Higher testosterone is associated with higher HDL-cholesterol and lower triglyceride concentrations in older women: an observational study.

OBJECTIVE: This study aimed to determine whether concentrations of testosterone and its main precursor after menopause, dehydroepiandrosterone (DHEA), are associated with lipoproteins and other lipids in community-dwelling older women. METHODS: The Sex Hormones in Older Women (SHOW) study was an observational study of 6358 Australian women, aged at least 70 years, with no prior major adverse cardiovascular event who had sex hormones measured by liquid chromatography-tandem mass spectrometry. Associations between hormones and lipids were examined using multilinear regression adjusted for potential confounders. RESULTS: The cross-sectional analyses included 3231 participants, median age 74.0 (interquartile range 71.7-77.9) years. Compared with concentrations in the lowest quartile (Q1), testosterone concentrations in the highest quartiles (Q3 and Q4) were positively associated with high-density lipoprotein cholesterol (HDL-C) (p = 0.002 and p < 0.001, respectively) while Q4 testosterone concentrations were positively associated with total cholesterol (p = 0.038). Q2, Q3 and Q4 testosterone concentrations were significantly inversely associated with triglycerides (TG) (p = 0.024, p = 0.003 and p < 0.001, respectively). For DHEA, Q4 concentrations was positively associated with non-HDL-C (p = 0.024). CONCLUSIONS: In older women, higher endogenous testosterone concentrations are significantly associated with higher HDL-C and lower TG, indicating a less atherogenic profile. These findings suggest a neutral, or potentially protective, cardiovascular disease effect of testosterone in older women.

Compliance-Adjusted Estimates of Aspirin Effects Among Older Persons in the ASPREE Randomized Trial.

The Aspirin in Reducing Events in the Elderly (ASPREE) Trial recruited 19,114 participants across Australia and the United States during 2010-2014. Participants were randomized to receive either 100 mg of aspirin daily or matching placebo, with disability-free survival as the primary outcome. During a median 4.7 years of follow-up, 37% of participants in the aspirin group permanently ceased taking their study medication and 10% commenced open-label aspirin use. In the placebo group, 35% and 11% ceased using study medication and commenced open-label aspirin use, respectively. In order to estimate compliance-adjusted effects of aspirin, we applied rank-preserving structural failure time models. The results for disability-free survival and most secondary endpoints were similar in intention-to-treat and compliance-adjusted analyses. For major hemorrhage, cancer mortality, and all-cause mortality, compliance-adjusted effects of aspirin indicated greater risks than were seen in intention-to-treat analyses. These findings were robust in a range of sensitivity analyses. In accordance with the original trial analyses, compliance-adjusted results showed an absence of benefit with aspirin for primary prevention in older people, along with an elevated risk of clinically significant bleeding.

Sex hormones, SHBG and cognitive performance among older Australian women: an observational study.

OBJECTIVE: This study aims to explore the associations between sex hormones and cognitive performance in older women. METHODS: Associations between sex hormones, sex hormone binding globulin (SHBG) and cognitive performance were examined in women aged at least 70 years, without dementia and not using medications that influence sex hormones. Linear and generalized linear regression models included age, body mass index, education, smoking, alcohol, living circumstances, diabetes, hypertension, depression and impaired renal function. RESULTS: The included 5511 women had a median (interquartile range) age of 73.9 (71.6-77.6) years. No associations were found for estrone, estradiol, testosterone or dehydroepiandrosterone and cognitive performance. SHBG concentrations above quartile 1 (Q1) were significantly inversely associated with processing speed (Q2, ß = -0.94, 95% confidence interval [CI] - 1.64 to -0.24, p = 0.009; Q3, ß = -0.82, 95% CI -1.53 to -0.10, p = 0.025; and Q4, ß = -0.95, 95% CI -1.70 to -0.20, p = 0.013). CONCLUSIONS: Sex hormones were not associated with cognitive performance. The finding that low SHBG is associated with better processing speed warrants further investigation. The null findings for the sex hormones establish a firm baseline to confidently explore the association between sex hormones and longitudinal cognitive performance in this population. TRIAL REGISTRATION: International Standard Randomized Controlled Trial Number Register (ISRCTN83772183) and ClinicalTrials.gov (NCT01038583).

ASPREE-D: Aspirin for the prevention of depression in the elderly.

