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At least 19 recordsLinked to original sources
PubMed1979

Formation of the sleep-regulating mechanisms in vertebrates.

The paper presents new data concerning the mechanisms of regulation of sleep-like states in vertebrates. Somato-vegetative and behavioral correlates of primary sleep (fish, amphibians), intermediate sleep (reptiles), slow-wave and paradoxical sleep (birds) are described. The evolutionary more ancient hypothalamo-cortical and young thalamo-cortical levels of regulation of different forms of sleep are examined. Problems of existence of functional analogues of homoiotherms' sleep are discussed.

Amphibians↗
PubMed1977

[Hormonal regulation mechanisms during puerperium].

The regulation of the hypothalamic-hypophyseal-ovarian axis during puerperium is reviewed. The lactotrophic hormone prolactin is necessary for the growth of the milk producing system, initiation and maintenance of lactation. Inappropriate responsiveness of the hypothalamic-hypophyseal-ovarian system causes independent of the actual prolactin serum values postpartum amenorrhea during early puerperium. However, the duration of amenorrhea depends on the duration of breast-feeding. The prolactin peaks induced by suckling interfere with the reappearance of normal cyclic ovarian regulation.

Adult↗
PubMed1992

A novel transcriptional regulation mechanism in the flagellar regulon of Salmonella typhimurium: an antisigma factor inhibits the activity of the flagellum-specific sigma factor, sigma F.

We have studied the molecular mechanism of the negative regulation by flgM of the late operons of the flagellar regulon of Salmonella typhimurium. A 7.8 kDa protein that was identified as the flgM gene product was purified to homogeneity; its amino-terminal sequence was identical to the deduced sequence except for the lack of the initiating methionine. The purified FlgM repressed transcription from the fliC promoter, one that is activated by the sigma factor, FliA (sigma F). No DNA-binding activity was detected in FlgM. Chemical cross-linking experiments showed that the purified FlgM bound to sigma F and disturbed its ability to form a complex with RNA polymerase core enzyme. These results indicate that FlgM is a novel type of negative regulator that probably inactivates the flagellum-specific sigma factor through direct interaction, i.e. it is an anti-sigma factor.

Amino Acid Sequence↗
PubMed1976

Immunoglobulin allotypes of rabbit kappa chains: polymorphism of a control mechanism regulating closely linked duplicated genes?

The amino acid sequence of the constant (CK) region from the kappa immunoglobulin chains of a b9 rabbit is compared with the CK sequences, taken from the literature, of a b4 rabbit. These CK regions differ by 33% of their amino acid sequences and by three sequence insertions or deletions (sequence gaps). These extensive differences together with other published observations suggest that the b9 and b4 CK genes may not be simple alleles, but rather they may be encoded by closely linked CK genes present in every rabbit whose expression is regulated by a polymorphic control mechanism.

Alleles↗
PubMed1975

Inhibition of placental 3beta-hydroxy-steroid dehydrogenase by naturally occurring steroids. A potential mechanism regulating oestrogen synthesis from unconjugated precursors.

We have proposed that inhibition of placental steroid 3-sulphatase by endogenous steroids may regulate oestrogen synthesis during human pregnancy. The possibility that an additional regulatory mechanism, involving the placental 3beta-hydroxy-steroid dehydrogenase (SDH), may also be operative has now been examined. Inhibitory effects of naturally occurring steroids on SDH activity were determined from the reduction in initial rate of conversion of 3H-dehydroepiandrosterone to non-digitonin precipitable products by 10 000 x g supernatant from homogenates of human term placentae. The apparent Km for dehydroepiandrosterone was 0.33 x 10(-6) M. delta4-3-Oxo products of SDH action (4-androstene-3,17-dione, app. Ki=0.60x10(-6) M; progesterone, app. Ki=1.5x10(-6) M) were the most potent inhibitors and appeared to act non-competitively. Delta5-3beta-Hydroxy alternative substrates were less inhibitory and in the case of pregnenolone (app. Ki=4.5x10(-6) M) behaved competitively. 11beta-, 16alpha-, 17alpha- or 21-hydroxylation and epimerization of 3beta- or 17beta-hydroxyl functions of inhibitors decreased their activity. It is concluded that inhibition of both sulphatase and SDH by endogenous steroids may provide complementary methods of regulating placental oestrogen synthesis in vivo. The SDH mechanism may regulate oestrogen synthesis from unconjugated precursors, either formed within the placenta or derived from the circulation. The major potential inhibitors appear to be delta4-3-ketones, acting non-competitively, and formed within the placenta. In the sulphatase mechanism alternative substrates of extraplacenta origin, acting competitively, are the major potential inhibitors controlling utilization of conjugated precursors.

