Search PubMed⌕ Search

Biomedical subjects

J A Edwardson

Publications and source records attributed to J A Edwardson.

At least 109 records · Page 6Linked to original sources
PubMed1982

Characterization of corticotropin-like immunoreactive peptides in rat brain using high performance liquid chromatography.

The molecular nature of corticotropin (ACTH)-related peptides in rat brain has been studied using high performance liquid chromatography (HPLC) and radioimmunoassay. The major ACTH-immunoreactive species in rat hypothalamic extracts coelutes with corticotropin-like intermediate lobe peptide (CLIP); ACTH18-39) on two HPLC solvent gradients, and has 3-4 times more C-terminal than N-terminal immunoreactivity. N-terminal ACTH-immunoreactivity is composed of a number of peaks on HPLC with less than 10% eluting at the position of ACTH. Hypothalamic C-terminal ACTH immunoreactivity is also heterogeneous and resembles in some respect that seen in the rat neuro-intermediate lobe. Around 90% of the alpha-MSH immunoreactivity in the hypothalamus elutes as a single peak in the position of des[N-acetyl] alpha -MSH (ACTH1-13-NH2).

Adrenocorticotropic Hormone↗
PubMed1982

Failure of vasopressin to enhance memory in a passive avoidance task in rats.

Several authors have suggested that the neurohypophysial hormone arginine-8-vasopressin (AVP) facilitates both the consolidation and the retrieval of memory. This conclusion has relied mainly on the finding that AVP increases the latency of re-entry into a box where shock has previously been encountered, that is, in a passive avoidance task. Our results do not support this interpretation. On the contrary, we found that post-trial, intraventricular (i.t.) administration of AVP (1 ng in 1 microliter) produced relatively short as well as long latencies (a bimodal effect), suggesting that the peptide acts on motivational processes, for example by increasing arousal.

Animals↗
PubMed1982

Corticotrophin-related peptides in the intermediate lobe of the rodent pituitary gland: characterization by high performance liquid chromatography and radioimmunoassay.

High performance liquid chromatography (HPLC) and radioimmunoassay have been used to characterize corticotrophin-related peptides in extracts of the intermediate lobe of the rat and mouse pituitary gland. Multiple peaks have been observed, which resemble corticotrophin-like intermediate lobe peptide (CLIP) in that they cross-react with antisera raised against the COOH-terminal region of corticotrophin (ACTH) but not against NH2-terminal directed antisera. These CLIP-like peptides were released from the incubated neurointermediate lobe and their secretion was inhibited in the presence of dopamine. Heterogeneity of peptide species was also observed with antisera raised against alpha-MSH. Multiple peaks of CLIP and alpha-MSH-like material were identified in pituitary extracts from the mouse and levels were elevated in the genetically obese (ob/ob) animal. The nature and possible functions of multiple forms of intermediate lobe peptides are discussed.

Adrenocorticotropic Hormone↗
PubMed1982

Mechanism of neurotensin degradation by rat brain peptidases.

Neurotensin is degraded by peptidases present in soluble and particulate (25000 x g) fractions of rat hypothalamus, thalamus, cortex and pituitary, the soluble fraction of the hypothalamus having the highest activity. High performance liquid chromatography and amino acid analysis were used to identify the degradation pathway. The main product in both fractions was [1-8]neurotensin and the corresponding C-terminal fragment [9-13]neurotensin was identified. [1-10]Neurotensin was also identified, proportionately more of this peptide being produced by the particulate rather than the soluble fraction. In the presence of dithiothreitol, [1-7]neurotensin and [1-10]neurotensin were major products particularly in the soluble fraction. These results suggest that the main sites of cleavage of neurotensin by rat brain peptidases are the Arg8-Arg9, Pro10-Tyr11 and Pro7-Arg8 bonds.

Amino Acid Sequence↗
PubMed1982

Mechanism of luteinizing hormone-releasing hormone degradation by subcellular fractions of rat hypothalamus and pituitary.

The pathway of LH-RH degradation by two subcellular fractions (a soluble fraction and a 25 000 X g particulate fraction) of rat hypothalamus, pituitary and cerebral cortex has been studied using high performance liquid chromatography and amino acid analysis to identify the breakdown products. The primary cleavage point in the Tyr5-Gly6 bond giving [1-5] LH-RH and [6-10] LH-RH. In the presence of dithiothreitol, cleavage of LH-RH also occurred at the Pro9-Gly10 bond giving [1-9] LH-RH. The fragment [1-5] LH-RH is further degraded sequentially from the C-terminus and [1-4] LH-RH, [1-3] LH-RH, tyrosine and tryptophan were identified. The other major fragment, [6-10] LH-RH, is rapidly broken down, the only intermediate product positively identified being Arg-Pro.

Animals↗
PubMed1981

A rapid method for preparing synaptosomes: comparison, with alternative procedures.

