Effectiveness and process evaluation in obesity and type 2 diabetes prevention programs in children: a systematic review and meta-analysis

BACKGROUND

Obesity in children is one of the most severe public health challenges of the current century and Type 2 Diabetes Mellitus (T2DM) frequency is also escalating. More so, the importance of process evaluation (PE) in complex interventions is increasingly recognized. The present review, aims to identify the effectiveness in terms of body composition parameters in a generation of articles to prevent obesity and T2DM in children. We hypothesise that those studies reporting PE applying the latest implementation guidelines suggested by the researchers would potentially show positive changes in body composition compared to those not reporting it. Additionally, we will evaluate the implementation degree of PE in those articles considering it and describe the PE subcomponents. Lastly, we aim to assess the intervention target used and its results.

METHODS

A literature review was performed in parallel by 2 independent reviewers. A final number of 41 studies were selected for inclusion criteria.

RESULTS

Meta-analysis of BMI and zBMI found non-significant effects of the proposed interventions. Sub-group analysis revealed only a significant effect in studies which performed PE. Moreover, PE was reported in 42% effective studies and 57% non-effective studies. Fidelity and satisfaction were the most implemented PE subcomponents, although there was a generally low grade of PE use (7/41). The highest proportion of effectiveness (83%) was shown in interventions of physical activity alone while the intervention most used was 3-arm target (diet, PA and BS).

CONCLUSIONS

Overall, obesity and T2DM prevention studies included in this review are not effective in terms of BMI and zBMI. Those studies performing PE reported to be effective in terms of BMI, while studies not reporting PE did not have positive results in terms of BMI and zBMI. In addition, none of the intervention studies included all PE indicators and most studies, which included PE in their interventions, did not provide full report of the PE components, according to the guidelines used for the present review. PROSPERO registration number: CRD42018093667.

Physico-Chemical and Physiological Changes during Fruit Development and Ripening of Five Loquat (Eriobotrya Japonica Lindl.) Cultivars

Physico-chemical and physiological changes during development and ripening of five loquat cultivars ( Eriobotrya japonica Lindl., cv. Algerie, Cardona, Golden, Magdall and Peluche) were determined. Fruit growth showed a sigmoid curve in all loquat cultivars. A good relationship between duration of fast growth phase and fruit size was found. In addition, a positive correlation was also established between seed number and fruit size, and between seed weight and both fruit and flesh weight. Colour changes, sugar content increase and the decrease in fruit firmness and organic acids started simultaneously when loquat fruits were in the phase of fast growth, and at about 70-80% of their final weight. These physico-chemical changes related to fruit ripening coincided with an increase in both ethylene production rate and free and total 1-aminocyclopropane-1 -carboxylic acid (ACC) content in the flesh. In addition, a small respiration peak associated with ripening was also detected. These results indicated that loquat fruits of all five studied cultivars showed a pattern of ripening in the tree that could be classified as climacteric, with relatively low ethylene production evolving at an early phase of fruit development.

Is ATP a suitable co-transmitter in carotid body arterial chemoreceptors?

A review is presented on carotid body ATP content, effects and release, receptors involved and results of their block by purinergic antagonists, and the possibility of cholinergic-purinergic co-transmission in the carotid body. Glomus cells release ACh and ATP upon physiological stimulation. Both agents and their agonists have chemo-excitatory actions and their combined effects disappear upon blocking n-ACh and P2X receptors. Both ACh and ATP also are capable of exciting the somata of chemosensory neurons of petrosal ganglia. Although a combined cholinergic-purinergic block suppresses the chemosensory activity in neurons co-cultured with glomus cells and some carotid body preparations in vitro, basal chemosensory activity and chemosensory responses to hypoxic stimuli persist in cat carotid body preparations in situ and in vitro. Therefore, ATP is an effective excitatory agent for carotid body chemosensory activity, although less potent than ACh; their joint participation may contribute to -- but does not entirely explain -- the transfer of chemoreceptor excitation from glomus cells to sensory endings in carotid body.

Effects of combined cholinergic-purinergic block upon cat carotid body chemoreceptors in vitro

Since acetylcholine (ACh) and ATP have been proposed as excitatory co-transmitters at synapses between glomus cells and sensory nerve endings of the carotid body (CB), we tested such hypothesis by studying the effects of combined cholinergic-purinergic block on the chemosensory activity recorded from cat's carotid bodies perfused and/or superfused in vitro. The preparations were bathed with Tyrode's solution, either normoxic (PO2=98.5+/-13.5 Torr) or hypoxic (PO2=31.8+/-5.2 Torr), and the frequency of chemosensory impulses (fchi) was recorded from the carotid (sinus) nerve. Dose-response curves for fchi increases evoked by intra-stream boluses of acetylcholine, nicotine and ATP were studied. A combination of mecamylamine 2 microM and suramin 50 microM, applied through the perfusate or superfusate, suppressed nicotine- and ATP-induced increases in fchi, but the basal chemosensory activity in normoxia and the chemosensory excitation elicited by hypoxic superfusion were preserved, although variably reduced in most preparations. Thus, in spite of the excitatory effects provoked by applying ACh and ATP to the perfused/superfused CB in vitro, a co-release of these substances cannot account entirely for the chemosensory excitation induced by hypoxic stimulation of the CB.

