Amplification of nocturnal oscillations in PRA and aldosterone during continuous heat exposure

To assess the effect of continuous heat exposure on the nocturnal patterns of renin, aldosterone, adrenocorticotropic hormone (ACTH), and cortisol, six young men were exposed to thermoneutral environment for 5 days, followed by a 5-day acclimation period in a hot dry environment (35 degrees C). Blood was collected at 10-min intervals during the second night at thermoneutrality (N0) and during the first (N1) and the last (N5) nights of heat exposure. Polygraphic recordings of sleep were scored according to established criteria. Continuous heat exposure led to progressive decreases in the 24-h urinary volume and in Na excretion, whereas urinary osmolality increased. After 5 days of uninterrupted heat, significant increases were found in plasma volume (P less than 0.05), osmolality (P less than 0.01), plasma Na (P less than 0.01), and protein levels (P less than 0.05). Sweat gland output increased during the first 3 days and then declined without any concomitant increases in body temperature. Compared with N0, there were no differences in plasma renin activity (PRA) and aldosterone (PA) profiles during N1 at 35 degrees C. However, during N5 the mean PRA and PA levels were significantly (P less than 0.05) enhanced, and their nocturnal oscillations were amplified (P less than 0.05). This amplification occurred mainly in the second part of the night when regular rapid-eye-movement and non-rapid-eye-movement sleep cycles were observed, leading to a general upward trend in the nocturnal profiles. The relationship between the nocturnal PRA oscillations and the sleep cycles was not modified. ACTH and cortisol patterns were not affected by continuous heat exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum erythropoietin in humans at high altitude and its relation to plasma renin

Serum immunoreactive erythropoietin (siEp) was estimated in samples collected from members of two scientific and mountaineering expeditions, to Mount Kongur in Western China and to Mount Everest in Nepal. SiEp was increased above sea-level control values 1 and 2 days after arrival at 3,500 m and remained high on ascent to 4,500 m. Thereafter, while subjects remained at or above 4,500 m, siEp declined, and by 22 days after the ascent to 4,500 m was at control values but increased on ascent to higher altitude. Thus siEp was at a normal level during the maintenance of secondary polycythemia from high-altitude exposure. On descent, with removal of altitude hypoxia, siEp decreased, but despite secondary polycythemia levels remained measurable and in the range found in subjects normally resident at sea level. On Mount Everest, siEp was significantly (P less than 0.01) elevated above preexpedition sea-level controls after 2-4 wk at or above 6,300 m. There was no correlation between estimates of siEp and plasma renin activity in samples collected before and during both expeditions.     

Fructose and glucose ingestion and muscle glycogen use during submaximal exercise

Substrate utilization after fructose, glucose, or water ingestion was examined in four male and four female subjects during three treadmill runs at approximately 75% of maximal O2 uptake. Each test was preceded by three days of a carbohydrate-rich diet. The runs were 30 min long and were spaced at least 1 wk apart. Exercise began 45 min after ingestion of 300 ml of randomly assigned 75 g fructose (F), 75 g glucose (G), or control (C). Muscle glycogen depletion determined by pre- and postexercise biopsies (gastrocnemius muscle) was significantly (P less than 0.05) less during the F trial than during C or G. Venous blood samples revealed a significant increase in serum glucose (P less than 0.05) and insulin (P less than 0.01) within 45 min after the G drink, followed by a decrease (P less than 0.05) in serum glucose during the first 15 min of exercise, changes not observed in the C or F trials. Respiratory exchange ratio was higher (P less than 0.05) during the G than C or F trials for the first 5 min of exercise and lower (P less than 0.05) during the C trial compared with G or F for the last 15 min of exercise. These data suggest that fructose ingested before 30 min of submaximal exercise maintains stable blood glucose and insulin concentrations, which may lead to the observed sparing of muscle glycogen.     

