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T R Hall

Publications and source records attributed to T R Hall.

At least 55 records · Page 3Linked to original sources
PubMed1989

Tracer kinetic modeling approaches for the quantification of hepatic function with technetium-99m DISIDA and scintigraphy.

Serial scintigraphic images following injection of [99mTc]iminodiacetic acid compounds such as [99mTc]diisopropyl-iminodiacetic acid (DISIDA) provide qualitative information about liver function. We have investigated approaches for quantitatively describing liver function in terms of the kinetics of DISIDA extraction and excretion by the liver. Several compartmental model configurations were evaluated. A three-compartment model (blood, hepatic parenchyma, intrahepatic bile) was found to fit the data best and was used in conjunction with dynamic image data to obtain estimates of rate constants for liver extraction and excretion of DISIDA, and mean residence time (MRT) of DISIDA in the liver. A noncompartmental approach based on a parametric deconvolution technique was also used to estimate the noncompartmental mean residence time (MRTnc). To assess limitations of the noncompartmental approach, computer simulations were performed using the three-compartment model to generate time-activity curves followed by analysis of these curves by the noncompartmental method. The effect of plasma total bilirubin level on DISIDA uptake and MRT was also investigated. These techniques are readily adaptable to standard nuclear medicine computing facilities, and could be used in the clinical setting to numerically describe serial DISIDA studies (especially in liver transplant patients) efficiently and noninvasively.

Adult↗
PubMed1988

Stimulation of corticosterone release in the fowl by recombinant DNA-derived chicken growth hormone.

The effects of recombinant DNA-derived chicken growth hormone (rcGH) on plasma corticosterone in young broiler cockerels were investigated. A single injection of 200 micrograms/kg rcGH significantly increased plasma corticosterone concentrations 2 hr (but not 20 or 40 min) after treatment. Administration of 10 or 100 micrograms/kg rcGH also significantly increased plasma corticosterone levels after 2 hr, with the higher dose eliciting greater responses. Chronic treatment with seven daily injections of the same doses of rcGH gave similar increases in plasma concentrations of corticosterone. No obvious difference in magnitude of plasma corticosterone was observed between acute and chronic exposure to rcGH. In a further experiment in which serial blood sampling was performed after a single injection or five daily injections of vehicle or 200 micrograms/kg rcGH, there were significant increases in plasma corticosterone concentrations 40 min after acute rcGH treatment and 40 and 80 min after chronic treatment when compared with plasma corticosterone concentrations of vehicle-injected controls. However, the increases could have incorporated a stress response due to repeated sampling because the control birds also showed elevated plasma corticosterone concentrations. The corticosterone response did not diminish with repeated GH challenge. These results suggest that GH may play a role in the acute regulation of corticosterone secretion in intact chickens.

Animals↗
PubMed1988

Effects of passive immunization with antisomatostatin serum on plasma corticosterone concentrations in young domestic cockerels.

Young cockerels (6-8 weeks old) were injected with serum from sheep immunized against somatostatin-14 (anti-SRIF) or normal sheep serum (NSS). Blood samples were withdrawn periodically for the determination of plasma corticosterone concentration by radioimmunoassay. With frequent (every 10 min) sampling, NSS-treated control animals exhibited increased plasma corticosterone levels, presumably as a stress response to the experimental manipulation. Anti-SRIF stimulated a much greater increase in plasma corticosterone concentrations and a peak response was observed within 10 to 20 min, when the plasma corticosterone level reached more than twice that of the corresponding control value. With less frequent sampling, plasma corticosterone increased with anti-SRIF administration to as much as nine times the corresponding control value, and the peak response occurred much later. Under pentobarbitone anaesthesia, which itself increased basal corticosterone concentrations, anti-SRIF treatment promoted further increases in plasma corticosterone levels although to a smaller magnitude compared with conscious birds. The results suggest that endogenous somatostatin may play a role in the regulation of adrenocortical function in the domestic fowl. The mechanism of response may involve a central component.

Animals↗
PubMed1987

Somatostatin immunoneutralization overcomes the inhibitory effects of quipazine and pargyline on growth hormone secretion in domestic fowl.

