The influence of fitness on neuroendocrine responses to exhaustive treadmill exercise.

Neuroendocrine and sympathoadrenal responses to exhaustive graded treadmill exercise were examined in 17 male subjects of varying degrees of fitness. The mean duration of exercise to exhaustion was 15.2 +/- 0.7 (+/- SE) min. Exercise duration was inversely correlated with baseline heart rate (P less than 0.05). Compared to standing baseline values, mean plasma norepinephrine and epinephrine levels increased 339% and 301%, respectively, in an integrated 2-min blood sample collected immediately after completion of exercise. Mean adrenocorticotrophic hormone (ACTH), beta-endorphin (beta-EP), beta-lipotropin (beta-LPH), and prolactin levels increased 282%, 720%, 372%, and 211%, respectively, in an integrated 4-min blood sample beginning 2 min after completion of exercise. Cortisol levels increased 183% in the sample collected 17-21 min after exercise. The magnitude of these neuroendocrine responses to exercise was similar among individuals at the same relative intensity of exhaustive exercise, regardless of the duration of exercise. The exercise-induced increases of the pro-opiomelanocortin (POMC)-derived peptides, ACTH, beta-EP, and beta-LPH, were highly correlated with each other (P values less than 0.001), and were correlated with prolactin increases, (P values less than 0.05). During a 20-min recovery period after exercise, changes in heart rate, ACTH, and beta-LPH levels were correlated with duration of exercise, (P less than 0.01, P less than 0.03, and P less than 0.03, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium potentiates the cyclic nucleotide and phosphaturic response to parathyroid hormone infusion.

To determine whether calcium modulates the action of PTH, we measured the cyclic nucleotide and phosphaturic response to PTH following a 4-h infusion of glucose (day 1) and calcium (day 2). The 12 subjects were selected to provide a range of low, normal, and high endogenous PTH function. PTH stimulated nephrogenous cAMP [185 +/- 31 nmol/100 ml glomerular filtrate (GF)], cyclic guanosine monophosphate (0.44 +/- 0.09 mumol/g creatinine), and phosphate (367 +/- 59 mg P/g creatinine) excretion. Calcium infusion stimulated nephrogenous cAMP excretion in the hypoparathyroid subjects (1.42 +/- 0.35 nmol/100 ml GF) but reduced it in subjects with normal parathyroid function (-2.22 +/- 0.46 nmol/100 ml GF). Calcium infusion stimulated cGMP (0.64 +/- 0.1 mumol/g creatinine) and phosphate (113 +/- 48 P/g creatinine) excretion in all subject groups. Calcium infusion led to a 2-fold increase in the cyclic nucleotide and phosphaturic response to PTH in the normal and hypoparathyroid subjects, but had little effect on the PTH response in hyperparathyroid subjects. The extent to which calcium potentiated the ability of PTH to stimulate nephrogenous cAMP excretion correlated negatively with the basal nephrogenous cAMP excretion (r = -0.685, P less than 0.01). We conclude that calcium potentiates the acute effects of PTH on renal cyclic nucleotide and phosphate excretion. This effect is modified by the basal levels of PTH stimulation of the kidney such that it is reduced in magnitude when basal PTH stimulation is increased.

Calcium accumulation by chick intestinal mitochondria. Regulation by vitamin D-3 and 1,25-dihydroxyvitamin D-3.

We have the evaluated the effect of vitamin D-3 and its metabolite 1,25-dihydroxyvitamin D-3 on Ca2+ accumulation by chick intestinal mitochondria. Ca2+ accumulation appears to occur in two phases: an early, transient accumulation into an Na+-labile pool followed by an ATP-dependent accumulation into an Na+-resistant pool. Ca2+ accumulation is extensive at free Ca2+ concentrations greater than 3 . 10(-6) M in the presence of ATP. Ruthenium red and dinitrophenol block Ca2+ accumulation, but atractyloside does not. Oligomycin blocks ATP-supported accumulation completely with a partial inhibition of ATP and malate-supported accumulation. Little difference could be found in mitochondrial preparations from vitamin D-deficient chicks compared to those from vitamin D-3 (or 1,25(OH)2D-3)-supplemented chicks with respect to respiratory control, oxygen consumption, efficiency of oxidative phosphorylation, affinity for Ca2+, or the rate and extent of ATP-supported Ca2+ accumulation. Intestinal cytosol stimulated Ca2+ accumulation, but this was not specific with respect to vitamin D status or tissue of origin, nor was it duplicated by chick intestinal Ca2+-binding protein. 30 ng/ml 1,25(OH)2D-3 stimulated Ca2+ accumulation directly, regardless of the presence of intestinal cytosol. Other vitamin D metabolites were less potent: 25-hydroxyvitamin D-3 greater than 24,25-dihydroxyvitamin D-3 = vitamin D-3. Since increasing the free Ca2+ concentration from 3 . 10(-6) to 1 . 10(-5) M increased Ca2+ accumulation approx. 50-fold, whereas direct stimulation by 1,25(OH)2D-3 in vitro increased Ca2+ accumulation less than 2-fold, we conclude that 1,25(OH)2D-3 influences mitochondrial accumulation of Ca2+ in vivo primarily by altering cytosol concentrations of free Ca2+.

