Doses Of Corticotropin-releasing Factor Research Articles

Comparison of corticotropin-releasing factor and acetylcholine on catecholamine secretion in dogs.

To test whether corticotropin-releasing factor (CRF) is a secretagogue for adrenal secretion of catecholamines, a preparation was developed that permits measurement of adrenal venous output in response to in vivo arterial injection into the dog adrenal gland. Dogs were prepared with catheters in the lumboadrenal vein for monitoring adrenal blood flow and secretion rate of epinephrine and norepinephrine and in the lumboadrenal and inferior phrenic arteries for adrenal injection. Under pentobarbital anesthesia 48 h after surgery, dogs received a series of intra-adrenal injections that included acetylcholine (0.2-200 nmol), CRF (2.0-20.0 nmol), and diluent. There was a log dose-response relationship before epinephrine secretion and norepinephrine secretion to acetylcholine. Adrenal injection of CRF stimulated epinephrine and norepinephrine secretion at the highest dose tested (20 nmol). The response observed was equivalent to the response to 0.2 nmol acetylcholine. A similar dose of CRF given systemically produced hypotension without stimulating catecholamine responses. Adrenal catecholamine responses to acetylcholine were not augmented by addition of CRF. These findings show that arterial injection of CRF into the intact dog adrenal stimulates secretion of epinephrine and norepinephrine. However, the low potency of CRF relative to that of acetylcholine, the lack of a synergistic effect of CRF on catecholamine responses to acetylcholine, and the high dose of CRF required to achieve a response suggest that CRF does not function in the adrenal medulla as a physiologically important secretagogue for catecholamines.

Corticotropin-releasing factor antagonist blocks stress-induced fighting in rats

Corticotropin-releasing factor (CRF) has been shown to have potent central nervous system-activating effects when administered intracerebroventricularly (i.c.v.). In the present experiment, this activating effect was exaggerated by use of a stress-motivated behavioral paradigm. Low doses of CRF (0.01 and 0.1 μg/rat) administered i.c.v. facilitated stress-induced fighting. More importantly, α-helical CRF-(9–41), a CRF antagonist, blocked stress-induced fighting produced by higher levels of stress. These results suggest that CRF in the central nervous system may have a role in mediating behavioral responses to stress.

Effect of corticotropin-releasing factor on adrenal DBH and PNMT activity

The continuous administration of CRF (corticotropin-releasing factor) by the intraventricular route, 100 ng/day, to rats over a period of 7 days, results in significant increases of DBH (dopamine beta-hydroxylase) and PNMT (phenethanol N-methyltransferase) activities in the adrenal glands. The pattern of increase in DBH response to various doses of CRF does not correspond to the effects observed on plasma corticosterone, a result that suggests that CRF is acting to increase the adrenal enzyme by means other than through the pituitary-adrenal axis. In contrast, PNMT responds to CRF in a manner indicating a correlation with glucocorticoid availability. Moreover, PNMT induction by CRF persists even after adrenal denervation; it also occurs when CRF is given subcutaneously for 3 days, in a dose of 60 ng/day. Injection of reserpine did not potentiate the effect of intraventricularly administered CRF.

Abnormal response of adrenocorticotropin to corticotropin releasing factor in spontaneously hypertensive rats.

The pituitary-adrenocortical response to ovine corticotropin-releasing factor (CRF) was investigated in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) anesthetized with pentobarbital. After intravenous administration of various doses of CRF (0.1, 1.0 and 10 micrograms), the plasma levels of ACTH were significantly increased in both groups. ACTH increments after various doses of CRF were dose-dependent in WKY. ACTH increments after injections of 0.1, 1.0, and 10 micrograms of CRF in SHR were 123.2 +/- 36.5 (SE), 123.0 +/- 52.2 and 60.3 +/- 48.5 pg/ml at 5 min, and 386.3 +/- 73.8, 243.4 +/- 86.6 and 220.0 +/- 31.4 pg/ml at 15 min, respectively. The ACTH increments in SHR at 15 min after administration of 0.1 microgram of CRF were higher (p less than 0.02) than those in WKY. However, ACTH increments in SHR after administration of 10 micrograms of CRF were lower than those in WKY at 5 min (p less than 0.05) and 15 min. These data suggest that the plasma ACTH responses to various doses of CRF represent a dose-unrelated plateau response in SHR. The plasma levels of corticosterone after administration of various doses of CRF did not change significantly and there were no significant differences between the two strains. The results of these experiments suggest that SHR have an abnormal response of the pituitary-adrenocortical axis to CRF, and the abnormal response may be attributable to desensitization of the pituitary to CRF.

