Baroreflex activation in conscious rats modulates the joint inflammatory response via sympathetic function

The baroreflex is a critical physiological mechanism controlling cardiovascular function by modulating both the sympathetic and parasympathetic activities. Here, we report that electrical activation of the baroreflex attenuates joint inflammation in experimental arthritis induced by the administration of zymosan into the femorotibial cavity. Baroreflex activation combined with lumbar sympathectomy, adrenalectomy, celiac subdiaphragmatic vagotomy or splenectomy dissected the mechanisms involved in the inflammatory modulation, highlighting the role played by sympathetic inhibition in the attenuation of joint inflammation. From the immunological standpoint, baroreflex activation attenuates neutrophil migration and the synovial levels of inflammatory cytokines including TNF, IL-1β and IL-6, but does not affect the levels of the anti-inflammatory cytokine IL-10. The anti-inflammatory effects of the baroreflex system are not mediated by IL-10, the vagus nerve, adrenal glands or the spleen, but by the inhibition of the sympathetic drive to the knee. These results reveal a novel physiological neuronal network controlling peripheral local inflammation.     

Endogenous vasopressin and baroreflex mechanisms

This article reviews the anatomical and functional evidence for ascending pathways from specific brain regions to the PVN and SON which could influence AVP release. The majority of evidence favours the main projection being from a region in the caudal VLM which may coincide with the noradrenergic neurons of the A₁ cell group. However, the transmitter(s) involved have yet to be identified, and whether the pathway is excitatory and/or inhibitory remains to be fully resolved.Anatomical and functional evidence is reviewed for descending projections from the SON and PVN to specific brain regions involved in cardiovascular control, and their possible involvement in baroreflex mechanisms is discussed. However, there is little unequivocal evidence that AVP is the main neurotransmitter utilized by descending projections from PVN to NTS and DMX. While, in some situations, circulating endogenous AVP exerts cardiovascular effects, details of its putative influences on baroreflex mechanisms are lacking.     

Pressure-flow relationships of the canine iliac periphery and systemic hemodynamics: Effects of sodiumnitroprusside and adenosine

It has been reported that sodiumnitroprusside (SNP) decreases mean systemic pressure and simultaneously increases pressure pulse amplification towards the iliac periphery (Kenner and van Zwieten 1982). This unexpected finding was suggested to be due to a decrease in iliac peripheral resistance but an increase in iliac differential resistance. In order to investigate this apparent contradiction, the iliac periphery was hemodynamically isolated from the rest of the circulation and perfused with the dog's own blood by means of a pump. Perfusion pressure (P) and flow (F), femoral venous pressure (P_v), systemic pressure (P_s) and cardiac output (CO) were measured. Steady state pressure-flow relations of the isolated bed were obtained during control and during various i.v. infusion rates of SNP and adenosine (ADS) and were found to be straight (meanr=0.99). Their slope (P/F) was defined as differential resistance (R_d). Peripheral resistance (R_p) of the iliac bed was defined as R_p=(P-P_v)/F, calculated at the flow value where perfusion pressure equalled the prevailing systemic pressure. Total peripheral resistance (TPR) was defined as TPR=P_s/CO. The changes of R_d, R_p, P_s, CO and TPR with respect to control show that during low SNP infusion rates R_d and R_p were both increased while TPR was decreased. During all infusion rates of SNP CO did not change while P_s decreased. During low infusion rates of adenosine CO increased while P_s, R_d and R_p did not change and TPR decreased. During high infusion rates of ADS CO decreased again, R_d, R_p and P_s decreased, and TPR remained constant but at a decreased level.It is concluded that: (1) the suggestion of Kenner and van Zwieten is not supported, since SNP (as well as ADS) affects iliac peripheral and iliac differential resistance in a similar way; (2) SNP (as well as ADS) affects iliac peripheral resistance and total peripheral resistance in a differentiated way, and even in an opposite way during low infusion rates of SNP; (3) it is this opposite effect that explains the paradoxical observations of Kenner and van Zwieten; (4) for comparable reductions of TPR, CO is better maintained during infusion of SNP, while P_s is better maintained during infusion of ADS.     

Assessment of Baroreceptor Reflex Function During Mental Stress and Relaxation

This paper describes a method of measuring baroreceptor cardiac reflex sensitivity noninvasively from spontaneous patterns of blood pressure and interbeat interval, and the application of this technique in psychophysiology. Baroreflex function was assessed in 24 female volunteers during relaxation and performance of the cold pressor test and a non-verbal mental arithmetic task. Blood pressure and interbeat interval were monitored continuously from the finger using the vascular unloading technique. Sequences of three or more cardiac cycles were identified over which systolic blood pressure increased progressively in conjunction with lengthening interbeat interval, or systolic blood pressure decreased as interbeat interval was reduced. The regression between systolic blood pressure and interbeat interval was computed as an index of baroreflex sensitivity. Relaxation was associated with a small prolongation of interbeat interval, whereas baroreflex sensitivity increased from 17.1 to 19.8 ms/mmHg. Baroreflex sensitivity was reduced significantly during mental arithmetic (mean 14.2 ms/mmHg) but not during the cold pressor test (mean 17.4 ms/mmHg). The difference between mental arithmetic and the cold pressor test may be related to the relative intensity of cardiac and vascular responses in the two situations. The implications of these results for the understanding of behavioural influences on haemodynamic function are discussed and the advantages of noninvasive methods are considered.     

