Inhibitory effect of norepinephrine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of catecholamines on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Norepinephrine had a potent inhibitory effect on I-CRF release in a dose-dependent manner at 0.1 nM-1 microM concentrations, but dopamine did not. This inhibitory effect of norepinephrine was completely blocked by propranolol, but only partially blocked by phentolamine. Isoproterenol also had a potent inhibitory effect at 0.01-100 nM concentrations, and a high dose of phenylephrine (10 nM) inhibited I-CRF release. Clonidine did not influence I-CRF release. These results suggest that norepinephrine inhibits I-CRF release mainly through the beta-adrenergic receptor and partially through the alpha 1-receptor.     

Atrial natriuretic peptide correlates with pulmonary arterial pressure and cardiac output

Correlations between plasma atrial natriuretic polypeptide (ANP) levels and hemodynamic parameters were studied in the central circulation of 12 patients with angina pectoris. The average plasma ANP level determined in the aorta was found to be 619 +/- 140 pg/ml. The plasma ANP levels showed a significant positive correlation with mean pulmonary arterial (PA) pressure, right ventricular pressure, and with cardiac index. In contrast, there was no significant correlation between plasma ANP levels and other hemodynamic variables including atrial pressure. These results suggest that hemodynamics other than the atrial pressure may have some role in modulating ANP secretion in certain pathological states.     

Atrial natriuretic factor is biologically active also in the absence of vasopressin: studies on Brattleboro-strain diabetes insipidus rats

Since atrial natriuretic factor (ANF) has been shown to inhibit vasopressin secretion, the role of this effect in the acute biological actions of ANF was investigated using Brattleboro-strain diabetes insipidus (DI) rats. Under thiobarbital anesthesia, synthetic rat ANF of a 25 amino acid sequence was administered intravenously as a bolus (8 micrograms/kg) into the jugular vein. The urine volume, urinary sodium and potassium concentration, blood pressure, and heart rate were determined. It was found that ANF administered exogenously can exhibit its diuretic, natriuretic and vasorelaxant activities even in the absence of vasopressin. This indicates that the inhibition of vasopressin secretion is not an indispensible mechanism for acute biological effects of ANF.     

Hypercortisolism and the resistance to dexamethasone suppression during gestation

Maternal adrenocortical function was studied by measuring plasma cortisol and urinary free cortisol during gestation. Changes in suppressibility of pituitary-adrenocortical function were determined by dexamethasone administration. Urinary free cortisol as well as plasma cortisol increased during the course of gestation. The suppressibility by dexamethasone became less effective as pregnancy advanced. These results suggest that pregnant women have pituitary-adrenocortical hyperfunction and tissue refractoriness to glucocorticoid which increases during the course of gestation.     

Human corticotropin-releasing hormone test in normal subjects and patients with hypothalamic, pituitary or adrenocortical disorders

Human corticotropin-releasing hormone (hCRH) test was performed in 57 normal volunteers and 102 patients with hypothalamic, pituitary and adrenocortical diseases. Intravenous bolus injection of synthetic hCRH, 100 micrograms for adults or 1.5 micrograms/kg for children, increased plasma ACTH and cortisol levels in about 90% of normal subjects. In 47 patients with Cushing's disease, plasma ACTH tended to show an exaggerated response to hCRH and peak ACTH was the most frequent abnormal component among the several reaction parameters. Poor responders among normal subjects and patients with Cushing's disease had significantly higher plasma cortisol levels before CRH administration. Patients with hypothalamic hypopituitarism showed exaggerated response, whereas patients with primary pituitary lesion, isolated ACTH deficiency or adrenal Cushing's syndrome showed no ACTH response. These differences in the response of patients suggest the value of the hCRH test in their differential diagnosis.     

Atrial natriuretic factor inhibits vasopressin secretion from rat posterior pituitary

The effects of synthetic atrial natriuretic factor (ANF) were studied in superfused rat posterior pituitary gland. ANF (10(-6)M, 10(-10)M) significantly inhibited basal as well as KC1 (50 mM) or angiotensin II-stimulated immunoreactive arginine vasopressin secretion. The magnitude of inhibition was greater at 10(-6)M than at 10(-10)M. ANF also decreased cAMP secretion and increased cGMP secretion from the posterior pituitary. These results suggest that ANF directly acts on the posterior pituitary to inhibit arginine vasopressin secretion and that this effect is, at least, partly mediated by the changes in cyclic nucleotide production.     