Androstanes↗
PubMedDate not supplied

[Mechanisms regulating the selective release of follicle-stimulating hormone].

Selective secretion of FSH, involving no apparent changes in LH secretion, was studied in cycling rat females in the late proestrus and early estrus stages. The preovulatory wave of LH and FSH secretion, observed in the second half of the day of proestrus was associated with elevation of the levels of nuclear estrogenic and androgenic receptors. High concentrations of both receptor types were seen during a secondary elevation of FSH secretion early in the morning in the estrus stage. Administration of phentolamine (alpha-adrenoreceptor blocker) did not influence blood levels of FSH and LH in the estrus stage early hours. Administration of a dopamine blocker haloperidol inhibited the second wave of FSH secretion, this being paralleled by a reduction of the number of estradiol nuclear receptors. The authors suggest that estrogenic and androgenic receptors of adenohypophysis and dopaminergic systems of the brain contribute to the mechanism of regulation of the second phase of FSH increased secretion observed in the early morning hours of the estrus stage, the dopamine effect on FSH release being mediated via estradiol receptors.

Animals↗
PubMed1992

Neural mechanisms regulating neurohypophysial resistance arteries.

We defined the extent of vasoactive intestinal polypeptide (VIP) and noradrenergic influences on isolated 100- to 200-microns-diameter vessels from the resistance arterial circulation of the neurohypophysis. A dual extracranial (inferior hypophysial) and intracranial (superior hypophysial) arterial supply to the neurohypophysis was confirmed. The inferior hypophysial artery demonstrates noradrenergic and VIP-like perivascular nerves, whereas the superior hypophysial artery shows primarily VIP-like innervation. Pharmacological sensitivity of the inferior hypophysial to VIP [mean effective dose (ED50) = 10(-8.2) M] and to norepinephrine (ED50 = 10(-5.7) M) was demonstrated. The superior hypophysial reacted only to VIP (ED50 = 10(-8.6) M). The physiological relevance of these findings was tested with transmural nerve stimulation. Frequency-dependent vasodilation of both inferior and superior hypophysial arteries was demonstrated. This dilation could not be blocked with atropine or propranolol. Frequency-dependent vasoconstriction was identified in extracranial vessels including the inferior hypophysial artery. This constriction is only partially blocked by prazosin, phentolamine, and guanethidine. When neurohypophysial resistance vessels are compared with larger circle of Willis arteries and similar-size pial vessels of other cerebral regions, they appear to have regionally unique neural mechanisms for regulating blood flow. Specifically whether controlled by periarterial nerves or other tissue influences, the inferior hypophysial artery appears to meet anatomic, pharmacological, and physiological definitions of neural control for both dilator and constrictor activities of flow to the neurohypophysis.

Animals↗
PubMed1975

Development of the mechanism regulating the preovulatory surge of luteinizing hormone in sheep.

Development of the mechanism controlling cyclic LH secretion in the sheep was studied by examining the ability of estradiol to elicit LH surges in lambs at various ages. Silastic capsules containing estradiol were implanted sc for a 96-hour period at 3, 7, 12, 20, and 27 weeks of age. (First spontaneous ovulation occursss between 30 and 50 weeks). Although administration of estradiol failed to elicit a discharge of LH at 3 weeks of age, LH surges of progressively increasing magnitude (36 +/- 15, 73 +/- 28, 107 +/- 19 ng/ml) were elicited by estradiol as the lambs became older (7, 12, 20 weeks). By 27 weeks, the maximal serum LH level attained during the induced surge (123 +/- 29 ng/ml) was similar to that of the estrogen-induced LH surge in anestrous adults (179 +/- 23 ng/ml). Ovulation, however, did not occur in response to the induced LH surges. An additional experiment was performed to determine whether, as in the adult, progesterone can block the estradiol-induced LH discharge in the immature (12-week old) female. A sustained elevation of circulating progesterone to levels characteristic of the mid-luteal phase of the estrous cycle of the adult (3--4 ng/ml), beginning 24 h prior to insertion of the estradiol capsules, blocked the induced LH surge. These results demonstrate that, in immature female sheep, the LH surge mechanism is capable of functioning long before first ovulation occur and, further, suggest that timing of the initial preovulatory LH surge is limited by the ability of the ovary to produce the estradiol stimulus rather than by the ability of the hypothalamo-hypophyseal system to respond to the positive feedback action of estradiol. Additionally, the hypothalamo-hypophyseal mechanism whereby progesterone blocks the LH surge develops long before first ovulation.