Effects of Angiotensin II Blockade on the Responses of the Pituitary–Adrenal Axis to Corticotropin-Releasing Factor in Humans

We investigated the possibility that angiotensin II (ANGII) augments the sensitivity of the pituitary to corticotropin releasing factor (CRF) by comparing, in patients with essential hypertension, the responses of plasma adrenocorticotropic hormone (ACTH), cortisol, aldosterone, and renin activity to a bolus injection of either 0.5 or 1.0 microgram/kg of synthetic ovine CRF in control conditions and after chronic treatment with the converting enzyme inhibitor captopril to block the formation of ANGII; the effects of CRF were examined up to 4 h after its administration. In control studies, we found that the two doses of CRF induced similar increments in ACTH and cortisol, the levels of which remained elevated throughout the studies; these changes were associated with increments in plasma aldosterone that were dose dependent, less pronounced, and of shorter duration and with a slight decrease in plasma renin activity. Captopril treatment increased basal plasma renin activity and lowered plasma aldosterone while leaving basal ACTH and cortisol unchanged. During converting enzyme inhibition, the responses of ACTH and cortisol to CRF were similar to those observed in control studies, whereas the changes in plasma aldosterone and plasma renin activity were, respectively, smaller and greater. From these results, it appears that during ANGII blockade the sensitivity of ACTH to CRF stimulation is unaffected, whereas that of the adrenals to ACTH is selectively reduced at the level of the zona glomerulosa.

Effects of corticotropin-releasing factor on plasma motilin and somatostatin levels and gastrointestinal motility in dogs

The effects of intracerebroventricular and intravenous administration of corticotropin-releasing factor (CRF) on gastrointestinal motility, motilin-induced gastric motor response, and plasma motilin and somatostatin levels were investigated in fasted dogs chronically prepared with strain gauge transducers on the antrum and proximal jejunum. Administered intracerebroventricularly at doses of 20 and 100 ng/kg in fasted dogs, CRF suppressed for 4–5 h the gastric cyclic migrating motor complex. A similar dose (100 ng/kg) administered intravenously was inactive. Corticotropin-releasing factor administration by the intravenous route at 100 ng/kg did not alter the cyclic plasma motilin and somatostatin variations associated with the cyclic gastric motor events. During the blockade of antral migrating motor complex induced by intracerebroventricular administration of CRF, cyclic peaks of plasma motilin were absent whereas those of somatostatin persisted. The gastrointestinal migrating motor complex induced by the intravenous administration of porcine motilin (0.25 μg/kg) was abolished when motilin was injected 2 h after the intravenous administration of CRF (100 ng/kg), whereas a similar dose of CRF administered intracerebroventricularly did not abolish the antral and jejunal motor responses to motilin. It is concluded that in fasted dogs, CRF administered centrally affects the interdigestive gastric motility and the release of motilin but not that of somatostatin. These results also suggest that (a) the intracerebroventricular CRF-induced blockade of motilin release is responsible for the inhibition of gastric migrating motor complex and (b) circulating CRF is able to affect the gastric motor response to porcine motilin through a peripheral mechanism that does not involve somatostatin and motilin secretion.

Neonatal peptides affect developing rats: β-endorphin alters nociception and opiate receptors, corticotropin-releasing factor alters corticosterone

The dose-response relationship of neonatal (days 1–7) administration of β-endorphin (BE) and corticotropin-releasing factor (CRF) on body weight, eye opening, response to thermal pain, and concentrations of plasma and adrenal corticosterone were measured in developing rat pups. At the highest dose (50 μg/pup), neonatal CRF reduced body weight, while 10 and 50 μg/pup accelerated eye opening. In addition, a reduction in concentration of plasma and adrenal corticosterone was correlated with the dose of neonatal CRF, whereas adrenal weights were not altered. BE produced none of these effects, but 1, 10 and 50 μg/pup on days 1–7 significantly reduced baseline latencies in a novel water-bath tail-flick test on day 9. These same animals showed reduced numbers of brain opiate receptors on day 14. The results indicate that peptide administration during the sensitive neonatal period can alter the development of physiological processes that will later be influenced by the peptide.

