Nocturnal variation of prolactin secretion in the Mouflon (Ovis gmelini musimon) and domestic sheep (Ovis aries): seasonal changes

Seasonal changes in nocturnal prolactin secretion and their relationship with melatonin secretion were monitored in wild (Mouflon, Ovis gmelini musimon) and domesticated sheep (breed Manchega, Ovis aries). Two groups of eleven adult females each, were maintained outdoors under natural photoperiod. Plasma concentrations of prolactin and melatonin were determined during the summer and winter solstices and the autumn and spring equinoxes. Blood samples were collected every 3h during the night hours, and 1h before and after the onset of darkness and sunrise. Maximum mean plasma concentrations of prolactin during the dark-phase in Mouflons were observed in the summer solstice, (P<0.001) and in the summer solstice and spring equinox in Manchega ewes (P<0.001). Mean plasma concentrations of prolactin were higher in the wild species (P<0.001) during the summer solstice. In contrast, during the spring equinox, mean levels of prolactin were higher in Manchega ewes than in Mouflons (P<0.05). Plasma prolactin concentrations showed a nocturnal rhythm in both breeds, with seasonal variations (P<0.001). The increase in plasma melatonin levels during the first hour after sunset was accompanied to increasing concentrations of PRL 1h after the onset of darkness, only in the autumn and spring equinox for the Mouflon, and in the summer solstice and spring equinox for the Manchega ewes. In Mouflons, the fall of plasma PRL concentrations about the middle dark-phase in all the periods studied, coincided with high levels of melatonin. A similar relation was observed in Manchega ewes only in the winter solstice and spring equinox. The current study shows that the nocturnal rhythm of prolactin secretion exhibits seasonal variation; differences in the patterns of prolactin secretion between Mouflon and Manchega sheep are taken to represent the effects of genotype.     

Effects of indomethacin on cardiac output distribution in normal and asphyxiated piglets

We determined the effect of breathing 9% CO₂/10% O₂/81% N₂ (asphyxia) on cardiac output distribution (microspheres) in 4–5 day old unanesthetized, chronically instrumented piglets prior to and following intravenous indomethacin administration. Thirty minutes of asphyxia caused Pa_CO2 to increase from 35 ± 2 mmHg to 66 ± 2 mmHg, Pa_O2 to decrease form 73 ± 4 mmHg to 41 ± 1 mmHg, and pH to decrease from 7.52 ± 0.05 to 7.21 ± 0.07. Arterial pressure was increased slightly but cardiac output was not changed significantly. Asphyxia caused blood flow to the brain, diaphragm, liver, heart, and adrenal glands to increase while causing decreases in blood flow to the skin, small intestine, and colon. Blood flows to the stomach and kidneys tended to decrease, but the changes were not significant. Treatment with indomethacin during asphyxia did not alter arterial pressure or cardiac output but decreased cerebral blood flow to the preasphyxiated level and decreased adrenal blood flow about 20%. Indomethacin did not alter blood flow to any other systemic organ. At this time the piglet was allowed to breathe air for 2.5 hr undisturbed. Two and a half hours after indomethacin administration, blood flows to all organs returned to the preasphyxia control levels with the exception of cerebral blood flow which was reduced (93 ± 13 to 65 ± 5 ml/100 g·min. Three hours after indomethacin administration, the cerebral hyperemia caused by asphyxia was less (134 ± 17b ml/100 g·min) than prior to indomethacin (221 ± 15 ml/100 g·min. Indomethacin did not alter the asphyxia-induced changes to any other systemic organ. We conclude that in newborn pigs, systemic treatment with indomethacin decreases cerebral blood flow and cerebral hyperemia in response to asphyxia, without affecting blood flow to any other systemic organ.     