Carotid body chemosensory activity and ventilatory chemoreflexes in cats persist after combined cholinergic-purinergic block

Acetylcholine (ACh) and ATP have been proposed as excitatory co-transmitters operating at synapses between glomus cells and sensory nerve endings of the carotid body (CB). To test such hypothesis, we performed experiments on cats under pentobarbitone anesthesia and breathing spontaneously. Cholinergic and purinergic agonists and antagonists were given into one common carotid artery. Chemoreflex ventilatory changes initiated from the ipsilateral CB or chemosensory activity from the ipsilateral carotid nerve were recorded. Agonists ACh, nicotine, epibatidine, ATP, betagamma-methylene-ATP and gammaS-ATP induced transient chemoreflex enhancements of ventilation or increased chemosensory activity. When given in combination, mecamylamine and suramin suppressed both nicotine- and ATP-induced ventilatory chemoreflexes or chemosensory responses. However, neither chemoreflex hyperventilation induced by brief hypoxic exposures or steady-state hypoxic levels, nor chemosensory excitation elicited by these maneuvers were eliminated. Asphyxia-induced chemosensory excitation was not reduced by combined blockade of ACh and ATP receptors. Furthermore, ventilatory or chemosensory depression evoked by 100% O2 tests was unmodified, thus evidencing that basal chemosensory drive in normoxia was not suppressed by combined cholinergic-purinergic blockade. Therefore, although ACh and ATP may participate in chemoexcitation of the CB, their involvement fails to explain the origin of chemosensory discharges from synaptic transmission between glomus cells and chemosensory nerve endings of the CB.

[Arterial chemoreceptors: cellular and molecular mechanisms in the adaptative and homeostatic function of the carotid body]

The carotid body is a sensory chemoreceptor organ located in the vicinity of the carotid bifurcation. Structurally it is composed of cell clusters formed by chemoreceptor and supporting cells. The sensory nerve endings of the carotid sinus nerve penetrate the clusters to synapse with chemoreceptor cells. The carotid body plays an important role in the control of ventilation during hypoxia, hypercapnia and acidosis. Hypoxia and other natural stimuli are detected by chemoreceptor cells which upon stimulation increase their rate of release of neurotransmitters. Neurotransmitters in turn increase the action potential frequency in the carotid sinus nerve which via its central projections to the brainstem activates ventilation. This review is devoted to the cellular aspects of the function of this chemoreceptor organ. From a brief description of the complex structure of the carotid body, we go to present a summary of the main prevailing theories concerning the transduction mechanisms for hypoxic and acidic/hypercapnic stimuli, with special emphasis on the electrical properties of cultured chemoreceptors cells. A special attention is provided to the possible significance of reactive oxygen species as mediators of the hypoxic transduction cascade. The neurotransmission between chemoreceptor cells and the sensory nerve endings is also covered in certain detail. After a brief historical presentation of the theories of communication between these two structures, we examine, following the classical criteria of neurotransmission, the functional significance of acetylcholine, dopamine, substance P and other neurotransmitters known to be present in chemoreceptor cells.

Multiple regulation of adenylyl cyclase activity by G-protein coupled receptors in human foetal lung fibroblasts

The pharmacological profile of adenylyl cyclase activity was analysed in WI-38 human foetal lung fibroblasts. Among various agents that act through G-protein coupled receptors, only the beta-adrenergic agonist isoproterenol stimulated and the tetradecapeptide somatostatin (SRIF, sst) inhibited the enzyme activity. The use of the reverse transcription-polymerase chain reaction (RT-PCR) methodology with appropriate cDNAs allowed us to identify the expression of four subtypes of SRIF transmembrane receptors (sst1-4 but not sst5 receptors) in this cell line. By RT-PCR and immunochemistry techniques, we also demonstrated the expression of stimulatory (alpha(s)) and inhibitory (alpha(i1), alpha(i2) and alpha(i3)) G-protein subunits. The known role of the adenylyl cyclase system in cell proliferation and differentiation mechanisms together with the present analysis of the corresponding regulatory network in fibroblasts of human foetal lung add knowledge on the cell line WI-38 that is widely used as a model system in studying cell growth. The importance of this cell class in normal and abnormal lung function and development reinforces the significance of these results.

Acetylcholine sensitivity in sensory neurons dissociated from the cat petrosal ganglion

The petrosal ganglia contain the somata of the sensory fibers of the glossopharyngeal nerves, innervating structures of the tongue, pharynx, carotid sinus and carotid body. Petrosal ganglia were excised from adult cats and their neurons were dissociated and kept in tissue culture for 7-12 days. Intracellular recordings were obtained through conventional microelectrodes. In response to depolarizing pulses, most cells (41/60) presented a 'hump' in the falling phase of their action potentials (H-type), while the remaining neurons lack such hump (F-type). The two types of cells had no differences in resting membrane potential or action potential amplitude. Acetylcholine (ACh) applied locally elicited responses in nearly two thirds of both H-type and F-type neurons tested. Most H-type neurons (17/19) responded with a slow long lasting depolarization, while the remaining (2) did so by generating spikes. In contrast, half of F-type neurons (6/12) responded with one or more spikes and the other half only with a slow depolarization. These results indicate that ACh receptors are present in the soma of many petrosal ganglion neurons subjected to tissue culture, thus supporting the idea that - under normal conditions - their peripheral sensory processes may be excited by ACh.

Identification of functional somatostatin receptors and G-proteins in a new line of human foetal lung fibroblasts

A new line (FP) of human foetal lung fibroblasts was analysed for the expression of functional, G-protein coupled somatostatin receptors (SSTR). By means of RT-PCR, we identified the expression of SSTR1, SSTR2, SSTR3 and SSTR4, but not SSTR5, subtypes. The same technical approach evidenced the expression of stimulatory (alphas) and inhibitory (alphai1, alphai2 and alphai3) G-protein subunits. The functionality of SSTR was established from the observation of a dose-dependent inhibitory role of SST upon isoproterenol-stimulated adenylyl cyclase activity, an effect that involves G-protein action. Moreover, the functionality of G-proteins was assessed by means of experiments with forskolin and a nonhydrolysable GTP analogue that showed either Gi or Gs activation in the regulation of adenylyl cyclase. Present results represent a first pharmacological characterization of this new line of human foetal lung fibroblasts. The selective presence of some SSTR subtypes and G-protein subunits in addition to the regulatory network of the adenylyl cyclase pathway are features of recognized involvement in cell growth mechanisms. It is of interest for a cell class widely used to study this topic but also important in lung physiology and pathophysiology.