The inhibitory effects of pargyline and quipazine on chicken growth hormone secretion were overcome by passive immunoneutralization of endogenous somatostatin (SRIF)-14 or SRIF-28(1-14)-like immunoreactivity. Administration of the specific antisera to control birds pretreated with 0.9% NaCl elevated the basal plasma GH concentrations. These results suggest that peptides with SRIF-14 or SRIF-28(1-14)-like immunoreactivity tonically inhibit GH secretion and are at least partially responsible for the inhibitory effects of pargyline and quipazine on GH release in immature domestic fowl.

Animals↗
PubMed1987

Inhibition of growth hormone secretion in anaesthetized fowl: hypothalamic participation.

Sodium pentobarbitone anaesthesia lowered the circulating growth hormone (GH) concentration in immature chickens and reduced basal and stimulated pituitary GH release in vitro. The immunoneutralization of endogenous somatostatin (SRIF), by passive SRIF immunization, overcame the inhibitory effect of anaesthesia on basal GH secretion in vivo, but had no direct effects on GH release in vitro. However, while SRIF immunization restored the resting GH concentration in the anaesthetized birds, it increased greatly the GH level in conscious birds. These results therefore suggest that the inhibition of GH secretion in anaesthetized birds may be partly SRIF-mediated, although a suppression of hypothalamic stimulation may also be involved.

Anesthesia↗
PubMed1987

Calcium participation in thyroid function in fowl (Gallus domesticus).

The effects of the calcium antagonists ethyleneglycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraace tic acid (EGTA), cobalt chloride (CoCl2), and magnesium chloride (MgCl2) on the concentrations of plasma thyroxine (T4) and triiodothyronine (T3) and on the basal and stimulated release of T4 from incubated thyroid glands have been determined in the domestic fowl. Plasma T4 levels were consistently reduced 2 hr after the administration of each calcium antagonist, although only EGTA and CoCl2 lowered the concentration of plasma total calcium. Concentrations of plasma T3 were increased following MgCl2 treatment but reduced after CoCl2 administration. The basal release of T4 by incubated thyroid glands was reduced following in vivo EGTA and CoCl2 treatment, but increased after MgCl2 injection. The addition of bovine thyroid stimulating hormone (TSH, 200 mU) to the incubation consistently stimulated in vitro T4 release, although the magnitude of the stimulation was increased following in vivo EGTA or CoCl2 treatment and reduced after MgCl2 administration. These results demonstrate the involvement of calcium dependent mechanisms in the control of T4 release in fowl.

Animals↗
PubMed1987

Somatostatin-28(1-14) immunoneutralization stimulates growth hormone secretion in fowl.

Immunoneutralization of endogenous somatostatin (SRIF)-28(1-14) by the intravenous or intramuscular administration of a specific antiserum promptly enhanced the growth hormone (GH) concentration in the plasma of 4 to 8-week-old cockerels. The magnitude of the GH response was related to the volume of antiserum administered. The release of GH from chicken pituitary glands incubated with intact hypothalami was increased in the presence of anti-SRIF-28(1-14). These results suggest that SRIF-28(1-14)-like peptides are physiologically involved in the control of GH secretion in chickens, in which they may tonically inhibit GH release.

Animals↗
PubMed1987

Some biological activities of recombinant DNA-derived growth hormone on plasma metabolite concentrations in domestic fowl.

The biological activity of recombinant-DNA-derived chicken growth hormone (rcGH) has been examined in young broiler cockerels, by determining its effects on plasma concentrations of glucose, free fatty acids and alpha-amino nitrogen. A single injection of rcGH increased plasma glucose, which remained high for several hours, whereas daily treatment with rcGH for 1 week had no effect on basal plasma glucose concentrations but blunted the glucose response to a further rcGH challenge. Plasma free fatty acids were also promptly increased following acute rcGH treatment, and chronic exposure to rcGH again attenuated this response. The effects of rcGH on plasma alpha-amino nitrogen were more variable. The stress of repeated blood sampling tended to reduce alpha-amino nitrogen, and after rcGH, an increase relative to vehicle-injected controls was seen in both acute and chronically-treated birds. These data suggest that rcGH has both hyperglycaemic and lipolytic activity in chickens, and may also increase amino acid availability.

Amines↗
PubMed1987

Daily variations in monoamine turnover in the brain of the ring dove (Streptopelia risoria).

