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BACKGROUND AND PURPOSE:Acute intracranial hemorrhage represents a severe and time critical pathology that requires precise and quick diagnosis, mainly by performing a CT scan. The purpose of this study was to compare image quality and intracranial hemorrhage conspicuity in brain CT with sinogram-affirmed iterative reconstruction and filtered back-projection reconstruction techniques at standard (340 mAs) and low-dose tube current levels (260 mAs).

In an attempt to elucidate the significance of ACTH independent mechanisms in the regulation of cortisol secretion in man, the dynamics of plasma ACTH and cortisol levels were studied in response to different stimuli. The cortisol response to small amounts of exogenous ACTH and to insulin induced hypoglycemia was preceded by an increase in ACTH levels appropriate to explain the increase in cortisol. In contrast, after administration of methamphetamine, there was an increase in cortisol levels in the absence of any changes in ACTH concentrations. Apparently, the methamphetamine induced cortisol secretion was not mediated by radioimmunoassayable ACTH. A diurnal rhythm was observed for the responses to hypoglycemia and to methamphetamine with larger cortisol responses in the evening as compared to the forenoon. These changes were not accompanied by parallel changes in the ACTH responses. From these differences, additional evidence is provided for the importance of ACTH independent mechanisms in the regulation of cortisol secretion.

There is evidence for the existence of ACTH unrelated mechanisms in the regulation of cortisol secretion in man. This study was designed to elucidate the interrelationship between plasma ACTH and cortisol levels during the increase in cortisol levels, which occurs during morning hours. The results were compared with those of an artificial cortisol peak induced by administration of small amounts of ACTH, and with ACTH and cortisol values during insulin-induced hypoglycemia. In these control groups, the increase in cortisol levels was preceded by a large increase in ACTH levels; in the case of the physiological morning peak there was no adequate rise in mean ACTH levels. Thus, the spontaneously occurring increments in individual ACTH levels appear to be inappropriate for the increases in cortisol. This conclusion was corroborated by the finding that oscillations of plasma cortisol concentrations, comparable to the physiological morning peak, were demonstrable in ACTH-deficient patients when they were supplied with subthreshold amounts of exogenous ACTH. These findings argue against the classic concept that the adrenal cortex is invariably linked to immediately preceding episodes of pituitary ACTH secretion.