Studies on the corticotrophin-releasing activity of vasopressin, using ACTH secretion by cultured rat adenohypophyseal cells

Corticotropin response to combined administration of human corticotropin-releasing hormone and small-dose arginine vasopressin in normal subjects

Arginine vasopressin (AVP) is known to potentiate corticotropin (ACTH) secretion by human corticotropin-releasing hormone (hCRH), and a combined administration of hCRH and AVP appears useful as a pituitary ACTH reserve test. This study was designed to evaluate the appropriate dose of AVP and its route of administration, for better estimation of pituitary ACTH reserve in humans, when used in combination with a conventional hCRH stimulation test. First, intravenous (IV) doses of hCRH (100 micrograms) and AVP (0, 0.1, and 0.3 U) were administered simultaneously in six normal subjects. Second, IV hCRH was administered with intramuscular (IM) AVP (0, 1.0, 3.0, and 5.0 U) in 10 normal subjects. Blood samples for measurement of plasma ACTH were obtained at 0, 15, 30, 45, 60, 90, and 120 minutes after the hCRH with and without AVP administration. The order of AVP doses was randomly chosen in each subject. The peak plasma ACTH level was 65.0 +/- 16.0 pg/mL (30 minutes) with hCRH alone and 139.5 +/- 35.6 pg/mL (15 minutes) with hCRH plus 0.3 U IV AVP in six normal subjects. Similarly, the peak plasma ACTH level was 43.5 +/- 5.6 pg/mL (30 minutes) with hCRH alone and 116.0 +/- 19.6 (15 minutes) and 96.6 +/- 24.0 pg/mL (15 minutes) with hCRH plus 3.0 and 5.0 U IM AVP in 10 normal subjects, respectively. The hCRH-induced ACTH responses (delta ACTH) with both IV and IM AVP were significantly (P less than .05) greater than the respective control values with hCRH alone. The responses (delta ACTH) were comparable between the two phases of 3.0 and 5.0 U IM AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine vasopressin, but not corticotropin releasing factor, is a potent stimulator of adrenocorticotropic hormone following electroconvulsive treatment

Neuroendocrine responses to the hypothalamic pituitary-adrenal axis following electroconvulsive treatment (ECT) were evaluated in twelve depressed (6 males/6 females) patients. Plasma concentrations of arginine vasopressin (AVP), corticotropin releasing factor (CRF), corticotropin (ACTH), and cortisol were measured using radioimmunological methods at four different ECT occasions. At each occasion plasma samples were taken immediately before ECT, at the recovery of spontaneous breathing and at 10 and 30 minutes after the ECT. No changes were observed in the plasma CRF concentrations. A large and rapid increase in plasma AVP concentrations was seen after the ECTs. This was followed by increased plasma ACTH and plasma cortisol levels. It is generally believed that AVP exerts a modulatory potentiating action on the CRF-induced ACTH release. The present results demonstrate that AVP per se can cause a release of ACTH from the anterior pituitary.

Ovine corticotrophin releasing factor stimulates ACTH release from human corticotrophinoma cells in culture; interaction with hydrocortisone and arginine vasopressin

We have investigated the effects of ovine corticotrophin releasing factor (oCRF) and its interaction with hydrocortisone (HC), and arginine vasopressin (AVP) on ACTH release from human corticotrophinoma cells in culture. Tumour tissue was obtained from six patients (three with active Cushing's disease and three with Nelson's syndrome). Cultures were maintained for periods of up to six months. Ovine CRF (21 nmol) significantly (P less than 0.01) stimulated ACTH release from all tumours. Dose response (21 pmol-21 nmol) effects were observed for the three tumours investigated over 2 and 4 h. Cortisol (20 mumol) significantly (P less than 0.01) inhibited basal ACTH release from one tumour (Nelson's syndrome) by 75% over 4 h, and completely prevented the stimulatory effects of oCRF. AVP directly stimulated ACTH release from two tumours (Nelson's syndrome), and also potentiated the stimulatory action of oCRF during 30 min incubations. These data show corticotrophinoma cells from subjects with Cushing's disease and Nelson's syndrome can be directly stimulated by hypothalamic oCRF and may be potentiated by AVP. Cortisol and oCRF have been shown in one tumour to have antagonistic actions at the pituitary level.