Muscle glycogen utilization during shivering thermogenesis in humans

The purpose of the present study was to clarify the importance of skeletal muscle glycogen as a fuel for shivering thermogenesis in humans during cold-water immersion. Fourteen seminude subjects were immersed to the shoulders in 18 degrees C water for 90 min or until rectal temperature (Tre) decreased to 35.5 degrees C. Biopsies from the vastus lateralis muscle and venous blood samples were obtained before and immediately after the immersion. Metabolic rate increased during the immersion to 3.5 +/- 0.3 (SE) times resting values, whereas Tre decreased by 0.9 degrees C to approximately 35.8 degrees C at the end of the immersion. Intramuscular glycogen concentration in the vastus lateralis decreased from 410 +/- 15 to 332 +/- 18 mmol glucose/kg dry muscle, with each subject showing a decrease (P less than 0.001). Plasma volume decreased (P less than 0.001) markedly during the immersion (-24 +/- 1%). After correcting for this decrease, blood lactate and plasma glycerol levels increased by 60 (P less than 0.05) and 38% (P less than 0.01), respectively, whereas plasma glucose levels were reduced by 20% after the immersion (P less than 0.001). The mean expiratory exchange ratio showed a biphasic pattern, increasing initially during the first 30 min of the immersion from 0.80 +/- 0.06 to 0.85 +/- 0.05 (P less than 0.01) and decreasing thereafter toward basal values. The results demonstrate clearly that intramuscular glycogen reserves are used as a metabolic substrate to fuel intensive thermogenic shivering activity of human skeletal muscle.     

Effects of warm exposure on adipose tissue and muscle metabolism in growing pigs.

1. Forty-eight pigs weaned at 3 weeks old and acclimated to the experimental temperatures for 2 weeks before the start of the experiment, were fed ad lib and used between 9 and 33 kg live weight to determine the effects of warm exposure (31.5 vs 18.5 degrees C) on adipose tissue and muscle metabolism. 2. Warm exposure induced a decline in the lipid content (P less than 0.01) of backfat whereas degree of saturation (P less than 0.05) and adipocytes size were increased (P less than 0.05). 3. At 31.5 degrees C, as compared to 18.5 degrees C, activities of malic enzyme and glucose-6-phosphate dehydrogenase were depressed by an average 33% in backfat (P less than 0.01) and 23% in leaf fat (P less than 0.05) while lipoprotein-lipase activity was stimulated by 60% (P less than 0.01) in leaf fat. 4. In warm conditions, the activities of the enzymes indicative of oxidative and glycolytic metabolism in muscle, i.e. lactate dehydrogenase, beta-hydroxyacyl coenzyme-A dehydrogenase, citrate synthase and cytochrome oxidase, were reduced in the longissimus dorsi muscle (P less than 0.05) and to a lesser extent in the trapezius muscle. 5. At 31.5 degrees C, pigs exhibit lower average plasma levels of insulin, T3 and T4 than those maintained at 18.5 degrees C.     

Heat-injured rats: pathochemical indices and survival time

Rats were exercised on a treadmill (9.14 m/min) in a hot environment (34.5 degrees C, 30% rh) until a rectal temperature of 42.0--42.5 degrees C was reached. Analysis of plasma constituents in subsequent serial blood samples demonstrated a highly significant inverse correlation between lactate concentration (P less than 0.001) and potassium levels (P less than 0.005) in blood samples taken immediately postexercise when both of these were correlated to survival time. Alternatively, plasma creatine phosphokinase (CPK) activity in these samples, although significantly elevated over control levels (P less than 0.001), was not correlated with either survival time or lactate-potassium concentrations. When fluid was administered prior to the run and immediately thereafter to repress pathological effects, there occurred no changes in plasma lactate and potassium levels between the postrun sample and a second sample taken 60 min later, while CPK levels were significantly reduced (P less than 0.01) in the second sample. However, levels of all three indices were significantly elevated (P less than 0.01) in a third sample taken terminally despite the fact that the animals were restrained and sedentary during this interval. These findings indicate that the hyperthermic injury may have had fundamental pathological effects on metabolism and membrane integrity producing lactacidemia and hyperkalemia of sufficient magnitude to compromise cardiovascular performance.     

