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A Foldes

Publications and source records attributed to A Foldes.

At least 19 recordsLinked to original sources
PubMed2003

Role of hypothalamic inputs in maintaining pituitary-adrenal responsiveness in repeated restraint.

The role of hypothalamic structures in the regulation of chronic stress responses was studied by lesioning the mediobasal hypothalamus or the paraventricular nucleus of hypothalamus (PVH). Rats were acutely (60 min) and/or repeatedly (for 7 days) restrained. In controls, a single restraint elevated the plasma adrenocorticotropin (ACTH), corticosterone, and prolactin levels. Repeated restraint produced all signs of chronic stress, including decreased body and thymus weights, increased adrenal weight, basal corticosterone levels, and proopiomelanocortin (POMC) mRNA expression in the anterior pituitary. Some adaptation to repeated restraint of the ACTH response, but not of other hormonal responses, was seen. Lesioning of the mediobasal hypothalamus abolished the hormonal response and POMC mRNA activation to acute and/or repeated restraint, suggesting that the hypothalamo-pituitary-adrenal axis activation during repeated restraint is centrally driven. PVH lesion inhibited the ACTH and corticosterone rise to the first restraint by approximately 50%. In repeatedly restrained rats with PVH lesion, the ACTH response to the last restraint was reduced almost to basal control levels, and the elevation of POMC mRNA level was prevented. PVH seems to be important for the repeated restraint-induced ACTH and POMC mRNA stimulation, but it appears to partially mediate other restraint-induced hormonal changes.

Adrenal Glands↗
PubMed1994

Melatonin and farm animals: endogenous rhythms and exogenous applications.

Studies on farm animals have contributed significantly to our increased understanding of basic melatonin-related physiological mechanisms, as well as to the regulation of reproduction and pelage in individual domestic species. This review concentrates on recent work on the role of melatonin in the regulation of porcine reproduction, cervine endocrine, and behavioral cycles and wool and cashmere production which has added to this knowledge base. Early studies of the domestic pig indicated that melatonin secretion in this species differed markedly from that in other domestic and laboratory animals. There is now clear evidence that this is not the case and that the domestic pig uses a circadian rhythm of melatonin release for the transduction of photoperiodic information. Apparent inconsistencies among reports may be due, in part, to differences in the conditions under which the experiments were performed and to the assay systems employed to measure circulating melatonin, the concentrations of which are much lower than in other domestic species. Appropriately administered exogenous melatonin advances the onset of puberty in gilts, and may prove to be effective in overcoming seasonal infertility in female pigs. Appropriately timed melatonin and/or photoperiod treatments, administered to ruminants in utero, influence the reproductive physiology of the offspring, indicating that even in species which don't develop an endogenous melatonin rhythm till some weeks postnatally, awareness of photoenvironment, presumably via maternal melatonin, predates birth. Pre- or early postnatal melatonin-related treatments also influence the development/cycle frequency of pelage. Areas requiring further investigation include the hormonal/growth factors involved, reasons for the transient nature of the effects in sheep and goats, and the reason for similar effects on pelage of augmenting or inactivating melatonin. Aspects of endogenous melatonin rhythms in farm species which require further study include: the significance of the abolition of the nocturnal melatonin peak in the sheep by prolonged short day exposure; the increased pineal bloodflow in sheep bred to produce high wool yields; the presence of high daytime melatonin levels immediately prior to the rut in the fallow buck; and the low amplitude of the rhythm in the domestic pig.

Animals↗
PubMed1993

Effect of pinealectomy and plane of nutrition on wool growth in Merino sheep.

The effects of surgical pinealectomy and plane of nutrition on wool growth and plasma prolactin concentrations in young Merino wethers were investigated. In young pinealectomized wethers maintained at a low live weight under conditions of minimal stress, the decline of conditioned clean wool production on midside patches was slowed when compared to pineal-intact controls. This difference appeared to be due in part to the observed greater secondary wool follicle density in the pinealectomized wethers; mean fiber diameter was affected to a smaller extent, while staple length growth rate was not significantly altered. Circulating prolactin profiles showed a seasonal variation (high in summer, low in winter) in both pinealectomized and control wethers. There was no difference in wool production between pinealectomized and control wethers when the diet of the same wethers was subsequently supplemented with formaldehyde-treated cottonseed meal. While the role of melatonin in the regulation of wool growth remains to be determined, it is suggested that the hormone may have a transient effect on wool production in young wethers under conditions of limited nutrition, but not at higher nutritional levels, and that melatonin may be involved in partitioning of nutrients to the wool follicle.

