Heart failure alters the strength and mechanisms of the muscle metaboreflex. Am. J. Physiol. Heart Circ. Physiol. 278: H818-H828, 2000.-We hypothesized that excessive sympathoactivation observed during strenuous exercise in subjects with heart failure (HF) may result from tonic activation of the muscle metaboreflex (MMR) via hypoperfusion of active skeletal muscle. We studied MMR responses in dogs during treadmill exercise by graded reduction of terminal aortic blood flow (TAQ) before and after induction of HF by rapid ventricular pacing. At a low workload, in both control and HF experiments, large decreases in TAQ were required to elicit the MMR pressor response. During control experiments, this pressor response resulted from increased cardiac output (CO), whereas in HF CO did not increase; thus the pressor response was solely due to peripheral vasoconstriction. In HF, MMR activation also induced higher plasma levels of vasopressin, norepinephrine (NE), and renin. At a higher workload, in control experiments any reduction of TAQ elicited MMR pressor responses. In HF, before any vascular occlusion, TAQ was already below MMR control threshold levels and reductions in TAQ again did not result in higher CO; thus SAP increased via peripheral vasoconstriction. NE rose markedly, indicating intense sympathetic activation. We conclude that in HF, the MMR is likely tonically active at moderate workloads and contributes to the tonic sympathoactivation. dynamic exercise; hormones; dogs; Frank-Starling; rapid ventricular pacing WHEN OXYGEN DELIVERY to active skeletal muscle is insufficient for the ongoing metabolic demands, metabolites accumulate and stimulate afferents within the active skeletal muscle that elicit a powerful pressor response known as the muscle metaboreflex. Activation of the muscle metaboreflex during exercise elicits increases in heart rate, cardiac output, systemic arterial pressure, ventricular performance, central blood volume mobilization, and vasoconstriction in the renal and nonischemic active skeletal muscle vasculatures (9,11,12,14,16,17,22,23,25,33). In addition, metaboreflex activation can also increase the circulating levels of vasoactive hormones (13,18). These marked cardiovascular responses are buffered by arterial (23) and cardiopulmonary (4) baroreflexes. Studies from our laboratory and from others (11, 12, 16-18, 22, 23, 33) have shown that in dogs during mild exercise a clear threshold exists for metaboreflex activation, i.e., initial reductions in blood flow to active skeletal muscle (i.e., hindlimbs) do not elicit any metaboreflex responses. Only when oxygen delivery is reduced below a threshold level do substantial metaboreflex pressor responses occur (25). In contrast, during moderate workloads no clear threshold exists, indicating that the metaboreflex may be tonically active or that the prevailing level of blood flow approximates the threshold for the reflex, and any reduction in perfusion to the active skeletal muscle will engage the muscle metaboreflex (20,22,33).The cardiovas...
Mutual policing is an important mechanism that maintains social harmony in group-living organisms by suppressing the selfish behavior of individuals. In social insects, workers police one another (worker-policing) by preventing individual workers from laying eggs that would otherwise develop into males. Within the framework of Hamilton's rule there are two explanations for worker-policing behavior. First, if worker reproduction is cost-free, worker-policing should occur only where workers are more closely related to queen- than to worker-produced male eggs (relatedness hypothesis). Second, if there are substantial costs to unchecked worker reproduction, worker-policing may occur to counteract these costs and increase colony efficiency (efficiency hypothesis). The first explanation predicts that patterns of the parentage of males (male parentage) are associated with relatedness, whereas the latter does not. We have investigated how male parentage varies with colony kin structure and colony size in 50 species of ants, bees, and wasps in a phylogenetically controlled comparative analysis. Our survey revealed that queens produced the majority of males in most of the species and that workers produced more than half of the males in less than 10% of species. Moreover, we show that male parentage does not vary with relatedness as predicted by the relatedness hypothesis. This indicates that intra- and interspecific variation in male parentage cannot be accounted for by the relatedness hypothesis alone and that increased colony efficiency is an important factor responsible for the evolution of worker-policing. Our study reveals greater harmony and more complex regulation of reproduction in social insect colonies than that expected from simple theoretical expectations based on relatedness only.
