Tuberculosis among Children and Adolescents at HIV Treatment Centers in Sub-Saharan Africa

HIV-infected children and adolescents are at increased risk for tuberculosis (TB). Antiretroviral therapy (ART) reduces TB risk in HIV-infected adults, but its effectiveness in HIV-infected children and adolescents is unknown. We analyzed data from 7 integrated pediatric HIV/TB centers in 6 countries in sub-Saharan Africa. We used a Bayesian mixed-effect model to assess association between ART and TB prevalence and used adaptive lasso regression to analyze risk factors for adverse TB outcomes. The study period encompassed 57,525 patient-years and 1,160 TB cases (2,017 cases/100,000 patient-years). Every 10% increase in ART uptake resulted in a 2.33% reduction in TB prevalence. Favorable TB outcomes were associated with increased time in care and early ART initiation, whereas severe immunosuppression was associated with death. These findings support integrated HIV/TB services for HIV-infected children and adults and demonstrate the association of ART uptake with decreased TB incidence in high HIV/TB settings.

Adapting HIV services for pregnant and breastfeeding women, infants, children, adolescents and families in resource-constrained settings during the COVID-19 pandemic

INTRODUCTION

The COVID-19 pandemic has impacted global health service delivery, including provision of HIV services. Countries with high HIV burden are balancing the need to minimize interactions with health facilities to reduce the risk of COVID-19 transmission, while delivering uninterrupted essential HIV prevention, testing and treatment services. Many of these adaptations in resource-constrained settings have not adequately accounted for the needs of pregnant and breastfeeding women, infants, children and adolescents. We propose whole-family, tailored programme adaptations along the HIV clinical continuum to protect the programmatic gains made in services.

DISCUSSION

Essential HIV case-finding services for pregnant and breastfeeding women and children should be maintained and include maternal testing, diagnostic testing for infants exposed to HIV, index testing for children whose biological parents or siblings are living with HIV, as well as for children/adolescents presenting with symptoms concerning for HIV and comorbidities. HIV self-testing for children two years of age and older should be supported with caregiver and provider education. Adaptations include bundling services in the same visit and providing testing outside of facilities to the extent possible to reduce exposure risk to COVID-19. Virtual platforms can be used to identify vulnerable children at risk of HIV infection, abuse, harm or violence, and link them to necessary clinical and psychosocial support services. HIV treatment service adaptations for families should focus on family based differentiated service delivery models, including community-based ART initiation and multi-month ART dispensing. Viral load monitoring should not be a barrier to transitioning children and adolescents experiencing treatment failure to more effective ART regimens, and viral load monitoring for pregnant and breastfeeding women and children should be prioritized and bundled with other essential services.

CONCLUSIONS

Protecting pregnant and breastfeeding women, infants, children and adolescents from acquiring SARS-CoV-2 while sustaining essential HIV services is an immense global health challenge. Tailored, family friendly programme adaptations for case-finding, ART delivery and viral load monitoring for these populations have the potential to limit SARS-CoV-2 transmission while ensuring the continuity of life-saving HIV case identification and treatment efforts.

Management of the newborn baby of a mother with suspected or confirmed Covid-19 positivity

The Sars-CoV-2 pandemic has created concern and uncertainty about the management of the newborn and breastfeeding, particularly if the mother has suspected or known coronavirus positivity. In our neonatology department, a second-level center, separate pathways were defined for Covid-positive (or suspected) and Covid-free patients at the beginning of March 2020; isolation rooms were identified, and indications were given regarding the management of the newborn in the delivery room and within the Neonatal Pathology department, with the aim of preventing the spread of the SARS-Cov-2 infection and encouraging breastfeeding.

Resuscitation of the newborn occurs according to the recommended guidelines, taking care to quickly clean the newborn of the mother's blood and fluids. At the end of the stabilization of the newborn, four scenarios can occur:

Newborn who does not require intensive care, born of a mother in good condition and with a positive SARS-CoV-2 swab; follows the mother as she is transferred to the maternal ward of the Covid Hospital (superHub Padova).

Newborn born to a suspected mother, who does not require intensive or semi-intensive assistance; can be managed by favoring rooming-in, compatibly with the mother's conditions.

Newborn who needs intensive or semi-intensive care for neonatal reasons, born from a suspected or SARS-CoV2-positive mother; requires STEN - Neonatal Emergency Transport Service, according to the procedure and dedicated routes.

Newborn born to a positive or suspected mother, who has severe symptoms of respiratory infection or general state impairment; will be separated from the mother and placed in semi-intensive isolation in a dedicated incubator in the neonatal ward.

This paper provides a proposal for the management of the newborn born to a suspected or coronavirus-positive mother, and was formulated to avoid the spread of the infection and to implement neonatal care.

PEPFAR's response to the convergence of the HIV and COVID-19 pandemics in Sub-Saharan Africa

INTRODUCTION

The COVID-19 pandemic reached the African continent in less than three months from when the first cases were reported from mainland China. As COVID-19 preparedness and response plans were rapidly instituted across sub-Saharan Africa, many governments and donor organizations braced themselves for the unknown impact the COVID-19 pandemic would have in under-resourced settings with high burdens of PLHIV. The potential negative impact of COVID-19 in these countries is uncertain, but is estimated to contribute both directly and indirectly to the morbidity and mortality of PLHIV, requiring countries to leverage existing HIV care systems to propel COVID-19 responses, while safeguarding PLHIV and HIV programme gains. In anticipation of COVID-19-related disruptions, PEPFAR promptly established guidance to rapidly adapt HIV programmes to maintain essential HIV services while protecting recipients of care and staff from COVID-19. This commentary reviews PEPFAR's COVID-19 technical guidance and provides country-specific examples of programme adaptions in sub-Saharan Africa.

DISCUSSION

The COVID-19 pandemic may pose significant risks to the continuity of HIV services, especially in countries with high HIV prevalence and weak and over-burdened health systems. Although there is currently limited understanding of how COVID-19 affects PLHIV, it is imperative that public health systems and academic centres monitor the impact of COVID-19 on PLHIV. The general principles of the HIV programme adaptation guidance from PEPFAR prioritize protecting the gains in the HIV response while minimizing in-person home and facility visits and other direct contact when COVID-19 control measures are in effect. PEPFAR-supported clinical, laboratory, supply chain, community and data reporting systems can play an important role in mitigating the impact of COVID-19 in sub-Saharan Africa.

CONCLUSIONS

As community transmission of COVID-19 continues and the number of country cases rise, fragile health systems may be strained. Utilizing the adaptive, data-driven programme approaches in facilities and communities established and supported by PEPFAR provides the opportunity to strengthen the COVID-19 response while protecting the immense gains spanning HIV prevention, testing and treatment reached thus far.