BACKGROUND: Not only is depression associated with increased inflammation but inflammation is a risk factor for the genesis of depression. Many of the environmental risk factors for depression are transduced through inflammatory signaling. Anti-inflammatory agents show promise for the management of depression in preclinical, epidemiological, and early clinical studies. This opens the door to the potential for anti-inflammatory agents to treat and prevent depression. There are no evidence-based pharmacotherapies for depression prevention. METHOD: ASPREE-D, aspirin in the prevention of depression in the elderly, is a sub study of ASPREE, which explores the potential of aspirin to prevent a range of inflammation related disorders in the elderly. With a sample size of 19,114, and a duration of 5 years, this placebo controlled study will be one of the largest randomized controlled trials in psychiatry and will provide definitive evidence on the ability of aspirin to prevent depression. RESULTS: This paper presents the rationale for the study and presents a summary of the study design. CONCLUSIONS: ASPREE-D may not only define novel therapy but will provide mechanistic proof of concept of the role of inflammation in depression.

Correlates of Meal Skipping in Community Dwelling Older Adults: A Cross-Sectional Study.

In this cross-sectional analysis of 10,071 community dwelling adults aged ≥70 years, we examined factors associated with meal skipping (self-reported) using multivariable logistic regression. Prevalence of meal skipping in this study was 19.5%. The adjusted odds (aOR [95%CI]) of meal skipping were lower in those 85+ years (vs. 70-74.9 years, 0.56 [0.45-0.70]), and in those in regional areas (vs. urban area, 0.81 [0.72-0.92]). Higher odds of meal skipping were observed for those living alone (vs. living with someone, 1.84 [1.64-2.05]), current smokers (vs. non-smokers, 2.07 [1.54-2.80]), consumers of high amounts of alcohol (vs. abstainers 1.93 [1.35-2.75]), those with poor oral health (vs. excellent oral health, 1.71 [1.07 -2.73]) diabetes (vs. not 1.26 [1.06-1.50]), or frailty (vs. not, 1.63 [1.09-2.43]). This study identified socio-demographic, social, behavioural and biomedical correlates of meal skipping in later life, which may assist in targeting interventions to address meal skipping.

Self-Reported Early and Later Life Weight and the Risk of All-Cause Mortality in Older Adults.

OBJECTIVES: The extent to which body weight in early adulthood is associated with late-life mortality risk is unclear. This study aimed to determine the association between body mass index (BMI) in early adulthood (at 18 years of age) and older age (70 years and over), and the risk of mortality in later life. DESIGN: Secondary analysis of the ASPREE Longitudinal Study of Older Persons (ALSOP). SETTING, PARTICIPANTS: Data were from 14,853 relatively healthy community-dwelling Australians aged ≥ 70 years when enrolled in the study. MEASUREMENTS: Self-reported weight at age ≥ 70 years and recalled weight at age 18 years were collected at ALSOP study baseline. Height was measured with a stadiometer and was used for calculation of BMI at both timepoints. BMI at each timepoint was defined as: underweight, normal weight, overweight and obese. Individuals were categorised into one of five 'lifetime' BMI groups: normal weight (BMI between 18.5 and 24.9 at both times), overweight (25.0-29.9 at either or both times), obesity to non-obese (≥30.0 at age 18 and <30.0 ≥ 70 years), non-obese to obesity (<30.0 at age 18 and ≥30.0 at age ≥ 70 years), and early and later life obesity (≥30.0 at both times). RESULTS: During a median 4.7 years follow-up, 715 deaths occurred. Obesity at 18 years, but not in older age (p=0.44), was significantly associated with the risk of mortality in later life, even after accounting for current health status (HR: 2.35, 95% CI: 1.53-3.58, p<0.001). Compared with participants with normal BMI at both time points, being obese at both time points was associated with increased mortality risk (HR=1.99, 95% CI: 1.04-3.81, p=0.03), and the risk was even greater for individuals who were obese at 18 years but were no longer obese in older age (HR=2.92, 95% CI: 1.65-5.16, p<0.001), in fully adjusted models. Participants who were normal weight at 18 years and were obese in later life, did not have an increased mortality risk (p=0.78). CONCLUSIONS: Obesity in early adulthood, and obesity in both early and later life, were associated with increased mortality risk in later life. This highlights the importance of preventing obesity in early adulthood and maintaining a normal weight over an adult lifespan.

The Association between Metabolic Syndrome, Frailty and Disability-Free Survival in Healthy Community-dwelling Older Adults.

