The catecholamine (CA) depletion degree in rat adrenal medulla, the survival time (ST) and rectal temperature changes induced by combined thermal and immobilization stress were examined with the aim to prove tha alpha- and beta-adrenoreceptor sensitivity decrease implication in 24 hour fasting-induced changes of the above mentioned phenomena. The significant ST increase in strong stressful situations and the adrenal CA turnover augmentation in fed and fasted- propranolol or dihydroergotamine pretreared rats compared to untreated ones provided evidence that alpha- and beta adrenoreceptor blockade causes adrenal CA turnover increase and ST prolongation similar to effects observed in our previous experiments. Thus the implication of fasting induced adrenoreceptor downregulation in adrenal CA turnover augmentation and ST prolongation of fasted rats in strong stressful conditions was suggested and the possible mechanisms of these phenomena have been discussed.

1.1. Ten guinea-pigs with hypothalamic and subcutaneous interscapular thermocouples ran up to exhaustion at 1.5 km/h. Blood lactate concentrations were determined before and after exercise. Four animals exercised at constant ambient temperatures of 15 and 35°C and six other animals ran at variable ambient temperatures, adjusted to stabilize their hypothalamic temperature at 39.5, 40.5 and 41.5°C.2.2. Ambient temperature did not influence exercise performance directly. Duration of running was inversely proportional to hypothalamic temperature. There were no correlations between lactate concentration and exercise performance nor between lactate concentration and body temperatures.3.3. The results suggest a progressive decrease in exercise performance occurs with increasing body temperature.

The lipolytic response to fatigue-induced stress was studied in fed and fasted rabbits and in fed propranolol-treated rabbits. The initial plasma glycerol level was higher and the increase in glycerol after stress was lower in fasted as compared to fed animals. Propranolol lowered the initial glycerol level and attenuated the fatigue-induced rise in glycerol concentration. The data suggest that in rabbits, as in other species, catecholamines increase lipolysis through stimulation of beta-adrenoceptors. The increment in alpha-adrenergic responsiveness during fasting may contribute to decreased glycerol response to stress observed in fasted rabbits.

The effect of fatigue-induced stress and of alpha- and beta-adrenoceptor antagonists (phentolamine and propranolol) on plasma free fatty acids (FFA) level was studied in fed and 24 h fasted rabbits. The initial FFA level was significantly higher in the fasted animals than in the fed ones. In the fed control rabbits immediately after stress the FFA level did not change as compared with its initial level. In the fasted control animals directly after stress a marked decrease in the FFA level was observed as compared with its initial value. 15 and 30 min after fatigue-induced stress, both in the fed and fasted control rabbits, a decrease in the FFA level was recorded as compared to that immediately after stress. It was found that propranolol had no significant influence on the FFA level, both in the fed and fasted animals, and phentolamine produced a distinct increase in the FFA level in the fed rabbits only. Immediately after stress the FFA level in the fed propranolol-treated rabbits was unchanged, but in the fed phentolamine-treated animals it was markedly decreased. Directly after stress a decrease of the amount of FFA in the fasted adrenolytic-treated rabbits was recorded, 15 and 30 min after stress the FFA level decreased both in the fed and fasted adrenolytic-treated rabbits. However, this decrease was not as marked as in the fed and fasted control animals. The possible role of lactate and of catecholamines in the changes of plasma FFA concentration was discussed.

Changes in plasma dopamine-beta-hydroxylase (DBH) activity were studied in rabbits subjected to two kinds of acute stress: insulin-induced hypoglycaemia and fatigue. A significant elevation of DBH levels was found both 30 minutes after fatigue-induced stress (p less than 0.001) and 90 minutes after insulin injection (p less than 0.01) when compared with the control values. Responses to these two kinds of stress are reported to be mediated by the sympathetic nervous system, mainly by the adrenal glands. Thus, these results suggest that plasma DBH level is a good index of acute alterations in sympathetic activity in rabbits.

Plasma dopamine-beta-hydroxylase (DBH) activity was measured both in women during labour and postpartum periods and in their newborns in the umbilical cord blood and during the first days of the postnatal life. The maternal enzyme activity determined in three phases of labour and two postpartum periods was compared to that on the fourth day post partum (control level). As compared to the control level, a significant increase in the mean DBH activity was found in all phases of labour and during 10-15 min after delivery. The enzyme activity reached its highest value during delivery and 24 h after delivery it returned to the control level. The mean DBH activity of the umbilical cord plasma was significantly higher when compared with that determined in newborns at 24 h after birth. The latter remained essentially unchanged throughout the first three days of the postnatal life.

The influence of mental work on urinary catecholamine excretion and on plasma dopamine-beta-hydroxylase (DBH) activity was investigated in 8 healthy women during the ovulatory, premenstrual and other periods of the menstrual cycle. It was found that mental work performed during the ovulatory period (OP) significantly increased both adrenaline and noradrenaline excretion, whereas work performed during the premenstrual period (PMsP) and also during the other periods of the menstrual cycle significantly increased adrenaline excretion only. No changes in plasma DBH activity were observed after mental work either in OP or in PMsP.