A model of internal control may improve the response time of an automatic arterial pressure controller

A simplified model for the arterial pressure control system was implemented on a personal computer using Matlab Simulink. Model responses to variations of systemic vascular resistance were comparable to those predicted by physiology. Computer simulation suggested that including this model of the internal pressure control system within the design of an external controller would achieve better arterial pressure control and faster response than previous systems.

Lack of correlation between cholinergic-induced changes in chemosensory activity and dopamine release from the cat carotid body in vitro

We studied the effects of nicotine, acetylcholine (ACh) and dopamine (DA) on the frequency of chemosensory discharges (f(x)) and catecholamine (CA) efflux in the cat carotid body superfused in vitro. CA efflux was measured by changes in CA concentration (DeltaCA) determined by chronoamperometry with nafionated carbon-fiber microelectrodes inserted in the carotid body, while f(x) was recorded simultaneously from the carotid (sinus) nerve. Nicotine (10-20 microg) and ACh (>100 microg) increased f(x) in all carotid bodies (n=16), but produced a delayed DeltaCA ( approximately 0.65 microM) in only half of them. Eserine potentiated ACh-evoked increases in f(x) and CA effluxes. Nicotine and ACh-induced DeltaCA were rapidly reduced upon repeated administration. While f(x) increases evoked by low doses of nicotine or ACh were reduced or abolished by prior administration of exogenous DA (>100 microg), CA effluxes were enhanced and hastened. Thus, cholinergic-induced changes in f(x) are dissociated from CA efflux.

Adenosine triphosphate-induced peripheral nerve discharges generated from the cat petrosal ganglion in vitro

Since nucleotides have been postulated as transmitters between glomus cells and chemosensory nerve endings in the carotid body, we studied the effects of their application to the petrosal ganglion, where the perikarya of carotid (sinus) nerve are located. Cat petrosal ganglia were superfused in vitro, while electrical activities of their peripheral processes (carotid nerve and glossopharyngeal branch) were recorded simultaneously. Adenosine triphosphate (ATP) evoked dose-dependent bursts of impulses in carotid nerve, while those in glossopharyngeal branch were less intense and consistent. Adenosine monophosphate was less effective than ATP. ATP-induced carotid nerve responses presented no temporal desensitization and persisted after applying P(2Y) receptor blocker Reactive Blue 2 to the ganglion. The results indicate that ATP has an excitatory effect on the perikarya of the population of petrosal ganglion neurons projecting peripherally through the carotid nerve.

Responses to hypoxia of petrosal ganglia in vitro

NaCN is a classical stimulus used to elicit discharges from carotid body chemoreceptors. The effect is assumed to be mediated by glomus (type I) cells, which release an excitatory transmitter for the excitation of carotid nerve endings. Since the sensory perikarya of the glossopharyngeal nerve (from which the carotid nerve branches) are located in the petrosal ganglion, we tested whether application of this drug to the petrosal ganglion superfused in vitro elicits antidromic discharges in the carotid nerve. NaCN did indeed cause an intense and prolonged burst of nerve impulses in the carotid nerve, while provoking a less intense and much briefer burst of discharges in the glossopharyngeal branch. Carotid nerve responses to NaCN were reduced and shortened by prior or following application of dopamine to the ganglion. Sodium azide applied to the petrosal ganglion evoked a less intense and much briefer burst of impulses in the carotid nerve. Ganglionar application of 2,4-dinitrophenol did not induce discharges in the carotid nerve. Switching the superfusion of the ganglion from a normoxic to a hypoxic solution did not evoke discharges in the carotid nerve. Therefore, the perikarya of carotid nerve neurons are sensitive to NaCN, but are not excited by reducing the pO(2) of the superfusing solution.

Dopamine modulates carotid nerve responses induced by acetylcholine on the cat petrosal ganglion in vitro

We have recently reported that application of acetylcholine (ACh) or nicotine to the petrosal ganglion-the sensory ganglion of the glossopharyngeal nerve-elicits a burst of discharges in the carotid nerve branch, innervating the carotid body and sinus, but not in the glossopharyngeal branch, innervating the tongue and pharynx. Thus, the perikarya of sensory neurons for the carotid bifurcation exhibit selective cholinosensitivity. Since dopamine (DA) modulates carotid nerve chemosensory activity, we searched for the presence of DA sensitivity at the perikarya of these neurons in the cat petrosal ganglion superfused in vitro. Applications of DA in doses of up to 5 mg to the ganglion did not modify the rate of spontaneous discharges in the carotid nerve. However, if DA was applied 30 s before ACh injections, ACh-evoked reactions were modified: low doses of DA enhanced the subsequent responses to ACh, while high doses of DA depressed the responses to ACh. This depressant effect of DA on ACh responses was partially antagonized by adding spiroperone to the superfusate. Our results show that the response to ACh of petrosal ganglion neurons projecting through the carotid nerve is modulated by DA acting on D(2) receptors located in the somata of these neurons. Thus, dopaminergic modulation of cholinosensitivity could be shared also by the membranes of peripheral endings and perikarya of primary sensory neurons involved in arterial chemoreception.