Effects of thermal stress on plasma concentrations of luteinizing hormone, progesterone, prolactin and testosterone in the cycling ewe

Naturally cycling white faced ewes were utilized to study the effects of continuously elevated environmental temperature and/or humidity on plasma concentrations of luteinizing hormone (LH), prolactin (PRL), progesterone (P4) and testosterone (TE) during the estrous cycle. Fourteen ewes were randomly allocated on the day of estrus (day 0) to either thermoneutral conditions (21.1 degrees C, 65% relative humidity) or elevated ambient temperature/humidity conditions (36.1 degrees C, 71% relative humidity) producing an average 1.4 degrees C hyperthermia. Animals remained in their respective environments and blood samples were collected daily until the next estrus or day 20, whichever occurred first. Starting at noon on day 14, blood was sampled every 2 hours. Concentrations of LH, PRL, P4 and TE were quantified using validated radioimmunoassays. Hyperthermic ewes exhibited 1) a significant decrease (P<0.05) in the incidence of behavioral estrus and a preovulatory LH surge at the expected time of the estrous cycle, 2) significantly lower (P<0.05) plasma P4 between days 7 and 13 of the cycle, 3) a six-fold increase of PRL levels (P<0.01). Plasma levels of TE were not significantly affected by hyperthermia. The only two experimental ewes which exhibited estrus and an LH surge also showed an unusual and significant peak in plasma P4 two days before estrus. These results confirm that elevated environmental temperatures that result in hyperthermia can induce endocrine imbalances in the ewe which may contribute to decreased reproductive efficiency in the heat-stressed female.     

Plasma catecholamines in rats during rewarming from induced hypothermia

The present study sought to quantitate the levels of plasma catecholamines [norepinephrine (NE), epinephrine (E), and dopamine (DA)] during induction and rewarming from hypothermia. Male rats (317 +/- 8 g) were made hypothermic by exposure to 0.9% halothane at -10 to -15 degrees C while blood pressure (carotid artery), heart rate, and colonic temperature (Tc) were monitored. Anesthesia was discontinued when Tc reached 28 degrees C. Tc continued to fall but was held at 20-20.5 degrees C for 30 min. Rewarming was then initiated by raising ambient temperature to 22 degrees C. Arterial blood samples were taken 1) before cooling, 2) just before rewarming, 3) when Tc reached 22 degrees C during rewarming, and 4) when Tc reached 27 degrees C during rewarming. Plasma was assayed radioenzymatically for catecholamines using both phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase procedures, and hypothermic induction resulted in significant increases in NE, E, and DA above control levels (P less than 0.01). With rewarming to Tc = 22 degrees C, all catecholamines increased above the level observed during hypothermia (P less than 0.01), and NE and DA increased still further (P less than 0.01) when Tc reached 27 degrees C. The levels of plasma catecholamines observed during hypothermia and during the rewarming phase indicate a role of the sympathoadrenal medullary system in the metabolic adjustments associated with hypothermia and recovery. During rewarming, the levels of E and NE attained exceed those at which both substances may be expected to act as circulating hormones.     

Sex-linked differences in activity of enzymes in the blood of the urodele amphibian Pleurodeles waltl.

Few data are available on enzyme activity in amphibian plasma or erythrocytes. We measured the activity of several blood enzymes in the urodele amphibian Pleurodeles waltl reared under standard laboratory conditions. In subsequent experiments, we will estimate and compare the physiological and biochemical conditions of P. waltl when reared under extreme temperature or microgravity conditions. The enzymes selected were glutamate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, superoxide dismutase, catalase, isocitrate dehydrogenase and glucose-6-phosphate dehydrogenase. In fresh plasma samples, enzyme activity in females was higher than in males, except for aspartate and alanine aminotransferases, which were equivalent in females and males. Glutamate dehydrogenase activity was higher in males than in females. In female erythrocytes, the activity of all enzymes was higher than in male erythrocytes. We have also studied the storage conditions of samples and observed that for most enzymes, the activity in freshly isolated plasma and erythrocyte preparations decreased after storage at -18 or +4 degrees C.     