A method for measuring the concentration and turnover of serotonin, dopamine and noradrenaline in small amounts of brain tissue was validated for the ring dove (Streptopelia risoria). Turnover rates of the catecholamines calculated as the rate of depletion after tyrosine hydroxylase inhibition agreed well with turnover rate measured as rate of accumulation after inhibition of monoamine oxidase at 2.5 h, but not 5 h, after drug administration. Using the monoamine oxidase inhibitor, pargyline, turnover of serotonin, dopamine and noradrenaline were estimated in the same tissue. Both the concentration and turnover of the amines in hypothalamus, paleostriatum and hyperstriatum fluctuated over a 24 h period. Serotonin turnover was greatest during the middle of the dark period in all three tissues. In contrast, for both dopamine and noradrenaline the highest turnover was observed during the light period and the lowest during the dark period.

Animals↗
PubMed1987

Serotoninergic regulation of corticosterone secretion in domestic fowl.

The effects of serotoninergic drugs on adrenocortical function in domestic fowl were examined. Administration of the serotonin receptor agonist 2-(1-piperazinyl)quinoline maleate (quipazine), an inhibitor of serotonin metabolism, N-methyl-N-2-propynylbenzylamine HCl (pargyline), as well as serotonin itself, all increased plasma concentrations of corticosterone. The maximum responses to serotonin and quipazine occurred 1 h after treatment. The quipazine-stimulated response was partly prevented by the serotonin antagonist cyproheptadine. Cockerels pretreated with dexamethasone, a synthetic steroid known to inhibit pituitary ACTH release, showed attenuated responses to subsequent quipazine, pargyline or serotonin injection. Serotonin, quipazine and cyproheptadine did not affect corticosterone release directly from the adrenal gland incubated in vitro, nor did they affect adrenal responsiveness to ACTH stimulation. The neurotoxin 5,6-dihydroxytryptamine injected into day-old chicks decreased plasma concentrations of corticosterone for up to 7 days after treatment, with corresponding decreases in the hypothalamic concentration of serotonin, but not dopamine or noradrenaline concentrations. These results show that adrenal corticosterone secretion is regulated by a central serotoninergic system, probably acting on the hypothalamo-pituitary-adrenal axis.

5,6-Dihydroxytryptamine↗
PubMed1986

In vitro release of triiodothyronine and thyroxine from thyroid glands of the domestic fowl (Gallus domesticus).

Basal and thyrotrophin (TSH)-stimulated release of iodothyronines (triiodothyronine, T3, and thyroxine, T4) from intact chicken thyroid glands was determined in vitro. In the absence of TSH, T3 and T4 were released in measurable amounts in the incubation media. The release of both iodothyronines was directly related to the media TSH concentrations and incubation period. Lineweaver-Burke analysis revealed that the Vmax for T3 was 99.4 pg/gland, with an apparent Km of 17.8 mU TSH, and that the Vmax for T4 was 323.35 ng/gland, with an apparent Km of 51.5 mU TSH, demonstrating that T4 is the major iodothyronine released by avian thyroid glands. The basal release of T4 was suppressed by the addition of a calcium chelator (ethyleneglycol-bis-(beta-aminoethylether)-N,N,N', N'-tetraacetic acid; EGTA), a calcium antagonist (cobalt chloride, CoCl2), or prostaglandin E1 (PGE1) to the incubation media. Basal T4 released was increased in the presence of a calcium agonist (lanthanum chloride, LaCl3), a calcium ionophore (A23187), dibutyryl cyclic adenosine 3'3'-monophosphate (dbcAMP), isobutylmethylxanthine (IBMX), indomethacin, magnesium chloride (MgCl2), and potassium iodide (KI). Thyrotrophin-stimulated T4 release was reduced by CoCl2, PGE1, and indomethacin but enhanced by LaCl3, MgCl2, and KI. These results demonstrate that it is possible to measure the release of thyroid hormones in an in vitro system in the chicken. Basal and stimulated iodothyronine release from the chicken thyroid gland appears to be mediated by calcium- and cAMP-dependent mechanisms.

Animals↗
PubMed1986

Somatostatin immunoneutralization affects plasma metabolite concentrations in the domestic fowl.