Effects of living at two ambient temperatures on 24-h blood pressure and neuroendocrine function among obese and non-obese humans: a pilot study

The effects of environmental temperature on blood pressure and hormones in obese subjects in Japan were compared in two seasons: summer vs winter. Five obese (BMI, 32?±?5 kg/m²) and five non-obese (BMI, 23 ±3 kg/m²) men participated in this experiment at latitude 35°10′ N and longitude 136°57.9′ E. The average environmental temperature was 29?±?1 °C in summer and 3?±?1 °C in winter. Blood samples were analyzed for leptin, ghrelin, catecholamines, thyroid stimulating hormone (TSH), free thyroxine (fT₄), free triiodothyronine (fT₃), total cholesterol, triglycerides, insulin and glucose. Blood pressure was measured over the course of 24 h in summer and winter. A Japanese version of the Profile of Mood States (POMS) questionnaire was also administered each season. Systolic and diastolic blood pressures in obese men were significantly higher in winter (lower environmental temperatures) than in summer (higher environmental temperatures). Noradrenaline and dopamine concentrations were also significantly higher at lower environmental temperatures in obese subjects, but ghrelin, TSH, fT₃, fT₄, insulin and glucose were not significantly different in summer and winter between obese and non-obese subjects. Leptin, total cholesterol and triglyceride concentrations were significantly higher in winter in obese than non-obese men. Results from the POMS questionnaire showed a significant rise in Confusion at lower environmental temperatures (winter) in obese subjects. In this pilot study, increased blood pressure may have been due to increased secretion of noradrenaline in obese men in winter, and the results suggest that blood pressure control in obese men is particularly important in winter.     

Seasonal changes in the cardiorespiratory responses to hypercarbia and temperature in the bullfrog, Rana catesbeiana

We assessed the seasonal variations in the effects of hypercarbia (3 or 5% inspired CO2) on cardiorespiratory responses in the bullfrog Rana catesbeiana at different temperatures (10, 20 and 30 degrees C). We measured breathing frequency, blood gases, acid-base status, hematocrit, heart rate, blood pressure and oxygen consumption. At 20 and 30 degrees C, the rate of oxygen consumption had a tendency to be lowest during winter and highest during summer. Hypercarbia-induced changes in breathing frequency were proportional to body temperature during summer and spring, but not during winter (20 and 30 degrees C). Moreover, during winter, the effects of CO2 on breathing frequency at 30 degrees C were smaller than during summer and spring. These facts indicate a decreased ventilatory sensitivity during winter. PaO2 and pHa showed no significant change during the year, but PaCO2 was almost twice as high during winter than in summer and spring, indicating increased plasma bicarbonate levels. The hematocrit values showed no significant changes induced by temperature, hypercarbia or season, indicating that the oxygen carrying capacity of blood is kept constant throughout the year. Decreased body temperature was accompanied by a reduction in heart rate during all four seasons, and a reduction in blood pressure during summer and spring. Blood pressure was higher during winter than during any other seasons whereas no seasonal change was observed in heart rate. This may indicate that peripheral resistance and/or stroke volume may be elevated during this season. Taken together, these results suggest that the decreased ventilatory sensitivity to hypercarbia during winter occurs while cardiovascular parameters are kept constant.     

Dynamic cerebral autoregulation is preserved during acute head-down tilt.

