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Biomedical subjects

S Harvey

Publications and source records attributed to S Harvey.

At least 235 records · Page 13Linked to original sources
PubMed1985

Growth hormone secretion in anaesthetized fowl. 1. Refractoriness to repeated stimulation by human pancreatic growth hormone-releasing factor (hpGRF) or thyrotrophin releasing hormone (TRH).

The intravenous (iv) administration of thyrotrophin releasing hormone (TRH, at 1.0 or 10.0 micrograms/kg) or human pancreatic growth hormone-releasing factor (hpGRF(1-44)NH2, at 10 micrograms/kg) markedly increased the growth hormone (GH) concentration in the plasma of immature or adult cockerels anaesthetized by sodium pentabarbitone (30 mg/kg, iv). A second injection of either TRH or hpGRF failed to increase the GH concentration in immature chicks when administered 15, 30, or 60 min after the first injection. However, significant GH responses to TRH or hpGRF were observed when the interval between injections was either 120 or 240 min. The magnitude of the GH responses to TRH were, however, diminished by 83.3 and 26.7% when given 120 or 240 min after the initial TRH injection, and the responses to hpGRF were similarly reduced by 68.3 and 33.6%. A similar period of GH refractoriness to TRH or hpGRF stimulation was also observed in adult birds, although the recovery of GH responsiveness occurred earlier. While a second injection of hpGRF was ineffective in increasing the plasma GH concentration if given within 30 min of the first, it was fully effective when the interval between injections was greater than 60 min. In response to a second injection of TRH, the GH concentration was elevated when the interval between injections was greater than 120 min, after which the magnitude of the response evoked was greater than that induced by the initial injection. Growth hormone secretion secretion in immature and adult fowl is therefore refractory to repeated provocative stimuli, although the mechanism involved is unknown.

Anesthesia↗
PubMed1985

Growth hormone secretion in anaesthetized fowl. 2. Influence of heterologous stimuli in birds refractory to human pancreatic growth hormone-releasing (hpGRF) or thyrotrophin releasing hormone (TRH).

In anaesthetized young (6 weeks old) and adult (22-30 weeks old) domestic fowl, the administration of thyrotrophin releasing hormone (TRH; 1.0 micrograms/kg in young birds; 10.0 micrograms/kg in adults) or human pancreatic growth hormone-releasing factor (hpGRF(1-44)NH2; 10.0 micrograms/kg in both cases) markedly increased the growth hormone (GH) concentration in plasma samples collected 10 min later. In birds injected with TRH, this stimulation of GH secretion attenuated the GH response to a second TRH challenge (given 15 or 60 min after the first in adult or young birds, respectively); similarly, hpGRF pretreatment blunted the GH response to a further hpGRF injection. However, the administration of hpGRF to both immature and adult birds made refractory to TRH challenge was followed by increased GH secretion and vice versa. Moreover, the GH secretory response to hpGRF in birds pretreated with TRH was greater (1.99-fold in young birds, 1.52-fold in adults) than the increase in plasma GH concentration following hpGRF administration in untreated birds. Similarly, prior exposure to hpGRF also increased the GH response to TRH stimulation (by 2.24-fold in the young, 3.56-fold in the adults). These results demonstrate that TRH not only overcomes GH refractoriness to hpGRF and vice versa, but the GH response to heterologous provocative stimuli is potentiated in birds refractory to TRH or hp GRF challenge.

Anesthesia↗
PubMed1985

Transitory corticosterone responses of ducks (Anas platyrhynchos) to exercise.

Horizontal treadmill exercise induced a marked (P less than 0.001) but transitory increase in the level of circulating corticosterone in the plasma of adult male ducks. The decline in corticosterone concentration during exercise is unlikely to be due to a depletion of adrenocortical stores since a marked (P less than 0.001) corticosterone response to adrenocorticotrophin (ACTH) administration was observed immediately after exercise, and was of similar magnitude to that induced in nonexercised controls. The corticosterone response to repeated exercise is also transitory, habituating completely within 28 days of the start of daily training. The corticosterone response (P less than 0.001) to ACTH challenge is not, however, diminished by training. These results indicate that the habituation of the corticosterone response to either acute or repeated exercise is due to a reduction in endogenous ACTH secretion. A similar mechanism appears to be responsible for the habituation of the corticosterone response to handling and confinement in nonexercised control birds. A marked (P less than 0.001) increase in the level of circulating corticosterone was, however, elicited when these birds were exercised, indicating that despite adaptation to handling and confinement the birds remained responsive to the novel stressor of exercise. The corticosterone response of these birds was, however, less than that in untrained birds indicating that the corticosterone response in untrained birds is due to both workload and the stress of handling and confinement.