Isolation and characterization of hydrocarbon-degrading bacteria from gas station leaking-contaminated groundwater in the Southern Amazon, Brazil

Abstract Twenty-three hydrocarbon-degrading bacteria strains were isolated from gas station leaking-contaminated groundwater located in the Southern Amazon, Brazil. Based on hydrocarbon (diesel, hexadecane, benzene, toluene and xylene) degradation ability, two strains were selected for further study. The amplification and sequencing of the 16S rRNA gene showed that these two strains belonged to the genus Bacillus (Bacillus sp. L26 and Bacillus sp. L30). GC-MS analysis showed that strain L30 was the most effective in degrading n-alkane (C10-C27) from diesel after 7 days of cultivation in mineral medium. Both strains produced biosurfactants and showed emulsification activity, specially the strain L30. Alkane hydroxylase gene (group III), which is important for alkane biodegradation, was present in strains. As a result, this study indicated that these bacteria could have promising applications in hydrocarbon bioremediation.

Pursuing use of optimal formulations for paediatric HIV epidemic control - a look at the use of LPV/r oral pellets and oral granules

INTRODUCTION

Despite a significant reduction in mother-to-child transmission of HIV, an estimated 180,000 children were infected with HIV in 2017, and only 52% of children under 15 years of age living with HIV (CLHIV) are on life-saving antiretroviral therapy (ART). Without effective treatment, half of CLHIV die before the age of two years and only one in five survives to five years of age.

DISCUSSION

Over the past four years, the United States Food and Drug Administration tentatively approved new formulations of lopinavir/ritonavir (LPV/r) in the form of oral pellets and oral granules. However, the slow uptake of the aforementioned formulations in the low- and middle-income countries with the highest paediatric HIV burden is largely due to three challenges: limited manufacturing capacity; current unit cost of the pellets and granules; and slow uptake of these new formulations by policy makers and health care workers.

CONCLUSIONS

Solutions to overcome these barriers include ensuring availability of an adequate supply of LPV/r oral pellets and oral granules, considering all programmatic and clinical factors when selecting paediatric ART formulations, and leveraging current resources to decrease paediatric HIV morbidity and mortality.

Integration of Neonatal and Child Health Interventions with Pediatric HIV Interventions in Global Health

BACKGROUND/OBJECTIVES

In the last decade, many strategies have called for integration of HIV and child survival platforms to reduce missed opportunities and improve child health outcomes. Countries with generalized HIV epidemics have been encouraged to optimize each clinical encounter to bend the HIV epidemic curve. This systematic review looks at integrated child health services and summarizes evidence on their health outcomes, service uptake, acceptability, and identified enablers and barriers.

METHODS

Databases were systematically searched for peer-reviewed studies. Interventions of interest were HIV services integrated with: neonatal/child services for children <5 years, hospital care of children <5 years, immunizations, and nutrition services. Outcomes of interest were: health outcomes of children <5 years, integrated services uptake, acceptability, and enablers and barriers. PROSPERO ID: CRD42017082444.

RESULTS

Twenty-eight articles were reviewed: 25 (89%) evaluated the integration of HIV services into child health platforms, while three articles (11%) investigated the integration of child health services into HIV platforms. Studies measured health outcomes of children (n=9); service uptake (n=18); acceptability of integrated services (n=8), and enablers and barriers to service integration (n=14). Service integration had positive effects on child health outcomes, HIV testing, and postnatal service uptake. Integrated services were generally acceptable, although confidentiality and stigma were concerns.

CONCLUSION AND GLOBAL HEALTH IMPLICATIONS

Each clinical "touch point" with infants and children is an opportunity to provide comprehensive health services. In the current era of flat funding levels, integration of HIV and child health services is an effective, acceptable way to achieve positive child health outcomes.

BUTIMBA: Intensifying the Hunt for Child TB in Swaziland through Household Contact Tracing

Background

Limited data exists to inform contact tracing guidelines in children and HIV-affected populations. We evaluated the yield and additionality of household contact and source case investigations in Swaziland, a TB/HIV high-burden setting, while prioritizing identification of childhood TB.

Methods

In partnership with 7 local TB clinics, we implemented standardized contact tracing of index cases (IC) receiving TB treatment. Prioritizing child contacts and HIV-affected households, screening officers screened contacts for TB symptoms and to identify risk factors associated with TB. We ascertained factors moderating the yield of contact tracing and measured the impact of our program by additional notifications.

Results

From March 2013 to November 2015, 3,258 ICs (54% bacteriologically confirmed; 70% HIV-infected; 85% adults) were enrolled leading to evaluation of 12,175 contacts (median age 18 years, IQR 24–42; 45% children; 9% HIV-infected). Among contacts, 196 TB cases (56% bacteriologically confirmed) were diagnosed resulting in a program yield of 1.6% for all forms of TB. The number needed to screen (NNS) to identify a bacteriologically confirmed TB case or all forms TB case traced from a child IC <5 years was respectively 62% and 40% greater than the NNS for tracing from an adult IC. In year one, we demonstrated a 32% increase in detection of bacteriologically confirmed child TB. Contacts were more likely to have TB if <5 years (OR = 2.0), HIV-infected (OR = 4.9), reporting ≥1 TB symptoms (OR = 7.7), and sharing a bed (OR = 1.7) or home (OR = 1.4) with the IC. There was a 1.4 fold increased chance of detecting a TB case in households known to be HIV-affected.

Conclusion

Contact tracing prioritizing children is not only feasible in a TB/HIV high-burden setting but contributes to overall case detection. Our findings support WHO guidelines prioritizing contact tracing among children and HIV-infected populations while highlighting potential to integrate TB and HIV case finding.

A bitter pill to swallow: the need for better medications for drug-resistant tuberculosis in children

The large and growing access gap between the number of children who become sick with drug-resistant tuberculosis (DR-TB) and those who are treated for the disease each year represents a significant health systems failure. While there are multiple reasons why children with DR-TB are not diagnosed and treated, a serious challenge is the medications used to treat the disease. This paper presents three child DR-TB cases who were treated incorrectly; the cases are used to illustrate some of the problems with existing second-line medications. Challenges, including the perception that the drugs are more dangerous than the disease, lack of proper dosing recommendations and formulations, and the high cost of current treatment, all contribute to a perverse situation in which the most vulnerable pediatric patients are provided with a lower standard of care. This situation can be reversed with novel partnerships and training models, pharmacokinetic studies of the relevant drugs, increased collaboration, and dedicated funding, grounded in a rights-based approach to DR-TB in children.

Behavioural stress blunts the creatinine clearance increase induced by a protein load in healthy subjects

BACKGROUND

The aim of this study was to investigate how behavioural states related to different levels of stress affected the increments of glomerular filtration rate induced by an acute protein load.