Animal Nutritional Physiological Phenomena↗
PubMed1992

Effect of immunization against melatonin on seasonal fleece growth in feral goats.

Four vaccination protocols were utilized to investigate the effects of immunoneutralizing circulating melatonin on the annual cashmere growth cycle and cashmere production in Australian feral goats. A fluctuating anti-melatonin antibody response, achieved by repeated booster vaccinations, resulted in an acceleration of the growth cycle in goats which exhibited a significant immune response, compared to sham-immunized controls. Responding goats showed two cycles of cashmere length growth in the first 16 months and increased annual cashmere production in the first year. However, in the second year, these effects were no longer apparent, suggesting either some form of desensitization to melatonin, or a diminished response due to declining antibody titre. The effects of immunization were observed in both sexes; the effect on cashmere length was greater in wethers than in does. Cashmere fibre growth in response to a continuously declining plane of specific antibody showed increased cycle frequency, albeit with a decreased amplitude; guard hair growth cycles were affected to a much lesser extent. Small transient peaks of specific immunity at the summer or winter solstice were without significant effect on cashmere growth. Immunization to provoke a persistent anti-melatonin antibody response at the winter solstice resulted in significantly increased greasy fleece weight, % cashmere yield, and mass of cashmere produced, but no change in fibre diameter in both sexes. Thus the timing of cashmere growth cycles in goats may be, at least transiently, altered by appropriately timed immunization against melatonin. The mechanism of pineal-mediated regulation of cashmere growth cycles may involve (i) entrainment of an endogenous rhythm by melatonin, or (ii) seasonal alteration of cashmere follicle sensitivity to the effect of melatonin.

Animals↗
PubMed1992

Effects of pinealectomy on wool growth and wool follicle density in merino sheep.

There is evidence to indicate that pinealectomy may enhance wool growth in the sheep. The aim of this study was to determine the effect of pinealectomy on wool growth and wool follicle density in Merino sheep. Castrated Merino rams (4 months old) were either pinealectomized (P), sham-pinealectomized (S) or not treated (C). Wool growth on mid-side patches was measured every 4 weeks and follicle density was monitored in skin biopsies collected before treatment and at regular intervals for 60 weeks. Venous blood samples were taken on each of these occasions for prolactin analysis. Melatonin concentrations were determined in venous blood collected pre- and posttreatment from samples taken over a 24-hr period during the winter solstice. Pre- and posttreatment plasma melatonin levels (mean +/- SEM) 65 +/- 17 and < 13 pg/ml for P, 86 +/- 21 and 69 +/- 20 pg/ml for S, and 94 +/- 41 and 122 +/- 37 pg/ml for C, respectively, indicated that the pineal glands had been successfully removed. Wool growth, total follicle density and liveweight (mean +/- SEM) did not differ between treatment groups. Measurements at week 60 were 3.9 +/- 0.3, 4.1 +/- 0.2, and 3.8 +/- 0.3 gm clean wool/100 cm2; 66 +/- 6, 69 +/- 7, and 64 +/- 3 follicles/mm2; and 50.4 +/- 1.3, 50.8 +/- 1.4, and 52.6 +/- 1.1 kg liveweight for groups P, S, and C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Concentrations of plasma melatonin and luteinizing hormone in domestic gilts reared under artificial long or short days.

