Activity of adrenal catecholamine-producing enzymes and their regulation after stress

Comparison of ear tattoo, ear notching and microtattoo in rats undergoing cardiovascular telemetry

Individual and permanent identification of experimental animals is a common and often essential research practice. There is little information available on the short-term effects of these procedures on the animals. In this study, seven rats were implanted with telemetric devices. The effects of three different identification methods (ear tattoo, ear notching and microtattoo) were compared. Cardiovascular data were collected for 24 h after the procedures. Time periods of 0-1, 1-4, 4-16 h (dark) and 16-24 h after the procedure were analysed separately. The most pronounced differences in measured parameters were observed during the first hour after the procedures were performed. Mean arterial pressure (MAP) was significantly higher (P < 0.012) following the ear tattoo than the microtattoo procedure by a difference of approximately 5 mmHg. Heart rate (HR) was significantly elevated (P < 0.001) after ear tattoo compared with both ear notching (Δ = 31 beats per minute [bpm]) and microtattoo (Δ = 44 bpm). During the 1-4 h period and the following dark period, the MAP was highest in the ear notching group, but no differences were observed in the HRs. During the following dark period (4-16 h) and the next day (16-24 h) differences in MAP and HR were minor. In conclusion, microtattoo appears to cause the mildest changes in HR and blood pressure. Based on these results, ear tattoo and ear notching should be replaced by microtattoo whenever possible.

The diet board: welfare impacts of a novel method of dietary restriction in laboratory rats

Laboratory rats are commonly fed ad libitum (AL). Moderate dietary restriction (DR) decreases mortality and morbidity when compared with AL feeding, but there are several obstacles to the implementation of DR. Traditional methods of restricted feeding disrupt normal diurnal eating rhythms and are not compatible with group housing. We have designed a novel method, the diet board, to restrict the feeding of group-housed rats. Animals fed from the diet board had 15% lower body weight than the AL-fed animals at the age of 17 weeks. The welfare effects of diet board feeding were assessed by comparing the stress physiology of diet board fed animals with that of AL-fed animals. Diet board feeding was associated with higher serum corticosterone levels and lower faecal secretion of IgA, suggesting the diet board causes a stress reaction. However, the AL-fed group had larger adrenal glands with higher adrenaline and noradrenaline content than the diet board animals. No gastric ulcers were found in any of the animals at necropsy. The diet board thus appears to cause a stress reaction when compared with AL-fed rats, but no apparent pathology was associated with this reaction. The diet board could help to solve the health problems associated with AL feeding, while allowing the rats to be group-housed and to maintain their normal diurnal eating rhythms. The diet board can also be seen as a functional cage furniture item, dividing the cage into compartments and thus increasing the structural complexity of the environment. In conclusion, the diet board appears to possess refinement potential compared with traditional methods of DR.

Influence of prior experience with homotypic or heterotypic stressor on stress reactivity in catecholaminergic systems

Here we review how prior experience with stress alters the response to a subsequent homotypic or heterotypic stressor, focusing on the catecholaminergic systems in the adrenal medulla and the locus coeruleus (LC). The changes in response to homotypic stress differ depending on the stressor applied. With immobilization stress (IMO), transcriptional responses in the adrenal medulla to a single exposure are pronounced and several of the transcription factors and signaling kinases induced or activated are reviewed and compared to the longer term alterations with repeated stress, consistent with persistent activation of gene expression of catecholamine (CA) biosynthetic enzymes. In the LC, transcriptional and post-transcriptional activation of gene expression are shown to be important. Repeated IMO stress triggers further activation of a number of signalling pathways. Neither adrenal medulla nor LC display habituation to long term repeated stress. In contrast, gene expression for CA biosynthetic enzymes habituates to prolonged cold stress in the adrenal medulla and LC, but displays an exaggerated response with exposure to a novel or heterotypic stressor such as IMO. Some of the transcriptional pathways displaying sensitization are described.