METHODS

Thirteen healthy subjects were enrolled. Each subject was studied from 9:00 h to 15:00 h on two consecutive days. In random order, after a protein meal (1.2 g/kg b.w. of protein), each subject was required to remain in a relaxing, sitting position (resting period, R), or to solve graphical and mathematical problems (behavioural stress period, S). Mean blood pressure (MBP) and heart rate (HR) were monitored by an ambulatory blood pressure device. Urine samples collected in each period were used to measure glomerular filtration rate (GFR, creatinine clearance) and urinary sodium excretion (UNa+V).

RESULTS

Significant decreases in MBP and HR were observed during the resting period after the protein load, which significantly increased GFR. There was also a large increase of UNa+V. During S, the GFR changes were no longer seen whereas the increse of UNa+V was maintained. HR and MBP did not change compared to the prestimulus period.

CONCLUSIONS

We conclude that in healthy subjects behavioural stress can blunt the increase in GFR that follows a protein load, presumably by neuro-humoral activated mechanisms. In our experimental conditions, behavioural stress did not affect UNa+V.

Role of the renal nerves in the control of renin synthesis during different sodium intakes in the rat

OBJECTIVE

The aim of this study was to evaluate the role of the renal nerves in the regulation of renin synthesis in normotensive rats at different sodium balance.

METHODS

Forty-eight male Sprague-Dawley rats were divided in six experimental groups, combining three diets at different NaCl content (normal 0.4%, low 0.04% or high 4.0%), and the surgical, bilateral renal denervation or the sham procedure. After 7 days of dietary treatment, all rats were sacrificed and plasma renin activity (PRA) was measured. Renin messenger RNA (mRNA) levels in the renal cortex were determined by semiquantitative polymerase chain reaction.

RESULTS

PRA was higher in animals fed the low sodium diet compared with those at standard diet, while it was lower in animals fed the high sodium diet. Renal denervation decreased PRA in normal and low sodium groups, while it did not alter the PRA values in the high sodium group. Renin gene expression significantly increased in rats fed with the low sodium diet compared with the standard diet group, and significantly decreased in rats fed the high sodium diet Renal denervation significantly reduced renin mRNA levels in rats receiving the low sodium diet, but did not produce any significant change in normal or high-sodium groups.

CONCLUSION

The activation of renin gene expression during sodium depletion in rats is dependent on the presence of the renal nerves, while the suppression of renin gene expression during a sodium load seems to be due to the macula densa mechanism alone.

Dexamethasone does not affect vasopressin release in bronchopulmonary dysplasia

Elevated levels of vasopressin (AVP) have been found in premature infants with bronchopulmonary dysplasia (BPD), and may be related to abnormalities of water handling, and to non-pulmonary signs of edema. Dexamethasone treatment improves pulmonary function in infants with BPD, and is frequently associated with a significant increase in diuresis and a decrease in weight gain. To determine whether this diuresis is primarily the result of AVP inhibition (potentially induced by steroid treatment), we measured endogenous AVP levels in nine premature babies with BPD [birth weight 802 +/- 141 (SD) g; gestation 26 +/- 2 weeks, age 26 +/- 17 days], before initiation, and 3 and 7 days after the start of dexamethasone therapy (0.5 mg/kg/day). All study infants required mechanical ventilation, and none was receiving diuretics or cardiac inotropes during the study. Results indicated that premature infants with BPD have functionally unmodified AVP levels after 3 and 7 days of dexamethasone therapy (pre-dexamethasone 5.9 +/- 2.1 ng/l vs post-dexamethasone 7.0 +/- 3.0 and 8.0 +/- 1.9 ng/l at 3 and 7 days, respectively). Pulmonary function improved with oxygenation indexes decreasing (pre-dexamethasone 14 +/- 7 vs post-dexamethasone 9 +/- 7 and 7 +/- 4 at 3 and 7 days, respectively). A concurrent reduction in weight gain occurred (pre-dexamethasone 12 +/- 10 g/kg/day vs post-dexamethasone 7 +/- 3 g/kg/day and 3 +/- 1.5 g/kg/day on days 3 and 7, respectively). These data suggest that the improvement in lung function with dexamethasone treatment for BPD in premature infants does not correlate with a diuresis that results from vasopressin inhibition, and potentially induced by dexamethasone.

Short-term analysis of the relationship between blood pressure and urinary sodium excretion in normotensive subjects

The aim of this study was to investigate whether, in the short term, physiological blood pressure changes are coupled with changes in urinary sodium excretion in normotensive subjects, maintained at fixed sodium intake and under controlled postural and behavioural conditions. Twelve normotensive subjects were recruited. For each subject, seven urine samples were collected at fixed time intervals during an overall 26 h period: late afternoon (16.00-20.00 hours), evening (20.00-24.00 hours), night (24.00-06.00 hours), quiet wakefulness (06.00-09.00 hours), morning (09.00-12.00 hours), post-prandial (12.00-15.00 hours) and afternoon (15.00-18.00 hours). Blood pressure was monitored by an ambulatory blood pressure device during the whole 26 h period. Each urine sample was used to measure urinary sodium excretion and glomerular filtration rate (creatinine clearance). Blood pressure, heart rate, urinary sodium excretion and glomerular filtration rate recorded in the daytime were higher than those measured during the night-time. A significant positive correlation between mean blood pressure and urinary sodium excretion was found during the night, over the whole 26 h period, and during two subperiods of the daytime: quiet wakefulness and the post-prandial period. The coefficient of the pressure-natriuresis curve was significantly decreased by postural changes. We conclude that, in normotensive subjects, blood pressure and urinary sodium excretion are coupled in the short term. The assumption of an upright posture can mask this relationship, presumably by activating neurohumoral factors.

Effects of adenosine receptor agonists on efferent renal nerve activity in anesthetized rats

The aim of this study was to investigate the effects of A1 and A2 adenosine-receptor activation on the sympathetic nervous system. The effects on efferent renal nerve activity of selective A1 (CCPA; 2-chloro-N-6-cyclopentyladenosine) and A2 (2HE-NECA; 2-hexynyl-5'-N-ethylcarboxamidoadenosine) adenosine-receptor agonists were studied in anesthetized rats either with intact baroreflexes (intact rats) or with bilateral sinoaortic denervation and vagotomy (denervated rats). After a control period of 5 min, A1 or A2 agonist or vehicle were intravenously infused for 8 min in separate groups of intact or denervated rats, in which arterial pressure and heart rate were continuously recorded. CCPA (5.0 microg/kg/min) and 2HE-NECA (0.7 microg/kg/min) were selected to obtain comparable blood pressure changes over the period of observation. Arterial pressure significantly and equally decreased during the A1 (-41 +/- 8%), and A2 (-35 +/- 5%) agonist administration. Heart rate significantly decreased during A1 agonist infusion, but it did not change during A2 agonist administration. Bilateral sinoaortic denervation and vagotomy did not modify the hemodynamic responses to both drugs. The A1 and A2 administration caused a large and significant increase in efferent renal nerve activity (+66 +/- 22% and +76 +/- 15%, respectively), and this effect was entirely abolished in denervated rats. A linear relation with a significant negative slope between changes in arterial pressure and changes in neural discharge was observed for each treatment. The comparison of the regression slopes showed that the reflex increase of efferent sympathetic activity caused by the administration of both agonists was significantly smaller than the increment induced by equipotent hypotensive dose of sodium nitroprusside (10 microg/kg). These data show that the selective activation of A1 and A2 receptors elicits a reflex increase in efferent renal nerve activity. This neural activation is smaller as compared with the effect of equihypotensive doses of sodium nitroprusside, thus indicating a blunting effect of both adenosine agonists on baroreceptor sensitivity.