Complete ganglion blockade alters dynamic cerebral autoregulation, suggesting links between systemic autonomic traffic and regulation of cerebral blood flow velocity. We tested the hypothesis that acute head-down tilt, a physiological maneuver that decreases systemic sympathetic activity, would similarly disrupt normal dynamic cerebral autoregulation. We studied 10 healthy young subjects (5 men and 5 women; age 21 +/- 0.88 yr, height 169 +/- 3.1 cm, and weight 76 +/- 6.1 kg). ECG, beat-by-beat arterial pressure, respiratory rate, end-tidal CO2 concentration, and middle cerebral blood flow velocity were recorded continuously while subjects breathed to a metronome. We recorded data during 5-min periods and averaged responses from three Valsalva maneuvers with subjects in both the supine and -10 degrees head-down tilt positions (randomized). Controlled-breathing data were analyzed in the frequency domain with power spectral analysis. The magnitude of input-output relations were determined with cross-spectral techniques. Head-down tilt significantly reduced Valsalva phase IV systolic pressure overshoot from 36 +/- 4.0 (supine position) to 25 +/- 4.0 mmHg (head down) (P = 0.03). Systolic arterial pressure spectral power at the low frequency decreased from 5.7 +/- 1.6 (supine) to 4.4 +/- 1.6 mmHg2 (head down) (P = 0.02), and mean arterial pressure spectral power at the low frequency decreased from 3.3 +/- 0.79 (supine) to 2.0 +/- 0.38 mmHg2 (head down) (P = 0.05). Head-down tilt did not affect cerebral blood flow velocity or the transfer function magnitude and phase angle between arterial pressure and cerebral blood flow velocity. Our results show that in healthy humans, mild physiological manipulation of autonomic activity with acute head-down tilt has no effect on the ability of the cerebral vasculature to regulate flow velocity.     

Effects of indomethacin on cardiac output distribution in normal and asphyxiated piglets

We determined the effect of breathing 9% CO2/10% O2/81% N2 (asphyxia) on cardiac output distribution (microspheres) in 4-5 day old unanesthetized, chronically instrumented piglets prior to and following intravenous indomethacin administration. Thirty minutes of asphyxia caused PaCO2 to increase from 35 +/- 2 mmHg to 66 +/- 2 mmHg, PaO2 to decrease from 73 +/- 4 mmHg to 41 +/- 1 mmHg, and pH to decrease from 7.52 +/- 0.05 to 7.21 +/- 0.07. Arterial pressure was increased slightly but cardiac output was not changed significantly. Asphyxia caused blood flow to the brain, diaphragm, liver, heart, and adrenal glands to increase while causing decreases in blood flow to the skin, small intestine, and colon. Blood flows to the stomach and kidneys tended to decrease, but the changes were not significant. Treatment with indomethacin during asphyxia did not alter arterial pressure or cardiac output but decreased cerebral blood flow to the preasphyxiated level and decreased adrenal blood flow about 20%. Indomethacin did not alter blood flow to any other systemic organ. At this time the piglet was allowed to breathe air for 2.5 hr undisturbed. Two and a half hours after indomethacin administration, blood flows to all organs returned to the preasphyxia control levels with the exception of cerebral blood flow which was reduced (93 +/- 13 to 65 +/- 7 ml/100 g X min). Three hours after indomethacin administration, the cerebral hyperemia caused by asphyxia was less (134 +/- 17 ml/100 g X min) than prior to indomethacin (221 +/- 15 ml/100 g X min). Indomethacin did not alter the asphyxia-induced changes to any other systemic organ.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of magnesium sulfate administration on subendocardial and subepicardial perfusion

The objective of this study was to determine the effect of systemic MgSO₄ infusion on subendocardial and subepicardial perfusion. Seventeen spontaneously breathing piglets were examined. Myocardial perfusion was measured using radiolabeled microspheres at baseline, 30 and 60 min after either MgSO₄ (80 mg/kg) or saline infusion. Blood pressure, heart rate, and cardiac output were also measured at these time intervals. Comparison of the magnesiuminduced changes in systemic blood pressure and on subendocardial and subepicardial perfusion at 30 and 60 min with values obtained with saline solution at 30 and 60 min, yielded no statistically significant difference (Tables 1–3). The ratio of subendocardial/subepicardial blood flow and subendocardial and subepicardial coronary vascular resistance at 30 and 60 min revealed no statistically significant differences between the magnesium and the control group (Table 3). There were no statistically significant difference in cardiac output and heart rate during any of the measured periods (Table 2). Our results suggest that the administration of MgSO₄ does not alter the ratio of subendocardial/subepicardial blood flow and the ratio of subendocardial/subepicardial coronary vascular resistance.     

