Studies were performed on the reactivity of the hypothalamopituitary-adrenocortical axis of intact, gonadectomized, and testosterone-or estradiol-replaced rats to standard ether stress. Plasma ACTH and corticosterone (B) levels, anterior pituitary ACTH, and adrenal B content were estimated 20 and 40 min after stress application and in unstressed animals. Ether stress resulted in an increase in plasma ACTH and B levels and in adrenal B content while pituitary ACTH content was notably lower when compared with unstressed rats. The response was markedly higher in female than in male rats. After orchiectomy and testosterone replacement, plasma ACTH and B responses to ether stress were similar to those observed in intact male rats. On the other hand, ovariectomized females responded to ether stress like intact males, while after estradiol replacement the pattern of plasma ACTH and B concentration and adrenal B content was similar to that in intact female rats. Thus, the higher responsiveness of the pituitary-adrenal cortex axis of female rats to ether stress depends on stimulatory or facilitatory effect of estradiol.

Studies with isolated rat adrenocortical cells have shown that neuropeptide Y (NPY) inhibits both basal and ACTH-stimulated corticosterone secretion. These results suggest the regulatory role of NPY in corticosterone secretion from the adrenal gland, especially during stress.

This study aims to examine the effects of low dexamethasone (DX) doses on cellular and functional changes in the rat adrenal cortex and to observe the recovery of the gland from DX-induced partial atrophy.Within seven days doses of 15, 30 and 60 tg DX! 100 g/day resulted in a dose dependent decrease in body and adrenal gland weight. Within two weeks the lowest DX dose tested caused further decrease in adrenal weight. DX markedly lowered plasma ACTH and corticosterone (B) level, B content in the gland and B output by adrenal slices.Adrenocortical atrophy induced by 15 .tg DX was dependent upon the linear decrease in the volume of fasciculata and reticularis zones, in the average volume of the fasciculata cell and in the number of adrenocortical cells in the entire cortex.

Plasma ACTH and corticosterone (B) concentration, ACTH content in the anterior pituitary gland and B content in the adrenals were measured in intact, gonadectomised and testosterone or estradiol replaced rats.Plasma ACTH and B levels and adrenal B content were higher in female than male rats. Neither orchiectomy nor testosterone replacement had an effect on plasma ACTH and B concentration. Orchiectomy did not affect adrenal B content and decreased pituitary ACTH while testosterone significantly lowered ACTH and B content in studied glands. On the other hand ovariectomy did not change pituitary ACTH and adrenal B content and notably lowered concentrations of these hormones in the blood. Estradiol replacement resulted in an increase in plasma ACTH and B concentrations, an effect accompanied by a marked drop in pituitary ACTH and an increase in adrenal B.These findings indicate the distinct sex differences in basal plasma ACTH and B concentrations with higher values in female rats, an effect dependent on the stimulatory action of estradiol on pituitary-adrenocortical axis.

The functional characteristics at rest in responding to stepwise acute exposure to simulated altitude (6000 m) were compared in 10 acclimatized mountaineers (highlanders), residents of Zermatt (1616 m) working at an altitude up to about 4000 m, and in 11 nonacclimatized control subjects (lowlanders) living and working in Zurich (450 m). In comparison with the lowlanders, the highlanders showed at altitude significantly greater hyperventilation, lower heart rate and systolic blood pressure, smaller haemoconcentration, lower urodilatin secretion and natriuresis, and a preserved neuropsychological ability (attentiveness) and vasomotor tone (diastolic blood pressure); the critical altitude at which hypoxic short-term adaptation became insufficient was 6000 m. The lowlanders, however, manifested reduced tolerance of hypoxia, i.e. insufficient short-term adjustment with subjective and objective distress coinciding with the first signs of hypoxia of the central nervous system, already apparent at and above 4000 m. It was concluded that the functional differences between highlanders and lowlanders in responding to acute gradual hypoxia indicated factors contributing to altitude acclimatization.