An analysis of theα-adrenoceptor modulation of vasomotor tone at the level of lateral medullary pressor area (LMPA)

Summary Microinjection of noradrenaline and clonidine into lateral medullary pressor area (LMPA) of chloralose anaesthetized cats produced dose dependent decrease in blood pressure without affecting heart rate, while phenylephrine did not elicit any cardiovascular response. Selective ₂-adrenoceptor, antagonists idazoxan and piperoxan, microinjected locally, blocked the effects of the agonists but prazosin and phenoxybenzamine, which are relatively selective for ₁-adrenoceptors, failed to do so. Clonidine did not elicit any response in guanethidine pretreated cats but noradrenaline microinjected into LMPA of these animals induced a pressor response which was blocked by prazosin pretreatment. It is concluded that catecholaminergic fibres impinging upon this are inhibit the activity of the inhibitory second order baroreceptor neurone by activating ₁-adrenoceptors while ₂-adrenoceptors situated presynaptically on these inhibitory catecholaminergic nerve terminals are responsible for the manifestation of the hypotensive effect of clonidine and exogenously administered noradrenaline.     

The effects of butorphanol on baroreflex control of heart rate in man

The effects of butorphanol injection on baroreflex control of heart rate were investigated using both pressor and depressor tests in eighteen adult patients. Baroreflex sensistivity was attenuated after butorphanol injection in the pressor test using phenylephrine, whereas it was unchanged in the depressor test using nitroglycerine. No resetting of the baroreflex occurred after butorphanol injection. After the administration of butorphanol, plasma epinephrine and norepinephrine levels increased. These results suggest that it is safe to use butorphanol clinically even when a reduction in blood pressure due to hypovolemia or unclamping of the major artery is expected and that it is disadvantageous to administer the drug when an increase in blood pressure due to cross-clamping of the major artery is predicted.(Wajima Z, Inoue T and Ogawa R: The effects of butorphanol on baroreflex control of heart rate in man. J Anesth 7: 411--418, 1993)     

Adolescent vulnerability to cardiovascular consequences of chronic emotional stress: Review and perspectives for future research

Emotional stress has been recognized as a modifiable risk factor for cardiovascular diseases. Adolescence has been proposed as a developmental period of vulnerability to stress. This idea has been mainly supported by experimental research in animals demonstrating a higher impact of chronic emotional stress in adolescents compared with adults. Adolescent vulnerability is also based on evidence that stress during this developmental period affects development, so that enduring changes are found in adult animals that experienced stress during adolescence. The purpose of the present review is to discuss experimental research in rodent models that investigated the impact of long-term exposure to stressful events during adolescence on cardiovascular function. The development of cardiovascular function and autonomic activity in rodents is initially reviewed. Then, a discussion of an adolescent vulnerability to cardiovascular effects of chronic stress is presented. From the reviewed literature, perspective for future research is proposed to better elucidate adolescent vulnerability to cardiovascular complications evoked by chronic emotional stress.     

Arterial blood pressure response to head-up tilt test and orthostatic tolerance in nurses

Objectives

High tolerance to postural changes was examined in nurses.

Methods

Twelve female nurses and 12 healthy controls underwent a 70° head-up tilt (HUT) test for 10 min. Blood pressure (BP), heart rate (HR), pulse pressure, and hormone levels were measured. Baroreceptor sensitivity (BRS) was calculated using a sequence technique.

Results

HR increased during HUT in both subject groups, with no difference between groups. Systolic BP was rapidly increased by HUT in both subject groups, and was higher in the nurse group than in the control group during the first 2 min of HUT. Pulse pressure decreased during 1–2.5 min of HUT in the control group, but there was no decrease in the nurse group. BRS was decreased by HUT in the nurse group, while it tended to be decreased in the control group. Both during baseline and HUT, BRS was lower in the nurse group than in the control group. Plasma noradrenaline increased with HUT, and the increase was greater in the nurse group than in the control group.

Conclusions

Although nurse subjects had a lower BRS during HUT than control subjects, they were able to effectively maintain BP during HUT, suggesting that nurse subjects had higher orthostatic tolerance. The better maintenance of BP in nurse subjects appeared to be associated with a compensatory mechanism other than the arterial baroreflex and/or a hemodynamic mechanism.     

Lower cardiovagal tone and baroreflex sensitivity associated with hepatic insulin resistance and promote cardiovascular disorders in Tibetan minipigs induced by a high fat and high cholesterol diet

Aims

A long-term high-fat/cholesterol (HFC) diet leads to hepatic insulin resistance (IR), which is associated with autonomic dysfunction and cardiovascular diseases risk increasing. However, whether this occurs in Tibetan minipigs remains unknown. We tested that a long-term HFC diet caused hepatic IR and promote cardiovascular disorders in Tibetan minipigs, and are associated with the reduction of cardiovagal tone and baroreflex sensitivity (BRS).