Plasma melatonin concentrations were measured every 1-2 h over 24 h and plasma luteinizing hormone (LH) concentrations every 15 min over 12 h in domestic gilts reared under artificial light regimens that had previously been used to demonstrate photoperiodic effects on puberty. In Expt 1, the light regimens both commenced at 12 h light: 12 h dark (12L:12D) and either increased (long-day) or decreased (short-day) by 15 min/week until the long-day gilts were receiving 16L:8D and the short-day gilts 8L:16D at sampling. In Expt 2, both light regimens commenced at 12L:12D and either increased (long-day) or decreased (short-day) by 10 or 15 min/week to a maximum of 14.5L:9.5D or a minimum of 9.5L:14.5D before being reversed. Sampling took place when daylength had returned to 14L:10D (long-day) or 10L:14D (short-day). In immature gilts housed at 12L:12D (Expt 1) and in postpubertal (Expt 1) and prepubertal (Expt 2) gilts reared under long-day or short-day light regimens, mean plasma melatonin concentrations were basal (3.6 pg/ml) when the lights were on and increased to peak concentrations greater than 15 pg/ml within 1-2 h after dark, before declining gradually to basal concentrations at or near the end of the dark phase. In prepubertal gilts bearing subcutaneous melatonin implants and reared under long-days (Expt 2), mean plasma melatonin concentration in the 6 h before dark was 91.9 +/- 5.26 pg/ml and 125.0 +/- 6.66 pg/ml 1 h after dark, but this increase was not statistically significant. In Expt 2, the short-day gilts had fewer LH pulses (2.6 +/- 0.25 vs. 4.6 +/- 0.24; P less than 0.01) in the 12-h sampling period than the long-day gilts, but the amplitude of the pulses (2.28 +/- 0.23 vs. 1.26 +/- 0.16 ng/ml; P less than 0.01) and the area under the LH curve (78.8 +/- 5.60 vs. 47.3 +/- 6.16; P less than 0.01) was greater in the short-day gilts. In the short-day, but not in the long-day, gilts LH pulses were more frequent (2.0 +/- 0.0 vs. 0.6 +/- 0.25; P less than 0.01), but had a smaller area (61.9 +/- 7.2 vs. 120.2 +/- 23.6; P less than 0.05) in the 6 h of dark than in the 6 h of light, which together made up the 12-h sampling period.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Seasonal inhibition of puberty in domestic gilts is overcome by melatonin administered orally, but not by implant.

The ability of exogenous melatonin, applied either orally or by implant, to overcome the seasonal inhibition of puberty in domestic gilts was tested in two experiments. In Expt 1, 24 gilts received two melatonin implants at 126 days of age and again at 161 days and 196 days, while 24 gilts acted as controls. All gilts were slaughtered at a mean age of 223 days. Blood samples were collected by venepuncture from eight gilts in each treatment at 126, 144 and 178 days of age and the plasma was assayed for melatonin concentration by direct radioimmunoassay. In Expt 2A, four gilts (125 days of age) were fed either 0, 1, 2 or 4 mg of melatonin at 14:00 h on each of four consecutive days. Blood samples for melatonin assay were collected via indwelling jugular catheters every 30 or 60 min from 12:00 to 22:00 h. In Expt 2B, 27 gilts were fed 1 mg of melatonin at 15:00 h each day from 129 days of age until slaughter at 221 days, while 25 gilts acted as controls. In both experiments, the presence of morphologically normal corpora lutea at slaughter was the criterion for puberty. In Expt 1, constant-release melatonin implants had no effect on the percentage of gilts which reached puberty. Among the 24 control gilts, two (8.3%) reached puberty compared with one of the 24 (4.2%) gilts with implants. In all the samples from control gilts, and in the samples taken from treated gilts prior to implantation at 126 days of age, mean plasma melatonin concentration was below the sensitivity of the assay (3.6 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1991

Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes.

Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.

Animals↗
PubMed1989

Seasonal modification of ovine pineal function. I. Interaction of gonadal steroids and sympathetic innervation on beta-adrenoceptors.

The results of a seasonal study of the regulation by steroids of ovine pineal beta-adrenoceptors are reported. The effects of ovariectomy, steroid implants and superior cervical ganglionectomy were investigated in Merino ewes. The results confirm earlier observations showing a seasonal variation in the sensitivity of the receptors to modification by gonadal steroids. A marked difference in receptor density and affinity between the follicular and luteal phases of the estrous cycle is shown for the first time, a difference which can be modified by appropriate steroid-related treatments. A season-dependent antagonism between the sympathetic innervation of the gland (presumably acting via the neurotransmitter noradrenaline) and gonadal steroids in the regulation of ovine pineal beta-adrenoceptor function is also shown.

Animals↗
PubMed1989

Seasonal modification of ovine pineal function. 2. Steroidal effects on melatonin and prolactin profiles.

Pineal beta-adrenoceptor density and affinity in ewes are modified in a season-dependent manner by gonadal steroids and by the sympathetic innervation of the gland. The present study was undertaken to relate the steroidal effects on the receptors to post receptor endocrine events, and to investigate the influence of the sympathetic innervation of the pineal gland on these events. Plasma melatonin and prolactin profiles were determined during anestrus and during the normal breeding season in ewes subjected to sympathetic denervation of the pineal and/or a range of steroid-related treatments. Wherever valid comparisons could be drawn between effects of the treatments on beta-adrenoceptor variables and on circulating hormone levels, similar effects were noted. Further, ganglionectomy influenced hormone profiles similarly to estradiol under all conditions tested. It appears that gonadal steroids (estradiol) and the sympathetic neurotransmitter noradrenaline have opposing actions on prolactin levels, just as they have on pineal beta-adrenoceptor binding affinity. These findings suggest that steroid-mediated changes in receptor number and affinity are reflected in post receptor endocrine events. In addition, other factors (e.g. photoperiodic information transmitted via the sympathetic innervation) also play important roles in the regulation of the observed hormonal profiles. A steroid-mediated feedback regulation of pituitary prolactin release, partly direct and partly via pineal melatonin release, is suggested.