Time structure, temporal correlation and coherence of chemosensory impulses propagated through both carotid nerves in cats

In spontaneously breathing, pentobarbitone anesthetized cats, we recorded simultaneously the impulses in the chemosensory fibers of both carotid (sinus) nerves, to analyze the correlations between the frequencies of chemosensory discharges (f chi) and their activation (¿df chi/dt¿a) and deactivation (¿df chi/dt¿d) rates. We studied the chemosensory responses to brief exposures to hypoxia (100% N2; 5-s and 10-s) and hyperoxia (100% O2; 30-s), and intravenous injections of excitatory (NaCN 0.2-100 micrograms/kg) and inhibitory (dopamine hydrochloride 0.02-20 micrograms/kg) chemoreceptor agents. Hypoxia increased f chi, with a high temporal correlation between frequency levels in both nerves. Prolonging hypoxic stimulation increased ¿df chi/dt¿d, with preservation of ¿df chi/dt¿a. Hyperoxic exposure produced highly correlated decreases in f chi in both nerves, but reduced correlation in df chi/dt. Increasing doses of NaCN produced analogous increments in f chi, df chi/dt and their correlations, the ¿df chi/dt¿a/¿df chi/dt¿d ratio remaining constant along all the experimental range, except in one animal in which the ratio increased in both nerves alike. Dopamine reduced f chi bilaterally, with chemosensory silencing being reached with doses of about 0.2-0.5 microgram/kg, the correlations between f chi's of both nerves remaining constant within the range analyzed. Maximal ¿df chi/dt¿d was not affected along the range of dopamine doses, except in one animal in which it increased in both nerves. It is concluded that both carotid nerves convey similar quantitative information to the brain stem. Thus, the carotid nerves constitute either cooperative inputs or redundant afferences contributing to a high safety factor.

Selective activation of carotid nerve fibers by acetylcholine applied to the cat petrosal ganglion in vitro

The petrosal ganglion innervates carotid body chemoreceptors through the carotid (sinus) nerve. These primary sensory neurons are activated by transmitters released from receptor (glomus) cells, acetylcholine (ACh) having been proposed as one of the transmitters involved in this process. Since the perikarya of primary sensory neurons share several properties with peripheral sensory endings, we studied the electrical responses of the carotid nerve and glossopharyngeal branch to ACh locally applied to the cat petrosal ganglion superfused in vitro. Ganglionar applications of AChCl (1 microg-1 mg) generated bursts of action potentials conducted along the carotid nerve, while only a few spikes were exceptionally recorded from the glossopharyngeal branch in response to the largest doses. Carotid nerve responses to ACh were dose-dependent, the higher doses inducing transient desensitization. Application of nicotine to the petrosal ganglion also evoked dose-dependent excitatory responses in the carotid nerve. Responses to ACh were reversibly antagonized by adding hexamethonium to the superfusate, more intense and prolonged block of ACh responses being produced by mecamylamine. Ganglionar applications of gamma-amino butyric acid and serotonin, in doses of up to 5 mg, did not induce firing of action potentials in any of the branches of the glossopharyngeal nerve. Our results indicate that petrosal ganglion neurons projecting through the carotid nerve are selectively activated by ACh acting on nicotinic ACh receptors located in the somata of these neurons. Thus, cholinosensitivity would be shared by the membranes of peripheral endings and perikarya of primary sensory neurons involved in arterial chemoreception.

Dissociation of hypoxia-induced chemosensory responses and catecholamine efflux in cat carotid body superfused in vitro

1. To examine the correlation between chemosensory response and dopamine release induced by hypoxic stimulation, we studied carotid bodies excised from anaesthetized cats. 2. The carotid bodies with their carotid (sinus) nerves were superfused in vitro with modified Tyrode solution (pH 7.40, at 37.5 degrees C) equilibrated with 20 or 100% O2. The PO2 of the superfusing channel was monitored polarographically. The frequency of chemosensory discharges (fx) was recorded from the whole carotid nerve. Catecholamine (CA) efflux-mostly consisting of dopamine-was measured by high-speed chronoamperometry, through Nafion-coated carbon electrodes placed on the carotid body tissue. Chemosensory stimulation was induced by intrastream injections of NaCN, by superfusion with 100% N2-equilibrated saline (lowering PO2 to 25-40 Torr) or by flow interruption. 3. Low doses of NaCN increased fx, but had no measurable effect on CA efflux, while larger doses produced fast increases in fx, preceding delayed and prolonged increases in CA efflux. Repeated injections of NaCN, still increasing fx, gave reduced CA effluxes. 4. Switching to hypoxic superfusion for 6-8 min produced large and fast fx increases, but delayed and prolonged augmentations of CA efflux. 5. Administration of three to four boluses of dopamine (7-15 micrograms; augmenting CA concentration by up to 35 microM) initially decreased fx, after which hypoxic stimulation resulted in enhanced and faster CA effluxes, without changing the speed and intensity of chemosensory responses. 6. Flow interruptions induced fast increases in fx and delayed increases in CA efflux. Repeated flow interruptions produced similar increases in fx but progressively attenuated CA effluxes. 7. Our results suggest that CA efflux is not essential for hypoxia-induced chemosensory excitation in the cat carotid body. They also suggest the presence of two pools of releasable CAs in the carotid body, one of slow turnover and release, and another of recently incorporated dopamine and fast release, both pools being rapidly depleted by repeated stimulation of the carotid body.

