Predicting lactate threshold using ventilatory threshold.

Lactate threshold is an important reference point when setting training intensities for endurance athletes. Ventilatory threshold has been used as a noninvasive estimate of lactate threshold, but appears to underestimate training intensity for many athletes. This study evaluated whether data obtained during a noninvasive, maximal exercise test could be used to predict lactate threshold. Maximal oxygen consumption (55+/-2 ml O(2) x kg(-1) x min(-1)) and heart rate at the ventilatory threshold (V-slope method) were determined for 19 cyclists (10 men, 9 women, 35+/-2 years). Cyclists also performed a lactate threshold test, consisting of 8 min stages at power outputs below, at, and above the ventilatory threshold. Heart rate associated with the lactate threshold was determined using the Dmax method. The correlation coefficient between heart rates at the ventilatory and lactate thresholds was 0.67, indicating 45% shared variance. The best fitting model to predict heart rate at the lactate threshold included heart rate at the ventilatory threshold, gender, body weight, and an interaction between gender and body weight. Using this model, R(2) was 0.70. Thus, heart rate at the ventilatory threshold may be adjusted to more accurately predict a heart rate that corresponds to the lactate threshold for recreational cyclists.

Nutritional status modifies insulin-mediated glucose uptake in spontaneously hypertensive rats.

In this study we quantified insulin-mediated glucose uptake in weight-matched (260-330 g) fed (6-8 h fast) and fasted (24 h fast) male rats with spontaneous hypertension (SHR) and control Wistar-Kyoto (WKY) rats. To accomplish this goal, rats were infused continuously for 165 min with glucose and insulin. Blood was taken at frequent intervals from 120-165 min, and the values averaged to determine the steady-state plasma glucose (SSPG) and insulin (SSPI) concentrations. In some studies epinephrine and propranolol were added to the infusate in order to suppress endogenous insulin secretion. Steady-state plasma insulin (SSPI) concentrations were similar in SHR and WKY during the three infusion studies (382-483 pmol/L). However, SSPG was significantly higher in fed SHR as compared to fed WKY during infusions performed with (9.4 +/- 0.8 vs 7.0 +/- 0.4 mmol/L, p < 0.05) or without (8.6 +/- 0.2 vs 7.0 +/- 0.6 mmol/L, p < 0.05) epinephrine and propranolol in the infusate. In contrast, SSPG concentrations (mmol/L) were similar in SHR (6.8 +/- 0.3) and WKY rats (6.5 +/- 0.6) when they were studied after a 24 h fast. These results demonstrates that differences in insulin-mediated glucose removal from plasma between SHR and WKY rats will vary as a function of nutritional status.

Effects of gemfibrozil on triglyceride metabolism in Dahl salt-sensitive rats.

Hypertriglyceridemia is a common feature of patients with increased blood pressure as well as several rodent models of hypertension. The goal of this study was to evaluate the effects of gemfibrozil on established abnormalities of triglyceride (TG) secretion and TG clearance in the Dahl salt-sensitive rat. Consequently, Dahl salt-sensitive rats received 12 days treatment with gemfibrozil (30 mg/kg/day) or vehicle by p.o. gavage and the following measurements were made: 1) fasting plasma TG levels; 2) TG secretion rate after suppression of TG removal with Triton WR 1339; 3) TG removal rate (half-time of disappearance of prelabeled very low density lipoprotein); and 4) lipoprotein lipase (LPL) activity and mRNA in soleus muscle, fat and liver tissues. Gemfibrozil produced a 50% reduction in fasting plasma TG concentrations, with no effect on TG secretion rate (17 +/- 2 vs. 15 +/- 1 mg/100 g b.wt./hr). The half-time of prelabeled very low density lipoprotein-TG removal was significantly lower in drug-treated animals (3.9 +/- 0.3 vs. 6.1 +/- 0.9 min), and this was associated with a tissue-specific increase in LPL activity in soleus muscle (153 +/- 5 vs. 135 +/- 5 U/g, P < .02). Expression of LPL mRNA, relative to beta-actin mRNA, was similar in both groups of rats. Thus, in this rodent model of hypertension and dyslipidemia, gemfibrozil lowers plasma TG levels by 50% with no effect on TG secretion; the hypotriglyceridemic effect is due mainly to an increase in TG removal rate associated with a post-transcriptional increase in LPL activity in skeletal muscle.

Mechanism of hypertriglyceridemia in Dahl rats.