Adrenocorticotropic Hormone↗
PubMed1985

Adrenocortical responses to novel stressors in acutely or repeatedly starved chickens.

The effect of starvation on the corticosterone responses of immature cockerels to acute, novel stress has been determined. The marked corticosterone responses of fed birds to either horizontal treadmill exercise (0.04 km/hr) or intravenous adrenocorticotrophic hormone (ACTH) administration (P less than 0.001 in both cases) were reduced by starvation (P less than 0.01 and P less than 0.001, respectively). This reduction did not appear to be due to either feedback inhibition of corticosterone on the hypothalamus or pituitary, or to reduced adrenal responsiveness to endogenous ACTH. Starvation significantly elevated the basal level of circulating corticosterone (P less than 0.001), but the magnitude of this elevation and the level of corticosterone attained were less (P less than 0.05) in birds that were accustomed to starvation. This habituation of adrenocortical activity may be due to reduced pituitary ACTH secretion, and was specific in that the corticosterone responses to novel stressors were unaffected.

Acute Disease↗
PubMed1985

Maturational changes in T4 to T3 conversion in domestic fowl.

The in vivo conversion of thyroxine (T4) to triiodothyronine (T3) has been determined in fed and 24 hr-fasted thyroidectomized cockerels at 4, 7, 13 and 23 weeks of age. The conversion of T4 to T3 in pubertal (13-week-old) and adult (22-week-old) cockerels was greater than that in immature (less than 7-week-old) chicks. The deprivation of food for 24 hr markedly reduced the rate of T4 to T3 conversion, especially in immature chicks. These maturational changes in T4 to T3 conversion may be related to differences in metabolic rate.

Aging↗
PubMed1985

Effects of putative neurotransmitters on release of prolactin from pituitary glands of the domestic fowl co-incubated with hypothalamic tissue.

Pituitary glands and hypothalami from broiler fowl heads were incubated alone or together with histamine, gamma-aminobutyric acid (GABA) or acetylcholine (ACh) as well as with catecholamines or neurotransmitter antagonists. Histamine and ACh stimulated, whereas GABA inhibited, the hypothalamus-induced release of prolactin, responses blocked by their specific antagonists. The dopamine antagonist pimozide, but not adrenergic (both alpha and beta), serotoninergic or cholinergic antagonists, prevented the actions of histamine and GABA. None of the antagonists except the cholinergic blocker, atropine, affected ACh-induced release of prolactin. Neither histamine nor ACh prevented inhibition of prolactin release by dopamine or stimulation of prolactin release by noradrenaline. GABA did not affect the response to noradrenaline. Furthermore, histamine, GABA and ACh had no effects on thyrotrophin releasing hormone-stimulated release of prolactin directly at the pituitary level. These results suggest that histamine and GABA affect prolactin release from chicken pituitaries in vivo by modifying the activity of the dopaminergic system. Acetylcholine may stimulate the secretion of prolactin releasing factor from the hypothalamus.

Acetylcholine↗
PubMed1985

Adrenergic stimulation of adrenocortical secretion in immature fowl.

In 5-6-week-old cockerels the circulating corticosterone concentration was significantly increased in birds i.m. injected 30 and 60 min previously with adrenaline (0.33 mg/kg), noradrenaline (0.33 mg/kg) or a beta-adrenergic agonist (isoprotorenol, 1 mg/kg), but was reduced in birds pretreated with an alpha-adrenergic agonist (phenylephrine, 1 mg/kg). The stimulation of corticosterone secretion induced by a 30 min period of forced exercise (0.04 km/hr; 0 degree incline) was potentiated by noradrenaline, isoprotorenol and phentolamine pretreatment. In response to exogenous adrenocorticotrophin (ACTH, 8 i.u./kg), administered i.v., the increase in the plasma corticosterone concentration was elevated above that in the controls in birds pretreated with adrenaline, noradrenaline, isoprotorenol or phentolamine (an alpha antagonist administered at 1 mg/kg). The corticosterone response to ACTH was suppressed by phenylephrine pretreatment. These results demonstrate that both basal and stimulated levels of adrenocortical activity may be subtly regulated by adrenergic mechanisms acting at a site(s) within the hypothalamo-pituitary-adrenal axis.

Adrenal Cortex↗
PubMed1985

Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). I. Characteristics of MAO activity in vitro.