Effects of dopaminergic blockade upon carotid chemosensory activity and its hypoxia-induced excitation

The effects of domperidone, antagonist of D2 receptors, on arterial chemoreceptor activity were studied in spontaneously breathing and pentobarbitone anesthetized cats, in which recordings of chemosensory impulse activity were obtained simultaneously from both cut carotid (sinus) nerves. Intravenous injections of domperidone 50 micrograms/kg produced a maintained increase in the basal frequency of chemosensory discharges, after which hyperoxic tests (breathing 100% O2 for 30 s) evoked larger falls in the rate of chemosensory impulses. Chemosensory responses evoked by hypoxic hypoxia (100% N2 tests) and by cytotoxic hypoxia (i.v. injections of NaCN) reached higher impulse rates after domperidone treatment. The effects of domperidone reveal that a resting release of dopamine from glomus cells maintains a low level of basal chemosensory activity under normoxic conditions. Domperidone turns off such restraining dopaminergic control and enhances the transient chemosensory responses to hypoxic stimuli. Present data support a modulatory role for dopamine within the chemoreceptor process, but not its participation as excitatory transmitter between glomus cells and sensory nerve endings.

Thermal dependence of chemosensory activity in the carotid body superfused in vitro

We studied the relationship between chemosensory activity and temperature in carotid bodies excised from pentobarbitone-anesthetized cats, and superfused in vitro at flows between 0.4 and 2.0 ml/min with modified Tyrode's solution buffered with HEPES at pH 7.43. The basal frequencies of chemosensory discharges were recorded from the entire carotid nerve at different steady thermal conditions. For preparations superfused with saline equilibrated with 100% O2, thermally dependent increases in frequency were observed, with significant differences between all nearby thermal stages separated by 0.5 degrees C steps between 36.0 and 38.5 degrees C. The larger gains were recorded between higher temperatures at high flows, between mid temperatures at intermediate flows, and between lower temperatures at low flows. The critical temperature for the calculated maximal gain was directly correlated to superfusion flow. The basal frequencies were consistently elevated when switching to saline equilibrated with 20% O2 and no significant differences in mean ranks were recorded between 36 and 37 degrees C, as between 38 and 39 degrees C, but frequencies at 36-37 degrees C were significantly higher than those at 38-39 degrees C. Brief rises in chemosensory discharges were evoked by injections of NaCN applied to carotid bodies superfused with saline equilibrated with 100% O2. The least effective dose was lower at 40 degrees C than at 37.5 degrees or 35.0 degrees C, but the reactivity and slope were not significantly different. It is concluded that the carotid body chemoreceptors fulfill the criteria for being considered as thermosensors, and that their frequency of discharges is thermally modulated within a range close to physiological body temperature.

Comparison of the subcellular distribution of alveolar surfactant in two mammalian species of similar body weight: cat and rabbit

1. We studied the total amount and subcellular distribution of alveolar surfactant, extracted through bronchoalveolar lavage of anesthetized cats and rabbits. This was correlated to several morphometric and ventilatory variables of these animals. 2. Lung weight was significantly larger in the cat while respiratory frequency and minute ventilation were significantly larger in the rabbit. No significant differences were observed in tidal volume, total lung capacity, P(a)O2, P(a)CO2 and pH(a). 3. While both species had similar protein contents in the bronchoalveolar lavage, rabbits had larger phospholipid contents, mostly distributed in the lighter, more active subfractions. 4. With regard to the estimated values obtained from allometric equations derived for mammals, the rabbit presented a lung weight of nearly one-third of the estimated one, an exceedingly larger minute ventilation (by nearly 60%) and a respiratory frequency twice the calculated one. 5. We suggest that the different distribution of alveolar surfactant in these species may be explained by disparities in their ventilatory demands, the rabbit having a higher respiratory frequency and a larger minute ventilation, performed by a mass of lung tissue lower than that corresponding to its body mass.

Effects of body temperature on chemosensory activity of the cat carotid body in situ

The effects of changes in body core temperature (TB) upon the frequency of chemosensory discharges (fx) from one carotid nerve were studied in pentobarbitone anesthetized cats. Raising TB from 35 to 40 degrees C increased fx in some cats, an effect more commonly seen after contralateral carotid neurotomy. In other animals, the simultaneously increased alveolar ventilation counteracted the above effect. A multiple correlation analysis of global data showed predicted increases in fx in response to raising TB at different CO2 levels.

Thermal effects on ventilation in cats: participation of carotid body chemoreceptors

In pentobarbitone anesthetized cats, raising body temperature from 37 to 40 degrees C by external heat increased respiratory frequency, tidal volume, frequency of spontaneous gasps and mean inspiratory flow. It reduced end-tidal CO2 pressure, together with inspiratory and expiratory durations. After bilateral section of the carotid nerves, raising body temperature still induced hyperventilation, but the increase in gasp frequency was less pronounced and no significant change in tidal volume was observed. In comparison to steady ventilatory values in the intact condition, significant reductions in tidal volume at 38 degrees C and in gasp frequency at 37, 39 and 40 degrees C were observed after bilateral carotid neurotomy. Brief hyperoxic tests induced transient decreases in tidal volume and increases in end-tidal CO2 pressure which were significantly larger at 40 degrees C than at 37 degrees C. These changes disappeared after bilateral carotid neurotomy. Anesthetic block of both carotid nerves produced transient reductions in tidal volume at any given temperature. We conclude that carotid body afferents contribute to the hyperventilation evoked by hyperthermia. After their interruption, such contribution is replaceable from other thermal afferents.

