PubMed Health⌕ Search

Biomedical subjects

Robert J Richards

Publications and source records attributed to Robert J Richards.

7 recordsLinked to original sources
PubMed2005

Leptin, adiposity, and testosterone in captive male macaques.

Leptin is considered to act as a signal relating somatic energetic status to the reproductive system. However, the nature of that signal and its relationship with male reproductive function across nonhuman primate species are unclear. We suggest that species-specific differences in leptin physiology may be related to the degree of environmental variation and variation in the importance of energy stores for male reproduction. In order to test the role of seasonality in species differences among nonhuman primates, we compared leptin, testosterone, and body composition in male rhesus (n = 69) and pig-tailed (n = 43) macaques. Despite having larger abdominal fat deposits, the rhesus macaques did not exhibit significantly higher leptin levels (rhesus, 2.21 +/- 0.43 ng/ml; pig-tailed, 2.12 +/- 0.39 ng/ml). Both species showed increases in leptin across adolescent, subadult, and adult age-groups (P = 0.036 for rhesus; P = 0.0003 for pig-tailed by ANCOVA). Testosterone was not significantly associated with leptin in either the rhesus (r = 0.039; P = 0.754) or pig-tailed (r = 0.2862; P = 0.066) samples. Comparison of leptin levels across the two species using univariate modeling procedures showed no significant age-group by abdominal fat interaction. These findings suggest little difference in leptin production between these two closely related species, despite the difference in breeding seasonality.

Age Factors↗
PubMed2003

Leptin: sympathetic and cardiovascular effects.

Shortly after leptin was first discovered, it was hailed as the key to understanding obesity. However, it didn't take long for investigators to realize that the hormone was more than a feedback signal to inhibit further food intake. Since those early days, leptin has been well characterized in rodents. It exerts an influence in many physiologic processes, including food intake, thermoregulation, fertility, thyroid function, adrenal function, sympathetic nerve activation, renal function, blood vessel tone, and blood pressure. No longer a satiety hormone, it is being looked at from many different perspectives. One such perspective is its influence on the cardiovascular system. This review highlights some of the work in this area.

Animals↗
PubMed2003

Dehydroepiandrosterone-sulfate as a biomarker of senescence in male non-human primates.

Numerous studies have suggested important and varying roles for dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEA-S) in primate physiological functions. Despite these numerous claims, specific actions and significance of DHEA and DHEA-S are still equivocal. A decline of these hormones in adult humans may have functional significance, yet there is no clear relationship between functional impairments of aging and the decline in DHEA or DHEA-S levels. This current study attempts to address the natural history of adrenal hormones by presenting non-human primate evidence of the endocrinology of aging; the age-related patterns of adrenal hormone decline in three species of the subfamily Cercopithecinae, Macaca mulatta, Macaca nemestrina, and Papio cynocephalus are compared. It is concluded that DHEA-S and cortisol represent lineage specific markers of senescence among primates and that parallel age-related patterns of DHEA-S and cortisol likely reflect lineage specific effects, or rather, phylogenetic similarities of endocrine senescence. The use of relative adrenal hormone levels to approximate species' life expectancies is discussed.

Adrenal Cortex Hormones↗
PubMed2002

Timing of prophylactic surgery in prevention of diverticulitis recurrence: a cost-effectiveness analysis.

Although surgery is recommended after two or more attacks of uncomplicated diverticulitis, the optimal timing for surgery in terms of cost-effectiveness is unknown. A Markov model was used to compare the costs and outcomes of performing surgery after one, two, or three uncomplicated attacks in 60-year-old hypothetical cohorts. Transition state probabilities were assigned values using published data and expert opinion. Costs were estimated from Medicare reimbursement rates. Surgery after the third attack is cost saving, yielding more years of life and quality adjusted life years at a lower cost than the other two strategies. The results were not sensitive to many of the variables tested in the model or to changes made in the discount rate (0-5%). In conclusion, performing prophylactic resection after the third attack of diverticulitis is cost saving in comparison to resection performed after the first or second attacks and remains cost-effective during sensitivity analysis.

Cohort Studies↗
PubMed2002

Racial differences in use of colonoscopy, sigmoidoscopy, and barium enema in Medicare beneficiaries.

Colorectal cancer is often diagnosed at a later stage in blacks. We wanted to know if racial differences existed in the use of tests for detection of colorectal cancer. A 5% random sample was obtained of all Medicare beneficiaries with Part B coverage, aged 65 years and older and classified as white or black race. The numbers of colonoscopies, flexible sigmoidoscopies, and barium enemas were determined from the Physician/Supplier file. Blacks were 18% less likely to receive colonoscopy and 39% less likely to receive flexible sigmoidoscopy after controlling for age, sex, income, and access to care in a multivariable logistic regression model. Barium enema was not significantly different between the races. Black men had 25% lower use of colonoscopy and 50% decreased use of flexible sigmoidoscopy. Blacks receive less colonoscopy and flexible sigmoidoscopy than whites. Black men are particularly vulnerable to the under-use of these tests.

Black or African American↗
PubMedDate not supplied

Postprandial hyperglycemia.

Much attention has been paid to fasting glucose levels in both the diagnosis and management of diabetes mellitus. This test is well ingrained in clinical practice and well accepted by our patients. However, does a fasting glucose level give the clinician a complete picture? Is postprandial hyperglycemia associated with adverse events? This article will explore postprandial glucose levels and compare them to fasting glucose levels. The importance of postprandial and post-challenge (2 hours after a standard oral glucose tolerance test) glucose levels will be discussed. Drugs which address postprandial hyperglycemia will be reviewed briefly.

Adult↗