Serum enzyme activities in premature infants with bronchopulmonary dysplasia

Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyltranspeptidase (gamma-GT) and lactate dehydrogenase (LDH) activities were measured in 26 premature infants with bronchopulmonary dysplasia (BPD) (group 1), and in 24 premature controls, matched for gestational age and birth weight (group 2). Blood samples were taken serially on 3, 10, 20, 30 and 60 postpartum days. Group 1 and group 2 premature infants showed statistically higher LDH activities on the 3rd postpartum day. These differences disappeared later and LDH activities progressively decreased with time in both premature groups. Mean AST values of group 1 and group 2 premature infants were also significantly higher on the 3rd postpartum day. Subsequently, in all groups, AST showed a postpartal decrease, and a stabilization from the 10th day of life until the 2nd postnatal month. Mean ALT values were instead, comparable on the 3rd postnatal day and subsequently increased, although not significantly. Like the AST, gamma-GT of group 1 and group 2 premature infants were slightly more elevated on the 3rd postpartum day. The subsequent decrease was however transitory, and at 1 and 2 postnatal months a noticeable, significant progressive increase in mean values was found. It is concluded that serum ALT, AST, LDH and gamma-GT measurement of sick premature infants within the first 2 months of life are not significantly altered by the occurrence of BPD.

Role of the renal nerves and angiotensin II in the renal function curve

The relationship between renal perfusion pressure and urinary sodium is involved in arterial pressure regulation. The aim of this study was to investigate the role of renal nerves and angiotensin II in the pressure-natriuresis relationship. Experiments were performed in anaesthetised cats in which one kidney was surgically denervated. Renal perfusion pressure (RPP), renal blood flow (RBF) glomerular filtration rate (GFR, creatinine clearance), urinary volume (V) and sodium excretion (Una + V) were separately measured from both kidneys. RPP was progressively reduced in two consecutive steps by a suprarenal aortic snare. Two groups of animals were studied: the first without any pharmacological treatment (Untreated), the second during treatment with an angiotensin converting enzyme inhibitor (Captopril, 0.4 mg/Kg intravenously followed by an infusion of 0.4 mg/Kg/h). In the Untreated group RPP was reduced from 152.4 +/- 7.3 to 113.6 +/- 5.8 and 83.0 +/- 4.4 mmHg during the first and second step respectively. RBF and GFR were only slightly reduced during the second step of reduced RPP. In control conditions V and UNa + V were greater in the denervated compared to the innervated kidney. The graded decrease in RPP reduced both V and UNa + V in the innervated as well as in the denervated kidney. In the Captopril group V and UNa + V were larger than in the Untreated group in both the innervated and the denervated kidney. A decrease of RPP similar to that observed in the Untreated group, produced similar haemodynamic changes. Also in the Captopril group the graded decrease in RPP reduced both V and UNa + V in the innervated as well as in the denervated kidney. Matching UNa + V against RPP values significant correlations were found in the innervated and denervated kidneys of both groups. Both renal denervation and ACE inhibition were accompanied by an increased gain of the pressure-natriuresis curve, but only renal denervation shifted the crossing of the pressure axis to the left. In the ACE inhibited animals renal denervation only shifted the curve to the left. In conclusion our data suggest that i) at each level of RPP renal nerves and angiotensin II decrease renal sodium excretion, ii) renal nerves and angiotensin II increase the slope of the renal function curve, iii) renal nerves shift to the right the renal function curve.

Risk factors of hypoglycemia in premature infants

Hypoglycemia is a frequent complication of preterm birth and may lead to later CNS damage. The hypoglycemia incidence and the relative risk factors for the affected preterm infants were assessed. We examined 1,500 preterm infants (<37 weeks of gestational age) consecutively admitted between January 1994 and December 1996 at the Department of Pediatrics of Padua University, and screened for hypoglycemia by Dextrostix within the first hour of life. Hypoglycemia was defined as blood glucose levels <40 mg% at Dextrostix. Among study prematures, 35% had hypoglycemia; while the incidence was 9% at levels of Dextrostix <20 mg%. The relative risk for hypoglycemia (odds ratio, OR) was computed assuming a 99% confidence interval (CI). We found 5 risk factors for hypoglycemia: cesarean section (OR 2.24, CI 1.66-3.03), intrauterine malnutrition (SGA) (OR 1.65, CI 1.08-2.53), NICU hospitalization (OR 1.45, CI 1. 09-1.93), gestational age between 30 and 33 weeks (OR 1.93, CI 1. 34-2.78), and twinning (OR 2.49, CI 1.77-3.56). At levels of Dextrostix <20 mg%, 3 more risk factors were found: cardiopulmonary resuscitation at birth (OR 4.06, CI 2.52-6.54), neonatal respiratory distress syndrome (OR 2.21, CI 1.34-3.36) and gestational age between 26 and 29 weeks (OR 2.16, CI 1.02-4.25). The identification of relative risk factors could be useful in improving the hypoglycemia prophylaxis, and in reducing related later CNS abnormalities.

Effects of adenosine receptor agonists on renal function in anaesthetized rats

OBJECTIVES

To investigate the effects of the interaction between adenosine receptors and renal nerves on urinary sodium excretion and glomerular filtration rate.

METHODS AND DESIGN

The effects on water and sodium excretion and glomerular filtration rate of A1 [2-chloro-N6-cyclopentyl-adenosine (CCPA)] and A2 [2-hesinyl-5'-N-ethyl-carboxamido-adenosine (2HE-NECA)] adenosine agonists were studied in anaesthetized rats with one kidney surgically denervated. Arterial blood pressure, heart rate and rate of urine flow from each kidney were continuously recorded; inulin clearance was used as an index of glomerular filtration rate. The experiments were performed with three groups of rats, into which, after a control period of 20 min, CCPA, 2HE-NECA or vehicle was infused for two subsequent 20 min periods.