Free fatty acid availability and temperature regulation in cold water

The purpose of this study was to investigate whether a reduced availability of plasma free fatty acids (FFA) would impair human temperature regulation during cold exposure. Seven seminude male subjects were immersed on two occasions in 18 degrees C water for 90 min or until their rectal temperature (Tre) decreased to 35.5 degrees C. The immersion occurred after 2 h of intermittent oral ingestion of either nicotinic acid (NIC) or a placebo (PLAC). Plasma FFA levels immediately before the immersion were significantly lower in NIC (87 +/- 15 mumol/l) than in PLAC (655 +/- 116 mumol/l, P less than 0.05). Although FFA levels increased by 73% in NIC during the immersion (P less than 0.05), they remained significantly lower than in PLAC (151 +/- 19 vs. 716 +/- 74 mumol/l, P less than 0.05) throughout the immersion. Muscle glycogen concentrations in the vastus lateralis decreased after cold water immersion in both trials (P less than 0.05), but the rate of glycogen utilization was similar, averaging 1.00 +/- 0.27 mmol glucose unit.kg dry muscle-1.min-1). Plasma glucose levels were significantly reduced after immersion in both trials (P less than 0.05), this decrease being greater in NIC (1.3 +/- 0.2 mmol/l) than in PLAC (0.7 +/- 0.1 mmol/l, P less than 0.05). O2 uptake increased to 3.8 +/- 0.3 times preimmersion values in both trials (P less than 0.05). Mean respiratory exchange ratio (RER) immediately before the immersion was greater in NIC (0.87 +/- 0.02) than in PLAC (0.77 +/- 0.01, P less than 0.05). Cold exposure increased RER in PLAC but not in NIC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of bromocriptine and perphenazine on prolactin and progesterone concentrations in pregnant pony mares during late gestation

Pregnant pony mares in Group A (n = 4) received i.m. injections at 07:00 and 17:00 h of 0.8 mg bromocriptine/kg body weight 0.75 per day beginning on Day 295 of gestation and continuing until parturition. Group B (n = 4) was treated similarly, but perphenazine was administered orally at 0.375 mg/kg body weight twice a day beginning on Day 305 of gestation and continuing until parturition. Mares in Group C (n = 3) received i.m. injections of saline. Mean plasma prolactin and progesterone concentrations were greater (P less than 0.05) for mares in Group C than in Groups A and B from 295 to 309 days of gestation. From 305 days of gestation, plasma prolactin and progesterone concentrations were greater (P less than 0.05) in Group B and C than in Group A mares. Progesterone and prolactin concentrations increased over this period for Group B and Group C mares, but remained constant in Group A mares. From 10 days pre partum through foaling, mares in Group A had lower progesterone (P less than 0.05) and prolactin (P less than 0.01) concentrations than Group B and C mares. All mares in Group A were agalactic at foaling, while all mares in Groups B and C had normal milk secretion. Gestation was longer (P less than 0.05) in Group A than in Group C mares. In Group A, 2 mares retained the placenta for greater than 3 h, 3 mares had dystocia and all 4 mares had thickened, haemorrhagic placentae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous activity and brain 5-hydroxyindole levels measured in rats tested in two designs of elevated X-maze

