Vukosava Davidović

Sympatho-adrenal activity and metabolic responses in fasted rats--the role of interscapular brown adipose tissue.

1. Sympatho-adrenal (SA) and metabolic responses to fasting were studied in sham-operated (SHAM) rats and in those with interscapular brown adipose tissue (IBAT) removed. 2. Fasting significantly increased adrenaline (A) excretion and serum free fatty acids (FFA), but decreased noradrenaline (NA) excretion and blood glucose level in SHAM rats. 3. IBAT removal did not change metabolic responses while it markedly altered the SA activity. Fasting in animals void of IBAT potentiated the activity of adrenal medulla, inhibited the FFA rise and prevented glucose reduction, which is normally observed in SHAM-fasted rats. 4. Results suggest the significance of IBAT in the regulation of the blood level of energy substrates in fasted rats and in maintaining the basal level of NA excretion.

Activities of Antioxidant Enzymes and Monoamine Oxidase-A in the Rat Interscapular Brown Adipose Tissue: Effects of Insulin and 6-Hydroxydopamine

The effects of different doses of insulin (INS) (0.4 or 4.0 IU/kg body mass, i.p., for 3 hr) and 6-hydroxydopamine (6-HDA) (100 mg/kg., i.p.) on the activities of antioxidant enzymes--copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT) and catecholamine degrading enzyme monoamine oxidase (MAO-A)--in the rat interscapular brown adipose tissue (IBAT) were studied. In vivo 6-HDA administration, which induces the destruction of sympathetic nerves, markedly reduced IBAT CuZnSOD activity but did not change MnSOD and CAT activities. However, the low dose of INS, which did not induce hypoglycemia, significantly increased the activity of both IBAT mitochondrial enzymes (MnSOD and MAO-A) of control rats. This INS effect on MnSOD was abolished by 6-HDA. On the contrary, CuZnSOD activity was markedly reduced under the influence of INS in both control and 6-HDA-treated rats, whereas for the maintenance of the control level of this enzyme activity, the intact sympathetic nervous system (SNS) is necessary. INS, independent of the dose applied, did not affect CAT activity in control rats, whereas only low INS dose increased the activity of this enzyme in 6-HDA-treated rats. The results indicate that the stimulatory effect of INS on the IBAT mitochondrial enzymes studied is dose dependent and in the case of MnSOD is mediated by SNS. However, the depression in the activity of CuZnSOD is independent of the above-mentioned factors.

Chronic Effect of Insulin on Monoamine Oxidase and Antioxidant Enzyme Activities in the Rat Brainstem

It was shown that hydrogen peroxide (H2O2) is a possible intracellular second messenger in specific insulin action. Because its concentration in the cell depends on the activity of both antioxidant enzymes and monoamine oxidase (MAO), we studied the influence of different insulin doses (0.4 and 4.0 IU/kg body mass, i.p., daily injected over 3 days) on the activity of MAO, types A and B, copper zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and catalase in the rat brainstem. Chronic insulin treatment significantly increased Vmax of MAO-A and B activities (P < 0.05, P < 0.025, respectively) independent of the dose applied. CuZnSOD activity was also increased (P < 0.025), but only when higher dose of hormone was injected. However, insulin had the opposite effect on MnSOD and catalase causing a decrease in their activities (P < 0.005). The observed changes in the activities of the enzymes studied are possible compensations that potentially maintain an optimal H2O2 level in the brainstem, which might be important for insulin action.

The Activities of Antioxidant Enzymes and Monoamine Oxidase and Uncoupling Protein 1 Content in Brown Fat of Hypo‐ and Hyperthyroid Rats

Abstract: We have studied the activities of antioxidant enzymes (AOE), namely, copper‐zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and catalase (CAT), and the activity of catecholamine‐degrading enzyme monoamine oxidase (MAO) and uncoupling protein 1 (UCP1) content in brown fat (BF) of hypo‐ and hyperthyroid rats. We found that hypothyroidism decreased BF UCP1 content and increased MAO, MnSOD, and CAT activities. T3 increased UCP1 content and MnSOD activity and decreased CuZnSOD, MAO, and CAT activities, while T4 significantly altered (decreased) only CAT activity. This study shows that UCP1 content and MAO and AOE activities in rat BF are notably affected by changed thyroid status.

Apoptosis in the rat brown adipose tissue after insulin treatment

Abstract In this study it is demonstrated that chronically applied high dose (4 IU/kg) of insulin induced apoptosis of rat brown adipocytes in vivo. A qualitative morphological study was performed on the brown adipose tissue using light and electron microscopy, and revealed that: (1) apoptotic areas occurred in parenchyma; (2) morphological changes observed closely resembled the apoptotic body. These results indicate that apoptosis appears to be the mechanism responsible for the loss of brown adipocytes caused by hyperinsulinaemia.