RESULT

During infusion of CCPA, the slight decrease in arterial pressure was associated with a transient decrease in glomerular filtration rate and marked long-lasting decreases in heart rate, water and sodium excretion and fractional sodium excretion. The response of the innervated kidney was similar to the response of the denervated kidney. Infusion of 2HE-NECA caused decreases in arterial pressure, glomerular filtration rate and excretion of water and sodium associated with an increase in heart rate. The reduction of water and sodium excretion from the innervated kidney was larger than that from the denervated kidney.

CONCLUSIONS

Activation both of A1 and of A2 receptor causes a reduction in urinary water and sodium excretion. The renal response to activation of A2 receptors is enhanced by the presence of renal nerves, whereas the response to activation of A1 receptors is not influenced by renal nerves.

Effects of erythropoietin administration on blood pressure and urinary albumin excretion in rats

The effects of recombinant human erythropoietin (rHuEPO) administration on blood pressure and urinary albumin excretion were studied in normotensive Wistar-Kyoto rats (WKY), in spontaneously hypertensive rats (SHR), and in SHR rats treated with an angiotensin converting enzyme inhibitor (SHR-ACEi). Rats were housed in metabolic cages and treated with rHuEPO (150 U/kg body weight [bw] three times a week) for 6 weeks. Control animals received the vehicle only (0.25 mL of physiological saline). An angiotensin converting enzyme inhibitor was administered in the drinking water for 6 weeks (spirapril 5 mg/kg bw). Systolic blood pressure (SBP), and 24 h urinary albumin excretion (UAE) were measured once a week. No significant differences in SBP were observed between rHuEPO and vehicle-treated normotensive animals at the end of the treatment (171.9 +/- 4.9 v 172.1 +/- 5.6 mm Hg, respectively). After 6 weeks, SBP was significantly higher in SHR and SHR-ACEi groups treated with rHuEPO than in control groups (239.8 +/- 7.3 and 243.0 +/- 7.3 mm Hg v 218.1 +/- 6.0 and 187.9 +/- 4.6 mm Hg, respectively); UAE was significantly higher in groups treated with rHuEPO than in control groups (WKY: 265.9 +/- 19.5 v 127.0 +/- 12.3 microg/100 g bw, SHR: 1668.4 +/- 564.6 v 234.8 +/- 22.9 microg/100 g bw, and SHR-ACEi: 1522.7 +/- 448.3 v 143.0 +/- 18.9 microg/100 g bw, respectively). We concluded that erythropoietin treatment causes an increase in arterial pressure in SHR only, and an increase in UAE in both normotensive and hypertensive rats. The albuminuric effect was not entirely dependent on increased blood pressure. The treatment with an angiotensin converting enzyme inhibitor did not modify either the proteinuric or the pressor effects.

Renal afferents responsive to chemical and mechanical pelvic stimuli in the rabbit

1. Afferent nerve fibres sensitive to changes in the renal chemical environment have been found in the rat. To verify the existence of these fibres in the rabbit and their response pattern, afferent renal nerve activity was recorded during pelvic perfusions with NaCl solutions at different concentrations. 2. The experiments were carried out in 13 anaesthetized rabbits. Arterial pressure from a femoral catheter and afferent renal nerve activity from the distal stump of a cut renal nerve bundle were recorded. Three catheters were inserted into the renal pelvis to measure pelvic pressure, to allow pelvic perfusions at constant rates and to drain pelvic fluids. 3. After a control period, the pelvis was perfused with physiological saline (0.14 mol/l for 2 min), followed by one of a series of solutions containing increasing concentrations of NaCl (0.5, 0.75, 1.0 and 1.5 mol/l for 2 min). Pelvic perfusion was performed both at a low (0.2 ml/min) and a high (0.8 ml/min) flow rate for each solution tested. 4. In all animals arterial pressure was not modified during pelvic perfusions. Physiological saline did not change afferent renal nerve activity at the low perfusion rate, but it significantly increased afferent renal nerve activity and pelvic pressure at the high rate. Hypertonic NaCl solutions caused progressive increases in afferent renal nerve activity at both perfusion rates, and these effects were larger at the high perfusion rate. 5. These data demonstrate, in the rabbit, the existence of renal afferent nerves sensitive to discrete changes in pelvic ionic or osmotic concentration. The neural response is enhanced when renal mechano- and chemo-receptors are simultaneously activated.

Excretory responses to renal nerve stimulation during inhibition of neutral metalloendopeptidase and angiotensin-converting enzyme in the rat

To evaluate the interaction between renal nerves, the atrial natriuretic peptide (ANP), and the renin-angiotensin system (RAS), electrical stimulation of renal nerves was performed in spontaneously hypertensive rats (SHR) and in their normotensive controls, Wistar Kyoto rats (WKY), before and after pharmacologic treatment with (a) a neutral endopeptidase inhibitor (NEP-i) to enhance the intrarenal ANP activity; (b) an ACE inhibitor (ACE-i) to block RAS; (c) both NEP-i and ACE-i; and (d) the vehicle of the drugs. Renal nerve stimulation did not change arterial pressure (AP) but reduced renal blood flow (RBF), glomerular filtration rate (GFR), and urinary sodium excretion (UNa+V) in both WKY and SHR. NEP-i treatment in WKY and SHR had no systemic or renal hemodynamic effects but increased GFR and urinary cyclic guanosine monophosphate (GMP) excretion; UNa+V increased (+2.78 +/- 0.31 microEq/min) in WKY, whereas it did not change in SHR (+0.83 +/- 0.79 microEq/min). In both strains, ACE-i treatment reduced AP, increased RBF, and did not change GFR and UNa+V. The combined treatment with NEP-i and ACE-i did not modify the natriuretic effect observed in NEP-i treated WKY (+4.29 +/- 1.25 microEq/min), but it elicited a natriuretic effect in SHR (+3.98 +/- 1.29 microEq/min). Pharmacologic treatment did not change the hemodynamic and excretory responses to renal nerve stimulation in both WKY and SHR. In conclusion, NEP-i treatment increased UNa+V in normotensive rats without changing AP. In hypertensive rats, the natriuretic effect of NEP-i became evident only after block of RAS by ACE-i. Neither NEP-i nor ACE-i, even in combination, could modify the renal responses to sympathetic stimulation.