OBJECTIVES: To examine the association between metabolic syndrome (MetS) and frailty, and determine whether co-existent MetS and frailty affect disability-free survival (DFS), assessed through a composite of death, dementia or physical disability. DESIGN: Longitudinal study. SETTING AND PARTICIPANTS: Community-dwelling older adults from Australia and the United States (n=18,264) from "ASPirin in Reducing Events in the Elderly" (ASPREE) study. MEASUREMENTS: MetS was defined according to American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines (2018). A modified Fried phenotype and a deficit accumulation Frailty Index (FI) were used to assess frailty. Association between MetS and frailty was examined using multinomial logistic regression. Cox regression was used to analyze the association between MetS, frailty and DFS over a median follow-up of 4.7 years. RESULTS: Among 18,264 participants, 49.9% met the criteria for MetS at baseline. Participants with Mets were more likely to be pre-frail [Relative Risk Ratio (RRR): 1.22; 95%Confidence Interval (CI): 1.14, 1.30)] or frail (RRR: 1.66; 95%CI: 1.32, 2.08) than those without MetS. MetS alone did not shorten DFS while pre-frailty or frailty alone did [Hazard Ratio (HR): 1.68; 95%CI: 1.45, 1.94; HR: 2.65; 95%CI:1.92, 3.66, respectively]. Co-existent MetS with pre-frailty/frailty did not change the risk of shortened DFS. CONCLUSIONS: MetS was associated with pre-frailty or frailty in community-dwelling older individuals. Pre-frailty or frailty increased the risk of reduced DFS but presence of MetS did not change this risk. Assessment of frailty may be more important than MetS in predicting survival free of dementia or physical disability.

Self-reported oral health status, edentulism and all-cause mortality risk in 12 809 Australian older adults: a prospective cohort study.

OBJECTIVE: To investigate the association between oral health status and all-cause mortality in older adults using prospective cohort study design. SETTING AND PARTICIPANTS: In total, 12 809 adults aged ≥70 years (54.3% females) were participants of the ASPREE Longitudinal Study of Older Persons (ALSOP). METHODS: Participants self-reported the presence of natural teeth and oral health status. The association of self-reported oral health, edentulism and the integrative measure of the two with all-cause mortality were explored using the Cox-regression models adjusted for age, gender, socio-economic status, health-related behaviours, weight status, aspirin and polypharmacy. Hazard ratios (HRs) and 95% confidence intervals (CIs) were reported. RESULTS: In total, 22.2% of participants reported edentulism and 13.8% had fair/poor oral health. After adjustment for confounders, risk of all-cause mortality was higher among those with edentulism (vs. no edentulism) HR (95% CI) 1.43 (1.18, 1.73); and those with edentulism and reporting poor/fair oral health HR (95% CI) 1.69 (1.02, 2.82), or with no edentulism but reporting poor/fair oral health HR (95% CI) 1.46 (1.19-1.80) vs. no edentulism and reporting good/very good/excellent oral health. No association was observed between self-reported oral health alone and all-cause mortality. CONCLUSIONS: The risk of all-cause mortality was 69% higher among older adults reporting both edentulism and poor/fair oral health compared with those with teeth and more favourable self-reported oral health. © 2023 Australian Dental Association.

The relationship between long-term blood pressure variability and cortical thickness in older adults.

High blood pressure variability (BPV) is a risk factor for cognitive decline and dementia, but its association with cortical thickness is not well understood. Here we use a topographical approach, to assess links between long-term BPV and cortical thickness in 478 (54% men at baseline) community dwelling older adults (70-88 years) from the ASPirin in Reducing Events in the Elderly NEURO sub-study. BPV was measured as average real variability, based on annual visits across three years. Higher diastolic BPV was significantly associated with reduced cortical thickness in multiple areas, including temporal (banks of the superior temporal sulcus), parietal (supramarginal gyrus, post-central gyrus), and posterior frontal areas (pre-central gyrus, caudal middle frontal gyrus), while controlling for mean BP. Higher diastolic BPV was associated with faster progression of cortical thinning across the three years. Diastolic BPV is an important predictor of cortical thickness, and trajectory of cortical thickness, independent of mean blood pressure. This finding suggests an important biological link in the relationship between BPV and cognitive decline in older age.

Accelerated Epigenetic Aging in Peripheral Blood does not Predict Dementia Risk.