Dependence of the sympatho-adrenal activity on the nutritional status in corticosterone treated rats

1. An integrated sympatho-adrenal (SA) activity, expressed in terms of urinary catecholamines (CA) excretion, and direct sympathetic activity in the interscapular brown adipose tissue (IBAT), expressed in terms of noradrenaline (NA) turnover, were studied in corticosterone treated stock fed and sucrose overfed rats. 2. Corticosterone in stock fed rats significantly decreased both the rate of IBAT NA turnover and its mass as well as urinary NA excretion but did not change either IBAT NA content, urinary adrenaline excretion or adrenal CA content. 3. Sucrose overfeeding significantly increased SA activity, i.e. the rate of NA turnover in the IBAT and urinary excretion of CA. However, corticosterone did not inhibit the sucrose-induced sympathetic nervous system activation but potentiated the activity of adrenal medulla. 4. The results suggest that the effect of corticosterone treatment on the SA activity in rats is dependent, in addition to other factors, on the nutritional status of the animals.

Chemical sympathectomy and diurnal fluctuations of noradrenaline calorigenic action in the rat

In the rat, in which a diurnal fluctuation of the sensitivity to noradrenaline was previously found, the effect of injected 6-hydroxydopamine (6-OHDA) was investigated. The heat production and catecholamines contents in the interscapular brown adipose tissue, heart and adrenals were measured. Chemical sympathectomy induces a disappearance of diurnal fluctuation in the sensitivity to injected noradrenaline. In these animals a lower capacity for heat production was found. However, a significant calorigenic effect of injected noradrenaline in 6-OHDA-treated animals was still present. In sympathectomized animals a depletion of noradrenaline from interscapular brown adipose tissue and the heart was observed. Besides, a change in adrenaline/noradrenaline ratio was found in the adrenals.

Effect of Cold Exposure on Serum DBH and Interscapular Brown Adipose Tissue MAO Activity in Hypothyroid T3- and T4-Treated Rats

Abstract: As the indicators of sympathetic nervous system (SNS) function, the activity of serum dopamine‐β‐hydroxylase (DBH) and interscapular brown adipose tissue (IBAT) monoamine oxidase (MAO) were examined in rats that were chemically thyroidectomized (TX), treated with thyroid hormones, and exposed to cold (4°C). In TX animals, body temperature (bt) significantly decreased, and relative IBAT mass increased as compared with control, euthyroid animals, independent of the ambient temperature. The bt fall in TX cold‐exposed animals was more severe, provoking hypothermia after 4 h. Under the same experimental conditions, the SNS function was enhanced as judged by the increased serum DBH and IBAT MAO activities. The treatment of TX animals with T4 and T3 re‐established the temperature (bt was at the level of controls) and sympathetic homeostasis (DBH activity was at the level of controls) in animals maintained at room temperature but not in those kept under cold conditions. T4 and T3 did not affect IBAT MAO activity of TX rats: It remained significantly above the control values whether the animals were maintained at room temperature or exposed to cold. In conclusion, the IBAT of TX cold‐exposed rats is incapable of responding to the enhanced thermogenic needs despite the increased SNS activity and thyroid hormone substitution.

Influence of fasting and dopamine on the tissue catecholamines diurnal variations

To define the role of catecholamines (CA) in the metabolic adaptation to fasting we examined the effect of exogenous dopamine(DA) on heat production(HP) and CA content in the interscapular brown adipose tissue(IBAT) and adrenals of control-fed and 2-day fasted rats in the morning(M) and in the evening(E). DA stimulates HP in fed rats in the M by 45% but the thermogenic effect of this CA is markedly higher in the E. However, DA had no thermogenic effect in fasted rats. The tissue CA in fed rats fluctuates diurnally: in the IBAT noradrenaline(NA) was much higher in the E while adrenaline(A) in adrenals was lower. DA in fed rats did not change the adrenal A but reduced NA content both in the adrenals and in the IBAT all over the day. Fasting depleted A from adrenals but increased NA content both in the M and in the E. Unlike the adrenals in the IBAT fasting did not affect NA content. In the adrenal gland of fasted rats DA significantly increased the A content to the equal degree during the day, while this CA had no effect on NA content of the IBAT.

Diurnal variations in the catecholamine content in rat tissues Effects of exogenous noradrenaline

Endogenous noradrenaline (NA) content of the interscapular brown adipose tissue (IBAT), and of the hypothalamus, as well as adrenaline (A) and NA content of the adrenals were measured in the morning and in the evening in rats treated with saline (controls) or with NA (1.6 mg kg-1 pp). NA content in IBAT and in hypothalamus of control animals varies diurnally. NA content in IBAT was significantly higher in the evening than in the morning. In the hypothalamus, these variations were different of those found in the IBAT. Exogenous NA applied both in the morning and in the evening increases significantly NA content in IBAT both in the morning and in the evening, but more in the evening. Unlike IBAT, NA content of the hypothalamus after NA administration does not change essentially. In the adrenal gland of control rats, A content only is changed during the day, being markedly lower in the evening. After NA injection both A and NA are not changed significantly.