ACTH-Bestimmungen im Plasma aus dem Bulbus cranialis venae jugularis

Der Anstieg der Corticosteroninkretion in das Nebennierenvenenblut frisch hypophysektomierter Ratten diente zur Bestimmung von ACTH-Spiegeln in 1 ml nativen, menschlichen Plasma. Normale ACTH-Plasmaspiegel sind sowohl bei Punktion der Vena cubitalis als auch des Bulbus cranialis venae jugularis durch diese Methode nicht oder nur ungenau zu erfassen. Bei Patienten mit pathologisch erhöhten ACTH-Spiegeln in der Vena cubitalis sind die ACTH-Spiegel im Bulbus cranialis venae jugularis signifikant höher. Es ließ sich eine Beziehung zwischen ACTH-Spiegel in der Peripherie (Vena cubitalis), Differenz der ACTH-Spiegel zwischen Bulbus cranialis venae jugularis und Vena cubitalis und biologischer Halbwertszeit von endogenem ACTH aufstellen. Nach den Ergebnissen der Bestimmung von ACTH-Spiegeln bei Nebennierengesunden läßt sich folgern, daß die biologische Halbwertszeit von endogenem ACTH größer als 4 min sein muß. Bei Patienten mit erhöhten ACTH-Spiegeln ließ sich die biologische Halbwertszeit von endogenem ACTH größenordnungsmäßig mit ca. 40 min berechnen. Bei diesen Patienten betrug die mittlere tägliche ACTH-Inkretion ca. 100 E.ACTH-contents of 1 ml specimens of human plasma were assayed by measurement of increases of corticosterone output in the adrenal vein of acutely hypophysectomized rats. This procedure is not sensitive enough to measure normal ACTH-levels acurately, neither when blood was drawn from the bulbus cranialis venae jugularis, nor from the vena cubitalis. In patients having pathologically elevated ACTH-levels, the ACTH-content of plasma is significantly higher in the bulbus cranialis venae jugularis than in peripheral venous blood. An equation is presented formulating the relation of peripheral ACTH-levels, differences of ACTH-levels between bulbus cranialis venae jugularis and vena cubitalis, and of the biological halflife of endogenous ACTH. On the basis of the results of the determinations of socalled normal ACTH-levels it can be concluded, that the biological halflife of endogenous ACTH is longer than 4 min. From the data of patients with elevated ACTH-levels a halflife of approximately 40 min and a mean ACTH-secretion of approx. 100 units per day could be calculated

Negative Feedback Regulation following Administration of Chronic Exogenous Corticosterone

Administration of exogenous glucocorticoids is known to suppress the HPA axis and has been reported to occupy brain glucocorticoid receptors, eventually leading to down-regulation. To determine the effects of chronic corticosterone administration on HPA axis function, corticosterone was administered as both 25% and 50% corticosteronekholesterol pellets. Rats were sacrificed 6 days after corticosterone pellet implantation. The 25% corticosterone pellets produced a small increase in morning corticosterone concentrations but no change in evening ACTH or corticosterone secretion. The 50% corticosterone pellets produced constant corticosterone concentrations of 5–6 pg/dl, with no circadian variation in corticosterone, indicating inhibition of evening ACTH and corticosterone secretion. The 25% corticosterone pellets produced no significant decrease in thymus weight or in adrenal weight; 50% corticosterone pellets produced significant decreases in thymus weight and adrenal weight. Neither 25% nor 50% corticosterone pellets produced significant decreases in GR in hippocampus and cortex. The 50% corticosterone pellets treatment resulted in a decrease in anterior pituitary POMC mRNA levels, a decrease in baseline and oCRH stimulated ACTH release from the anterior pituitary, and a near complete inhibition of the AM and PM response to restraint stress. These results suggest that: 1) the HPA axis was able to adjust to the small increase in glucocorticoids produced by the 25% cort pellets with minimal disturbances in function and 2) 50% corticosterone pellets exert a significant inhibitory effect on stress and diurnal ACTH secretion which appears to be exerted at the pituitary as well as possible inhibitory effects on brain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72571/1/j.1365-2826.1995.tb00665.x.pd