Biomedical subjects

G B Martin

Publications and source records attributed to G B Martin.

At least 91 records · Page 5Linked to original sources

PubMed1997

Alleles of Pto and Fen occur in bacterial speck-susceptible and fenthion-insensitive tomato cultivars and encode active protein kinases.

The Pto gene was derived originally from the wild tomato species Lycopersicon pimpinellifolium and confers resistance to Pseudomonas syringae pv tomato strains expressing the avirulence gene avrPto. The Fen gene is also derived from L. pimpinellifolium and confers sensitivity to the insecticide fenthion. We have now isolated and characterized the alleles of Pto and Fen from cultivated tomato, L. esculentum, and designated them pto and fen. High conservation of genome organization between the two tomato species allowed us to identify the pto and fen alleles from among the cluster of closely related Pto gene family members. The pto and fen alleles are transcribed and have uninterrupted open reading frames that code for predicted proteins that are 87 and 98% identical to the Pto and Fen protein kinases, respectively. In vitro autophosphorylation assays revealed that both the pto and fen alleles encode active kinases. In addition, the pto kinase phosphorylates a previously characterized substrate of Pto, the Pto-interacting Pti1 serine/threonine kinase. However, the pto kinase shows impaired interaction with Pti1 and with several previously isolated Pto-interacting proteins in the yeast two-hybrid system. The observation that pto and fen are active kinases and yet do not confer bacterial speck resistance or fenthion sensitivity suggests that the amino acid substitutions distinguishing them from Pto and Fen may interfere with recognition of the corresponding signal molecule or with protein-protein interactions involved in the Pto- and Fen-mediated signal transduction pathways.

Alleles↗

PubMed1997

Vasopressin can increase coronary perfusion pressure during human cardiopulmonary resuscitation.

OBJECTIVES: To determine the hemodynamic effect of vasopressin on coronary perfusion pressure (CPP) in prolonged human cardiac arrest. METHODS: A prospective, open-label clinical trial of vasopressin during cardiac resuscitation was performed. Ten patients presenting in cardiac arrest initially received resuscitative measures by emergency physicians according to Advanced Cardiac Life Support (ACLS) guidelines. A central venous catheter for fluid and drug administration and a femoral artery catheter for measurement of CPP (aortic minus right atrial relaxation phase pressures) were placed. When each patient was deemed nonsalvageable, 1.0 mg epinephrine was given and CPP was measured for 5 minutes, followed by a dose of vasopressin (1.0 U/kg). CPP measurements were continued for another 5 minutes. RESULTS: The mean duration of cardiac arrest (out-of-hospital interval plus duration of ED ACLS) was 39.6 +/- 16.5 min. There was no improvement in CPP after 1.0 mg of epinephrine. Vasopressin administration resulted in a significant increase of CPP in 4 of the 10 patients. Patients responding to vasopressin had a mean increase in CPP of 28.2 +/- 16.4 mm Hg (range: 10-51.5), with these peak increases occurring at 15 seconds to 4 minutes after administration. The increases in the vasopressin levels after administration did not differ between the responders and nonresponders. CONCLUSIONS: In this human model of prolonged cardiac arrest, 40% of the patients receiving vasopressin had a significant increase in CPP. This pilot study suggests that investigation of earlier use of vasopressin as a therapeutic alternative in the treatment of cardiac arrest is warranted.

Adult↗

PubMed1997

Effects of nutrition on testicular growth in mature Merino rams actively immunized against GnRH.

Nutrition-induced changes in testicular size in Merino rams appear to involve both GnRH-dependent and -independent pathways. This hypothesis was tested by feeding mature Merino rams that had been actively immunized against BSA or GnRH conjugated to BSA a diet that maintained initial body weight or the same diet supplemented daily with 1.5 kg of lupin grain. Blood was sampled every 20 min for 24 h on days-1, 19 and 70 relative to the change in diet. The plasma was used to assess the effects of treatments on changes in LH, FSH and testosterone concentrations. In the group immunized against BSA, FSH increased in lupin-supplemented rams compared with maintenance-fed rams, while LH and testosterone were not affected by diet. In comparison, the concentrations of LH, FSH and testosterone were significantly lower in the group immunized against GnRH than in rams immunized against BSA, but none of these endocrine variables was affected by nutrition. With both immunization treatments, the testes were significantly larger in lupin-supplemented than in maintenance-fed rams. In the group immunized against BSA, this difference was caused by testicular growth in lupin-supplemented rams, whereas in the group immunized against GnRH, lupin supplementation effectively maintained testicular mass, rather than allowed the regression observed in maintenance-fed rams. In conclusion, differences in testicular growth that were induced by dietary treatments in rams immunized against GnRH were not associated with changes in gonadotrophin or testosterone secretion. This supports the hypothesis that part of the effect of nutrition on testicular growth is independent of changes in GnRH secretion. The differences in testicular size observed in control rams were of similar magnitude to those observed in treated rams, but associated with large differences in plasma FSH concentrations, suggesting that this hormone plays an important role in this effect.