A method for the rapid (1-1.5 h) preparation of nerve ending particles (synaptosomes) from rat cerebral cortex is described. The synaptosome fraction has been characterized by quantitative electron microscopy and enzyme distribution studies. By these criteria, the fraction showed a degree of enrichment in synaptic structures which was comparable to that of the standard (4-5 h) preparation, and substantially better than an alternative fast (2-2.5 h) method. On incubation, synaptosomes obtained by the new procedure accumulated a high tissue concentration of potassium and showed a high, linear rate of oxygen uptake. Depolarization by veratrine caused a significant increase in the rate of respiration and in the release of the physiologically active amino acids; glutamate, aspartate and GABA, as well as a significant reduction in tissue potassium. Thus, the new procedure compared favourably with alternative methods as judged by these indices of metabolic and functional performance. The new preparation method has been found to be of value in metabolic studies of synaptosomes prepared from human post-mortem brain.

Amino Acids↗
PubMed1981

Characterization and determination of neuropeptides by high-performance liquid chromatography and radioimmunoassay.

A method is described for the separation and analysis of a variety of neuropeptides using reversed-phase high-performance liquid chromatography coupled with radioimmunoassay. The solvent system (an acetonitrile gradient containing 0.08% trifluoroacetic acid) allows UV detection at 206 nm, gives good resolution and, by being volatile, is readily compatible with radioimmunoassay. Three applications of the method are described: (a) thyrotropin releasing hormone immunoreactivity in the rat brain has been characterized; (b) ACTH immunoreactivity in the rat pituitary pars intermedia has been resolved into its component peptides; (c) degradation of luteinizing hormone releasing hormone in vitro has been followed.

Adrenocorticotropic Hormone↗
PubMed1981

Degradation of luteinizing hormone-releasing hormone by serum and plasma in vitro.

Luteinizing hormone-releasing hormone (LH-RH) is degraded in vitro by serum and plasma from several species (human, rat, guinea-pig and cattle). Separation of the degradation products by high-performance liquid chromatography (HPLC) followed by amino acid analysis and radioimmunoassay showed that the main sites of cleavage are the Trp3-Ser4 and Tyr5-Gly6 bonds. Two peptidases are responsible since the cleavage at Trp3-Ser4 can be selectively inhibited by EDTA. In human plasma, the peptidase responsible for Trp3-Ser4 hydrolysis has a Km of 2.9 . 10(-4) M and V of 30 nmol/h per ml plasma. The half-life in vitro of LH-RH in serum and plasma from various species ranges from 3 h (guinea-pig) to 9.8 h (human). The peptidase cleaving LH-RH at Tyr5-Gly6 is present as an impurity in some commercial bovine serum and plasma albumins. Such contamination may have important practical implications for work involving peptide assays where albumins are used as carrier proteins.

Amino Acids↗
PubMed1980

Dopamine stimulates the degradation of gonadotropin releasing hormone by rat synaptosomes.

Immunohistochemical studies have shown the existence of synapses between nerve endings containing dopamine and gonadotropin releasing hormone (LH-RH) respectively in the hypothalamic median eminence. It is generally accepted that this transmitter is involved in the regulation of gonadotropin secretion as a modulator of LH-RH release, although the evidence is conflicting and both inhibitory and excitatory actions of dopamine have been reported. In vitro studies support the excitatory effect and low doses of dopamine have been shown to release LH-RH from incubated hypothalamic fragments and synaptosomes. This report describes studies with nerve endings isolated from the rat hypothalamus in which dopamine at higher concentrations than those used previously has been found to stimulate the degradation of LH-RH but not thyrotropin releasing hormone (TRH). This mechanism seems to be physiological in that it is calcium-dependent, requires the structural integrity of the nerve endings and fluctuates with the reproductive state of the animal.

Animals↗
PubMed1979

Metabolic and secretory processes in nerve-endings isolated from post-mortem brain.

Isolated nerve ending particles (synaptosomes) prepared from rat and human cerebral cortex, after varying conditions of post-mortem storage were shown to possess good structural and morphological integrity and metabolic activity. Respiration, potassium retention, lactate dehydrogenase content, and stimulus-induced release of transmitter candidate amino acids, as well as the neuropeptide somatostatin, were measured. These preparations from post-mortem material showed properties which were closely comparable with similar preparations from fresh material. The relevance of these findings to studies on human post-mortem material is discussed.

Aged↗
PubMed1976

Application of an in-vitro perifusion technique to studies of luteinizing hormone release by rat anterior hemi-pituitaries: Self-potentiation by luteinizing hormone releasing hormone.

A technique is described for the continuous perifusion of rat adenophypophyses. Exposure of the perifused glands to repeated equal 5 min stimuli with hypothalamic extract resulted in a series of equal peaks of corticotrophin secretion, the response was proportional to log dose over the range 0 - 25-2 - 0 rat hypothalamic equivalents/ml. Repeated equal stimuli with hypothalamic extract, or with luteinizing hormone releasing hormone (LH-RH) at concentrations of 2 or 10 ng/ml, resulted in a progressively increasing series of peaks of LH secretion, i.e. a self-potentiating or priming effect. The effect took between 30 min and 1 h to develop. A delayed increase in the responsiveness of the glands was also seen with continuous incubation of anterior pituitaries with LH-RH. The relevance of these observations to the physiological control of LH secretion is discussed.

Adrenocorticotropic Hormone↗