Dissociation of locus coeruleus activity and blood pressure: Effects of clonidine and corticotropin-releasing factor

In order to determine whether pharmacologically-induced alterations in the spontaneous activity of neurons in the locus coeruleus are associated with changes in blood pressure, the activity of the locus coeruleus and blood pressure were recorded simultaneously in anesthetized rats after the administration of agents known to affect both of these parameters. Spontaneous activity of the locus coeruleus was decreased by intracerebroventricular (i.c.v.) administration of both clonidine and St 91, [2,(2,6-diethylphenylimino)imidazolidine chloride], a charged analogue of clonidine. However, only clonidine decreased the mean blood pressure after intracerebroventricular administration suggesting that either the receptors mediating decreases in the activity of the locus coeruleus are different to those mediating hypotension, or that St 91 does not distribute to sites involved in the control of blood presure even after intracerebroventricular administration. Intravenous administration of clonidine, but not of St 91, decreased the activity of the locus coeruleus and produced a prolonged hypotension, thus suggesting a central mechanism for these effects. Both clonidine and St 91 administered intravenously, produced a brief initial period of hypertension which was not associated with consistent changes in the spontaneous activity of the locus coeruleus. Thus, noradrenergic agonists can decrease the activity of the locus coeruleus without affecting blood pressure, and increase blood pressure without affecting the activity of the locus coeruleus. The spontaneous activity of cells in the locus coeruleus was increased by 100% after the intracerebroventrieular administration of corticotropin-releasing factor (CRF; 3.0 μg). However, blood pressure was not altered by this dose of corticotropin-releasing factor. This demonstrates that increasing the spontaneous activity of the locus coeruleus does not directly affect blood pressure. The results of the present study demonstrate that the activity of the locus coeruleus can be decreased or increased without a resulting change in blood pressure, and conversely, that an increase in blood pressure need not be accompanied by changes in the spontaneous activity of the locus coeruleus.

By 95 days of gestation CRF increases plasma ACTH and cortisol in ovine fetuses.

Plasma adrenocorticotropin (ACTH) and cortisol (F) responses to 15-min intravenous infusions of synthetic ovine corticotropin-releasing factor (CRF) were measured by radioimmunoassay in three groups of chronically cannulated ovine fetuses. Fetuses (n = 7) in group I were 107 +/- 2 days gestation (0.72 G) and fetuses (n = 7) in group II were 126 +/- 2 days gestation (0.86 G). Group III fetuses (n = 5) were studied at 5-day intervals during the last 2 wk of gestation. Resting fetal plasma ACTH levels were not significantly different among the three experimental groups. Infusions of CRF (50 ng X kg-1 X min-1) provided similar, significant increases in fetal plasma ACTH concentrations in the three groups. In the young fetuses (group I) the ACTH responses to 500 ng X kg-1 X min-1 infusions of CRF were greater than responses to 50 ng X kg-1 X min-1 infusions P less than 0.001. In group II both doses of CRF produced equivalent increases in ACTH that were comparable with the responses to 50 ng X kg-1 X min-1 infusions in Group I. This suggests that fetal ACTH responsiveness to large doses of CRF decreases between 0.72 and 0.86 G. Resting fetal plasma F levels increased during gestation (P less than 0.01). There was an F response (P less than 0.001) to CRF in all groups with greater responses observed in the older fetuses. This suggests that fetal adrenal responsiveness to ACTH or other peptides released by CRF increases during gestation.