Anestrus↗
PubMed1986

Pineal indoles: significance and measurement.

Despite intensive investigation, particularly over the past fifteen years, many aspects of pineal function with respect to mammalian physiology remain obscure. Much of this work is reviewed and particular attention focussed on indole metabolism within the pineal gland. Emphasis is placed on the development of new analytical techniques with special reference to high performance liquid chromatography coupled with electrochemical detection. The growth in knowledge regarding pineal indole synthesis which can be attributed to the use of this technique is discussed. The possibility that pineal indoles other than melatonin may function as hormones or neuromodulators is considered. A functional role for 5-hydroxytryptophol as a neuromodulator, possibly associated with diffuse neuroendocrine function (amine precursor, uptake and decarboxylation, APUD) is suggested.

Animals↗
PubMed1985

Seasonal changes in the sensitivity of ovine pineal beta-adrenoceptors to steroids.

Immunoneutralization of endogenous gonadal steroids has recently been shown to modify pineal beta-adrenoceptor function in intact Merino ewes. In the current study, interactions between gonadal steroids and these receptors have been further investigated. beta-Adrenoceptor density and binding affinity both showed time-related changes in ewes; the significance of these changes requires further study. Two observations, firstly modification of beta-adrenoceptor function by androstenedione and 17 beta-estradiol in ovariectomized, but not in intact ewes, and secondly that steroid-mediated effects on receptor density and binding affinity in the pineal of ovariectomized Merino ewes could be demonstrated during anestrus, but not during the breeding season for intact ewes, indicate that gonadal steroids may regulate pineal beta-adrenoceptor variables in Merino ewes. It is suggested that gonadal steroids may regulate ovine pineal function in ewes, and that the seasonal differences in sensitivity of luteinizing hormone release to steroid feedback may be mediated in part via effects on the pineal gland.

Androstenedione↗
PubMed1984

Response of pineal beta-adrenoceptors in different breeds of sheep to immunization against selected steroids.

Active immunization of Merino and Wiltshire Horn X Merino cross-bred sheep against a range of gonadal steroids has revealed that pineal beta-adrenoceptors in both breeds are sensitive to hormonal modification by androgens, but only in the less seasonal, non-shedding Merino do these receptors appear to be sensitive to regulation by estrogens. Neither breed showed sensitivity of its pineal beta-adrenoceptors to active immunization against the pineal hormone melatonin under either normal or reversed photoperiod treatment. These results (a) suggest that pineal related seasonal differences between the breeds (i.e. wool shedding and/or reproductive function) may reside in differential sensitivity of the pineal gland to regulation by specific circulating steroid hormones, and (b) indicate an absence of end-product regulation of beta-adrenoceptor-mediated pineal melatonin biosynthesis in both seasonally shedding and non-shedding sheep.

Androgens↗
PubMed1984

Sheep pineal beta-adrenoceptor function--interaction with gamma-aminobutyric acid.

To clarify the role and site of action of gamma-aminobutyric acid (GABA) in ovine pineal glands, we have investigated the effects of aminooxyacetic acid (AOAA), an inhibitor of GABA transaminase, on endogenous GABA content and beta-adrenoceptor mediated pineal function in Merino sheep. A significant elevation of endogenous GABA levels was noted in the glands, but no effect was observed on radioligand binding in vitro to pineal beta-adrenoceptors following in vivo administration of AOAA. Incubation of washed pineal membranes with GABA or AOAA had no effect on ligand binding to beta-adrenoceptors. Incubation of Merino pineal slices with GABA inhibited isoprenaline-stimulated but not basal serotonin N-acetyltransferase (NAT) activity. Incubation of whole pineal homogenates with GABA was without effect on either isoprenaline-stimulated or basal adenyl cyclase activity. Thus, Merino pineal glands resemble bovine pineals in that beta-adrenoceptor mediated melatonin biosynthesis in both species may be regulated in part by GABA. Our results indicate that GABA may exert its effect on Merino pineal NAT activity at a locus distal to the site of action of adenyl cyclase; however, the detailed mechanism and physiological role of this regulation remain to be elucidated.