Factors affecting distribution of alveolar surfactant during resting ventilation

Few studies have been done to establish the ventilatory factors affecting alveolar surfactant under resting conditions. Experiments in which ventilatory variables were recorded for 4 h were performed in 12 adult cats breathing spontaneously under pentobarbital sodium anesthesia. After the animals were killed and bronchoalveolar lavages (BALs) were performed, the resulting fluid was subjected to differential centrifugation and determinations of proteins, phospholipids (PL), and disaturated phosphatidylcholine (DSPC). Pellet P1+2 was obtained by two centrifugations at 140 g; the supernatant was centrifuged at 1,000 g to obtain pellet P3 and subsequently at 60,000 g to obtain P4. Pellets P3 and P4 had the higher contents of PL and DSPC. Bivariate and multivariate correlational analyses indicate that 1) total PL in BAL was not related to any of the ventilatory variables studied, 2) PL in P3 and P4 fractions was directly correlated to the physiological range of variations in the frequency of large spontaneous gasps (fL), and 3) PL in P1+2 fraction was inversely related to fL. Cats subjected to bilateral section of carotid nerves, although presenting reduced chemosensory drive and ventilatory chemoreflexes, did not exhibit significant differences in resting ventilatory variables nor in alveolar surfactant components. Present results indicate that the total content of alveolar surfactant is not modified by ventilatory variations within physiological range but that the spontaneous occurrence of large gasps increases the proportion of more active forms of alveolar surfactant. This may mediate the role of augmented breaths in keeping lung compliance and preventing atelectasis under resting ventilatory conditions.

Functional recovery of the ventilatory chemoreflexes after partial chronic denervation of the nucleus tractus solitarius

In pentobarbitone-anesthetized cats breathing spontaneously, we studied whether excision of one petrosal ganglion would modify the reflex efficacy of the remaining carotid and aortic chemoafferences in ventilatory control. Resting ventilation was not affected shortly after the ganglionectomy, but decreased sensitivities and reactivities for changes in tidal volume and respiratory frequency were revealed by dose-response curves for ventilatory chemoreflexes evoked by NaCN i.v. After 2 weeks of ganglionectomy, basal tidal volume was increased, being slightly reduced by contralateral carotid neurotomy, but persisting above control after section of all buffer nerves. The ventilatory chemosensory drive--tested by breathing 100% O2--was unmodified with respect to the acute condition, but the tonic ventilatory influence exerted by the right carotid nerve was diminished. Dose-response curves for reflex changes in tidal volume exhibited increased sensitivity, while those for changes in respiratory frequency showed increased reactivity. Thus, partial chemosensory denervation of the nucleus tractus solitarius triggers a slowly developing increase in the reflex efficacy of the remaining chemosensory inputs. The recovery of sensitivity for reflex changes in tidal volume required the presence of contralateral carotid afferents, while the increased reactivity in respiratory frequency needed the integrity of aortic afferents. The results also suggest an enhanced contribution of central structures other than chemosensory inputs in respiratory control after partial deafferentation.

Disappearance of opioidergic tone on LH secretion in underfed prepubertal sheep

A study was conducted to determine whether an opioid tonus inhibitory of LH secretion is present in underfed prepubertal sheep. Ten Suffolk ewe lambs were subjected to food restriction during 60 days. During this period they were allowed to pasture only 2 hours per day while control ewe lambs were allowed for 10 hours. Body weight and plasma blood levels of glucose, urea and total proteins were measured weekly. At the end of this period, an intravenous injection of Naloxone (NAL, 1.5 mg/kg BW) was given to control and underfed animals followed 60 min later by an intravenous injection of LHRH to test the pituitary responsiveness. Underfed animals did not show an increase in plasma LH while control animals presented a rise from 0.28 +/- 0.08 to 2.02 +/- 0.6 ng/ml after the NAL stimulus (P less than 0.05). The response to LHRH was similar in both group of animals. Basal plasma levels of insulin were lower in underfed ewe lambs than in control animals (P less than 0.05). Underfed animals were placed on plain feeding with a schedule similar to control lambs for 30 days and the same experiment was repeated. During this occasion, NAL increased plasma LH concentration in both group of lambs. Levels of plasma insulin were not different in both groups. The lack of effect of NAL on LH secretion in food restricted ewe lambs suggests that the opioid modulation of LH secretion is absent by underfeeding in female prepubertal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlative contribution of carotid and aortic afferences to the ventilatory chemosensory drive in steady-state normoxia and to the ventilatory chemoreflexes induced by transient hypoxia

The contributions of the peripheral arterial chemoreceptors to the tonic and phasic reflex ventilatory regulation were studied in spontaneously breathing pentobarbitone anesthetized adult cats. The chemosensory drive during eucapnic normoxia was inferred from the transient ventilatory effects induced by anesthetic blockade of the buffer nerves. Aortic nerves block did not modify ventilation. Carotid nerves block provoked transient ventilatory depression, decreasing VT by 46% and fR by 26%, followed by recovery to steady-state values in VT, fR and PETCO2. Changes in PETCO2 were correlated with those in VT, but not with those in fR. The ventilatory effects of blocking a given carotid nerve were more intense when the contralateral carotid nerve was already blocked. This effect may be an expression of hypoadditive interactions between carotid nerves inputs with respect to chemosensory drive of ventilation. Analysis of the dose-response curves for the ventilatory reflexes evoked by NaCN i.v., before and after blockade of the buffer nerves, revealed major contributions of the carotid nerves, with small contributions of the aortic nerves to the those responses to high doses of NaCN. The contributions of each carotid nerve to the tonic chemosensory drive and to the phasic ventilatory chemoreflexes were highly correlated (rs = 0.90; p less than 0.01). We propose that a family of modulatory functions may describe the effects exerted by the peripheral arterial chemoreceptors upon the tonic ventilatory drive in normoxia and the phasic reflex responses evoked by hypoxia. While the carotid nerves mediated modulation is evident in normoxia, that provided by both aortic nerves is only expressed during pronounced hypoxia.