Sympatho-adrenal medullary functions in response to intracerebroventricularly injected corticotropin-releasing factor in anesthetized rats

Effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) on adrenal sympathetic efferent nerve activity, adrenal catecholamine secretion rate and cardiovascular function (i.e. blood pressure, heart rate and renal nerve activity) were investigated in halothane-anesthetized rats. Administration (i.c.v.) of CRF resulted in a dose-dependent increase (to 140% of control, for a 6.4 nmol dose) in adrenal sympathetic nerve activity which began several minutes after injection and reached maximum values approximately 30–60 min later. This increase was significant, when tested against vehicle injected controls, for doses of 6.4 nmol and 640 pmol; however, a 64 pmol dosage did not produce significant effects. Acute hypophysectomy did not influence the response of adrenal nerve activity to i.c.v. injection of CRF. Intravenous administration of CRF (6.4 nmol) did not produce any significant increases in ongoing activity of the adrenal nerve. Following i.c.v. administration of CRF (640 pmol), epinephrine and norepinephrine secretion, as measured from adrenal venous blood samples, showed a similar response pattern to that of the adrenal nerve. Significant increases (maximum increases, from 13.2 to 31.5 ng/kg/min and from 4.1 to 8.6 ng/kg/min for epinephrine and norepinephrine secretion rates, respectively) were observed over the 90 min blood sampling period. The present study demonstrates by direct recording of adrenal sympathetic nerve activity and measurement of adrenal catecholamine secretion rate, that i.c.v. administered CRF can increase adrenal sympathetic efferent nerve activity resulting in increases in catecholamine secretion. In addition, renal nerve activity also showed dose-dependent increases after CRF i.c.v. administration (to 160% of control, for a 6.4 nmol dose) as did heart rate (increases of 35 beats/min for a 6.4 nmol dose). However, blood pressure did not change with the same dose of CRF administered intracerebroventricularly, possibly as a result of direct effects of halothane upon peripheral blood vessels.

EEG stability following corticotropin releasing factor in rats

The EEG and behavioral effects of intracerebroventricular (i.c.v.) injections of low doses of corticotropin releasing factor (CRF) (0.0015 and 0.015 nM) were studied in rats. Compared to saline injections, CRF produced a significant increase in the ‘stability’ of EEG waveforms over time in several frequency bands. The behavioral effects of CRF were consistent with previous reports of CRF-induced arousal and autonomic activation without frank increases in locomotion. These studies suggest that measures of EEG stability should be investigated as a potential biologic correlate in diseases wherein hypercortisolism associated with CRF release is a prominent feature.

The regulation of the corticomelanotropic cell activity in aves—II. Effect of various peptides on the release of ACTH from dispersed, perfused duck pituitary cells

1.1. We have estimated the corticotropin-releasing activity (CRA) of different neurohypophyseal peptides and synthetic corticotropin-releasing factor (CRF) in the duck, using perfused dispersed pituitary cells and an ACTH radioimmunoassay adapted to duck material.2.2. Log dose—response curves were obtained for different doses of arginine-vasopressin (AVP), argininevasotocin (AVT), mesotocin (MT), oxitocin (OT) and ovine CRF (oCRF) and compared to the response obtained with dilutions of duck median eminence extracts (DME). All peptides tested behaved as partial agonists compared to DME. AVT and MT were the most potent of all peptides tested, with a capacity of 60% relative to DME. CRF was a weak agonist together with AVP and OT.3.3. AVT and CRF perfused together at equal doses significantly potentiated the effect of each other, yielding a dose-response line whose slope approximated that of DME.4.4. A similar design was used to test the CRA of the same substances in the rat. The main difference in the pattern of response between the two species was the low potency displayed by all the neurohypophyseal peptides in the rat, compared with CRF which, in contrast with what occurred with the duck system, was the most potent secretagogue of all peptides tested.5.5. It is concluded that in birds, as in mammals, the control of ACTH secretion may be exerted by neurohypophyseal peptides and a CRF-like peptide acting synergistically upon the corticomelanotropic cell.

Corticotropin-releasing factor stimulation of adrenocorticotropin and beta-endorphin release: effects of acute and chronic stress.