Determination of membrane potential with lipophilic cations: correction of probe binding

The binding of lipophilic ions to the membrane of envelope vesicles from Halobacterium halobium was examined in the absence and presence of membrane potential. The lipophilic ions used constitute a homologous series of (Phe)₃-P⁺-(CH₂)_n-CH₃ (n = 0–4) and tetraphenylphosphonium (TPP⁺). In the absence of membrane potential, the amounts of binding were proportional to the probe concentration in the medium when the concentration is dilute. Upon illumination, interior negative membrane potential is generated which induces the uptake of phosphonium cation probe. 2 μM were employed as the initial probe concentration. The real membrane potential was evaluated by means of extrapolation to the state of no binding: The values of for various probes are plotted against the binding coefficient. Here, C_i^app is the apparent intra-vesicular concentration of the probes which is calculated without consideration of bound probes. The ordinate intercept of the plot gives the true concentration ratio, and from this the membrane potential is evaluated. The membrane potential-dependent binding was analysed with a model: the membrane is split into two halves, outer and inner half, and the amounts of bound probes in each region are governed by the concentration in the contiguous solution. We obtained a formula which describes amounts of binding as a function of the membrane potential.     

Presence of immunoreactive dynorphin in human cerebrospinal fluid

Immunoreactive dynorphin (I-dynorphin) was measured by radioimmunoassay in human cerebrospinal fluid (CSF). I-dynorphin concentration in CSF was 30 +/- 2 pg/ml. Sephadex G-25 column chromatography showed the main peak eluted at the position of dynorphin-(1-17). HPLC elution profile of this major peak from gel filtration showed a large peak corresponding to the position of dynorphin-(1-17) and small peaks corresponding to the positions of dynorphin-(1-13), dynorphin-(1-12) and other unknown peptides.     

In vitro release of growth hormone-releasing factor from rat hypothalamus: effect of insulin-like growth factor-1

The release of growth hormone-releasing factor (GHRF) from rat hypothalamus was investigated in vitro. After 60 min preincubation the released GHRF from sliced rat hypothalamic fragments during 60 min incubation was detected by a highly specific and sensitive radioimmunoassay for rat GHRF. The release of GHRF was Ca2+-dependent and enhanced by high concentration of K+. Insulin-like growth factor-1 (IGF-1) significantly decreased GHRF release to 65% and 84% of the control at concentrations of 10(-8) M and 10(-7) M, respectively. These results suggest that this in vitro system is useful for the investigation of the mechanism of GHRF release from the hypothalamus and that IGF-1 is probably involved in the feedback inhibition of growth hormone secretion by attenuating GHRF release from the hypothalamus besides countering the effect of GHRF on the pituitary.     

The hemolymph coagulation system in invertebrate animals

A hemocyte lysate from horseshoe crab produced a gel, when exposed to Gram-negative bacterial endotoxins. This gelation reaction of the lysate, so-called Limulus test, has been widely employed as a simple and very sensitive assay method for endotoxins. Recent biochemical studies on the principle of Limulus test indicate that the hemocytes contain several serine protease zymogens, which constitute a coagulation cascade triggered by endotoxins, and that there is a (1 3)--d-glucan-mediated coagulation pathway which also results in the formation of gel. Up to now, six protein components, designated coagulogen, proclotting enzyme, factor B, factor C, factor G and anti-LPS factor, all of which are closely associated with the endotoxin-mediated coagulation pathway, have been purified and biochemically characterized. Among these components, the complete amino acid sequences of coagulogens isolated from one American and three Asian species of horseshoe crabs have been established. Moreover, the reconstitution experiment using the isolated clotting factors, C, B, proclotting enzyme and coagulogen in the presence of endotoxin, leads to the formation of coagulin get. Based on these results, we propose here a mechanism for the Limulus coagulation cascade.