The influence of exercise and diet on myoglobin and metmyoglobin reductase in the rat.

This study was designed to evaluate the influence of exercise and diet on selected aspects of heme protein metabolism in the rat. Two levels of treadmill exercise and three levels of dietary restriction were imposed on growing male rats over a 12-week experimental period. Neither training nor diet had any effect on erythrocyte NADH-MetHB reductase. The group undergoing the highest level of treadmill exercise had a significantly lower HB concentration. The activity of NADH-MetMB reductase was increased in the group undergoing the highest level of training and decreased in the groups whose diet was restricted by 25% and 35%. These changes were seen only in the soleus muscle. Other muscles, including the heart, psoas, and quadriceps were unaffected by either exercise of diet. Both levels of exercise were effective in increasing muscle MB concentration, but only in the quadriceps and soleus muscles. These data illustrate the adaptive nature of muscle MB and NADH-MetMB reductase. They also illustrate the different adaptive patterns of these two components of muscle.

Thiamin requirement of the adult human.

Young adult male subjects maintained on a metabolic ward were fed diets providing controlled intakes of thiamin and either 2800 or 3600 kcal. The higher level of calories was attained by an increased intake of carbohydrates. Constant weights were maintained by the subjects by adjusting daily activity and exercise schedules. Thiamin requirements were evaluated in terms of erythrocyte transketolase activity and urinary excretion of the vitamin. The results of the study revealed that a relationship exists between thiamin requirement and caloric intake and expenditure. Thus, when the calories being utilized were derived primarily from carbohydrate sources, the minimum adult male requirement for thiamin appeared to be 0.30 mg of thiamin per 1000 kcal. Urinary excretion of thiamin and erythrocyte transketolase activity appear to be reasonably reliable reflections of thiamin intakes and thiamin nutritional status. The use of these measurements in nutrition surveys appears justified. The microbiological assay (Lactobacillus viridescens) for measuring thiamin levels in urine samples appears to be a somewhat more sensitive but valid procedure as an alternate for the thiochrome method. Judged from the results of this study, the recommended intake for the adult human of 0.40 mg of thiamin per 1000 kcal by FAO/WHO and the recommended allowance of 0.5 mg per 1000 kcal by the Food and Nutrition Board of the NAS-NRC appear reasonable and amply allow for biological variations and other factors that may influence the requirement for this vitamin.

Stimulation of chick gut alkaline phosphatase activity by actinomycin D and 1,25-dihydroxyvitamin D3: evidence for independent mechanisms.

We observed that inhibitors of RNA synthesis, actinomycin D and cordycepin, stimulate chick duodenal alk Pase activity by means which are additive to the stimulaation by the biologically active metabolite of vitamin D3, 1,12(OH)2D3, and its analogue, 1 alpha OH D3. The protein synthesis inhibitor, cycloheximide, inhibited basal alk Pase activity and blocked its stimulation by actinomycin D and 1,25(OH)2D3. Both actinomycin D and cycloheximide blocked the ability of 1,25(OH)2D3 and 1 alpha OHD3 to raise serum calcium levels. The paradoxical stimulation of duodenal alk Pase activity by RNA synthesis inhibitors additive to the stimulation by 1,25(OH)2D3 suggests that alk Pase activity is controlled by mechanisms other than gene activation. (J LAB CLIN MED 94:88, 1979.)

Metmyoglobin reductase. Identification and purification of a reduced nicotinamide adenine dinucleotide-dependent enzyme from bovine heart which reduces metmyoglobin.

Beef heart muscle has been found to contain an enzyme which will rapidly and directly reduce metmyoglobin in vitro. Reduction rates are far greater than any previously reported for nonspecific or nonenzymatic systems. The enzyme is NADH-dependent and requires the presence of ferrocyanide ion for in vitro assay. The artificial electron carriers, dichlorophenolindophenol and methylene blue, are not required. Nonenzymatic reduction of metmyoglobin, which has previously been reported, was not encountered under the assay conditions described herein. Demonstration of enzymatic activity is dependent on a suitable myoglobin substrate, NADH, and ferrocyanide. An equimolar amount of cytochrome b5 was more effective than ferrocyanide in the enzymatic reduction of metmyoglobin. The methods for preparation of beef heart myoglobin and for purification of the enzyme are presented. The enzyme has been purified over 2000-fold. The enzyme has a pH optimum about 6.5 and a Km of 5.0 x 10(-5) M, and is unaffected by the absence of O2. Sodium dodecyl sulfate-gel electrophoresis revealed a molecular weight around 30,000. Purified enzyme does not react with lipoamide. The reaction is markedly influenced by the composition of the buffering milieu. Enzyme activity is inhibited by p-chloromercuriphenyl sulfonic acid, quinacrine dihydrochloride, and N-ethyl-maleimide. Activity was slightly stimulated by FMN. The characteristics of the enzymatic activity and the assay system are similar to those reported by Hegesh et al. (J. Lab. Clin. Med. 72, 339-344, 1968) for erythrocyte methemoglobin reductase.