Acetyltransferases↗
PubMed1983

Modification of sheep pineal beta-adrenoceptors by some gonadal steroids but not by melatonin.

The effects of active immunization against a range of gonadal steroids on pineal beta-adrenoceptors were studied in cycling Merino ewes. In selected cases, the effects of exogenous steroids were also investigated. Immunization against progesterone had no detectable effect on pineal beta-adrenoceptor density or ligand binding affinity. Immunization against estrone or 17 beta-estradiol significantly increased binding affinity and decreased beta-receptor density. Testosterone immunization in ewes caused similar effects but to a lesser degree. In contrast, immunization against androstenedione resulted in a decreased affinity and an increase in receptor density in ewes. In subsequent experiments, some parameters of pineal function in intact cycling and ovariectomized ewes were compared; a significant decrease in beta-receptor density and an increase in binding affinity were noted in the ovariectomized animals. Androstenedione-releasing implants decreased beta-receptor density and increased beta-receptor affinity in pineals from intact ewes, but these implants had no effect on pineal parameters in ovariectomized ewes. Immunization of ewes against 17 beta-estradiol had no significant effects on basal or isoprenaline-stimulated N-acetyltransferase or adenyl cyclase activities. Immunization of ewes against melatonin, or in vitro incubation of pineal glands with the hormone had no effects on the pineal parameters studied. It is concluded that estrogens affect the pinealocyte beta-receptors in ewes, while specific androgens may act indirectly on these receptors to modify their interaction with estrogens.

Androstenedione↗
PubMed1982

The role of adrenergic mechanisms in thermoregulatory control of blood flow through capillaries and arteriovenous anastomoses in the sheep hind limb.

The possible role of adrenergic mechanisms in thermoregulatory changes in the partition of femoral blood flow between nutrient (capillary) and non-nutrient (arteriovenous anastomoses, AVA) circuits in the hind limb of conscious sheep has been investigated employing radioactive microsphere and electromagnetic blood flow measurement techniques. Constriction of AVAs, normally induced by spinal cooling, could be inhibited by phentolamine, whereas dilatation of AVAs, normally induced by spinal heating, could be inhibited by noradrenaline or methoxamine. AVA constriction could be induced by noradrenaline or methoxamine, or dilatation by phentolamine. Isoprenaline had a small dilator and propranolol a small constrictor effect on AVAs. It is concluded that adrenergic pathways involving predominantly alpha-receptors play a role in thermoregulatory changes in skin blood flow (through AVAs) elicited by manipulation of CNS temperature; under these conditions, beta-receptors do not play any role, although manipulation of their activity will influence AVAs under non-thermoregulatory conditions. Capillary blood flows in skin, bone and fat were sensitive, at different ambient temperatures and to varying degrees, to some alpha- and beta-adrenergic agents.

Animals↗
PubMed1982

Effects of steroids on beta-adrenergic binding sites in sheep pineal glands.

As an initial step in investigations of putative differences between central nervous system light-sensitive mechanisms in seasonally shedding and non-shedding breeds of sheep, some beta-adrenoceptor characteristics of Merino sheep pineal glands were determined, using [3H]dihydroalprenolol as the labelled ligand. Overall, a dissociation constant of 17.2 +/- 2.6 nmoles/l and a daytime beta-receptor density of 1.6 +/- 0.3 pmoles/mg were determined at 37 degrees. The binding sites exhibited stereospecificity, saturability and apparent homogeneity. 17 beta-Estradiol and progesterone implants that provided hormone concentrations in the physiological range had no significant effect on pineal beta-receptors in male sheep castrated shortly after birth. Dexamethasone injections, on the other hand, in doses sufficient to loosen the attachment of wool fibres to the skin, resulted in decreased pineal beta-receptor density and increased receptor affinity for dihydroalprenolol. This effect was apparently not mediated by altered plasma catecholamine concentrations, since the glucocorticoid treatment did not affect jugular venous noradrenaline, adrenaline or dopamine levels. The possible involvement of glucocorticoids in the regulation of wool growth could thus have a central neuronal component, medicated via action on pineal beta-adrenoceptors in sheep; however, the existence of the putative gonadal steroid feedback on beta-adrenoceptor-mediated pineal function remains to be demonstrated in this species.

Animals↗