Acute noise stress, ACTH administration, and blood pressure alteration.

Two groups of male Wistar rats were submitted to a single noise exposure (2640 Hz, 30 W, 102 dB, 15 min) (St group) or to a single dose of ACTH (1.5 IU/100 g b.wt.) (Ac group), respectively. A control group of nontreated rats (Co group) was used. Blood pressure (BP) was measured using an indirect tail cuff method and corticosterone (B) levels were measured by specific RIA. Haematocrit (Hc) and blood pH values were also evaluated. Acute treatments of both noise exposure and ACTH administration produced corticosterone hypersecretion and blood pressure elevation, with lower haematocrit and higher blood pH values than those found in the Co group. No differences were found between St and Ac treatments.

Effect of chronic stress in the blood pressure in the rat: ACTH administration.

We have studied the effect of chronic noise stress (St) and ACTH administration (Ac) affecting blood pressure and plasma corticosterone levels in male Wistar rats. Both chronic treatments elicited an increase in plasma corticosterone and blood pressure levels. The blood pressure increased from the first week of treatment period in St and Ac rats and remained high 4 weeks after the end of the stress period. However, blood pressure elevation decrease progressively during the first three weeks of post-treatment in ACTH administrated rats. The rise of blood pressure levels was due to the effect of chronic treatment. This was demonstrated by the absence of differences between the two values of blood pressure measurement with and without daily treatment in both St and Ac groups. Increased corticosterone levels decreased rapidly during the post-treatment period in St and Ac rats. The results suggest a possible relationship between the development of hypertension and the Hypothalamus-Hypophysis-adrenal (HHA) axis stimulation in rats.

Behavioral and physiologic effects of early nutrition and social factors in the rat.

Two experimental methods to provoke caloric restriction during suckling were used. Each of the methods utilized two different rat groups: Low Growth (LG) and High Growth (HG). In one method, the groups also differed in a social factor, litter size: crowded (Cr) and control (Co). Growth differences and high levels of social competition were found among pups of the crowded group with Low Growth (CrLG) compared to the group with High Growth and small litters (CoHG). Both methods resulted in growth differences between respective groups from the first week of suckling. Differences in animal groups persisted forty days after weaning. LG animals had higher defecation scores with lower activity in the open-field test, higher susceptibility to restraint ulcers and adrenal hypertrophy than HG rats, in litters of equal size. However, early stimulation from social competition among pups in larger different litters in CrLG group counteracted nutritional factor effects. Elevated open-field defecation and ulceration scores with adrenal hypertrophy were found in CoHG rats.

Chronic noise stress and dexamethasone administration on blood pressure elevation in the rat.

In order to evaluate the role of ACTH and corticosterone in the elevated blood pressure produced by chronic noise, we have studied the effect of dexamethasone administration on blood pressure. Adrenal response was measured by alterations in plasma corticosterone levels in two experimental groups (Dexamethasone treated rats, Dexamethasone-noise stressed rats) and compared with a Control and a Noise-stressed group. Chronic noise stress with a frequency of 2640 Hz, power of 30 w and duration of 15 min daily was used for 30 consecutive days. Dexamethasone was administered by subcutaneous injection of 100 micrograms/100 g b.wt daily. Blood pressure was measured by an indirect tail cuff method and corticosterone levels by specific RIA. Dexamethasone administration decreases corticosterone levels but increases blood pressure. Dexamethasone-treated noise stressed rats show higher residual corticosterone levels and a more marked increase on blood pressure than rats treated with dexamethasone alone. Thus noise-stress and dexamethasone administration have opposing effects on corticosterone release and a synergistic effect on blood pressure elevation.

Body weight gain, food intake and adrenal development in chronic noise stressed rats.

Wistar chronic treated rats (30 days) were used to investigate the effect of hypothalamic-pituitary-adrenal activity on growth, food intake and adrenal development (weight and DNA content). The animals were submitted to noise stress, ACTH administration and dexamethasone suppression test. Noise stress decreased body weight gain and food intake. No adrenal hypertrophy was observed but an increase in relative DNA content by stress has been found. ACTH and dexamethasone treated rats showed a body weight and food intake decrease vs. controls. The effect on body weight was higher in dexamethasone treated rats. Adrenal hypertrophy and hyperplasia were found in ACTH treated rats, whereas dexamethasone provoked adrenal atrophy with a decrease in DNA content.