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Biomedical subjects

N White

Publications and source records attributed to N White.

At least 163 records · Page 9Linked to original sources
PubMed1976

Hypothalamic inactivation of thyrotrophin-releasing hormone.

Following the demonstration of peptidases in the rat hypothalamus which inactivate thyrotrophin-releasing hormone (TRH), a sensitive and specific radioimmunoassay for the releasing hormone was used to investigate the presence of similar peptidases in the rabbit hypothalamus. TRH was found to be rapidly inactivated by supernatant and particulate hypothalamic fractions, with higher peptidase activity in the supernatant than in the particulate fraction. An optimum pH of 7.3 within physiological limits was obtained for the enzymes in both the fractions examined. The results obtained confirm that the rabbit hypothalamus contains enzymes capable of inactivating TRH, and since it has been found that such peptidases interfere with studies on TRH biosynthesis, it is possible that the peptidases may play a part in controlling the releasing hormone's production. The specificity of the antiserum used in the radioimmunoassay has also suggested that the peptidases may cleave the C-terminal-ProNH2,-NH2 or both from the TRH molecule to cause inactivation.

Animals↗
PubMed1976

The role of physical dependence in animal models of human alcoholism.

This paper critically examines the concept that physical dependence is a necessary attribute for animal models of human alcoholism. On the basis of a review of the literature, it is argued that, since the production of physical dependence requires the presence of continuous high blood-alcohol levels, and since the production of preference for alcohol requires intermittent presentation of alcohol, the two cannot, in principle, be established in the same organism at the same time. It is further argued that physical dependence does not play a role in the development of high alcohol intake in animals. The implications of these observations for human alcoholism are discussed.

Alcoholism↗
PubMed1976

Effect of thyroid status on the thyrotrophin-releasing hormone-degrading activity of rat serum.

The TRH-degrading activity of rat serum in vitro is five times more potent than that of human serum. In rats, it is significantly reduced in hypothyroidism (thiouracil-induced) and significantly increased in hyperthyroidism (T3 or T4-induced). This suggests a possible role in the regulation of adenohypophysial-thyroid function which is probably, in turn, dependent on thyroid hormone, rather than TSH, levels.

Animals↗
PubMed1975

Distribution of thyrotropin-releasing hormone (TRH) in the central nervous system as revealed with immunohistochemistry.

With the indirect immunofluorescence technique TRH-containing nerve terminals were found in the medial part of the external layer of the median eminence, the dorsomedial nucleus and the perifornical area, in extrahypothalmic nuclei such as nucleus accumbens, the lateral septal nucleus and in several motor nuclei of the brain stem and spinal cord. These findings suggest that TRH may act both as a hormone, released into the portal vessels, as well as a neurotransmitter or modulator, released at synapses in discrete regions of the brain and spinal cord.

Animals↗
PubMed1975

The inactivation of thyrotrophin releasing hormone by plasma in thyroid disease.

The inactivation of immunoreactive TRH in vitro by human plasma has been investigated. In a preliminary study, 2.5 ng TRH was destroyed by 50 mul plasma at a mean rate of 1.7%/min in eight subjects. The per cent inactivation of the same amount of TRH at three plasma dose levels was measured after 60 min in seventy unselected patients attending a thyroid clinic. There was no significant difference in the results obtained in those subsequently shown to be euthyroid (forty-three patients), hyperthyroid (eighteen patients) or hypothyroid (nine subjects).

Blood↗
PubMed1975

Clearance and identification of thyrotrophin releasing hormone in human urine after intravenous injections.

The urine clearance of TRH after intravenous injection in man has been measured by radioimmunoassay. Between 4.4 percent and 10.7 percent of the dose was excreted within 90 min, the majority within 30 min. The TRH excreted was immunochemically and chromatographically indistinguishable from synthetic TRH and was inactivated by plasma enzymes with the same kinetic characteristics. The immunoreactive TRH-like material in basal urine samples was not TRH however: chromatographically and enzymatically it behaved differently from the synthetic tripeptide.

Chromatography, Ion Exchange↗
PubMed1975

Peptidases in the rat hypothalamus inactivating thyrotrophin-releasing hormone (TRH).

Peptidases capable of inactivating thyrotrophin-releasing hormone (TRH) have been demonstrated in the hypothalamus. With the development of a specific radioimmunoassay for TRH, this method was used to further study the enzymes acting on the releasing hormone. Whole hypothalamic homogenates from male and female rats inactivated TRH, with greater peptidase activity being found in the female animals. Separation of the homogenates into particulate (microsomal and mitochondrial) and supernatant (soluble/cytoplasmic) fractions showed approximately the same amounts of enzyme activity in both fractions, while dialysis of the fractions slightly reduced the TRH peptidase activity present, suggesting that a diffusible co-factor might be partially involved in the releasing hormone's degradation. These results confirm the presence of TRH-inactivating peptidases in the rat hypothalamus and suggest that the enzymes may be involved in some way in the mechanisms by which the brain controls thyrotrophin release by the anterior pituitary.

Animals↗
PubMed1975

Studies on the nature of mammalian hypothalamic thyrotrophin releasing hormone using immunochemical, chromatographic and enzymic techniques.

Hypothalamic extracts from three mammalian species (rat, rabbit and sheep) were found to contain several ng of immunoreactive thyrotrophin releasing hormone (TRH)-like activity. This substance chromatographed on ion exchange chromatography (carboxymethyl cellulose) as a single peak that was indistinguishable from synthetic TRH. Hypothalamic TRH was also inactivated by normal human plasma at a rate (1.21-1.46%/mul plasma/h and 1.59-1.77%/50mul plasma/min) similar to that of synthetic TRH (1.42%/mul plasma/h and 1.73%/50mul plasma/min). This combination of chromatographic and enzymic techniques can be applied to the identification of immunoreactive TRH in body fluids.

Animals↗