Peripheral inhibin levels in relation to climatic variations and stage of estrous cycle in buffalo (Bubalus bubalis )

The present study investigated the peripheral plasma inhibin levels in relation to 1) the stage of estrous cycle and the effect of climatic variations. Blood samples were collected from cyclic buffalo (n=5) once daily for 32 consecutive days during the tropical hot humid (summer) and cold (winter) seasons. Estrus was recorded by parading a vasectomized bull as well as by plasma progesterone determination. In the winter season, peripheral inhibin concentrations which were lowest (0.35 +/- 0.02 ng/ml) during the mid-luteal phase of estrous cycle (Day 6 to Day 14, Day 0 = day of estrus) increased significantly (P < 0.02) to 0.47 +/- 0.04 ng/ml during the late luteal phase (Day -4 to Day -2) and then further to 0.52 +/- 0.03 ng/ml (P< 0.02) during the periestrus phase (Day -1 to Day 1). Inhibin concentrations then decreased significantly (P < 0.02) to 0.40 +/- 0.03 ng/ml during the early luteal phase (Day 2 to Day 5). In the summer season the differences in peripheral inhibin concentrations among different phases of estrous cycle were found to be nonsignificant. A comparison of the circulating inhibin concentrations between the two seasons indicated that inhibin concentrations were significantly higher in the late luteal phase (P < 0.01) and periestrus phase (P < 0.05) during the winter season compared with corresponding periods during the summer season. The present study suggests that peripheral inhibin concentrations change in the estrous cycle during cooler breeding season and that environmental heat stress can cause a reduction in peripheral inhibin concentrations.     

Optic Nerve Head Blood Flow Autoregulation during Changes in Arterial Blood Pressure in Healthy Young Subjects

Aim

In the present study the response of optic nerve head blood flow to an increase in ocular perfusion pressure during isometric exercise was studied. Based on our previous studies we hypothesized that subjects with an abnormal blood flow response, defined as a decrease in blood flow of more than 10% during or after isometric exercise, could be identified.

Methods

A total of 40 healthy subjects were included in this study. Three periods of isometric exercise were scheduled, each consisting of 2 minutes of handgripping. Optic nerve head blood flow was measured continuously before, during and after handgripping using laser Doppler flowmetry. Blood pressure was measured non-invasively in one-minute intervals. Intraocular pressure was measured at the beginning and the end of the measurements and ocular perfusion pressure was calculated as 2/3*mean arterial pressure –intraocular pressure.

Results

Isometric exercise was associated with an increase in ocular perfusion pressure during all handgripping periods (p < 0.001). By contrast no change in optic nerve head blood flow was seen. However, in a subgroup of three subjects blood flow showed a consistent decrease of more than 10% during isometric exercise although their blood pressure values increased. In addition, three other subjects showed a consistent decline of blood flow of more than 10% during the recovery periods.

Conclusion

Our data confirm previous results indicating that optic nerve head blood flow is autoregulated during an increase in perfusion pressure. In addition, we observed a subgroup of 6 subjects (15%) that showed an abnormal response, which is in keeping with our previous data. The mechanisms underlying this abnormal response remain to be shown.     

The effect of acclimatization on blood flow and its distribution in normothermic and hyperthermic domestic fowl

Blood flow and its distribution was examined in summer and winter acclimatized normothermic and hyperthermic domestic hens. A clear trend of season on normothermic blood flow distribution was not noted; however, a significant tendency towards increased flow in summer was recorded. In 22 out of 28 organs or tissues examined, blood flow was lower in winter than in summer: pectoral muscle, adrenal and jejunum winter to summer ratios were 36, 64 and 76%, respectively (P less than 0.05). During hyperthermia, blood flow to visceral organ decreased in both groups; in summer this reduction was less severe in parts of the digestive system and more pronounced in parts of the reproductive system.     