Young leghorn cockerels were injected with antiserum to somatostatin (anti-SRIF) and plasma glucose, free fatty acids and alpha-amino nitrogen concentrations determined. Plasma glucose concentrations increased rapidly after anti-SRIF and remained high for up to 2 hr. Two different antisera tested had hyperglycaemic activity. Plasma free fatty acids also increased rapidly after administration of the two different anti-SRIFs, and remained high for about 1 hr. Plasma alpha-amino nitrogen increased during the first 30 min after anti-SRIF, then declined to levels significantly lower than control by 1-2 hr after injection. Anaesthesia reduced plasma concentrations of glucose and alpha-amino nitrogen, and also reduced the changes of these metabolites following anti-SRIF. The results show the importance of endogenous somatostatin in the regulation of plasma metabolite concentrations.

Animals↗
PubMed1986

The characteristics and distribution of monoamine oxidase (MAO) activity in different tissues of the rainbow trout, Salmo gairdneri.

Monoamine oxidase (MAO) activity was determined fluorometrically in brain, intestine, kidney and liver tissues of the rainbow trout, Salmo gairdneri. MAO activity was inhibited by various drugs in a concentration-related manner, with single sigmoid inhibition curves, the inhibitors of type A MAO, harmaline and clorgyline being more effective than deprenyl, an inhibitor of type B MAO. Intestine exhibited greatest MAO activity followed by liver and brain with kidney showing least activity. The Michaelis constants (Km) also showed variability between tissues. Inhibition of MAO by harmaline was non-competitive and dependent on the concentration of substrate present.

Animals↗
PubMed1986

Somatostatin immunoneutralization stimulates thyroid function in fowl.

The influence of somatostatin on thyroid function has been examined in immature domestic fowl passively immunized with somatostatin antiserum. Plasma thyroxine (T4) and tri-iodothyronine (T3) concentrations were markedly increased within 10 min of antisomatostatin administration and remained raised for at least 5 h. The increases in the T3 and T4 concentrations following somatostatin immunoneutralization were directly related to the volume of antisera administered. The increase in the T3 concentration exceeded the increase in the T4 concentration, resulting in a T3 : T4 ratio greater than unity. While the raised T4 concentration began to decline 30 min after antisomatostatin administration, raised T3 concentrations were sustained for at least 2 h, and further increased the plasma T3 : T4 ratio. These results demonstrate that somatostatin immunoneutralization stimulates thyroid function in fowl. The magnitude and rapidity of the thyroidal responses to somatostatin immunoneutralization suggests that they occur independently of the hypothalamic-pituitary-thyroid axis. Somatostatin appears to exert a tonic inhibitory control on avian thyroid function, possibly by effects mediated at the thyroid gland to inhibit T4 release and by peripheral effects to suppress the conversion of T4 and T3.

Animals↗
PubMed1986

Serotoninergic inhibition of LH secretion in the domestic fowl.

Immature cockerels were injected with drugs known to affect serotoninergic activity. The receptor agonist quipazine as well as pargyline, an inhibitor of serotonin breakdown, both reduced plasma LH concentrations in a time-dependent fashion. The effect of pargyline was also dose-related. The serotonin precursor, tryptophan, reduced plasma LH levels. Tryptophan and pargyline were as effective in pubertal cockerels as in 3-week-old birds. Responses to quipazine were attenuated by the antagonist, methysergide, although another antagonist, cyproheptadine, also reduced plasma LH levels. Serotonin itself had no effect on plasma LH levels. Parachlorophenylalanine, which blocks serotonin synthesis, had no effect on plasma LH by itself, but attenuated the tryptophan-induced inhibition of LH. These data indicate that serotoninergic mechanisms inhibit secretion of LH in domestic fowl. This mechanism probably operates through the central nervous system.

Animals↗
PubMed1986

Somatostatin tonically inhibits growth hormone secretion in domestic fowl.

Passive immunization of immature chickens with sheep somatostatin (SRIF) antiserum promptly increased the basal plasma GH concentration and augmented TRH-induced GH secretion. Although exogenous SRIF had no inhibitory effect on the basal GH concentration in untreated birds or birds pretreated with non-immune sheep serum, it suppressed the stimulatory effect of SRIF immunoneutralization on GH secretion. These results suggest that SRIF is physiologically involved in the control of GH secretion in birds, in which it appears to inhibit GH release tonically.

Animals↗