Plasma triglyceride concentrations were shown to be higher in hypertensive (153 +/- 2 mm Hg) male Dahl salt-sensitive rats than in control Sprague-Dawley rats (122 +/- 2 mm Hg). These differences in triglyceride concentrations were seen when blood was drawn at 9 AM from unfasted animals (229 +/- 27 versus 111 +/- 8 mg/dL), at 1 PM after a 4-hour fast (186 +/- 13 versus 88 +/- 4 mg/dL), or at 9 AM after a 13-hour fast (151 +/- 6 versus 90 +/- 6 mg/dL), all p < 0.001. Total triglyceride secretion was also compared in groups of rats by determining the increment in plasma triglyceride concentration for 2 hours after blocking triglyceride removal from plasma by injecting Triton. Studies performed at 1 PM and 9 AM, after the 4- and 13-hour fast, demonstrated that total triglyceride secretion was greater (p < 0.05) in Dahl rats only when studied at 1 PM. Direct estimates of hepatic triglyceride secretion at 1 PM also demonstrated a significant (p < 0.02) increase in secretion rate by perfused livers from Dahl rats, due in part to their increased liver size. In addition, removal of prelabeled very low density lipoprotein-triglyceride in the intact rat was significantly (p < 0.05) decreased in Dahl rats. Lipoprotein lipase activity measured in skeletal muscle, heart, and adipose tissue was also significantly decreased at 9 AM and 1 PM (after 0 and 4 hours of fasting) in tissue from Dahl rats. These data confirm that Dahl rats have higher plasma triglyceride concentrations than Sprague-Dawley rats. Since both total and hepatic triglyceride secretion were somewhat greater in Dahl rats, in association with a decrease in both removal of very low density lipoprotein from plasma and decreased muscle and adipose tissue lipoprotein lipase activity, it seems likely that hypertriglyceridemia in Dahl rats results from a combination of increased triglyceride secretion and decreased triglyceride removal.

Performance testing of the environmental TLD system for the Three Mile Island Nuclear Station.

Panasonic UD-801 thermoluminescent dosimeters ( TLDs ) containing two calcium sulfate phosphors were tested under Performance Specification 3.1 established by the American National Standard Institute ( ANSI75 ) and in the U.S. Nuclear Regulatory Commission's Regulatory Guide 4.13 ( NRC77 ). The specific qualifying tests included TLD uniformity, reproducibility, energy dependence and directional dependence. The overall measurement uncertainties and associated confidence levels are within the prescribed guidelines defined in the qualifying requirements for environmental TLDs .

Depth-dose curves for 90Sr and natural and depleted uranium in Mylar.

Strontium and uranium are common sources used to calibrate personal dosimeters and survey meters for beta radiation. Since the absorbed dose rate of low-penetrating beta radiation decreases significantly with increased depth in tissue or dosimeters, it is necessary to describe the dose rate accurately as a function of depth. Complete depth dose information from zero to 1000 mg/cm2 is currently unavailable for strontium and uranium. This paper describes the generation of accurate depth-dose curves in Mylar for 90Sr and slabs of natural and depleted uranium from 0 to 1000 mg/cm2, utilizing an extrapolation chamber. The absorbed dose rate produced by natural uranium was found to decrease from 235 mrad/hr at a depth of 7 mg/cm2 to 43 mrad/hr at 300 mg/cm2 to 4.8 mrad/hr at 1000 mg/cm2. The dose rate produced by depleted uranium was found to decrease from 205 mrad/hr at 7 mg/cm2 to 34 mrad/hr at 300 mg/cm2 to 2.3 mrad/hr at 1000 mg/cm2. A 1-mCi extended area 90Sr source (encapsulated in 50 mg/cm2 AG) was found to produce an absorbed dose rate of 16,997 mrad/hr at 57 mg/cm2, 5000 mrad/hr at 300 mg/cm2, and 27.1 mrad/hr at 1050 mg/cm2. Doses to deep organs have been determined historically at depths ranging from 300 to 1000 mg/cm2. The results of this study show that 90Sr and uranium produce significant absorbed dose rates at a depth of 300 mg/cm2. Thus, if doses for deep depths are determined at 300 mg/cm2 for mixed beta-gamma exposures, the dose will be overestimated due to the presence of the beta component. The depth-dose curves generated in this study can be used by dosimeter processors to normalize the response of their dosimeters to the shallow (7 mg/cm2) and deep (1000 mg/cm2) depths defined by the U.S. Nuclear Regulatory Commission.

Contamination of the home environment by patients treated with Iodine-131: initial results.

We have employed twin sodium iodide radiation detectors to analyze iodine-131 transfer from thyroid patients to their families. Unlike previous studies of this problem, we measured thyroid radioiodine activity directly and are able to detect as little as 92 pCi of iodine 131 in adult thyroids. As in previous studies, we have also measured direct radiation exposures of family members with wristband thermoluminescent dosimeters. Thus far, we have studied seven families with 17 persons. Eleven of these are children under age 16. Direct radiation exposure of family persons from proximity of these radioactive patients ranged from 0.17 to 126 mR per day (natural background radiation amounts to approximately 0.35 mR per day). The maximum activity of iodine-131 in family thyroids ranged from less than 92 pCi to as high as 110,000 pCi and resulted in thyroid dose equivalents of 4 to 1330 mrem. Based on recent estimates of thyroid cancer, the latter dose equivalent could possibly double the risk of thyroid malignancy in children over what is expected normally. Such a risk implies the addition of 10 induced cases to the 10 naturally occurring cases per million people per year.

The role of natural radiations in human leukemogenesis.

Some 3 billion years ago, life arose from a warm pool of primordial ooze amid a constant drizzle of radiation. Steadily, man evolved from the lesser forms of life because of or in spite of his natural background-radiation environment. This study is an attempt to determine to what extent these background radiations are responsible for human disease, namely leukemia. Dose rate data were compared with data on all forms of leukemia in the 50 United States for four population subgroups. For the total U. S., no relation between background radiation and leukemia is apparent. A positive correlation appears, however, if various states are deleted from the analysis. It appears that conditions relative to populations and their environment could mask a radiation effect if in fact one is present.