The function of daylight flying in British bats

A national survey of the incidence of daylight flying of bats in mainland Britain was organized from September 1985 until March 1988. A total of 420 records of daylight flying were received by 1 May 1988. One hundred and forty-four reports were from winter (October to March), 271 from summer (April to September) and five were undated. Peak activity occurred during April and in August/September.
Activity in both winter and summer was greatest between 12:00 and 16:00h. The numbers of bats involved in each sighting varied between 1 and 200. In summer 87% and in winter 91% of observations were of single individuals. Numbers of daylight-flying bats, relative to roost visitor reports sent to the Nature Conservancy Council, increased with increasing latitude during both summer and winter. This means that an individual is more likely to fly in daylight the further north in Britain it lives. The effect of day-to-day variation in climatic variables on emergence was investigated for records from 1987. In April 1987 emergence occurred on days which followed significantly cooler nights than nights preceding days without emergence. During the remainder of the summer of 1987, however, no climatic effects were significant. During winter 1987 emergence occurred on days which were significantly warmer and sunnier.
These data suggest that during summer the primary function of emergence during daylight is to feed to make good energy deficits that have accrued because of inadequate intake during nocturnal foraging. During winter, bats time their daylight emergences to coincide with good feeding conditions, as has been shown previously for winter nocturnal emergence. It is possible daylight emergence occurs during winter primarily because the endogenous cycle during hibernal torpor cannot accurately synchronize arousal with periods of darkness.     

Seasonal variation in serum levels of steroid hormones and their relation with seminal quality and libido in buffalo bulls

Blood samples from 15 breeding male Murrah buffaloes were collected during the winter, summer and monsoon seasons. Seminal characteristics and sexual behaviour were also studied. Serum samples were analysed for testosterone, progesterone and estradiol-17beta levels by radioimmunoassay. The studies showed significantly lower values for testosterone during winter (0.53 +/- 0.06 ng/ml) than during summer (1.22 +/- 0.19 ng/ml) and monsoon (1.06 +/- 0.12 ng/ml). The progesterone level was lowest during monsoon (84 +/- 9 pg/ml), intermediate during winter (115 +/- 14 pg/ml) and highest during summer (224 +/- 24 pg/ml). The mean level of estradiol-17beta was almost double (9 +/- 0.7 pg/ml) during monsoon as compared to winter (5 +/- 0.1 pg/ml). The correlations between hormone levels, seminal characteristics and sexual behaviour were of low magnitude.     

Temperature Response Pattern during Afterripening of Achenes of the Winter Annual Krigia oppositifolia (Asteraceae)

Abstract Freshly-matured achenes of Krigia oppositifolia Raf. were buried in soil at near-natural temperatures for 0–35 months and then exhumed and tested in light and darkness at (12/12 hr) daily thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20°C. Achenes required light for germination and exhibited an annual dormancy/nondormancy cycle, being dormant in spring and nondormant in autumn. High summer temperatures (30/15, 35/20°C) fully promoted afterripening, whereas low temperatures (5, 15/6°C) prevented it. As buried seeds came out of dormancy in summer, they first germinated at medium temperatures (20/10, 25/15°C), but with additional afterripening the maximum and minimum temperatures for germination increased and decreased, respectively. Thus, during afterripening, achenes exhibit type 3 temperature responses, which otherwise are known only in two perennial Asteraceae and one perennial Liliaceae. The physiological responses of achenes of K. oppositifolia are unlike those of most winter annuals, which have type 1 responses—i.e., the maximum temperature for germination increases during afterripening. Also, they are unlike the majority of Asteraceae, which have type 2 responses—i.e., the minimum temperature for germination decreases during afterripening. Type 1 responses, typical of most winter annuals, have yet to be reported in the Asteraceae.     