The effects of acute and chronic stress on the release of ACTH and beta-endorphin in response to stimulation by ovine corticotropin-releasing factor (CRF) and arginine vasopressin were examined. Pituitaries were removed from rats who had received either acute stress, chronic stress daily for 14 days with the last stress occurring 24 h before decapitation, or chronic stress followed by an acute stress immediately before decapitation (chronic stress-acute stress). Pituitaries from naive unstressed animals were used as the control group. After processing into single cell suspensions, the pituitaries were incubated with various doses of CRF (10(-11) M to 10(-9) M) and AVP (10(-10) M to 10(-8) M). Release of ACTH and beta-endorphin into the medium was measured by RIA. A clear dose-dependent response to both releasers was seen in control pituitaries. In acute stress, a decreased responsiveness to arginine vasopressin and CRF was seen. This same blunted response was not seen in chronic stress even if the animals are stressed immediately before decapitation. At higher doses of CRF (10(-9) M) a substantially increased release of ACTH and beta-endorphin was seen in the chronically stressed rats. When the content of the anterior pituitary lobe was assayed in these animals, both chronic stress groups show increased content of ACTH and beta-endorphin, which may indicate an increase amount of ACTH and beta-endorphin in the releasable pools in chronic stress. In addition, the failure of further stress to alter the response to CRF in the chronic stress-acute stress group may indicate a down-regulation of the steroid feedback on the pituitary. However, it is clear that no down-regulation of the CRF receptor occurs in this chronic stress paradigm.

Interaction of arginine vasopressin and corticotropin releasing factor demonstrated with an improved bioassay.

We developed an improved in vivo bioassay for corticotropin releasing factor (CRF) by modifying the injection schedule in the standard chlorpromazine-morphine-pentobarbital assay procedure. A combined injection of chlorpromazine and morphine followed 75 min later by injection of pentobarbital produced low basal levels of corticosterone and rendered the animals highly sensitive to synthetic CRF but insensitive to the stress of ether or histamine. The lowest dose of CRF that significantly elevated plasma corticosterone levels was 0.01 micrograms/kg. Using this assay, we studied CRF-arginine vasopressin (AVP) interactions at doses that were expected to raise systemic peptide concentrations to levels measured in hypophysial portal blood. The threshold for a significant corticosterone response was found to be at least 250-fold lower for CRF-41 than for AVP. The order in which CRF and AVP are injected was also found to be important, potentiation being greater if CRF was given first. In addition, rats deprived of water for 24 hr were more sensitive to CRF than normally hydrated animals.

Corticotropin-releasing factor-induced adrenocorticotropic hormone release in the sheep fetus: Blockade by cortisol

We administered intravenous injections of synthetic ovine corticotropin-releasing factor to chronically cannulated sheep fetuses and monitored fetal plasma adrenocorticotropic hormone and cortisol concentrations. The three doses of corticotropin-releasing factor used (10, 100, or 1000 ng · kg−1) increased fetal plasma adrenocorticotropic hormone; fetal plasma cortisol levels rose with the highest dose of corticotropin-releasing factor. Administration of corticotropin-releasing factor at these concentrations did not change fetal heart rate or blood pressure. Elevation of fetal plasma cortisol levels to 40 to 80 ng · ml−1 by infusions of the steroid blocked the adrenocorticotropic hormone responses to all three doses of corticotropin-releasing factor. These data indicate that corticotropin-releasing factor can increase plasma adrenocorticotropic hormone concentrations in the late-gestation fetus and that these increases can be blocked by elevations in fetal plasma cortisol levels within a physiologic range. This suggests that cortisol modulates adrenocorticotropic hormone release by the fetal pituitary gland late in gestation.

Effect of naloxone on the hormone response to CRF in normal man.

Ovine corticotropin releasing factor (CRF) was administered to six normal men and the plasma ACTH and cortisol responses compared with those following the same dose of CRF (200 micrograms) plus the opiate receptor blocker naloxone (20mg). The addition of naloxone was associated with a significant increase in plasma ACTH, cortisol and aldosterone responses. No change was observed in peripheral plasma levels of epinephrine, norepinephrine, arginine vasopressin, angiotensin II or renin activity in response to CRF plus naloxone. It is concluded that endogenous opioid peptides may inhibit the ACTH response to CRF. However the addition of naloxone does not increase the ACTH response to CRF sufficiently to constitute a useful test of pituitary function.