Animal Nutritional Physiological Phenomena↗

PubMed1997

Stimulation of LH secretion in sheep by central administration of corticotrophin-releasing hormone.

Corticotrophin-releasing hormone (CRH) has been proposed as a mediator of the antireproductive effects of stress through an action within the hypothalamus to inhibit GnRH secretion. This hypothesis was tested in sheep by studying the responses to central administration of CRH in both sexes and in both seasons. Sexually mature, Ile-de-France ewes and Romanov rams that had been gonadectomized and implanted with a permanent guide cannula into the third cerebral ventricle were used. Ewes were studied in the presence and absence of exogenous oestradiol plus progesterone, in both the breeding and anoestrous seasons. All rams were treated with testosterone and were studied only during the breeding season. Each observation involved serial samples (every 10 min) of jugular blood for 5 h before (control) and 5 h after an intracerebroventricular (i.c.v.) injection of either saline (vehicle) or 5 nmoles CRH in 20 microliters vehicle. The saline injections did not affect any of the endocrine variables measured; however, CRH always increased cortisol concentrations in jugular plasma. In the absence of treatment with replacement sex steroids, icv injection of CRH had no effect on pulsatile LH secretion in females either during the breeding season or during anoestrus. However, LH pulse frequency and mean LH concentrations increased significantly on every occasion on which animals were treated with sex steroids. Treatment with CRH also increased LH secretion in the testosterone-treated rams. It is concluded that, contrary to the hypothesized role of CRH as an inhibitor of reproductive activity, this neuropeptide stimulates pulsatile LH (and thus GnRH) secretion, at least in this species. The fact that gonadal steroids seem to be obligatory for the expression of this effect suggests that the protocols used in past studies need to be reassessed.

Animals↗

PubMed1997

Signal recognition and transduction involved in plant disease resistance.

Gene-for-gene relationships, in which plant disease resistance involves a single resistance (R) gene in the plant which responds specifically to a single avirulence (avr) gene in the pathogen, have been described in numerous plant-pathogen interactions. R genes encode proteins that appear to be involved in both recognition of the pathogen and in signal transduction. Physical interaction of R gene products and Avr proteins provides an explanation for the molecular basis of some gene-for-gene interactions. Multiple signalling pathways lie downstream of R gene products and lead to the hypersensitive response and activation of specific defence-related genes. Plants use diverse mechanisms to defend themselves from pathogens including the generation of active oxygen species, cell wall strengthening, production of defence-related proteins and localized cell death.

Genes, Plant↗

PubMed1996

Effect of nutrition on the balance of production of ovarian and pituitary hormones in ewes.

Nutrition-induced changes in liveweight can induce changes in ovarian function and ovulation rate. This study was designed to test the hypothesis that heavy ewes are able to maintain similar concentrations of follicle-stimulating hormone (FSH) to light ewes through a loss of responsiveness to ovarian negative feedback. This hypothesis leads to the prediction that administration of ovarian hormones on the basis of metabolic body weight would result in the same gonadotrophin (FSH) concentrations in-light and heavy ovariectomised ewes. We therefore examined the ovarian content of oestradiol and inhibin, and the FSH response to administration of these ovarian hormones in acutely ovariectomised heavy and light Merino ewes produced by differential feeding. At ovariectomy, follicular fluid was aspirated from the 6 largest follicles in each ewe and assayed for oestradiol and inhibin. Six days later, blood was sampled every 6 h for 2 days. Ewes were then given two subcutaneous progesterone implants and injected subcutaneously every 6 h for 5 days with oestradiol (37.4 ng kg-0.75) and charcoal-stripped bovine follicular fluid (0.04 ml kg-0.75). Blood was sampled before each injection and the plasma was assayed for FSH and inhibin. Oestradiol and its receptors were assayed in uterine tissue. Nutrition-induced increases in liveweight led to increases in the number of oestrogenic, potentially ovulatory ovarian follicles and the total ovarian content of oestradiol and inhibin. In the uterus, more oestradiol receptors and a higher oestradiol uptake were observed in light than in heavy ewes. After ovariectomy, FSH concentrations were inversely related to liveweight. However, when the ewes were treated with doses of ovarian hormones that were proportional to liveweight, the slope of the decline in FSH concentrations was independent of liveweight. We conclude that nutrition alters the balance between pituitary FSH secretion and gonadal feedback by changing the responsiveness to the inhibitory effects of oestradiol and inhibin.