Aging↗
PubMed1991

[The functional tasks of the activity of the mechanism regulating the cerebral circulation].

Modern experimental and clinical data suggest that physiological mechanism, responsible for maintaining adequate brain blood supply under different conditions has a complex functional task, which besides sufficient metabolic transport to brain tissue, consists in supporting of water balance of brain tissue and evacuation of wastes. These functions realize by synergistic acting of several control links--neurogenic, metabolic, myogenic and humoral, every one of them has its own channel of input information and feedback. Physiological reactions of cerebrovascular system to adequate sensory activation have a task, first of all, to support of metabolic supply of nerve tissue. Therefore, after the beginning of sensory activation, oxygen availability in brain tissue is significantly increase, but at the same time some changes of hydratation nerve tissue is taking place. The last is possible to observe by analysis of changes in amplitude and configuration of electrical impedance pulsations, recording from brain implanted electrodes. These changes of hydratation of nerve tissue is observing during short time period and then is compensating. During during neuronal activation the concentration of wastes in brain tissue is slightly increase, which reflects in changes of brain tissue pH and pCO2. However, in situations, closed to extreme ones, a some hierarchic relationships between particular functional tasks of cerebrovascular control mechanism are observed. (1) Under arterial hypertension, when it is impossible to maintain at the same time both metabolic supply of brain tissue and to support water balance of nerve tissue, experimental and clinical data indicates, that the leader place take processes, responsible for the hydration of nerve tissue. So, the same decrease of cerebral blood flow during arterial hypertension indicates, that the action of control mechanism of cerebral circulatory system directed to minimization of a risk of developing of brain edema. (2) In cases of arterial hypotension, which accompanying by chronic cerebral circulatory insufficiency, the main functional task of cerebrovascular control mechanism becomes to direct to evacuation of wastes, because they are slowly collecting in brain tissue, although the metabolic supply of brain tissue is often in sufficient limits. In such conditions vasodilator drugs with a short time period of action (30-40 min.) have a comparative long (3-5 hours) positive effect for patients. During time period of increased brain blood flow, washing out of brain tissue from wastes is taking place. Generally, the first of mentioned processes is forming the left and the second--right parts of the curve, which represents the autoregulator phenomenon.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Mechanisms regulating renal sodium excretion during development.

The present review focuses on the ontogeny of mechanisms involved in renal sodium excretion during renal maturation. The effect of birth on renal excretion of sodium and the role played by the different tubular segments in the regulation of sodium excretion during maturation are discussed. The influence of circulating catecholamines and renal sympathetic innervation in regulating sodium excretion during renal development is reviewed. The effects of aldosterone, atrial natriuretic factor, and prostaglandins on sodium regulation during renal maturation are discussed. Special emphasis is given to the potential role of glucocorticoids in modulating sodium excretion early in life.

Aldosterone↗
PubMed1976

[Mechanisms regulating citric acid metabolism in the brain].

The changes in the rates of citrate biosynthesis and utilization in rat brain, liver, kidney and heart, produced by hypoxia, action of 2,4-DNP and thyreotoxicosis, were compared with changes of some regulatory parameters under the same conditions. The comparison of citrate-synthase activities, citrate levels in tissues and 14C-incorporation from different precursors into citric acid permitted us to establish that the biosynthesis of citrate in brain was more intensive than in other tissues studied. The main source of acetyl-CoA for citrate-synthase reaction in brain is the oxidation of pyruvate. The ratio of adenine nucleotides plays an important role in the control of citrate-synthase activity in brain, where the oxaloacetate control is not as significant as in liver. NAD-specific isocitrate dehydrogenase reaction was found to be the dominant pathway for citrate oxidation in brain: more than 60 percent of brain citrate were oxidized by NAD-ICDH, while less than 10 percent of citric acid were utilized by this enzyme in other tissues studied. The existance of an adenine nucleotide control of NAD-ICDH activity in brain may be an additional mechanism for the regulation of the first steps of energy metabolism in brain.

Acetyl Coenzyme A↗
PubMed1992

Studies of a proposed mechanism regulating parietal cell emptying.