Catecholamine secretory vesicles. Augmented chromogranins and amines in secondary hypertension

Chromogranins A and B are major soluble proteins in chromaffin granules. Their adrenomedullary content is increased in the spontaneously (genetic) hypertensive rat. Is augmented catecholamine vesicular storage of the chromogranins a specific feature of genetic hypertension? To explore this question, we measured chromogranin A immunoreactivity, using a novel, synthetic peptide radioimmunoassay, in rat adrenal medullas 4-6 weeks after induction of the two-kidney, one clip Goldblatt model of renovascular hypertension and in unmanipulated control animals. We also measured messenger RNAs of chromogranins A and B and dopamine beta-hydroxylase by Northern blot. Immunoreactive adrenal chromogranin A was 3.3-fold higher (p < 0.01) in clipped rat adrenals. Adrenal catecholamine concentrations and phenylethanolamine-N-methyltransferase activity were also higher in clipped rats. Adrenal dopamine beta-hydroxylase activity (both membrane-bound and soluble forms) and corticosterone (glucocorticoid) concentration did not significantly differ between the groups. Adrenal medullary chromogranin A messenger RNA levels in clipped rats were 3.2-fold higher (p = 0.029) than those in the control group, and chromogranin B messenger RNA levels were 4.6-fold higher (p = 0.05). Dopamine beta-hydroxylase messenger RNA levels were 2.9-fold higher (p = 0.038). Thus, augmented synthesis and storage of adrenomedullary chromogranins A and B, catecholamines, and their biosynthetic enzymes appear to be characteristic of both acquired and genetic hypertension.

Influence of hypothyroidism on the ontogenic development of tyrosine hydroxylase induction in the adrenal glands of the rat

The ontogenic development of the transsynaptic induction of adrenal tyrosine hydroxylase (TH), evoked by reserpine and nicotine was studied in control and hypothyroid young rats, aged 3-52 days. The enzymatic induction was measured as an increase in the enzyme activity, since this increase was shown to be impaired either by an inhibitor of RNA synthesis or by a ganglionic blocker. In the control animals, TH induction elicited by reserpine increases between 3 and 32 days of age. In the hypothyroid rats, the enzymatic induction is impaired up to 32 days; at 52 days the induction is similar in both groups of animals. When nicotine is used as a stimulating agent, hypothyroidism still impairs the enzymatic induction at 5 and 21 days, indicating that at least one of the mechanisms inhibited by hypothyroidism is localized in the adrenal chromaffin cells. The present results, taken together with previous findings dealing with adrenal epinephrine secretion, show that the thyroid hormones play a crucial role in the responses of the adrenal medulla to a stimulation in the developing rat, while they have no effect in the adult.

The effect of carbon monoxide on hormone levels and organ weights in rats

Male Wistar rats were exposed continuously for 1 or 2 months to 25 or 100 ppm CO. The concentrations of noradrenaline in the hypothalamus, corticosterone and thyroxine in serum and of adrenal catecholamines were estimated. After exposure to 25 ppm CO no significant changes were observed in the serum corticosterone and thyroxine, hypothalamic noradrenaline, adrenal catecholamines levels, or in the weights of lung, spleen, adrenal glands, liver and the whole body. Exposure to 100 ppm CO induced a decrease in hypothalamic noradrenaline and serum thyroxine and an increase in adrenal catecholamines and serum corticosterone. Whole-body and organ weights were unchanged except for a slight decrease in liver weight. The results suggest a non-specific stress response in the rat to 100 ppm CO whilst concentration of 25 ppm CO was without any stress effect.

Adrenal dopamine beta-hydroxylase induction in the young rat: influence of thyroid hormones

The adrenals of 14-day-old control and hypothyroid rats have been stimulated by insulin-induced hypoglycaemia, and the subsequent induction in dopamine beta-hydroxylase (DBH) has been studied. In control rats, DBH induction was maximum 48 h after insulin administration. Hypothyroidism completely suppressed DBH induction.

Catecholamines, adrenal hormones, and stress

From its beginnings about a century ago, research into the mechanisms underlying the stress response has led by many avenues to the adrenal medulla and its chromaffin cells. The latter possess cholinergic synapses that, when activated by a wide variety of stimuli, trigger discharge of catecholamines directly into the blood. Control of the response is mediated by a final common pathway arising in the hypothalamus and/or midbrain.