Animal Nutritional Physiological Phenomena↗

PubMed1996

The Pto kinase mediates a signaling pathway leading to the oxidative burst in tomato.

The Pto gene encodes a serine/threonine kinase that confers resistance in tomato to Pseudomonas syringae pv. tomato strains that express the avirulence gene avrPto. Partial characterization of the Pto signal transduction pathway and the availability of transgenic tomato lines (+/- Pto) make this an ideal system for exploring the molecular basis of disease resistance. In this paper, we test two transgenic tomato cell suspension cultures (+/-Pto) for production of H2O2 following independent challenge with two strains of P. syringae pv. tomato (+/-avrPto). Only when Pto and avrPto are present in the corresponding organisms are two distinct phases of the oxidative burst seen, a rapid first burst followed by a slower and more prolonged second burst. In the remaining three plant-pathogen interactions, we observe either no burst or only a first burst, indicating that the second burst is correlated with disease resistance. Further support for this observation comes from the finding that both resistant and susceptible tomato lines produce the critical second oxidative burst when challenged with P. syringae pv. tabaci, a nonhost pathogen that elicits a hypersensitive response on both tomato lines. The Pto kinase is not required, however, for the oxidative burst initiated by non-specific elicitors such as oligogalacturonides or osmotic stress. A model describing a possible role for the Pto kinase in the overall scheme of oxidative burst signaling is proposed.

Journal Article↗

PubMed1996

Interactions between nutrition, testosterone and inhibin in the control of gonadotrophin secretion in mature rams.

The role of negative feedback by two testicular hormones, testosterone and inhibin, in the gonadotrophin responses of mature male sheep to changes in nutrition was tested. Six days after castration, 24 Merino rams were assigned to groups that were fed either a diet that maintained their initial liveweight (Intermediate diet), or about half of the Intermediate diet (Low diet), or the Intermediate diet with a supplement of lupin grain (High diet). One week after the change of diet, all animals were given subcutaneous testosterone implants, providing plasma testosterone concentrations of 3.06 +/- 0.14 ng mL-1 (mean +/- s.e.m.; n = 24). The implants were left in place for 7 days, during which time all the rams were also injected subcutaneously with 2 mL steroid-free bovine follicular fluid (bFF) every 8 h, to provide inhibin at mean plasma concentrations of 0.40 +/- 0.04 ng mL-1 (n = 24; compared with 1.50 +/- 0.12 ng mL-1 when the animals were intact). Five days after castration, there were significant increases in the frequency of luteinizing hormone (LH) pulses (from 1.83 +/- 0.23 to 17.3 +/- 0.96 pulses per 12 h; mean +/- s.e.m.; n = 24) and concentrations of FSH (from 0.45 +/- 0.07 to 14.19 +/- 2.7 ng mL-1; n = 24). Dietary treatment did not significantly affect these responses. Treatment with bFF and testosterone for 7 days reduced LH-pulse frequencies and follicle-stimulating hormone (FSH) concentrations in all groups. The degree of reduction was least in the group on the High diet, for which the FSH concentration (6.49 +/- 1.96 ng mL-1) and frequency of LH pulses (7.00 +/- 2.31 pulses per 24 h) were significantly higher than those observed in the other groups. The mean frequency of LH pulses did not differ significantly between the Intermediate group (0.88 +/- 0.61 pulses per 24 h) and the Low group (0.25 +/- 0.25 pulses per 24 h). Similarly, FSH concentrations did not differ significantly between these two groups (1.78 +/- 0.46 for the Intermediate group v. 1.33 +/- 0.26 ng mL-1 for the Low group). It is concluded that there is no response to diet in the absence of testicular hormones and the effects of nutrition on LH secretion in castrated rams given exogenous testosterone and inhibin are similar to those observed in intact rams.