The spontaneous activity of rats tested both acutely and chronically (15 minutes per day for 25 days) in an elevated X-maze composed entirely of open runways was found to be significantly less (P less than 0.01) than that measured for rats tested in a maze of similar dimensions composed entirely of enclosed runways. Acute exposure to both mazes caused significant increases (P less than 0.01) in plasma corticosterone when compared with unstressed control rats. Chronic exposure to the open, but not the enclosed maze caused a significant (P less than 0.01) attenuation of this response. Chronic exposure to the open maze caused significant increases (P less than 0.01) in the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus, hypothalamus and cerebral cortex when compared with unstressed control rats. When compared with the data for the rats tested repeatedly in the enclosed maze, chronic exposure to the open maze increased the 5-HT concentrations in hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01) and the 5-HIAA concentrations in hypothalamus (P less than 0.01) and hippocampus (P less than 0.01). The spontaneous locomotor activity of the rats tested in the open maze, correlated significantly (P less than 0.01) with plasma corticosterone and the 5-HIAA concentrations in hippocampus (P less than 0.01), hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01). In the rats tested in the enclosed maze, spontaneous activity only correlated significantly (P less than 0.01) with hippocampal 5-HIAA. It is concluded that the study has revealed clear differences in the behavioral, plasma corticosterone and brain 5-hydroxyindole responses to the two mazes but that the results do not provide unequivocal evidence that these differences occurred because the open maze was more aversive than the enclosed. It is also concluded that the study provides further support for the hypothesis that 5-HT turnover in the hippocampus may be directly related to the level of spontaneous locomotor activity.     

Effect of cold exposure on liver and muscle cAMP content and cAMP phosphodiesterase activity

Adenosine 3',5'-cyclic monophosphate (cAMP) concentration and 3',5'-cyclic-nucleotide phosphodiesterase (PDE) activity were measured in skeletal muscle, heart, and liver of rats exposed to 1, 3, 5, and 7 days of cold. Cyclic nucleotide concentration increased in fast-twitch red muscle at the same time that PDE activity was decreasing. Nucleotide concentration and enzyme activity of slow-twitch red muscle were not altered by the cold exposure. The PDE activity of fast-twitch white muscle was elevated approximately 50% above control after 1 and 3 days of cold exposure. By the 5th day in the cold, white muscle PDE activity had returned to control levels and remained there through the 7th day of experimentation. cAMP concentration in hearts of cold-exposed rats was significantly (P less than 0.01) elevated above control at all time points measured. Myocardial PDE activity was elevated above control (P less than 0.05) at 1 and 3 days of cold exposure but returned to control levels by the 5th day in the cold. Hepatic cAMP and PDE activity were elevated above control at all time points analyzed. These data suggest that changes in cyclic nucleotide metabolism play a role in attaining homeostasis during acute cold exposure.     

Acclimation of rats following stepwise or direct exposure to heat

The physiological changes in male rats during acclimation were studied following direct or stepwise exposure to heat (32.5 degrees C) in a controlled-environment room. The animals were exposed to each temperature for 10 days beginning at 24.5 degrees C and returning to 24.5 degrees C in the reverse order of initial exposure. Relative humidity of 50 +/- 2% and a 12-h light-dark photoperiod (light from 0900 to 2100 h) were maintained. Physiological changes in metabolic rate (MR), evaporative water loss (EWL), plasma corticosterone, body water turnover, and food and water intake were measured. The results indicate a significantly (P less than 0.001) elevated plasma corticosterone and MR in rats exposed directly to heat from control temperature (24.5 degrees C) but not in those animals exposed stepwise via 29.0 degrees C. All kinetic parameters of water pool changed (P less than 0.01) on direct exposure to heat, whereas rats exposed in a stepwise manner increased only pool turnover. In addition, exposure to experimental temperatures resulted in reduced (P less than 0.05) relative food intake and increased (P less than 0.05) water intake. Compared with the control condition of 24.5 degrees C, EWL was significantly (P less than 0.05) elevated when the animals were exposed either directly or in a stepwise fashion to 32.5 degrees C. These data suggest that the response to elevated temperatures is influenced by the temperature to which the rat is acclimated.     