Agroecosystem management for rare species of Paysonia (Brassicaceae): integrating their seed ecology and life cycle with cropping regimens in a changing climate

Dormancy break and germination of seeds are governed by climatic cues, and predicted changes in climate may impact the ecology and conservation of species. Paysonia perforata and P. stonensis are rare brassicaceous winter annuals occurring primarily in fields on floodplains, where corn or soybeans are recommended for habitat maintenance. We tested the effects of precipitation, based on two predictions of changes in climate, on seed germination in these two species and placed the results into a management framework. Seeds of both species, collected during peak dispersal in late April/early May, were given various periods of light (or darkness) followed by darkness (or light) at summer temperatures before placement in darkness during late summer/early autumn in both laboratory and field. The light requirement was met earliest at 10 wk (mid-July) on alternating wet/dry substrate (simulating current climatic conditions). However, seeds of P. perforata and P. stonensis were photostimulated earliest at 2 wk (mid-May) and 6 wk (mid-June), respectively, on a continuously moist substrate (simulating predicted future conditions). The soil seed bank could be depleted if plowing coincides with photostimulation of seeds. Fields should be prepared after dispersal but before seeds are photostimulated and harvesting completed before seed germination in early September. Because seeds are highly photostimulated in late summer, disturbance from harvesting must be low to prevent burial. Cultivation of soybean, particularly for forage, is better matched to the seed biology and life cycle of Paysonia than that of corn under current and predicted climates.     

Reductions in cardiac output in hypoxic young pigs: systemic and regional perfusion and oxygen metabolism

We tested the hypotheses that, in hypoxic young pigs, reductionsin cardiac output restrict systemic oxygen transport to a greaterextent than does hypoxia alone and that compensatory responses to thisrestriction are more effective in higher than in lower priorityvasculatures. To study this, 10- to 14-day-old instrumented awakehypoxic (arterial oxygen tension = 39 Torr) pigs were exposed toreduced venous return by inflation of a right atrial balloon-tipped catheter. Blood flow was measured withradionuclide-labeled microspheres, and oxygen metabolism was determinedwith arterial and venous oxygen contents from appropriate vessels.Hypoxia resulted in a reduction in oxygen tension; increases in cardiacoutput and perfusion to brain (72% over baseline), heart, adrenalglands, and liver without reductions to other organs except for thespleen; reductions in systemic and intestinal oxygen delivery; andincreases in systemic and intestinal oxygen extraction without changesin systemic, cerebral, or intestinal oxygen uptake. Duringhypoxia, decreasing venous return was associated with increases inarterial lactic acid concentration and central venous pressure;attenuation of the hypoxia-related increase in cardiac output;sustained increases in brain (72% over baseline) and heart perfusion;reductions in lung (bronchial artery), pancreatic, renal, splenic, andintestinal (50% below baseline) perfusion; decreases insystemic and gastrointestinal oxygen delivery; sustained increases insystemic and intestinal oxygen extraction; and decreases in intestinaloxygen uptake, without changes in cerebral oxygenmetabolism. We conclude that when venous return to theheart is reduced in hypoxic young pigs, the hypoxia-related increase incardiac output was attenuated and the relative reduction in cardiacoutput was associated with preserved cerebral oxygen uptake andcompromised intestinal oxygen uptake. Regional responses to hypoxiacombined with relative reductions in cardiac output differ from that ofhypoxia alone, with the greatest effects on lower priority organs suchas the gastrointestinal tract.

     

Cerebrovascular response to normal pregnancy: a longitudinal study

We used a longitudinal study design (gestational weeks 8, 15, 22, 29, and 36 and 12 wk postpartum ) to investigate the effect of normal pregnancy on cerebral autoregulation and pressor response. Blood flow velocities in the right internal carotid artery, end-tidal CO2, and mean arterial pressure (MAP) were simultaneously and continuously recorded in 16 healthy pregnant women during standardized hyperventilation and handgrip. Blood flow velocities were recorded using Doppler ultrasound sampled beat by beat using the ECG signal. The results demonstrate that the vasoconstrictor response to hyperventilation is unchanged during pregnancy. During standardized handgrip, MAP showed a statistically significant increase during pregnancy that did not affect cerebral blood flow. A statistically significant reduction in the MAP response to handgrip was seen in week 36. In conclusion, pregnancy has no impact on cerebral autoregulation. There is an impact on the pressor response resulting in a blunted reaction at week 36, probably caused by a fall in the baroreflex set point.     