Summary• In many organisms, individuals behave more altruistically towards relatives than towards unrelated individuals. Here, we conducted a study to determine if the performance of Arabidopsis thaliana is influenced by whether individuals are in competition with kin or non-kin.• We selected seven pairs of genetically distinct accessions that originated from local populations throughout Europe. We measured the biomass of one focal plant surrounded by six kin or non-kin neighbours in in vitro growth experiments and counted the number of siliques produced per pot by one focal plant surrounded by four kin or non-kin neighbours.• The biomass and number of siliques of a focal plant were not affected by the relatedness of the neighbour. Depending on the accession, a plant performed better or worse in a pure stand than when surrounded by non-kin plants. In addition, whole-genome microarray analyses revealed that there were no genes differentially expressed between kin and non-kin conditions.• In conclusion, our study does not provide any evidence for a differential response to kin vs non-kin in A. thaliana. Rather, the outcome of the interaction between kin and non-kin seems to depend on the strength of the competitive abilities of the accessions.
When oxygen delivery to active skeletal muscle is insufficient for the metabolic demands, afferent nerves within muscles are activated, which elicit reflex increases in heart rate (HR), cardiac output (CO), and arterial pressure (AP), termed the muscle metaboreflex (MMR). To what extent the increases in CO are the result of increased ventricular contractility is unclear. A widely accepted index of contractility is maximal left ventricular elastance (Emax), the slope of the end-systolic pressure-volume relationship, such as during rapidly imposed reductions in preload. The objective of the present study was to determine whether MMR activation elicits increases in Emax. Experiments were performed using conscious dogs chronically instrumented to measure left ventricular pressure and volume at rest and during mild or moderate treadmill exercise with and without partial hindlimb ischemia to elicit MMR responses. At both workloads, MMR activation significantly increased CO, HR, AP, and maximum rate of change of left ventricular pressure. During both mild and moderate exercise, MMR activation increased Emax to 159.6 Ϯ 8.83 and 155.8 Ϯ 6.32% of the exercise value under free-flow conditions, respectively. We conclude that the increase of ventricular elastance associated with MMR activation indicates that a substantial increase in ventricular contractility contributes to the rise in CO during dynamic exercise. elastance; pressor response; cardiac function DURING DYNAMIC EXERCISE, when oxygen delivery to active skeletal muscle is insufficient to meet the metabolic demands, metabolites (e.g., lactic acid, adenosine, potassium, diprotonated phosphate, H ϩ , arachidonic acid products, and others) accumulate within the active muscle and stimulate group III and IV afferent neurons. These sensory neurons project to the central nervous system, eliciting a reflex pressor response consisting of increases in efferent sympathetic nerve activity (SNA), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), plasma levels of vasoactive hormones, and peripheral vasoconstriction termed the muscle metaboreflex (MMR) (1, 2, 8, 12, 14, 19, 21, 25-28, 30, 32, 33, 35-38, 42, 44). These mechanisms act in concert to partially restore blood flow and arterial oxygen delivery to the hypoperfused muscles (27,31). Previous studies have shown that in normal dogs exercising at mild and moderate workloads, the increases in MAP elicited by this MMR activation are mainly due to increases in CO. The rise in CO likely results from increases in ventricular performance, HR, and central blood volume mobilization (26, 35). In this way the MMR-induced increases in ventricular performance act to sustain or slightly increase stroke volume (SV) despite decreases in ventricular filling time due to the reflex tachycardia (2, 26, 44). Furthermore, O'Leary an Augustyniak (26) showed that in normal dogs in which HR was fixed at 225 beats/min during mild exercise, MMR activation caused such a rise in SV that the increases in CO were approximately equal to t...
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