Assessment of a natural dietary extract, titrated in phenylpropanoid glycosides, on blood parameters and plasma oxidative status in intensively reared Italian hares (Lepus corsicanus)

Two different doses of a natural extract titrated in phenylpropanoid glycosides (PPGs) were evaluated for their effect on blood parameters and plasma oxidative status in pairs of intensively reared Italian hares. The study lasted 210 days, during which 45 couples of hares were divided into three homogeneous groups. A control group (CON) was fed a control diet while the two experimental groups were fed a diet supplemented with 1 or 2 kg/t of a supplement titrated in PPGs. Blood samples were obtained at 0, 70, 140 and 210 days and assayed for plasma lipid profiles, bilirubin, haematological parameters and indicators of oxidative status (reactive oxygen metabolites (ROMs), thiobarbituric acid reactive substances (TBARS), vitamins A and E). Although dietary treatment did affect the levels of triglycerides, total cholesterol and total bilirubin, all of which decreased markedly (P < 0.05), while significantly increasing the (P < 0.01) HDL cholesterol values, it also significantly improved the oxidative status of the blood, which displayed an increase in both vitamin E (P < 0.01) and vitamin A (P < 0.05) and a decrease in ROMs (P < 0.01) and TBARS (P < 0.05). The improvements in the blood parameters, lipid profile and plasma oxidative status continued to increase significantly as the trial progressed, indicating a positive effect with increased length of treatment. The results of this study demonstrate an important role for feed supplementation with respect to antioxidant activity on some blood parameters, including the lipid profile and the oxidative status of blood.     

Lymphocyte subset responses to repeated submaximal exercise in men

The effects of repeated bouts of submaximal cycle ergometry exercise on changes in the percentage of peripheral blood T-lymphocytes, the T-helper/inducer and T-cytotoxic/suppressor subsets, and natural killer (NK) cells were studied in 18 healthy young men who had no history of regular exercise training. Subjects were matched on the basis of maximal O2 uptake and assigned randomly to exercise or control groups, with controls resting quietly during the exercise sessions. The percentage of peripheral blood mononuclear leukocytes that reacted with monoclonal antibodies specific for T-lymphocytes (CD3+ cells), the helper/inducer subset (CD4+ cells) and cytotoxic/suppressor subset (CD8+ cells) of T-lymphocytes, and cells with NK activity (Leu7+ cells) were enumerated by fluorescence-activated flow cytometry for samples obtained immediately before and after exercise on days 1, 3, and 5 of a 5-day exercise regimen. The results of this study were mixed with decreases in the percentage of T-lymphocytes before vs. after exercise on days 1 and 3 (P less than 0.001), a decrease in the percentage of T-helper/inducer cells before vs. after exercise on day 3 (P less than 0.05), no effect of exercise on the percentage of T-cytotoxic/suppressor cells, and a marked increase in the percentage of NK cells after exercise on days 1 (P less than 0.05) and 3 (P less than 0.01). The total number of recovered NK cells in the mononuclear leukocyte fraction of blood also increased significantly after exercise on days 1 (P less than 0.05) and 3 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of polycythemia on blood volume and thermoregulation during exercise-heat stress

We studied the effects of autologous erythrocyte infusion on blood volume and thermoregulation during exercise in the heat. By use of a double-blind design, nine unacclimated male subjects were infused with either 600 ml of a NaCl-glucose-phosphate solution containing a approximately 50% hematocrit (n = 6, reinfusion) or 600 ml of this solution only (n = 3, saline). A heat stress test (HST) was attempted approximately 2-wk pre- and 48-h postinfusion during the late spring months. After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min treadmill walking) in a hot (35 degrees C, 45% rh) environment while euhydrated. Erythrocyte volume (RCV, 51Cr) and plasma volume (PV, 125I) were measured 24 h before each HST, and maximal O2 uptake (VO2max) was measured 24 h after each HST. Generally, no significant effects were found for the saline group. For the reinfusion group, RCV (11%, P less than 0.01) and VO2max (11%, P less than 0.05) increased after infusion, and the following observations were made: 1) the increased RCV was associated with a reduction in PV to maintain the same blood volume as during the preinfusion measurements; 2) polycythemia reduced total circulating protein but did not alter F-cell ratio, plasma osmolality, plasma protein content, or plasma lactate at rest or during exercise-heat stress; 3) polycythemia did not change the volume of fluid entering the intravascular space from rest to exercise-heat stress; and 4) polycythemia tended to reduce the rate of heat storage during exercise-heat stress.     