Flow-dependent chemosensory activity in the carotid body superfused in vitro

The relationship between carotid body chemoreceptor activity and flow was studied in preparations superfused in vitro. The carotid bodies were excised from pentobarbitone-anesthetized cats and superfused with modified Tyrode's solution, buffered with HEPES-NaOH to pH 7.41. The bath temperature was kept constant at 37.7 degrees C. The frequency of chemosensory discharges from the entire carotid nerve was determined during steady-state superfusion with 100% or 20% O2-equilibrated saline at flow rates between 0.15 and 2.95 ml/min, and during 5 min flow interruptions. The peak frequency evoked by flow interruptions was maximal and independent of previous superfusion flows, but the half-excitation time of chemosensory responses to flow interruption was minimal when preceded by superfusion with 100% O2-equilibrated saline at 0.7 ml/min. In steady-state conditions, mean chemosensory activity was higher at lower rates of flow, and, at constant flow, higher under 20% O2 than under 100% O2. To allow comparisons of all data, basal frequencies at given basal flows were referred to their own maximal frequencies evoked by flow interruptions. The best fitting for the relation between basal chemosensory activity and superfusion flow was provided by inverse sigmoid (logistic decay) curves: r = -0.90 and -0.84, at 100% and 20% O2 levels, respectively. The maximal gains were at about 0.78 and 0.86 ml/min, respectively. It is concluded that the chemosensory discharge frequency recorded from carotid bodies superfused in vitro is determined by the superfusion flow, when all other natural chemoreceptor stimuli are held constant.

Reflex effects evoked by stimulation of hypoglossal afferent fibers

In pentobarbitone-anesthetized cats, electrical stimulation of the central ends of the main trunks of transected hypoglossal nerves evoked vascular (pressor or depressor) reactions, mydriasis, slow and deep breathing, and reflex activation of laryngeal and facial muscles. Stimulation of the central end of the transected ramus descendens hypoglossi also provoked reflex contraction of cricothyroideus. These reflexes may be elicited also after intracranial section of hypoglossal nerve roots, but not after intracranial section of ipsilateral vagal roots. The above reflexes were abolished by acute section of the ipsilateral hypoglossonodosal branch, but they may be reproduced by electrical stimulation of the central end of this anastomotic branch between hypoglossal nerve and nodose ganglion. Stimulation of the central end of one transected hypoglossus evoked reflex efferent discharges in contralateral hypoglossus and contraction of contralateral tongue muscles. Stimulation of the central end of one transected hypoglossal end-branch inhibited efferent discharges in another end-branch. The crossed hypoglossohypoglossal reflex and the ipsilateral reflex inhibition were abolished by section of the hypoglossonodosal branch or vagal roots at the stimulated side. We conclude that reflexes evoked by stimulation of peripheral hypoglossal nerve in cats are mediated by afferent fibers directed to the nodose ganglion and entering the brain stem via vagal roots.

Bioelectric potentials in the carotid body

Simultaneous recordings of focal slow potentials (sVs) and chemosensory discharges were made from cat carotid body-nerve preparations in situ. Chemoreceptor stimulants (100% N2, asphyxia, NaCN, ACh and nicotine), and depressants (100% O2, spontaneous gasps and dopamine) changed receptor polarization. sVs evoked by stimulants had a negative polarity whereas depressants elicited positive deflections. There was a direct correlation between maximal frequency of chemosensory discharges and peak sV amplitude when NaCN injections or N2 inhalation were used. However, cholinergic agents, dopamine and substance P evoked sVs which lacked correlation in time-course, amplitude or polarity with changes in sensory frequency. After a 6-day carotid nerve crush, different stimuli still evoked sVs even in the absence of sensory discharges. Both sVs and chemosensory discharges were abolished after 1 h ischemia produced by ligature of carotid body blood vessels. Thus, sVs from carotid body chemoreceptors probably include a neuronal component (the generator potential) directly responsible for the origin of chemosensory discharges, and a non-neuronal component (receptor or secretory potentials) probably originating in glomus and/or sustentacular cells.

Blockade of dopamine-induced chemosensory inhibition by domperidone

The sensory discharges from the carotid body chemoreceptors of the cat are transiently inhibited by dopamine (DA) injections. This chemosensory inhibition was effectively blocked by domperidone, a selective antagonist of D2 dopaminoceptors. The basal frequency of spontaneous chemosensory impulses was immediately and sustainly increased after domperidone, suggesting the withdrawal of a tonic inhibition of chemosensory discharges by endogenous DA released from glomus cells. The peripheral dopaminergic modulation of chemoreflexes may be separately blocked by domperidone, a drug unable to cross the blood-brain barrier.

Perspectives in carotid body research

This review deals with some basic mechanisms that are operative in carotid body chemoreception. It describes the evolution of concepts and different hypotheses or theories developed to explain possible mechanisms responsible for the onset of sensory discharges in the carotid nerve. Unfortunately, no single hypothesis has been proved beyond doubt, and this may explain their variety. At present, we do not know why this task has been so difficult, although one may think of several possibilities. 1) Carotid body chemoreceptors are anatomically complex being formed by glomus (type I) and sustentacular (type II) cells. Branches of the carotid (sinus) nerve innervate the glomus cells forming sensory synapses oriented in either or both directions and the junction is enveloped by processes of the sustentacular cells. 2) Chemoreceptors are polymodal, since they respond to a variety of natural and chemical stimuli. 3) It is possible that various stimuli may act on different elements of the receptor complex. 4) It is also possible that stimuli may act using different mechanisms. In addition, the multitude of biochemical and biophysical processes (some of them still unknown) operating at different receptor levels has made it very difficult to propose a unified mechanism of action.