Functional evidence of inhibitory reno-renal reflexes in spontaneously hypertensive rats

The experiments were performed to study the role of the renal nerves and the reno-renal reflexes in the control of water and sodium excretion in spontaneously hypertensive rats (SHR) compared to their normotensive controls, Wistar Kyoto (WKY) rats. Unilateral renal denervation in anaesthetized animals produced a slight, progressive decrease in arterial pressure in both WKY and SHR rats. The glomerular filtration rate temporarily increased in the kidney that underwent the denervation in the SHR group only. After unilateral renal denervation a sharp increase in water and sodium excretion from the ipsilateral kidney was observed in both WKY and SHR. One hour after the denervation, the percent changes in water and sodium excretion were smaller in WKY (+32 +/- 19% and +24 +/- 17%) than in SHR rats (+84 +/- 15% and +93 +/- 20%). In the kidney contralateral to the denervation a reduction in water and sodium excretion was observed and this reduction was prompter in SHR than in WKY rats. One hour after the denervation, the percent changes in water and sodium excretion were similar in WKY (-21 +/- 8% and -18 +/- 7%) and SHR (-19 +/- 6% and -19 +/- 7%). In control groups, sham denervation did not cause significant changes in glomerular filtration rate, and urinary water and sodium excretion. Arterial pressure slightly and progressively decreased in both control groups. Electrical stimulation of the efferent renal nerves performed in WKY and SHR produced similar decreases in renal blood flow, glomerular filtration rate, and water and sodium excretion in the two groups for the same frequencies of stimulation. As this finding indicates that renal targets in hypertensive rats are normally responsive to the neural drive, our data demonstrate that renal responses to unilateral renal denervation in hypertensive rats are equal to the responses observed in normotensive rats. Our results indicate that tonically active inhibitory renorenal reflexes normally operate in spontaneously hypertensive rats.

Analysis of the dynamics of renal vascular resistance and urine flow rate in the cat following electrical stimulation of the renal nerves

In ten sino aortic denervated, vagotomized and aneasthetized cats, renal efferent nerves were stimulated for 30 s with trains of constant current pulses at frequencies in the range 5-30 Hz. The arterial pressure, heart rate, urine flow rate (electronic drop counter) and renal blood flow (electromagnetic technique) were recorded. Subsequent computer processing gave the true means of renal artery pressure (MRAP) and renal blood flow (MRBF) and hence the renal vascular resistance (MRVR), over each cardiac cycle. Recovery of MRVR after the end of stimulation exhibited two distinct time constants. The fast component had a time constant of 2.03 +/- 0.26 s and represented 60.2 +/- 1.71% of the recovery. The time constant of the slower component was 14.1 +/- 1.9 s and represented 36.0 +/- 1.6% of the recovery. The relationship between MRVR and stimulus frequency was sigmoidal with maximum sensitivity at stimulus frequencies of 12.6 +/- 0.76 Hz. Changes in urine flow rate, in contrast, followed a hyperbolic function with maximum response sensitivity occurring at very low stimulus frequencies. Changes in urine flow rate were 50% complete at stimulus frequencies of 5 Hz. Identification of two distinct components in the relaxation phase of renal vascular resistance leads to a reasonable hypothesis that 60% of total renal vascular resistance may lie proximal to the glomerulus, whereas 36% may be accounted for by the efferent arterioles.

Effects of adenosine-receptor agonists on renin release in anaesthetized rats

OBJECTIVE

To investigate the effects of the interaction between adenosine receptors and renal nerves on renin release.

MATERIALS AND METHODS

The effects on renin secretion of A1 (2-chloro-N6-cyclopentiladenosine) and A2 (2-hexynil-5'-N-ethyl-carboxamido-adenosine) adenosine-receptor agonists were studied in two groups of anaesthetized rats, each with one kidney surgically denervated. Arterial blood pressure and the renal blood flow of innervated and denervated kidneys were continuously recorded. Cannulae were inserted into both renal veins through femoral veins. After 1h of rest, A1 and A2 agonists were intravenously infused for 30 min in the two groups of rats. Plasma renin activity was measured by radioimmunoassay in blood samples drawn simultaneously from both renal veins and the femoral artery before and after the drug infusion.

RESULTS

Infusions of A1 and A2 agonists produced comparable hypotensive effects. During A1 agonist administration, the heart rate decreased significantly, but it did not change after A2 agonist treatment. Renal blood flow was reduced by administration of the A1 agonist in both kidneys, while A2 agonist administration significantly reduced the renal blood flow of the innervated kidney only. The veno-arterial difference in plasma renin activity decreased after the A1 agonist infusion in both kidneys, but after the A2 agonist infusion it increased significantly in the innervated kidney only.

CONCLUSIONS

Renal nerves do not influence the inhibition of renin release mediated by A1 adenosine receptors. In vivo, A2-receptor agonist administration can stimulate renin release only in the presence of intact renal nerves.

Renal afferents signaling diuretic activity in the cat

Mechanoreceptors and chemoreceptors have been identified inside the kidney, but their functional role is still largely unclear. The aim of this study was to investigate whether changes in urine output could modify the discharge rate of renal afferent fibers. Experiments were performed in anesthetized cats in which afferent renal nerve activity (ARNA) was recorded by standard electrophysiological techniques from a centrally cut renal nerve. Arterial pressure, renal blood flow velocity, urine flow rate, and renal pelvic pressure were also measured. Three diuretic maneuvers were tested in the same cat: intravenous administration of physiological saline (8 to 13 mL/min for 2 minutes), furosemide (1 mg/kg), and atrial natriuretic peptide (ANP, 1 microgram/kg). The three maneuvers increased urine flow rate and pelvic pressure, respectively, 137.0 +/- 20.6% and 136.8 +/- 21.1% (saline), 148.6 +/- 31.7% and 139.6 +/- 43.5% (furosemide), and 75.9 +/- 7.9% and 62.1 +/- 21.2% (ANP) at the time of the maximum response. Arterial pressure slightly increased after saline, did not change after furosemide, and slightly decreased after ANP. Renal blood flow increased after saline and did not change after furosemide and ANP. The three maneuvers increased ARNA by 98.4 +/- 15.2% (saline), 270.7 +/- 100.8% (furosemide), and 59.6 +/- 23.4% (ANP). Changes in ARNA significantly correlate with changes in both pelvic pressure and urine flow rate. Our data demonstrate that increments in urine flow rate increase the firing rate of renal afferent fibers and suggest that (1) pelvic pressure is the major determinant of the neural response, and (2) this increased afferent discharge is due to activation of renal mechanoreceptors.

Sympathorenal Interactions in the Control of Cardiovascular Functions

Efferent renal nerve activity participates in the control of several renal functions: hemodynamics, renin release, and excretory functions. These renal functions are involved in cardiovascular homeostasis either by affecting peripheral resistances or volume balance. Also, afferent renal nerve activity can influence peripheral resistances and volume balance.