Effects of a gonadotrophin-releasing hormone antagonist on gonadotrophin secretion and gonadal development in neonatal pigs

Male (N = 8) and female (N = 8) pigs were assigned to receive saline or a potent GnRH antagonist ([Ac-D2Nal1,D4-Cl-Phe2,D-Trp3,D-Arg6, D-Ala10]- GnRH*HOAc; 1 mg/kg body weight) at 14 days of age. The GnRH antagonist caused LH to decline (P less than 0.01) from 1.7 ng/ml at 0 h to less than 0.5 ng/ml during 4-32 h in males and females. Concentrations of FSH in gilts declined slowly from 75 +/- 8 to 56 +/- 5 ng/ml (P less than 0.05) at 32 h. In males FSH was low (5.7 +/- 0.5 ng/ml) at 0 h and did not change significantly. To observe the effect of long-term treatment with GnRH antagonist, 10 male and 10 female pigs, 3 days of age, were treated with saline or 1 mg GnRH antagonist per kg body weight every 36 h for 21 days. Concentrations of LH were reduced (P less than 0.01) to 0.2-0.4 ng/ml throughout the experimental period in male and female piglets treated with GnRH antagonist. Plasma FSH increased in control females, but remained suppressed (P less than 0.001) in females treated with GnRH antagonist. Treatment with the GnRH antagonist suppressed FSH levels in males on Days 8 and 16 (P less than 0.05), but not on Day 24. Treatment of females with the GnRH antagonist did not influence (P greater than 0.10) oestradiol-17 beta concentrations. Administration of GnRH antagonist to males suppressed testosterone and oestradiol-17 beta values (P less than 0.01) and reduced testicular weight (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

散放条件下春季梅花鹿行为时间分配的研究

梅花鹿 (Ｃｅｒｖｕｓｎｉｐｐｏｎ)是我国珍贵的经济动物 ,梅花鹿野生种群数量极少 ,主要分布在吉林东部、四川诺尔盖、江西彭泽、安徽南部以及浙江西部[14 ] ,是国家 1级保护动物。国内对梅花鹿行为学研究仅对活动节律[2 ] 、性行为[7] 、社群行为[12 ] 有一些零星报道[8,11,13,14 ] ,尚未见有关行为时间分配及其与性别和天气之间关系的报道。我们于 1998年4～ 5月对散放条件下东北梅花鹿 (Ｃ .ｎｉｐｐｏｎｈｏｒ ｔｕｌｏｒｕｍ)的行为时间分配进行了研究 ,为保护梅花鹿这一濒危物种研究提供基础资料。1　研究地区与方法1 1　自然概况黑…     

Sex-linked differences in activity of enzymes in the blood of the urodele amphibian Pleurodeles waltl

Few data are available on enzyme activity in amphibian plasma or erythrocytes. We measured the activity of several blood enzymes in the urodele amphibian Pleurodeles waltl reared under standard laboratory conditions. In subsequent experiments, we will estimate and compare the physiological and biochemical conditions of P. waltl when reared under extreme temperature or microgravity conditions. The enzymes selected were glutamate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, superoxide dismutase, catalase, isocitrate dehydrogenase and glucose-6-phosphate dehydrogenase. In fresh plasma samples, enzyme activity in females was higher than in males, except for aspartate and alanine aminotransferases, which were equivalent in females and males. Glutamate dehydrogenase activity was higher in males than in females. In female erythrocytes, the activity of all enzymes was higher than in male erythrocytes. We have also studied the storage conditions of samples and observed that for most enzymes, the activity in freshly isolated plasma and erythrocyte preparations decreased after storage at −18 or +4°C.