Work-induced muscle hypertrophy in vitamin D-deficient rats.

To determine if vitamin D deficiency would retard the ability of muscle to hypertrophy in response to mechanical stress, we severed the gastrocnemius tendon on one leg of rats in each of three groups, the treatment of which differed only in the amount of vitamin D in the diet. After 1 week the increased size of the soleus and plantaris in the leg in which the gastrocnemius was severed relative to that of the sham operated leg, was determined for each rat. Despite differences in body weight and serum calcium among the groups, we found no difference in the percent of muscle hypertrophy. We conclude that muscle hypertrophy can occur in response to local mechanical forces despite a deficient hormonal environment that otherwise retards growth.

Independence of 1,25-dihydroxyvitamin D3-mediated calcium transport from de novo RNA and protein synthesis.

The administration of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to rachitic chicks produces an increase in (a) RNA and protein synthesis, (b) calcium binding protein (CaBP) concentration, and (c) alkaline phosphatase activity in the duodenum. These events occur concomitantly with enhanced calcium transport. We inhibited RNA and protein synthesis in richitic chicks and measured the subsequent response to 1,25(OH)2D3. Actinomycin D, injected prior to and following 1,25(OH)2D3 administration, inhibited intestinal RNA polymerase activity, blocked the rise in serum calcium, reduced the amount of CaBP, and increased alkaline phosphatase activity. Cycloheximide injected in similar fashion, inhibited the 1,25(OH)2D3-mediated increase in intestinal protein synthesis, serum calcium, CaBP, and alkaline phosphatase activity. Neither inhibitor blocked the ability of 1,25(OH)2D3 to stimulate calcium transport as measured in isolated duodenal loops in vivo. The ability of either inhibitor to block 1,25(OH)2D3-mediated calcium transport despite inhibition of CaBP production and alkaline phosphatase activity (by cycloheximide) indicates that de novo RNA and protein synthesis, and in particular CaBP and alkaline phosphatase, are not required for the 1,25(OH)2D3 stimulation of calcium transport.

Improvement in jejunal enzyme adaptation in obese adult-onset diabetic patients following a 30-day fast.

The adaptive responses of gastrointestinal enzymes, glucose tolerance, and plasma insulin to diet, folic acid, and insulin of five obese adult-onset diabetic patients were studied before and after a 30-day fast. Their data were compared to the adaptive responses of gastrointestinal enzymes to diet, folic acid, and insulin of 15 normal male volunteer subjects, ages 18 to 24. Each group during each testing period received a carbohydrate diet (50% calories as carbohydrate consisting of 1/2 glucose and 1/2 fructose) and a noncarbohydrate diet (70% of calories as corn oil and 30% as sodium caseinate) each without and with folic acid (5 mg three times per day). The effect of insulin was studied only on the carbohydrate diet plus folic acid. Our data demonstrate that obese adult-onset diabetic patients have an impaired adaptive response of jejunal carbohydrate-metabolizing enzyme activities (hexokinase, pyruvate kinase, fructose-1-6-diphosphate aldolase, fructosediphosphatase) to dietary carbohydrate, oral folic acid, and insulin when compared to normal subjects and nondiabetic obese patients. Following a 30-day fast, the obese diabetic patients showed an improvement in glucose tolerance, hyperinsulinemia, and the adaptive response of the jejunal carbohydrate-metabolizing enzyme activities to dietary carbohydrate, folic acid, and insulin. The greatest improvement in the adaptive response of the jejunal enzyme activities occurred on the carbohydrate diet.

Acute effects of oral and intravenous ethanol on rat hepatic enzyme activities.

1. Oral administration of ethanol (3 ml) of 95% in 12 ml total volume over a two day period) significantly decrease plasma glucose and insulin levels and the activities of two key gluconeogenic enzymes, pyruvate carboxylase (pyruvate: CO2 ligase (ADP), EC 6.4.1.1) and fructose diphosphatase, (D-Fru-1,6-P2 1-phosphohydrolase, EC 3.1.3.11), and one glycolytic enzyme, fructose-1,6-P2 aldolase (Fru-1,6-P2 D-glyceraldehyde-3-P lyase, EC 4.1.2.13). In each instance, the administration of 2400 mug daily of oral folate in conjuction with the ethanol prevented these alterations in carbohydrate metabolism. 2. Intravenous injection of ethanol produced a rapid decrease (within 10--15 min) in the activities of hepatic phosphofructokinase, (ATP:D-fructose-6-phosphate 6-phosphotransferase, EC 2.7.1.11), pyruvate kinase, (ATP:pyruvate phosphotransferase, EC 2.7.1.40), fructose diphosphatase and fructose-1,6-P2 aldolase. 3. Intravenous ethanol significantly increased hepatic cyclic AMP concentration approximately 60% within 10 min, while oral ethanol did not alter hepatic cyclic AMP concentrations. 4. These data confirm the known antagonism ethanol and folate and suggest that oral folate might offer a protective effect against hypoglycemia in rats receiving ethanol.