Interactions between the sympathetic nervous system and atrial natriuretic factor in the control of renal functions

We studied neural influences on the renal actions of atrial peptides in anaesthetized cats by comparing the response to atrial natriuretic factor (ANF) infusion in the innervated kidney and in the contralateral surgically denervated kidney. During ANF infusion arterial pressure decreased, the heart rate did not change and blood flow to both kidneys increased slightly. Vascular conductances became slightly but significantly higher in the denervated kidneys than in the controls. In both kidneys, the glomerular filtration rate increased transiently and significantly. Inhibition of renin release was more prompt and larger in the innervated than in the denervated kidneys. ANF infusion caused a significant increase in sodium and water excretion from both the innervated and denervated kidneys. However, the diuretic and natriuretic effect in the innervated kidneys, although proportionally greater than that in the denervated kidneys, was of shorter duration and subsided after 20 min of ANF infusion. Efferent renal nerve activity did not change during the initial 10 min of ANF infusion but thereafter increased progressively and significantly. We conclude that the effects of atrial peptides on renin release and excretory functions are influenced by renal nerve activity.

Role of the renal nerves in the natriuretic response to vasopressin infusion

The present study was designed to determine whether renal nerves influence the natriuretic response to an infusion of vasopressin. Experiments were performed on anaesthetized rats in which the response to vasopressin of the innervated kidney was compared with that of the contralateral surgically denervated kidney. During the vasopressin infusion the natriuretic effect was evident in both kidneys and was proportionally greater in the innervated kidney than in the denervated one. Efferent renal nerve activity, recorded in three additional animals, decreased during the vasopressin infusion. Our data demonstrate that the natriuretic response of the innervated kidney is larger than that of the denervated kidney, probably because of an associated decrease in efferent renal nerve activity.

Neural control of renin release

Among the major mechanisms controlling the renal release of renin, renal nerves are known to exert a direct stimulating action on juxtaglomerular cells that is mediated by beta-adrenoceptors. Activation of the renal nerves also exerts an important permissive role in order to amplify and possibly accelerate responses to stimuli affecting the vascular and macula densa mechanisms. Reduction of renal perfusion pressure, intravenous infusion of furosemide, and captopril administration cause a greater increase in renin release from innervated kidneys than from denervated kidneys. A complex interaction between neural and non-neural mechanisms in the control of renin secretion is suggested. Efferent renal nerve activity controlling the renin secretion rate is mainly under the inhibitory influence of vagal afferent fibers originating from the cardiopulmonary region. Recent experiments have demonstrated that a similar reflex tonic inhibition of renin secretion is also exerted by renal afferent fibers.

Afferent pathways of neural reno-renal reflexes controlling sodium and water excretion in the cat

We have studied the role of afferent renal nerve fibres in anaesthetized cats in mediating the decrease in sodium and water excretion from the contralateral kidney caused by unilateral renal denervation. Transient denervation of one kidney obtained by cooling of the left renal nerves increases contralateral efferent renal nerve activity and decreased sodium and water excretion from the opposite kidney. The results observed in animals with intact neural pathways were compared with those obtained after the left kidney had been selectively deafferentated by cutting the dorsal roots from T9 to L4. Bilateral section of dorsal roots did not affect the increase in sodium and water excretion from the transiently denervated left kidney, but entirely abolished the decrease in sodium and water excretion from the contralateral kidney. Neither the left nor the right dorsal root section alone, affected the response of the contralateral right kidney. Our data demonstrate that afferent renal nerve fibres project bilaterally to the spinal cord and form the afferent branch of the reno-renal reflex by which one kidney can control the function of the opposite one.

Renal reflexes in the regulation of blood pressure and sodium excretion

The rich innervation of the kidney is distributed to all structures of renal parenchyma thus providing important anatomical support to the functional evidence that the renal nerves can control kidney functions and send signals on the kidney environment to the central nervous system. Efferent renal nerve fibres are known to influence renal haemodynamics by modifying arteriolar vascular tone, renin release by a direct action on juxtaglomerular cells, and the excretion of sodium and water by changing tubular reabsorption of sodium and water at the different tubular levels. Mechano- and chemo-receptors have been shown in the kidney. Afferent fibres connected with renal receptors convey signals to the central nervous system both at spinal and supraspinal levels. The central areas receiving inputs from the kidney are those involved in the control of cardiovascular homeostasis and fluid balance. Activation of renal receptors by the electrical stimulation of renal afferent fibres were found to elicit both excitatory and inhibitory sympathetic responses. Although the existence of excitatory renorenal reflexes has been suggested, electrophysiological and functional data demonstrate that neural renorenal reflexes exert a tonic inhibitory influence on the tubular sodium and water reabsorption and on the secretion of renin from the juxtaglomerular cells.

Cardiovascular effects of afferent renal nerve stimulation

Electrical stimulation of afferent renal nerves elicits an increase in arterial pressure and heart rate. The hypertensive response is presumably due to the widespread activation of the sympathetic nervous system leading to peripheral vasoconstriction. Interestingly, the kidney does not appear involved in this reflex excitatory response to afferent renal nerve stimulation since changes in vascular conductances and excretory functions are equal in both the innervated and denervated kidney, and secondary to changes in renal perfusion pressure. In addition, no changes in renin release from either kidneys are observed during afferent renal nerve stimulation. It is likely that the electrical stimulation of afferent renal nerves activates other reflexes exerting an inhibitory influence on efferent renal nerve activity. Indeed, neural renorenal reflexes which tonically inhibit renal functions have clearly been demonstrated. Furthermore, preferential inhibition of efferent renal nerve activity by cardiopulmonary and sinoaortic receptors has recently been shown during activation of other visceral afferents.

Effects of reversible renal denervation on haemodynamic and excretory functions of the ipsilateral and contralateral kidney in the cat

In anaesthetized cats reversible denervation of one kidney was performed by cooling of the left renal nerves to 3 degrees C for 16 min. The response of the left (ipsilateral) kidney was compared with the response of the right (contralateral) kidney twice in the same animal: (1) when the right kidney was still innervated, and (2) after it had been surgically denervated. Left renal nerve cooling did not cause any changes in arterial pressure. In the left kidney, blood flow, vascular conductance, sodium and water excretions increased, and renin release decreased. Simultaneously in the contralateral kidney, no haemodynamic changes were observed, glomerular filtration was only transiently decreased, whereas sodium and water excretion significantly decreased and renin release increased. When left renal nerve cooling was repeated after surgical denervation of the right kidney, similar changes were observed in the left (ipsilateral) kidney, whereas all contralateral effects were abolished. These experiments suggest that tonically active afferent fibres from one kidney exert a reflex inhibitory action on sympathetic activity directed to the contralateral kidney controlling tubular sodium reabsorption and renin release.