Animal Nutritional Physiological Phenomena↗

PubMed1995

The tomato gene Pti1 encodes a serine/threonine kinase that is phosphorylated by Pto and is involved in the hypersensitive response.

The Pto gene encodes a serine/threonine kinase that confers resistance to bacterial speck disease in tomato. Using the yeast two-hybrid system, we identified a second serine/threonine kinase, Pto-interacting 1 (Pti1), that physically interacts with Pto. Cross-phosphorylation assays revealed that Pto specifically phosphorylates Pti1 and that Pti1 does not phosphorylate Pto. Fen, another serine/threonine kinase from tomato that is closely related to Pto, was unable to phosphorylate Pti1 and was not phosphorylated by Pti1. Expression of a Pti1 transgene in tobacco plants enhanced the hypersensitive response to a P. syringae pv. tabaci strain carrying the avirulence gene avrPto. These findings indicate that Pti1 is involved in a Pto-mediated signaling pathway, probably by acting as a component downstream of Pto in a phosphorylation cascade.

Amino Acid Sequence↗

PubMed1995

Molecular genetic analysis of the ripening-inhibitor and non-ripening loci of tomato: a first step in genetic map-based cloning of fruit ripening genes.

Ripening represents a complex developmental process unique to plants. We are using tomato fruit ripening mutants as tools to understand the regulatory components that control and coordinate the physiological and biochemical changes which collectively confer the ripe phenotype. We have genetically characterized two loci which result in significant inhibition of the ripening process in tomato, ripening-inhibitor (rin), and non-ripening (nor), as a first step toward isolating genes likely to encode key regulators of this developmental process. A combination of pooled-sample mapping as well as classical restriction fragment length polymorphism (RFLP) analysis has permitted the construction of high-density genetic maps for the regions of chromosomes 5 and 10 spanning the rin and nor loci, respectively. To assess the feasibility of initiating a chromosome walk, physical mapping of high molecular weight genomic DNA has been employed to estimate the relationship between physical distance (in kb) and genetic distance (in cM) around the targeted loci. Based on this analysis, the relationship in the region spanning the rin locus is estimated to be 200-300 kb/cM, while the nor locus region ratio is approximately 200 kb/1 cM. Using RFLP markers tightly linked to rin and nor, chromosome walks have been initiated to both loci in a yeast artificial chromosome (YAC) library of tomato genomic DNA. We have isolated and characterized several YAC clones linked to each of the targeted ripening loci and present genetic evidence that at least one YAC clone contains the nor locus.

Base Sequence↗

PubMed1995

The disease-resistance gene Pto and the fenthion-sensitivity gene fen encode closely related functional protein kinases.

Resistance to bacterial speck in tomato is governed by a gene-for-gene interaction in which a single resistance locus (Pto) in the plant responds to the expression of a specific avirulence gene (avrPto) in the pathogen. Disease susceptibility results if either Pto or avrPto are lacking from the corresponding organisms. Leaves of tomato cultivars that contain the Pto locus also exhibit a hypersensitive-like response upon exposure to an organophosphorous insecticide, fenthion. Recently, the Pto gene was isolated by a map-based cloning approach and was shown to be a member of a clustered multigene family with similarity to various protein-serine/threonine kinases. Another member of this family, termed Fen, was found to confer sensitivity to fenthion. The Pto protein shares 80% identity (87% similarity) with Fen. Here, Pto and Fen are shown to be functional protein kinases that probably participate in the same signal transduction pathway.

Amino Acid Sequence↗

PubMed1995

Chromosome landing: a paradigm for map-based gene cloning in plants with large genomes.

The original concept behind map-based or positional cloning was to find a DNA marker linked to a gene of interest, and then to 'walk' to the gene via overlapping clones (e.g. cosmids or YACs). While chromosome walking is straightforward in organisms with small genomes, it is difficult to apply in most plant species, which typically have large, complex genomes. The strategy of chromosome walking is based on the assumption that it is difficult and time consuming to find DNA markers that are physically close to a gene of interest. Recent technological developments invalidate this assumption for many species. As a result, the mapping paradigm has now changed such that one first isolates one or more DNA marker(s) at a physical distance from the targeted gene that is less than the average insert size of the genomic library being used for clone isolation. The DNA marker is then used to screen the library and isolate (or 'land' on) the clone containing the gene, without any need for chromosome walking and its associated problems. Chromosome landing, together with the technology that has made it possible, is likely to become the main strategy by which map-based cloning is applied to isolate both major genes and genes underlying quantitative traits in plant species.

