults. This age-related characteristic may have physiological signifi cance in the regulation of thyroid function during develop ment [1,3,25], providing a means of controlling the activity of TRH at the pituitary level or elsewhere [I, 10,11,24,25], This age-related difference in plasma TRH-degrading ac tivity is unlikely to be due to differences in the affinity of the TRH peptidase enzymes or to the presence of inhibitory factors or inactive pre-enzyme forms of TRH peptidase in neonatal plasma [1,24,25],…”

Section: Discussionmentioning

confidence: 99%

TRH Stimulation of in vivo GH Release in the Domestic Fowl

Scanes

Harvey

1985

Neuroendocrinology

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Thyrotropin-releasing hormone (TRH) stimulated in vivo growth hormone (GH) release in conscious and anesthetized young domestic fowl. The administration of the presumed metabolites of TRH, deamido-TRH (TRH-OH) and histidyl-proline diketopiperazine (HPD), was followed by small but significant (p < 0.05) increases in the plasma concentrations of GH in both conscious and anesthetized chicks. However, the ability of TRH-OH or HPD to stimulate GH secretion was less than that observed with a 100-fold lower dose of TRH. The administration of either TRH-OH or HPD with TRH increased the GH response over that observed with TRH alone. The ability of chicken plasma to degrade exogenous TRH in vitro was determined by measuring immunoreactive TRH (IR-TRH) content and by assessing the ability of the incubated samples to increase the plasma concentration of GH when administered to young fowl. The in vitro half-life of TRH was estimated to be 9.8 (by immunoassay) and 9.6 (by a biological index) min for plasma from adult male chickens and 23.9 (by immunoassay) and 20.2 (by biological index) min for plasma from 6-week-old chicks. This difference in degradation may account, at least in part, for the observed age-related decrease in the plasma concentration of GH in birds and for the diminished GH responsiveness of adult birds to exogenous TRH.

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