Regulation of sodium and water excretions by neural renorenal reflexes in the cat

The reduction in sodium and water excretion observed in the right kidney when the left kidney is subjected to transient denervation, is entirely abolished by bilateral section of the dorsal roots from T9 to L4, whereas section of the left dorsal roots only, at the same spinal level, does not affect the contralateral renal response to left renal nerve cooling. The possibility that the bilateral dorsal roots section abolished the response of the right kidney because the afferent fibres from the left kidney travel in the right dorsal roots was explored in the present study. Experiments were performed in anaesthetized cats in which reversible denervation of the left kidney was done by cooling of left renal nerves (for 10 min) after cutting the right dorsal roots from T9 to L4. Cooling of left renal nerves caused a large increase in sodium and water excretion from the left kidney and a prompt decrease in sodium and water excretion from the right kidney. During the cooling period arterial pressure did not change and glomerular filtration rate slightly increased in the left kidney only. The results obtained in this group of animals were not significantly different from those previously observed in sham-operated cats or in cats with section of left dorsal roots only. As the contralateral antidiuretic and antinatriuretic response to renal denervation survives dorsal root section on either side but is prevented by bilateral section, this demonstrates that the inhibitory renal afferent fibres responsible for this renorenal reflex are distributed bilaterally to spinal dorsal roots.

Effects of afferent renal nerve stimulation on renal hemodynamic and excretory functions

In anesthetized cats (n = 9) renal afferent fibers were electrically stimulated for 11 min, and the response of the contralateral innervated kidney was compared with that of the ipsilateral denervated one. Before stimulation, renal blood flow, glomerular filtration rate, and water and sodium excretions were significantly lower in the innervated kidney than in the denervated one. Afferent renal nerve stimulation augmented arterial pressure and also increased sodium and water excretions from both kidneys without concomitant changes in glomerular filtration rates and renal blood flows. Absolute and percent changes in sodium and water excretions from the innervated kidney were similar to those observed in the denervated one. The same results were obtained in cats (n = 4) which underwent bilateral adrenalectomy to avoid the effect of circulating catecholamines. In another group of cats (n = 5), the increase in renal perfusion pressure due to the stimulation was prevented by an aortic snare: this resulted in a slight but equal decrease of all variables in both kidneys. These experiments do not show a reflex control of renal function from renal afferents.

Neural control of the kidney--are there reno-renal reflexes?

Circulatory, secretory (renin release) and excretory (tubular sodium and water reabsorption) renal functions are known to be under neural control exerted by sympathetic fibers. Influences on circulatory and secretory functions are modulated by vagally mediated reflexes originated from low pressure (or volume) receptors in the cardiopulmonary area. The possibility that reno-renal reflexes may also exist has raised interest recently. Mechanoreceptors and chemoreceptors have been described in the kidney, and electrophysiological evidence of reno-renal reflexes is available. However, electrical stimulation of afferent renal nerves has failed to reflexly influence circulatory, secretory and excretory functions of the contralateral kidney. Deafferentation studies have been more successful, however. Transient denervation of one kidney by renal nerve cooling is accompanied by reduction of sodium and water excretion from the contralateral kidney with negligible changes in blood flow and glomerular filtration rate. The contralateral antidiuretic activity is prevented either by denervation of the contralateral kidney or by interruption of the afferent fibers running in the spinal dorsal roots. This definitely shows that a reno-renal reflex exists, consisting in a tonic inhibition of contralateral sympathetic activity controlling tubular reabsorption of sodium and water, and renin release.

Do renal afferent fibres modulate the function of the contralateral kidney?

Denervation of one kidney has been shown to induce a prompt decrease in sodium and water excretion from the contralateral kidney. The present study was designed to clarify whether this response is due to suppression of a tonic inhibitory renorenal reflex. Experiments were performed in anaesthetized cats in which the renal nerves of the left kidney were transiently blocked by cooling and the effects of this blockade on either kidney were studied in three different groups of animals. The decrease in sodium and water excretion from the contralateral (right) kidney observed in the sham-operated group (intact dorsal roots) was still present, and substantially unchanged, in the second group of animals in which the ipsilateral (left) dorsal roots from T9 to L4 were cut. In the third group of cats, bilateral dorsal root section entirely abolished the response of the contralateral kidney to renal nerve cooling. These experiments demonstrate that the contralateral decrease in sodium and water excretion is due to the block of afferent renal nerve fibres which project bilaterally to the spinal cord.

Cryoactivation fails to augment plasma renin activity in the cat

1. Active and cryoactivated renin (plasma renin) activity after incubation at -5 degrees C for 4 days, were measured in cat plasma sampled before and during the following procedures: suprarenal aortic stenosis, electrical stimulation of the pons and mild hypotensive haemorrhage. 2. Under all experimental conditions the values of plasma renin activity for both the activated and non-activated samples were similar. 3. The absence of a cryoactivatable aliquot of renin suggests that in cat plasma the inactive form of the enzyme either is actually absent or has a liability to the action of cold different than in other animal species.

Vagal and sinoaortic reflexes in postural control of circulation and renin release

Anesthetized cats were subjected to two 10-min trials of head-up tilting spaced 60 min apart. Bilateral cervical vagotomy, performed after the first tilting episode, did not affect the hemodynamic response to the change in posture, but significantyly and markedly reduced the increase in renin release from the innervated kidney. After sinoaortic denervation a marked and sustained arterial hypotension occurred during tilting, and the postural increase in renin release, though still limited to the innervated kidney, was even greater. When pressure homeostasis to tilting was disturbed, the renin release response was seen to be independent of the vagi, as it occurred after combined vagotomy and sinoaortic denervation. Maintenance of arterial pressure during tilting is mainly due to sinoaortic reflexes, whereas vagal reflexes are mostly responsible for the postural increase in renin release. The vagally independent release of renin observed when the cardiovascular response to tilting is impaired, is probably due to a direct action of arterial hypotension on intrarenal receptors, an action occurring only in innervated kidneys.

Differences in reflex control of arterial pressure and renin release during head-up tilting in the cat

1. Anaesthetized cats were subjected to two 10 min trials of head-up tilting spaced 30 min. Arterial pressure, heart rate, blood flow to an innervated kidney and to the contralateral denervated one, and renin release from both kidneys were measured. 2. The same haemodynamic changes and comparable increases in renin release from innervated kidneys occurred during both episodes of tilting when cats were subjected to sham cervical vagotomy between the two tilting trials. 3. Bilateral cervical vagotomy, performed after the first episode of head-up tilting, did not affect the haemodynamic response to the change in posture, but significantly and markedly reduced the increase in renin release from the innervated kidney. 4. After sino-aortic denervation a marked and sustained arterial hypotension occurred during tilting, and the postural increase in renin release from the innervated kidney was even greater. 5. In no condition, even during the marked fall in blood pressure in sino-aortic denervated cats, did head-up tilting increase renin release from the denervated kidney. 6. It is concluded that maintenance of arterial pressure during tilting is mainly due to sino-aortic reflexes, whereas vagal reflexes are mostly responsible for the postural increase in renin release.