BACKGROUND: There is strong evidence that epigenetic age acceleration is associated with increased risk of later-life diseases and all-cause mortality. However, there is currently limited evidence that suggests accelerated epigenetic age is associated with dementia risk. OBJECTIVE: This study aims to clarify whether epigenetic biomarkers of accelerated aging can predict dementia risk, which is an important consideration as aging is the greatest risk factor for the disease. METHODS: DNA methylation was measured in peripheral blood samples provided by 160 participants from the ASPirin in Reducing Events in the Elderly study, including 73 pre-symptomatic dementia cases and 87 controls matched for age, sex, and smoking and education status. Epigenetic age was calculated using Horvath, Hannum, GrimAge and PhenoAge DNA methylation clocks, and age acceleration (the disparity between chronological age and epigenetic age) was determined. RESULTS: There was no difference in age acceleration between dementia cases and controls. In males, only Hannum's intrinsic epigenetic age acceleration was increased in pre-symptomatic dementia cases compared to controls (Δ +1.8 years, p = 0.03). CONCLUSION: These findings provide no strong evidence that accelerated epigenetic aging measured in peripheral blood can predict dementia risk.

The Association between Frailty and All-Cause Mortality in Community-Dwelling Older Individuals: An Umbrella Review.

Frailty is associated with multiple adverse health outcomes, including mortality. Several methods have been used to characterize frailty, each based on different frailty scales. These include scales based on phenotype, multidomain, and deficit accumulations. Several systematic reviews have examined the association between frailty and mortality; however, it is unclear whether these different frailty scales similarly predict mortality. This umbrella review aims to examine the association between frailty assessed by different frailty scales and all-cause mortality among community-dwelling older adults. A protocol was registered at PROSPERO, and it was conducted following the PRISMA statement. MEDLINE, Embase, PubMed, Cochrane Database of Systematic Reviews, Joanna Briggs Institute (JBI) EBP database, and Web of Science database was searched. Methodological quality was assessed using the JBI critical appraisal checklist and online AMSTAR-2 critical appraisal checklist. For eligible studies, essential information was extracted and synthesized qualitatively. Five systematic reviews were included, with a total of 434,115 participants. Three systematic reviews focused on single frailty scales; one evaluated Fried's physical frailty phenotype and its modifications; another focused on the deficit accumulation frailty index. The third evaluated the FRAIL (Fatigue, Resistance, Ambulation, Illness, and Loss of weight) scale. The two other systematic reviews determined the association between frailty and mortality using different frailty scales. All of the systematic reviews found that frailty was significantly associated with all-cause mortality. This umbrella review demonstrates that frailty is a significant predictor of all-cause mortality, irrespective of the specific frailty scale.

Use of aminoglutethimide as second-line endocrine therapy in metastatic breast cancer.

Sixty-five patients with advanced breast cancer, progressive despite prior endocrine therapy in all cases and prior chemotherapy in most cases, were treated with aminoglutethimide, 250 mg four times a day. At present, 52 are evaluable for response assessment, and of these 10 (19%) showed an overall objective response, major sites of response being soft tissue and lung. A further 12 patients (23%) had stable disease during aminoglutethimide therapy, while a total of 9 patients with bone metastases reported marked relief of pain without objective evidence of response. Forty-nine patients had received prior treatment with tamoxifen, and of the 10 tamoxifen responders 4 (40%) responded to subsequent aminoglutethimide, while of the 20 tamoxifen failures only 2 (10%) responded to subsequent aminoglutethimide. Aminoglutethimide was reasonably well tolerated, although 6 patients (0%) discontinued treatment because of intolerable side effects. Six of the 10 responding patients have subsequently relapsed, with a mean duration of response of 17 weeks, but 4 continued to respond at 24, 32, 55, and 111 weeks, respectively. The median survival from the start of aminoglutethimide therapy is in excess of 41 weeks for responders and 11 weeks for nonresponders, while the median survival from first relapse is 48 months for aminoglutethimide responders and 28 months for aminoglutethimide nonresponders. These results confirm that aminoglutethimide can offer a useful alternative form of endocrine therapy for advanced breast cancer, but the response rates obtained in heavily pretreated patients are inferior to those obtained when aminoglutethimide is used earlier in sequential treatment. For optimal results, particularly in terms of quality of life, aminoglutethimide should generally be used prior to chemotherapy.

Slowing the progression of age-related hearing loss: Rationale and study design of the ASPIRIN in HEARING, retinal vessels imaging and neurocognition in older generations (ASPREE-HEARING) trial.