In vivo potentiation of corticotropin releasing factor activity by vasopressin analogues

The ability of the neurohypophyseal hormones and related synthetic peptides to potentiate the action of synthetic ovine corticotropin releasing factor (CRF-41) was examined using male rats whose endogenous CRF release was blocked with chlorpromazine, morphine and nembutal. CRF potency was clearly related to the pressor activity of the analogues. However, the threshold dose for eliciting a significant corticosterone response with the neurohypophyseal hormones was greater than with CRF-41. When arginine vasopressin (AVP) was coadministered with CRF-41 at subthreshold doses of both peptides, a significant corticosterone response was observed. When the neurohypophyseal hormone analogues were compared with regard to intrinsic CRF bioactivity, it was observed that an L-basic residue in sequence position 8 is necessary for high intrinsic activity. With one exception, l-Deamino-(9-D-Ala) arginine vasopressin, the ability to potentiate the effect of CRF-41 was related to the intrinsic CRF potency of the analogues. These results support previous reports of in vitro potentiation of CRF-41 by AVP and point out the complexity of CRF-neurohypophyseal hormone interaction in vivo.

Interactions between CRF, epinephrine, vasopressin and glucocorticoids in the control of ACTH secretion

The secretion of ACTH by corticotrophs in the anterior lobe of the rat pituitary gland is under the stimulatory influence of at least three receptors, namely that for peptidic CRF (corticotropin-releasing factor), vasopressin and alpha 1-adrenergic agents. CRF is a potent stimulator of cyclic AMP accumulation as well as adenylate cyclase activity in the rat adenohypophysis, thus suggesting an important role of cyclic AMP as mediator of CRF action on ACTH secretion. Vasopressin causes a 2-fold increase of the stimulatory effect of CRF on ACTH release in rat anterior pituitary cells in culture. The potentiating effects of vasopressin on CRF-induced ACTH release are accompanied by parallel changes of intracellular cyclic AMP levels. Vasopressin, while having no effect on basal cyclic AMP levels, causes a 2-fold increase in CRF-induced cyclic AMP accumulation without affecting the ED50 value of CRF action. ACTH secretion is also stimulated by a typical alpha 1-adrenergic receptor. Epinephrine causes a marked stimulation of ACTH release which is additive to that of CRF. Epinephrine, in analogy with vasopressin, although having no effect alone on basal cyclic AMP levels, causes a marked potentiation of CRF-induced cyclic AMP accumulation. Glucocorticoids cause a near-complete inhibition of epinephrine-induced ACTH secretion within 4 h with the following order of ED50 values: triamcinolone acetonide (0.2 nM) greater than dexamethasone (1.0 nM) much greater than cortisol (11 nM) greater than corticosterone (22 nM). Similar effects are observed for CRF- and vasopressin-induced ACTH release. Although the activity of the pituitary-adrenocortical axis in the rat is highly dependent upon sex steroids, 17 beta-estradiol, 5 alpha-dihydrotestosterone and the pure progestin R5020 have no detectable effect on basal or epinephrine-induced ACTH release, thus illustrating the high degree of specificity of glucocorticoids in their feedback control of ACTH secretion. Moreover, glucocorticoids have no effect on CRF-induced cyclic AMP accumulation, thus indicating that their inhibitory effect is exerted at a step following cyclic AMP accumulation.