Differential behavioral actions of corticotropin-releasing factor (CRF)

In order to elucidate the involvement of the 41 amino-acid residue corticotropin-releasing factor (CRF) in the modulation of brain functioning, the behavioral profile of the releasing hormone was determined using tests for spontaneous behavior, grooming, active and passive avoidance behavior. Intracerebroventricular (ICV) administration of CRF in a dose that does not stimulate the pituitary-adrenal axis, resulted in an activation of open-field behavior, as measured by ambulation and rearing activities. Also grooming activity was significantly enhanced after central application of CRF. In hypophysectomized rats, which show an impaired shuttle-box avoidance acquisition, CRF restored acquisition for the duration of the treatment. Paradoxically, extinction of pole-jumping active avoidance behavior of intact rats was facilitated by the releasing factor, even in adrenalectomized animals. Passive avoidance behavior was affected bidirectional: higher doses of CRF (300 ng), given subcutaneously (SC), attenuated passive avoidance retention, probably via activation of the pituitary-adrenal system resulting in high corticosterone levels. Lower doses (30 ng), however, which were also given SC did not stimulate pituitary-adrenal activity, and facilitated retention of passive avoidance behavior. Central administration of CRF in very low doses (30 pg) had the same effect as higher doses of CRF given SC, i.e., inhibition of passive avoidance retention. Taken together, the data indicate that CRF can affect behavior via a direct action on the central nervous system. The question remains whether this activity is an intrinsic property of CRF, or mediated by the release of hormones or neuropeptides.

Plasma cortisol and catecholamine responses to intracerebroventricular administration of CRF to rhesus monkeys

Synthetic ovine corticotropin releasing factor (CRF) was administered directly into the 4th ventricle of rhesus monkeys. A dose dependent increase in plasma cortisol was observed following 10 μg/kg, 20 μg/kg, and 60 μg/kg of CRF. Increases in plasma epinephrine were also evident following the highest dose of CRF. Plasma norepinephrine, mean arterial pressure, and heart rate did not increase significantly following CRF administration. These data suggest that in the rhesus monkey, central administration of ovine CRF leads to activation of the pituitary-adrenocortical axis at doses that do not raise plasma catecholamines.

The effect of ovine corticotropin-releasing factor on catecholamine, vasopressin, and aldosterone secretion in normal man.

The 41-residue ovine corticotropin-releasing factor (CRF) was administered iv to five normal men. A significant rise in plasma corticotropin (ACTH), cortisol, and aldosterone was demonstrated after a dose of 200 micrograms. There was no demonstrable change in supine blood pressure, pulse rate, plasma vasopressin, renin, catecholamines, insulin, glucagon, or glucose. It is concluded that 200 micrograms ovine CRF stimulates ACTH and cortisol secretion independently of any change in peripheral plasma levels of vasopressin and catecholamines. The cortisol and ACTH responses to ovine CRF were less marked but more prolonged than those after insulin-induced hypoglycemia. The relatively small increment in plasma ACTH, which was well within the physiological range, was associated with a significant increase in plasma aldosterone. Posterior pituitary function was not affected by this dose of ovine CRF.

Interaction between hypothalamic peptides in a superfused pituitary cell system

Recently two hypothalamic releasing factors have been isolated, sequenced and synthesized: corticotropin-releasing factor (CRF) from sheep and rat hypothalami; and growth hormone-releasing factor (GH-RF) from tumors in human pancreas (hpGH-RF) and from rat hypothalami (rhGH-RF). Their biological potencies were tested by various laboratories in vivo and in vitro using rat pituitary cell cultures and the pituitary quarters method. In the present study, we investigated the dynamics of the release of pituitary hormones and the interaction between CRF and hGH-RF and several brain peptides in a pituitary cell-superfusion system. A dose-related ACTH release was found when the cells were superfused with different doses of synthetic CRF. Synthetic hGH-RF 44, hGH-RF 40, hGH-RF 1–29 and purified porcine hypothalamic GH-RF caused similar dose-related releases of GH. In this system, we demonstrated interactions between CRF and vasopressin, CRF and SP, hGH-RF and vasopressin and hGH-RF and PHI-27. We conclude that the control of pituitary hormone secretion is a complex process; several factors may interact with each releasing or inhibiting factor to modulate their effects.