BACKGROUND: Age-related hearing loss (ARHL) is a leading cause of disability in the elderly. Low-grade inflammation and microvessel pathology may be responsible for initiating or exacerbating some of the hearing loss associated with aging. A growing body of evidence demonstrates an association of hearing loss with cognitive decline. A shared etiological pathway may include a role of inflammation, alongside vascular determinants. The ASPREE-HEARING study aims to determine whether low-dose aspirin decreases the progression of ARHL, and if so, whether this decrease in progression is also associated with retinal microvascular changes and/or greater preservation of cognitive function. DESIGN AND METHODS: A three year double-blind, randomized controlled trial of oral 100mg enteric-coated aspirin or matching placebo, enrolling 1262 Australians aged ≥70years with normal cognitive function and no overt cardiovascular disease. The primary outcome is the change in mean pure tone average hearing threshold (decibels) in the better ear, over a 3-year period. Secondary outcomes consist of changes in retinal microvascular indicators, and changes in cognitive function. Participants are recruited from a larger trial, ASPirin in Reducing Events in the Elderly (ASPREE), which is designed to assess whether daily low dose aspirin will extend disability-free life. DISCUSSION: ASPREE-HEARING will determine whether aspirin slows development or progression of ARHL, and will interrogate the relationship between inflammatory and microvascular mechanisms that may underlie the effects of aspirin on ARHL. This study will improve understanding of the patterns of comorbidity with, and the relationships between, aging and ARHL, alongside modeling the impacts of ARHL.

A prospective randomized trial of single-agent versus combination chemotherapy in meningeal carcinomatosis.

Forty-four patients with documented meningeal carcinomatosis (small-cell lung carcinoma [SCLC], 29%; breast carcinoma, 25%) were treated in a prospective randomized trial with intrathecal methotrexate (MTX) 15 mg or MTX plus cytosine arabinoside (Ara-C) 50 mg/m2. Most patients received intrathecal hydrocortisone (HC) each treatment to minimize arachnoiditis. Overall response was 55%. Seven patients achieved complete response. Response to MTX was superior to combined MTX/Ara-C, but not significantly so (61% v 45%; P greater than .10). Response was more frequent if drugs were administered via Ommaya reservoir than by lumbar puncture (65% v 48%; P greater than .10). Concurrent radiotherapy to the CNS was associated with significantly better response (73% v 35%; P less than .05). Small-cell lung carcinoma patients showed the best response (69%). Overall median survival for the whole group was 8 weeks, but responders fared better than nonresponders (median survival, 18 v 7 weeks; P less than .05). Nausea and vomiting were the most common toxicities encountered (45%), but rarely proved limiting. An unusual, previously undocumented reaction to intrathecal HC was noted. MTX is moderately effective in nonleukemic meningeal carcinomatosis, but the addition of Ara-C does not appear to improve results. Pretreatment factors did not predict outcome in this trial.

Analysis of a prospectively randomized comparison of doxorubicin versus 5-fluorouracil, doxorubicin, and BCNU in advanced gastric cancer: implications for future studies.

A multi-institutional cooperative study of patients with locally advanced, recurrent, or metastatic gastric adenocarcinoma who had not previously received chemotherapy was conducted, prospectively randomizing patients to receive either doxorubicin or the three-drug combination, 5-fluorouracil (5-FU), doxorubicin (Adriamycin; Adria Laboratories, Columbus, Ohio), and BCNU (FAB). The 187 evaluable patients were initially stratified according to the presence of measurable or evaluable disease and performance status. There was a significantly higher response rate observed for FAB (40%) compared with doxorubicin (13%) among the 145 measurable-disease patients. Duration of response and survival were significantly longer for FAB in the measurable-disease group, but for the total patient population an early advantage for FAB in time to disease progression and survival was lost with continued follow-up. Median survival was 33 weeks for patients receiving FAB and 19 weeks for those receiving doxorubicin. Significant pretreatment factors adversely affecting survival included poor performance status, weight loss of greater than 10%, and more than two sites of metastases. Toxicity was not severe in either treatment arm, and only thrombocytopenia occurred significantly more often with FAB. It is contended that in the treatment of advanced gastric cancer, chemotherapy only exerts a relatively short-term and modest beneficial effect, most apparent in patients with intermediate tumor bulk. 5-FU remains the most active single agent, and combination chemotherapy has not yet proven its overall worth. Further studies are indicated comparing the most active combinations with 5-FU using optimal doses and schedules, and consideration must be given to the incorporation of no-treatment controls.

Effects of intravenous brain natriuretic peptide on regional sympathetic activity in patients with chronic heart failure as compared with healthy control subjects.