Chromosome Mapping↗

PubMed1995

Relationship between testicular morphology and sperm production following ischaemia in the ram.

Arteriosclerosis was induced in the internal spermatic artery of rams to determine if this condition is implicated in the aetiology of testicular pathology which causes male infertility. Data were collected on sperm concentration and motility for 56 days following surgery to provide an index of testicular function. Testes were then weighed and a testicular biopsy score count was performed on histological sections to assess spermatogenic potential of seminiferous tubules. Vascular disturbance caused focal damage of the seminiferous epithelium, similar to that seen among infertile men, and a reduction in ejaculate volume, sperm concentration and sperm motility. Sperm concentration decreased following ischaemia yet was maintained to some degree by a germ-cell depleted spermatogenic epithelium. Normal testicular morphology was maintained above a testis weight of about 120 g (for an individual testis), but below this threshold spermatogenesis was severely impaired. In conclusion, these data have provided information on the relationship between testicular morphology and function following ischaemia in the ram. Furthermore, the morphological changes induced in the testis were similar to those seen among infertile men and, by their focal nature, could explain the distinction between oligozoospermia and azoospermia in men exhibiting spermatogenic arrest.

Animals↗

PubMed1995

Reproductive research on farm animals for Australia--some long-distance goals.

In Australia, much of the research on the reproduction of farm animals has emphasised the technological manipulation of the reproductive tract, gametes and embryos. However, most of the animal production in Australia is still based on sheep and beef cattle enterprises that are managed on an extensive scale; the managers need technologies that can be easily and cheaply implemented on a large scale, and that are aimed at extensive control rather than intensive manipulation. For example, for synchronizing oestrus in the wool flocks the "ram effect' has, and probably always will have, far more impact on extensive grazing systems than technologies based on exogenous prostaglandins or progestagens. This can also apply to the newer animal industries (such as emu farming), to human problems (such as population control), and to environmental problems (such as control of feral animals). Moreover, under the pressure of public opinion, the industries that are currently intensive are going 'free range'. In addition, surgical managerial tools (such as castration) will probably have to be abandoned or replaced. To cope with such profound influences, new types of reproductive management systems will be needed. This paper is an attempt to broaden our research horizons by developing the concept of 'control systems technologies', aimed at controlling reproductive performance rather than simply improving it. Ideas for such technologies already exist and are evident in the responses to environmental factors that our farm animals developed under the pressure of natural selection (before domestication). Stress, nutrition, photoperiod, lactation, and socio-sexual cues (e.g. pheromones) can all exert profound effects on reproductive activity. We already have a good grasp of the final common pathway through which the brain responses to these factors affect gonadal activity, namely the hypothalamic system that generates pulses of gonadotrophin-releasing hormone. All we need to do is learn how the major environmental cues exert their impact on the systems that control the final common pathway. When we understand them, we shall be able to manipulate them. This is not too speculative; we already have several technologies that take advantage of this approach, including steroid-based contraceptives, the "ram effect', a vaccine-based antifertility treatment for rangeland cattle and the melatonin formulation used to control seasonal breeding in sheep. These and the other pathways linking environmental inputs to reproductive output are waiting to be explored, explained and exploited.

Animals↗

PubMed1995

A technique revisited: hemodynamic comparison of closed- and open-chest cardiac massage during human cardiopulmonary resuscitation.