Seasonal and diurnal changes in photosynthetic limitation of young sweet orange trees

This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO₂ assimilation to increasing air CO₂ concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO₂ assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference (VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature.     

Brain Ca2+/Mg(2+)-ATPase activity and seasonal adaptation of the Djungarian dwarf hamster Phodopus sungorus.

1. Of three sets of Djungarian dwarf hamster, two groups were raised during winter under greatly differing circumstances. One winter group was raised within a climate controlled cage in which the ambient temperature was maintained at 22 degrees C and whereby conditions of light vs darkness were maintained in a constant 12 hr cycle. The second winter group was raised out of doors whereby the hamsters were subjected to prevailing seasonal environmental conditions. A third group was studied under summer conditions, as well. Ca(2+)-, Mg(2+)- and (Ca2+/Mg2+)-ATPase activity was analysed in cellular (= total homogenate) and subcellular fractions (P1-, synaptosomal fraction, synaptic membranes) from cortex, cerebellum and basal brain. 2. The data obtained indicate similar ATPase activity in the cortical homogenates of the winter indoor and summer hamsters. 3. Winter outdoor animals experiencing normal torpidity, however, exhibited reduced ATPase activity by about 50%. 4. Cortical subcellular fractions yielded different results: both the winter and the summer groups showed high ATPase activity in the synaptosomal and synaptic membrane fractions. 5. In the total cerebellar homogenate, the hamsters raised under summer and winter conditions showed the greatest enzyme activity, although less activity was seen in the subcellular fractions. 6. The ATPase activity in the basal brain was found to be nearly identical in all three hamster groups.     

Effect of sodium hydroxybutyrate on cerebral circulation and regional vasomotor reflexes

In experiments on cats it was found using electromagnetic and resistographic methods that sodium hydroxybutyrate (100 mg/kg) considerably increases cerebral circulation. The drug also potentiates the blood flow to the brain during formation of pressor reflexes of the arterial pressure. The blood flow increase is also observed in the system of femoral arteries while in the intestinal artery, on the contrary, there is a reduction in the blood flow increase during vasomotor reflexes. The reflex changes of the resistance in regional vessels are also different: the inhibition of pressor reflexes in the cerebral vessels along with their facilitation in the intestinal and femoral arteries and the potentiation of the reflex dilatatory phase in the limb vessels are seen. Different sensitivity to the drug of synaptic formations in the central links of various regional vasomotor reflexes is likely to underlie the difference described.     

Seasonal changes in cardiovascular indices and monoamine content in the brain of rabbits

In our previous studies a rather substantial difference between the initial values of the cerebral blood flow was found. On the other hand the brain monoamine content varies in different months of the year when studied. Comparative analysis of these parameters in rabbit brain was the aim of this paper. The content of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in cortical and subcortical structures and the local cerebral blood flow (ICBF), the systemic arterial pressure (SAP) and pulse rate (PR) were studied. There were found seasonal variations in all parameters. A certain LCBF retardation in subcortical structures and cortex and the weakest effect of the stimulation was observed in May. There was a drop in SAP and some PR increase in the spring (April-May). Brain NA and 5-HT content showed seasonal changes with the lowest values near the winter months and reaching maximum in May as the PR does. Content of DA was low in May. So it seams possible that the ion ICBF in May can be explained by the decrease of brain DA at that time. The ICBF and the reactivity of cerebral microvessels seem to depend on the monoamine content and show seasonal variability.