Monoamine oxidase (MAO) activity was measured in ring dove (Streptopelia risoria) tissues using a fluorometric assay with kynuramine as substrate. Harmaline inhibited MAO activity in a time-dependent manner, and preincubation of enzyme with the drug did not affect its activity. Pargyline produced a slow-onsetting inhibition of activity which was enhanced by preincubation of enzyme and inhibitor. Harmaline displayed reversible non-competitive inhibition of MAO activity. Oxygen is also a substrate for dove MAO, and the reaction apparently involves "ping-pong", double-displacement kinetics. Dove MAO activity is temperature-dependent, with an activation energy of 13.1 kcal/mole.

Animals↗
PubMed1985

Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). II. Distribution of MAO in different tissues.

Monoamine oxidase (MAO) activity was measured fluorometrically in liver, kidney, intestine and brain of adult male and female ring doves. Liver MAO was inhibited in a concentration-related fashion by clorgyline and harmaline (MAO type A inhibitors) where a plateau in the inhibition curve occurred with about 15% activity remaining, and also by the type B inhibitor deprenyl, which produced a plateau when about 85% activity remained. Kidney, intestine and brain MAO were inhibited in a biphasic manner by harmaline. Results with inhibitors suggest that 85% of liver MAO, 86% of kidney MAO, 88% of intestine and 75% of brain MAO is type A. Using 10(-6) M harmaline to differentiate between MAO-A and MAO-B type activities, the apparent maximal velocities (Vmax) and Michaelis constants (Km) were determined in different tissues. Most activity occurred in the intestine, with proportionally lesser amounts of kidney, liver and brain. The majority of MAO present was in the A form. Except for kidney, Km of MAO-B was higher than that of MAO-A. Both MAO-A and -B activities were higher in the intestines of male birds, although sex differences in content and type of MAO activity were not observed in other tissues of the ring dove.

Animals↗
PubMed1985

The time sequence of adaptive changes to dietary phosphorus deficiency in the chick.

Ten-day old chicks were divided into 6 groups which were fed a low phosphorus (P) diet for periods of 0, 0.5, 1, 3, 7 or 11 days before killing at 3 weeks old. Labelled calcium (47Ca) was injected intraperitoneally into some birds 18 hours before killing. A marked fall in growth rate, plasma phosphorus level, plasma growth hormone level and renal 24-hydroxylase activity levels had occurred by 12 hours after the experimental diet had started. After one day on the diet, the rate of duodenal Ca absorption had risen and continued to rise up to the 11th day. During this period, the renal 25-hydroxyvitamin D-1-hydroxylase activity rose slightly while the 24-hydroxylase activity rose towards the control level. At 24 hours, the 47Ca level in the bone was markedly lower than in the control group and remained low. It was concluded that the first adaptive response of the chick to dietary P insufficiency was to suppress growth. Subsequent adaptive responses were to increase the rate of Ca and P absorption from the gut and mobilisation from the bone but despite these measures, the growth rate only recovered slightly and the plasma P level continued to fall.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1985

Synthetic pheromones that promote inter-male aggression in mice.

Two volatile constituents of male mouse urine, dehydro-exo-brevicomin and 2-(sec-butyl)-dihydrothiazole, have been found active in bioassays of inter-male aggressive behavior. The two synthetic compounds act synergistically when added to castrated male urine but not when added to water, and they provoke fighting that is quantitatively and qualitatively comparable to that elicited by intact male urine.

Aggression↗
PubMed1985

Effects of prostaglandin F2 alpha on prolactin secretion in the fowl.

The plasma concentration of prolactin in immature cockerels was increased between 10 and 40 min after the intravenous administration of prostaglandin (PG) F2 alpha (200 micrograms/kg body weight). Lower doses had no effect on plasma prolactin concentration. The addition of PGF2 alpha (10(-9) to 10(-6) M) to incubation media had no effect on the basal release of pituitary prolactin but reduced the release of prolactin from pituitary-hypothalamus co-incubations. The addition of noradrenaline (10(-7) M), serotonin (10(-7) M), acetylcholine (10(-6) M) or histamine (10(-6) M) to the co-incubation increased the hypothalamus-induced prolactin release, although these effects were not observed in the presence of 10(-7) M PGF2 alpha. The in vitro release of pituitary prolactin was increased by adding chicken hypothalamic extract in the presence or absence of PGF2 alpha. These results suggest a dual effect on PGF2 alpha of prolactin secretion in the fowl; its stimulation in vivo may result from a peripheral action.

Animals↗
PubMed1985

Growth hormone secretion and pancreatic function following somatostatin infusion in ducks (Anas platyrhynchos).