OBJECTIVE: To compare the hemodynamics of closed-chest cardiac massage vs. open-chest cardiac massage in patients resuscitated from cardiac arrest that occurred outside of the hospital. DESIGN: Prospective, non-outcome, case series. SETTING: Large urban emergency department. PATIENTS: Ten adult, normothermic, nontraumatic, out-of-hospital, cardiac arrest patients who failed advanced cardiac life support (ACLS) therapy. INTERVENTIONS: Patients presenting to the hospital in cardiac arrest were managed according to the ACLS protocol at the clinician's discretion. Proximal aortic and central venous pressure catheters were placed to measure arteriovenous compression- and relaxation-phase pressure gradients. After 5 mins of baseline measurements during closed-chest cardiac massage, patients underwent a left lateral thoracotomy, and open-chest cardiac massage was performed for 5 mins. MEASUREMENTS AND MAIN RESULTS: The mean coronary perfusion pressure and compression-phase pressure gradients were 7.3 +/- 5.7 and 6.2 +/- 5.4 mm Hg, respectively, during closed-chest cardiac massage, while increasing to 32.6 +/- 17.8 and 32.6 +/- 29.9 mm Hg, respectively, during open-chest cardiac massage. The differences between both measurements were statistically significant (p < .05). CONCLUSIONS: Open-chest cardiac massage is superior to closed-chest cardiac massage in providing relaxation-phase and compression-phase pressure gradients during cardiac arrest in patients failing current ACLS protocols. During open-chest cardiac massage, all patients exceeded the minimum coronary perfusion pressure of 15 mm Hg, which is recommended to obtain a return of spontaneous circulation. Further outcome studies are needed to determine the timeliness and appropriate indications for open-chest cardiac massage.

Aged↗

PubMed1995

The Pto bacterial resistance gene and the Fen insecticide sensitivity gene encode functional protein kinases with serine/threonine specificity.

The catalytic activity and amino acid specificity of the tomato Pto and Fen kinases were investigated. The Pto and Fen genes were fused to the carboxyl terminus of the maltose-binding protein and expressed in Escherichia coli. Incubation of the purified fusion proteins with [gamma-32P]ATP in an in vitro assay showed that both proteins were capable of autophosphorylation. Mutant fusion proteins in which the conserved lysine residue of subdomain II was changed to a glutamine were unable to autophosphorylate. Phosphoamino analysis of the active fusion proteins indicated that both kinases phosphorylate serine and threonine residues but not tyrosine.

Amino Acid Sequence↗

PubMed1995

The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency.

In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, non-breeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean +/- S.E.M.) 33.6 +/- 0.5 cm, body weight (mean +/- S.E.M.) 59.0 +/- 0.9 kg) were fed 900 g chaff + 1.6 kg lupin grain (High diet) or 360 g chaff + 60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n = 5/group). Blood was sampled every 20 min for 12 h on days-1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P < 0.001). In GnRH-infused rams, gonadotrophin secretion was not affected by diet and the patterns of secretion of LH and FSH were similar to those in saline-infused rams fed the High diet. This model was used for a more complete endocrine analysis in a longer experiment designed to test the hypothesis that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. The same treatments were imposed for 35 days on a different group of similar rams in March (autumn, mid-breeding season). Body weight and scrotal circumference were measured weekly and blood was sampled on days -1 and 14. On days -1 and 35, testosterone secretion in response to LH was tested by injecting exogenous ovine LH (NIADDK-oLH-25; 200 ng/kg body weight) to all rams. Body weight increased in rams fed the High diet and decreased in those fed the Low diet (P < 0.001) and was not affected by treatments as in experiment 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Animal Nutritional Physiological Phenomena↗

PubMed1995

The role of intracerebral insulin in the effect of nutrition on gonadotrophin secretion in mature male sheep.

The effect of nutrition on gonadotrophin secretion may be exerted through a central metabolic signal that reflects nutritional status. We have previously found that glucose and insulin concentrations are elevated in the cerebrospinal fluid (CSF) of rams in which the secretion of gonadotrophins has been stimulated by a nutritional supplement of lupin grain (Lupinus angustifolius). In the present study, we tested the hypothesis that insulin and/or glucose is a metabolic modulator of GnRH secretion and mediates the effects of nutrition on gonadotrophin secretion. Six mature rams were fed a diet that maintained live weight and then given a series of infusions, each for 12 h/day for 4 days, in a cross-over design. The treatments were: artificial CSF (aCSF), glucose (50 mumol/h) in aCSF, insulin (0.6 ng/h) in aCSF, and glucose (50 mumol/h) plus insulin (0.6 ng/h) in aCSF; all infused at a rate of 5 microliters/min. At the same time as the infusion treatments, two other groups of four rams without cerebral cannulae were fed either the maintenance diet or the same diet supplemented with 750 g lupin grain per head per day for 4 days, again in a cross-over design. Rams fed the lupin supplement showed an increase in both LH pulse frequency and mean FSH on day 4 (P < 0.05). Infusion of aCSF or glucose did not affect gonadotrophin secretion. Rams infused with insulin or insulin plus glucose showed an increase (P < 0.05) in LH pulse frequency but no increase in FSH concentrations on day 4 of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