We have proposed and provided experimental evidence for the existence of a mechanism controlling the output of hydrochloric acid from the parietal cells. On stimulation of the cells, histamine not only activates the H+/K-pump but also prevents acid from leaving the cell. The delay may be caused by cAMP activation. When the appropriate conditions have been obtained, the acid leaves the cell and enters the gastric lumen. A delay in onset of acid secretion is convenient from several points of view. For example, salivary amylase, which is responsible for approximately 50% of the carbohydrate digestion, will have time to exert its digesting effect in the stomach before the pH decreases and the enzyme becomes inactivated. Also, bicarbonate secretion will be started before high concentrations of acid have been obtained in the stomach and thereby contributes to protection of gastric mucosa.

Aminopyrine↗
PubMed2024

Cytoskeletal mechanisms regulating attaching/effacing bacteria interactions with host cells: It takes a village to build the pedestal.

The actin cytoskeleton is a key cellular structure subverted by pathogens to infect and survive in or on host cells. Several pathogenic strains of Escherichia coli, such as enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC), developed a unique mechanism to remodel the actin cytoskeleton that involves the assembly of actin filament-rich pedestals beneath the bacterial attachment sites. Actin pedestal assembly is driven by bacterial effectors injected into the host cells, and this structure is important for EPEC and EHEC colonization. While the interplay between bacterial effectors and the actin polymerization machinery of host cells is well-understood, how other mechanisms of actin filament remodelling regulate pedestal assembly and bacterial attachment are poorly investigated. This review discusses the gaps in our understanding of the complexity of the actin cytoskeletal remodelling during EPEC and EHEC infection. We describe possible roles of actin depolymerizing, crosslinking and motor proteins in pedestal dynamics, and bacterial interactions with the host cells. We also discuss the biological significance of pedestal assembly for bacterial infection.

Humans↗
PubMed1979

[The sympathetic neuron: regulation mechanisms for transmitter synthesis, transmitter release, and stimulus response (author's transl)].

A great multitude of factors acting at different sites of the afferent sympathetic nerve are capable to modify the magnitude of its stimulus-induced effects. 1) Specific receptors, located at the ganglionic synapse display inhibitory of facilitatory effects on the ganglionic transmission of the nerve impulse. 2) The rate of synthesis of the neurotransmitter noradrenalin is regulated at the level of the tyrosine hydroxylase. Transsynaptic mechanisms adapt the rate of synthesis of noradrenalin to nerve activity and transmitter release. 3) The amount of transmitter released per nerve impulse is controlled by a variety of receptors located presumably presynaptically at neuronal sites. Inhibitory and facilitatory "auto"-receptors stimulated by the released transmitter itself represent a local feed-back control. Similarly receptors for transmitters of cholinergic or serotoninergic neurons as well as autacoid hormones are involved in the local control of noradrenalin release. In addition, kinines, prostaglandins, or compounds like adenosine, some of them released from the target cells by the sympathetic stimuli or delivered by the blood stream are involved in the modulation of stimulus-evoked noradrenalin release. 4) Stimulus responses of the target cells can be modulated by similar mechanisms.

Humans↗
PubMed1978

[Relationships between central and local mechanisms regulating hemodynamics].

The quantitative analysis of hemodynamic shifts during cardiovascular responses to stimulation of central neural structures, and recording of electric activity from the sympathetic fibers elucidate different links in the complex mechanism of the hemodynamic control. Monosynaptic connections of the sino-aortic zone with some structures of the bulbar level seem to contain relevant information on the blood pressure and the gas content. Differentiated modulated influences project from the cerebellum to the bulbar level, and complex interrelationships of local metabolic and central reflex mechanisms occur during acute hypoxic hypoxia.

Animals↗
PubMed1992

The haematopoietic stem cell and its clonal progeny: mechanisms regulating the hierarchy of primitive haematopoietic cells.

Transplantation and marking studies have provided an accurate description of various aspects of developmental and proliferative behaviour of totipotent haematopoietic stem cells. In particular, the remarkable ability of different clones to contribute to all lineages in a continuous, stable and long term manner is a hallmark of stem cell behaviour. Taken together, in vivo reconstitution experiments also provide the basis for a model of stem cell regulation that incorporates stochastic and non-stochastic components. More recent approaches provide optimism that many descriptive aspects of stem cell biology will soon be supported by elucidation of molecular mechanisms.

Animals↗