The intravenous infusion of somatostatin (800 ng/kg min) reduced the concentration of growth hormone (GH) in the plasma of 4 to 5, 6 to 7 and 8 to 9 week-old ducklings, but not in adult ducks. The inhibition of GH secretion was not due to accompanying changes in pancreatic function, since the infusion of a lower dose of somatostatin (200 ng/kg min) increased glucagon release and decreased plasma free fatty acids (FFA), as observed with the higher dose, but had no effect on GH concentrations. The withdrawal of somatostatin inhibition resulted in rebound GH secretion in immature birds, the magnitude of which was directly related to the pre-treatment level. Following somatostatin infusion (800 ng/kg min) no modification in GH concentration was observed in adult ducks. These results demonstrate that basal GH release in young birds is not autonomous and is suppressible by somatostatin. The data provide further evidence for age-related changes in the control of avian GH and insulin release and for the independence of the effects of somatostatin on the pituitary and pancreas glands.

Age Factors↗
PubMed1985

Isolation of Campylobacter fetus from a pet turtle.

During the course of a Salmonella agona case investigation, Campylobacter fetus was isolated from a pet turtle. This is the first reported isolation of C. fetus from a turtle and suggests that turtles, in addition to being reservoirs for Salmonella species, may also be reservoirs for C. fetus.

Animals↗
PubMed1985

TRH stimulation of in vivo GH release in the domestic fowl. Influence of TRH metabolites and effect of age on in vitro degradation of TRH.

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 less than 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.

Age Factors↗
PubMed1985

Age-related changes in prolactin and growth hormone release from pituitary glands in vitro.

The basal release of prolactin from cockerel anterior pituitary glands in vitro declined between 1 and 7 weeks of age, to a level less than that released by pituitary glands from 18 week old (adult) cockerels and hens. Basal growth hormone (GH) release increased between 1 and 7 weeks of age but had declined in adults to a level similar to that released from 4 weeks old cockerels. The responsiveness of the pituitary gland to hypothalamic stimulation, using hypothalami from 8 week old broiler fowl, was also age-related. Prolactin release was considerably higher from pituitaries of 1 week old cockerels compared to the other age groups. Stimulation of GH release by the hypothalamus was higher from pituitaries of both 1 and 7 week old cockerels compared to the other groups of birds. The increase in release of prolactin following incubation with thyrotrophin releasing hormone (TRH) declined between 1 and 7 weeks, but increased slightly in adult birds, whereas the increase in release of GH following TRH was higher from pituitaries of both 1 and 7 week old cockerels. Hypothalamic prolactin (Prl) releasing activity, measured as the ability of the hypothalamus to stimulate hormone release from 8 week old broiler fowl anterior pituitary glands, declined with the age of the donor cockerels. The hypothalami from adult hens secreted significantly more Prl releasing activity than did adult cockerel hypothalami. The secretion of GH releasing activity decreased markedly with the age of the donor bird. These results suggest that maturational patterns of hormone secretion in fowl are partly due to changes in autonomous hormone release, to changing patterns of hypothalamic activity and to differences in pituitary responsiveness to provocative stimuli.

Age Factors↗
PubMed1985

Drinking-induced changes in fowl adrenocortical activity: effect of visual and non-visual stimuli.

The deprivation of drinking water for 30 h resulted in increased corticosterone concentrations in the plasma of 8- to 10-week-old chickens. When water-deprived birds were allowed to drink ad libitum the corticosterone concentration declined within 45 min, to the level in hydrated controls, and remained suppressed thereafter. Similar reductions in the corticosterone concentrations were also observed in water-deprived chicks which were allowed to drink for only 5 min, 1 min or 5 s. The involvement of visual stimuli in mediating this adrenocortical response was demonstrated by a comparable decline in the corticosterone concentration in water-deprived birds which were presented with water but not allowed access to it. Non-visual stimuli also appeared to be causally involved in the adrenocortical suppression after drinking, since the intraperitoneal injection of tap water (40 ml per bird) also resulted in a lowering of the corticosterone level. However, in the absence of appropriate reinforcement from metabolic stimuli, a rebound in the corticosterone concentration was observed in birds prevented from drinking, in birds unable to satiate their thirst and in birds rehydrated (orally or intraperitoneally) without feeding. These results demonstrate adrenocortical suppression in water-deprived chickens after free access to food and water and the involvement of visual and non-visual stimuli in mediating this response. The maintenance of adrenocortical suppression is dependent upon metabolic stimuli associated with food and water intake.

Adrenal Cortex↗