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S Saarela

Publications and source records attributed to S Saarela.

49 records · Page 3Linked to original sources
PubMed1980

Thermoregulatory responses to tyramine in the pigeon.

Intravenous injections of different doses of tyramine induced hypothermia in the pigeon in the cold and a moderate hyperthermia in the warm environment. The hypothermia was correlated with a dose-dependent decline in shivering. Hyperthermia was attributed to the chrono- and inotropic effects of tyramine. The indirect stimulatory effects of noradrenaline (NA) at the tissue level were studied. Pretreatment with alpha-methyl-para-tyrosine (alpha-MpT) and blocking alpha-adrenoceptors with phentolamine, diminished the hypothermia induced by tyramine in the cold. The results obtained indicate that the release of endogenous NA stimulated by tyramine might result either in hypothermia or hyperthermia, thus resembling similar effects obtained with exogenous NA in birds.

Animals↗
PubMed1980

Effects of blood pressure manipulations on shivering thermogenesis in the pigeon.

The effects of blood pressure (BP) manipulations on shivering thermogenesis were studied in conscious pigeons. A rise in BP induced by noradrenaline (NA) or equipotent doses of angiotensin II (Ang II) effectively suppressed shivering at +12 degree C and partly abolished the cold-induced vasoconstriction in the feet. The inhibition commenced when the rise in BP reached +40 mmHg, and a fall in body temperature followed these responses. Comparison of the trajectories in the BP-shivering plane revealed that the inhibition of shivering by Ang II could be completely explained by changes in BP, whereas NA had also another, more prolonged inhibitory action independent of baroreceptor activity. A similar dose-dependence for effects on BP and shivering could be established with both drugs. An acute reduction of BP by sodium nitroprusside had also a very potent inhibitory effect on shivering. In hypotensive pigeons elevation of BP with NA initially enhanced shivering, but when BP was raised beyond normal levels shivering was again suppressed. We conclude that both a rise and a fall in BP can inhibit shivering in the pigeon, and that normal levels of BP facilitate shivering. NA inhibits shivering by more than one mechanism, but the initial effect is mediated through a baroreflexive action. The interactions of thermoregulatory and cardiovascular mechanisms suggest an integrated control of body temperature and circulation, which should be considered in experimental approaches to these homeostatic systems.

Angiotensin II↗
PubMed1977

Effect of glucagon on thermogenesis in the pigeon.

The effects of glucagon injection on temperature regulation and some metabolic parameters were studied in the pigeon. Glucagon (100 microng/kg) always inhibited shivering and caused a fall in the oxygen consumption and body temperature of the unanesthetized pigeon at + 6 degrees C. At + 34 degrees C, the same dose of glucagon had no effect on these parameters. At 22 degrees C, glucagon produced an elevation in plasma free fatty acid (FFA) and blood glucose levels. The rise in FFA at 22 degrees C coincided with the suppression of shivering at 6 degrees C. The glucagon-mediated rise in plasma FFA, but not glucose level, was potentiated by cold ambient temperature. Adrenergic blocking agents given prior to glucagon did not abolish its effects. Phentolamine even prolonged the absence and accelerated the suppression of shivering. A dissociation in the mechanisms by which catecholamines and glucagon suppress shivering is suggested. Although mobilizing energy reserves, glucagon does not seem to be calorigenic in the pigeon at this dose. The interpretation of the changes in plasma FFA levels is discussed in relation to fuel consumption during shivering.

Animals↗
PubMed1976

Effect of adrenergic blocing agents on peripheral noradrenaline induced thermoregulatory responses in the pigeon at heat.

1. The hyperthermic effect of intramuscular NA at 32 degrees C was abolished by propranolol but not by phentolamine preinjection. 2. The lack of hyperthermic response was at least partly due to the blocking effect of propranolol on beta-receptor mediated in heart rate. 3. After NA the respiratory rate was gradually increased in birds preinjected either with propranolol or with phentolamine.

Animals↗
PubMedDate not supplied

Plasma urea, creatinine, and urea: creatinine ratio in reindeer (Rangifer tarandus tarandus) and in Svalbard reindeer (Rangifer tarandus platyrhynchus) during defined feeding conditions and in the field.

Variation in plasma urea and creatinine concentration and plasma urea:creatinine ratio (U:C) were studied in semidomestic free-ranging reindeer (Rangifer tarandus tarandus) on the Norwegian mainland, in wild Svalbard reindeer (Rangifer tarandus platyrhynchus), and in captive reindeer maintained either on a lichen-based diet or a protein-rich concentrate to investigate whether these parameters could be used as indicators of the nutritional status of reindeer. In the mainland animals, plasma creatinine concentration was high in winter and early spring and decreased by two-thirds toward the summer. The overall range in mean plasma creatinine concentration (+/-SE) was from 90+/-1.26 to 280+/-2.88 micromol/L. Mean plasma urea concentration (+/-SE) varied from 2.46+/-0.10 in winter up to 17.44+/-0.29 mmol/L in summer and autumn. Month of sampling explained 65% and 90% of the variation in plasma urea and creatinine concentrations, respectively, indicating that seasonality in the diet had the greatest influence on these parameters. Reindeer given lichens as the only feed showed an increase in plasma creatinine and a decrease in plasma urea concentration. Food restriction caused a temporary elevation in urea level but had no significant effect on plasma creatinine concentration. The slight effect of energy intake on urea and creatinine levels was supported by the fact that severe undernutrition in the Svalbard reindeer population had only a small effect on plasma urea and creatinine levels. Protein-rich pellet feed increased plasma urea from around 3 mmol/L to above 10 mmol/L and reduced creatinine concentrations to less than 100 micromol/L, suggesting that the protein content of forage is an important determinant of these blood parameters. Mean U:C ratio (+/-SE) in plasma varied from 8.9+/-0.28 to 120.8+/-1.88. Ratios above 20 appeared when protein intake was low and energy intake was restricted or when protein intake was high. Low ratios occurred when protein intake was low but energy intake adequate. Plasma urea and creatinine concentrations and the U:C ratio showed complex dynamics that were affected by both season and the protein and feed intake. We conclude that they appear to be difficult to interpret as single measures of nutritional status of reindeer.

Animals↗