Inhibition in carotid body chemoreceptors mediated by D-2 dopaminoceptors: antagonism by benzamides

Inhibition of chemosensory nerve impulses in the cat is evoked by dopamine (DA) applied to carotid body chemoreceptors. Pharmacological characterization of the dopaminoceptors involved in this action was determined through their blockade with benzamides, selective antagonists of D-2 receptors. Both metoclopramide and sulpiride were effective blockers of DA-induced chemosensory inhibition. Furthermore, both drugs induced an immediate increase in the frequency of carotid nerve chemosensory impulses, suggesting the presence of previous tonic inhibition of chemoreceptor discharges by endogenous DA released from glomus cells.

Cardiovascular responses to hypoxia in the spontaneously breathing cat: reflexes originating from carotid and aortic bodies

The heart rate (fH) and systemic arterial pressure (Pa) responses to transient anoxemic and cytotoxic hypoxia were studied in 18 pentobarbitone-anesthetized, spontaneously breathing cats, by applying N2 tests and i.v. injections of NaCN. Hyperventilation was accompanied by short-latency increases in Pa and fH; they persisted after bilateral vagotomy, sparing the aortic nerves. Acute section of carotid or aortic nerves in different sequences reduced both fH and Pa responses, the contribution of both pairs of nerves being similar. The recording of carotid chemosensory discharges showed transient stimulus-dependent increases in their frequency, to which the ensuing fH and Pa rises were correlated. After sectioning the four buffer nerves, hypoxia provoked long-lasting hypotension and bradycardia. Tachycardia was also observed in response to hypoxia in 4 out of 6 chloralose-anesthetized spontaneously breathing cats, the other two presenting bradycardia. The direction of these cyanide-induced changes in fH was not modified by bilateral vagotomy. It is concluded that tachycardia and hypertension in response to hypoxia are not vagally-mediated consequences of hyperventilation.

Ventilatory reflexes originated from carotid and extracarotid chemoreceptors in rats

Ventilatory responses to transient stimulation and inhibition of arterial chemoreceptors--by hypoxia and hyperoxia, respectively--were studied in 10 pentobarbitone-anesthetized rats. N2 tests and intravenous injections of NaCN provoked transient increases in tidal volume and respiratory frequency, while O2 tests elicited decreases of these parameters. After bilateral carotid neurotomy, ventilatory responses to N2 and NaCN were still present although reduced in all rats, while ventilatory depression in response to O2 tests was observed in 60% of these rats. Further bilateral sectioning of main vagus, aortic, and superior laryngeal nerves immediately below the nodose ganglia abolished the ventilatory responses to NaCN in only one of the five rats subjected to this procedure, the remaining animals showing moderate hyperventilation in response to large doses of this drug. Mild ventilatory depression in response to hyperoxia, indicative of a persistent peripheral chemosensory drive, was still present in two of these rats. It is concluded that, although the carotid bodies constitute the main source of ventilatory chemoreflexes in rats, other vagally and nonvagally innervated chemoreceptors (presumably thoracic and abdominal) may elicit ventilatory reflexes in this species.

Reversal of respiratory responses to dopamine after dopamine antagonists

The effects of dopamine (DA) antagonists upon resting ventilation and ventilatory reactions to DA, apomorphine, hyperoxia and hypoxia were studied in pentobarbitone-anesthetized cats. Intravenous administration of spiroperidol, haloperidol, perphenazine and chlorpromazine increased resting ventilation, the intensity and duration of the effect being dependent on the dose of the blocker. The enhanced ventilation was associated to increased frequency of chemosensory discharges recorded from one carotid nerve, and it was absent from section of the four buffer nerves. The drugs also provoked a dose-dependent block of the transient chemosensory inhibitions and ventilatory depressions induced by DA or apomorphine. In addition, spiroperidol and perphenazine reversed the inhibitory reactions to DA into excitatory ones, the ventilatory responses being abolished by section of carotid and aortic nerves. The ventilatory depressions caused by a few breaths of 100% O2 and the ventilatory excitations onset by a few breaths of 100% N2 persisted after applying DA blockers. Results indicate that DA antagonists enhance ventilation by increasing peripheral chemosensory drive and may invert DA-induced reflex withdrawal into transient ventilatory excitation, without reversing the reflex ventilatory depression provoked by hyperoxia.

Relative contribution of carotid and aortic bodies to cyanide-induced ventilatory responses in the cat

The participation of afferences from carotid and aortic bodies to the hyperventilation caused by cytotoxic hypoxia was assessed in pentobarbitone-anesthetized cats. Dose-response curves for the ventilatory effects induced by i.v. injections of NaCN were obtained before and after successive denervations of peripheral chemoreceptors, in different sequences. Bilateral aortic neurotomy (BAN) or unilateral carotid neurotomy (UCN) did not affect significantly the minimal sensitivity to the drug, although maximal reactivity was reduced in some cats. After bilateral carotid neurotomy (BCN), with preservation of aortic nerves, sensitivity was reduced, but hyperventilation was still provoked by large doses of cyanide. BAN + BCN abolished the ventilatory responses to the drug. In cats with BAN + UCN, ventilatory responses had a high degree of correlation with increases of carotid chemosensory discharges in the range between ca 200% of control and the gasping threshold. It is concluded that the aortic bodies of the cat play a significant role in the hyperventilation produced by cytotoxic hypoxia, although it is less marked than that induced through the carotid bodies.