OBJECTIVES: We sought to assess the effects of brain natriuretic peptide (BNP) on systemic and regional sympathetic nervous activity (SNA) in both patients with congestive heart failure (CHF) and healthy control subjects. BACKGROUND: Although the response of SNA to atrial natriuretic peptide (ANP) has been well documented, the response of SNA to BNP is largely unknown. METHODS: We assessed cardiac and whole-body SNA using the norepinephrine (NE) tracer dilution method before and after infusion of two doses of BNP (3 and 15 ng/kg body weight per min) in 11 patients with stable CHF (ejection fraction 24 +/- 2%) and 12 age-matched healthy control subjects. In addition, renal SNA and hemodynamic variables were assessed at baseline and after the higher BNP dose. RESULTS: Low dose BNP did not change blood pressure or whole-body NE spillover, but reduced cardiac NE spillover in both groups by 32 +/- 13 pmol/min (p < 0.05). In both groups, high dose BNP reduced pulmonary capillary pressure by 5 +/- 1 mm Hg (p < 0.001) and mean arterial pressure by 6 +/- 3 mm Hg (p < 0.05), without a concomitant increase in whole-body NE spillover; however, cardiac NE spillover returned to baseline levels. Renal NE spillover remained virtually unchanged in healthy control subjects (501 +/- 120 to 564 +/- 115 pmol/min), but was reduced in patients with CHF (976 +/- 133 to 656 +/- 127 pmol/min, p < 0.01). CONCLUSIONS: Our results demonstrate a sympathoinhibitory effect of BNP. Cardiac sympathetic inhibition was observed at BNP concentrations within the physiologic range, whereas high dose BNP, when arterial and filling pressures fell and reflex sympathetic stimulation was expected, systemic and cardiac SNA equated to baseline values. There was inhibition of renal SNA in patients with CHF, but not in healthy control subjects. Whether this effect is specific to BNP or related to reduced filling pressure remains to be determined.

Renal and systemic effects of enalapril in chronic one-kidney hypertension.

We have investigated the role of angiotensin II in the development of high blood pressure and in the maintenance of renal function during 2 weeks of one-kidney renal artery stenosis in conscious dogs. Responses to a fixed degree of inflation of a balloon cuff around the renal artery were compared in dogs with or without continuous enalapril (MK 421) treatment. In six untreated dogs, mean aortic pressure was increased by 17.1 +/- 2.0 mm Hg, due primarily to increases in total peripheral resistance with little change in cardiac output, while glomerular filtration rate, renal blood flow, renal artery pressure, and plasma renin activity were back to prestenosis levels. In seven enalapril-treated dogs mean aortic pressure was increased by 23.0 +/- 2.7 mm Hg and was not significantly different from that occurring in untreated dogs. This rise was due to increases in total peripheral resistance (10%) and cardiac output (12%). In the absence of angiotensin II, glomerular filtration rate remained low, at only 56 +/- 6% of prestenosis levels. Renal blood flow returned to normal, but the renal artery pressure remained 25% lower than control values. Thus, the main role of angiotensin II in chronic one-kidney Goldblatt hypertension does not appear to be through its pressor properties but rather through its actions in the kidney to preserve glomerular filtration. This effect on renal function persisted throughout the course of the hypertension, even when the plasma renin levels returned to normal.

Pressure range for release of renomedullary depressor substance in rabbits.

We investigated the relation between renal perfusion pressure and the release of a renal vasodepressor substance in vivo to determine whether this substance was released at physiological pressures. We perfused the left kidneys of anesthetized rabbits using an extracorporeal circuit that allowed renal perfusion pressures to be set at 65 mm Hg (control) and increased to 95, 125, 155, or 185 mm Hg for 30-minute experimental periods. Systemic blood pressure did not change significantly when renal perfusion pressure was maintained at 65 mm Hg throughout. When renal perfusion pressure was increased to 95, 125, 155, or 185 mm Hg, systemic blood pressure fell significantly at rates of 0.17 +/- 0.04, 0.79 +/- 0.31, 0.60 +/- 0.11, and 2.18 +/- 0.79 mm Hg/min, respectively (P < .05). Restoration of renal perfusion pressure to 65 mm Hg abruptly reversed the falls in systemic blood pressure in each group. There was a natriuresis and diuresis that were both pressure related and progressive in the face of each constant level of increased renal perfusion pressure. In summary, there was a continuum of arterial vasodepressor responses across a renal perfusion pressure range from resting pressure to 185 mm Hg. We suggest that the threshold level for the release of significant amounts of a renal medullary depressor substance, probably medullipin, is just above normal arterial blood pressure and that the rate of release increases with increasing arterial pressure.