Alpha 1-adrenergic stimulation of ACTH secretion in vivo in the rat

The alpha-adrenergic agonist phenylephrine (100 micrograms, i.v.) causes a rapid 5- to 10-fold elevation of plasma ACTH levels 5 min after its administration in adult ovariectomized rats, the concentration of the hormone remaining elevated up to at least 2h. Epinephrine (10 micrograms) causes also a rapid but shorter-lived stimulation of ACTH secretion. While having no effect alone under basal conditions (conscious freely-moving animals), the highly specific alpha 1-adrenergic antagonist prazosin (0.25 micrograms) almost completely reverses the stimulatory effect of phenylephrine. Pretreatment with dexamethasone inhibits basal plasma ACTH levels by 70% and almost completely prevents the stimulatory effect of phenylephrine on this parameter. Plasma levels of alpha-MSH, on the other hand, are only stimulated 1-fold above control 5 min after the administration of phenylephrine and are insensitive to corticosteroid treatment. Based on the specificity of action of prazosin on postsynaptic alpha 1-adrenergic receptors and of dexamethasone on the anterior lobe of the pituitary gland, the present data indicate that phenylephrine is a potent stimulator of ACTH secretion by a direct action on an alpha 1-adrenergic receptor in corticotrophs of the adenohypophysis. They also support the suggestion that epinephrine and/or norepinephrine could be involved as physiological corticotropin-releasing factor(s).

Hydrophobic high-performance liquid chromatography of hormonal polypeptides and proteins on alkylsilane-bonded silica

Thirty-two hormonal polypeptides and nine proteins (8-65 kD) have been used to evaluate the potential of high-performance liquid chromatography on alkylsilane-bonded silica for separating and recovering biologically active compounds of this type. The basic method used was gradient elution with acetonitrile in an acid phosphate buffer. Variation of key chromatographic parameters demonstrated that low pH (less than 4.0) and high buffer molarity (greater than 0.1 M) are mandatory for reproducible high efficiency polypeptide chromatography. Simple NaCl-HCl mixtures of appropriate acidity and molarity could be substituted for the acid phosphate buffer, with the advantage of minimising non-physiological ion contributions to eluted materials. Minor selective effects were noted with different organic modifiers, but variation of other parameters, including choice of specific alkylsilane packings, did not materially influence separations. Under optimal conditions all of the polypeptides tested could be efficiently chromatographed, and many simultaneously resolved, as could most of the proteins tested. Three of the more hydrophobic proteins could not, however, be eluted from the alkylsilane packings. Retention orders of smaller compounds (less than 15 residues) generally correlated with the sum of the Rekker fragmental constants of their strongly hydrophobic residues. Larger polypeptides showed numerous anomalies when ranked by this means, however, limiting its predictive value. The separation of at least eighteen discrete components from a partially-purified posterior pituitary extract has demonstrated the capability of alkylsilane-type reversed-phase packings for the hydrophobic high-performance liquid chromatography of complex biological mixtures.

Assays and dynamics of corticotropin-releasing factor activity in rat hypothalamus

Features of several assays for corticotropin-releasing factor (CRF) were compared, with reference to sensitivity, precision, specificity and convenience. In general, in vivo assays are less specific, whereas in vitro assays with isolated pituitary cells appear to suffer from vulnerability. Promising approaches for overcoming this difficulty are appearing: one is the cell culture technique and the other is the perfusion of pituitary cell column. However, the findings with vasopressin are again discordant. So far, the in vivo-in vitro assay system appears to be the most satisfactory. In this connection, special emphasis was laid on the CRF assay by out intrapituitary injection technique through the parapharyngeal approach, which has features of both in vivo and in vitro systems. The drawbacks with this assay are its complexity and relatively lower precision. Problems of the use of dexamethasone are discussed from a viewpoint of possible multistage feedback inhibition, as postulated by Yates et al. Several findings on the CRF dynamics were mentioned, in order to exemplify the findings obtained with our assay: it was shown that the two-peaked changes of CRF after ether-laparotomy stress in adult rats were composed of heterogeneous components, as revealed by differential effect of cycloheximide. Pretreatment with cycloheximide similarly abolished the delayed CRF peak that was observed in 2-day-old neonatal rats under stress. These findings suggest an operation of a biochemical denominator in common with both cases.