Changes in serum hormone and peptide levels in rats in experimental epilepsy

Serum levels of 7 hormones and neuropeptides were studied in the course of development of a generalized epileptic activity (EA) induced in rats by intraperitoneal administration of corasole (75 mg/kg), i.e. 30 s (latent period), 50-150 s, 5-10 min after epileptogenic administration. A significant increase in the levels of ACTH (5.2-fold), glucagon (1.8.-fold), angiotensin I and renin activity were shown to occur 90-180 s later. Further on in the course of EA the level of ACTH remained enhanced but the level of glucagon and renin-angiotensin activity returned to normal. The levels of cortisol, vasopressin and aldosterone were enhanced 2-3-fold 30 min later. The level of insulin 30 min later remained unchanged. The role of neuropeptides and hormones in the onset and suppression of EA is discussed.     

Is ethanol a stressogenic factor for rats with a developed alcohol motivation?

The male outbred rats, placed in common cages, demonstrated dose- and time-dependent increase of blood plasma ACTH level after handling and acute ethanol administration (1 and 4 g/kg). The pituitary response of isolated rats under condition of free choice between water and 15% ethanol solution was more pronounced after handling. Ethanol (4 g/kg) did not increase plasma blood level ACTH in isolated alcohol motivated rats. It also prevented blood plasma ACTH rise under condition of handling. The dual role of acute ethanol as a stressogenic and antistressogenic factor in naive and alcoholic rats is discussed.     

ACTH and corticosterone response to naloxone and morphine in normal, hypophysectomized and dexamethasone-treated rats

The effect of opiate receptors blocker naloxone on ACTH and corticosterone secretion in normal, dexamethasone-treated and hypophysectomized rats was studied. A dose-related increase in plasma corticosterone level was found at 45 min after s.c. injection of naloxone in a dose range of 0.25-2.0 mg kg-1. The rise in plasma corticosterone was preceded by a slight increase in plasma ACTH. Acute morphine administration in a relatively low dose (6 mg kg-1 s.c.) induced a significant rise in both plasma ACTH and corticosterone levels. Dexamethasone treatment was followed by low basal corticosterone level, by total inhibition of the stress response and response to morphine injection, while the response to ACTH administration was normal. Under these circumstances as well as in rats 6 days after hypophysectomy, naloxone failed to increase plasma corticosterone levels. It is concluded that a direct stimulation of corticosteroid biosynthesis in adrenal cortex is not involved in the mechanism of naloxone-induced activation of pituitary-adrenocortical function.     

Plasma concentrations of adrenocorticotropin-related peptides in lambs injected with ovine corticotropin releasing factor or vasopressin

Synthetic ovine corticotropin-releasing factor (oCRF) and arginine vasopressin (AVP) were intravenously injected each alone or in combination (each peptide: 1 microgram/kg body weight) in lambs on days 1, 3, 7 and 20 after birth. Plasma samples were collected just before and 10 and 30 min after injection. Plasma concentrations of cortisol and aldosterone were measured. Adrenocorticotropin (ACTH)-related peptides were isolated by Sephadex G50 column chromatography and measured by radioimmunoassay. Three different peaks with an ACTH immunoreactivity were found in lamb plasma: a "big" ACTH molecular form (Mr = 30,000), an "intermediate" (Mr = 8000) and a "little" (Mr = 4500). In 1 and 3 days-old lambs, both CRF and AVP increased preferentially "intermediate" ACTH. In 7 and 20 days-old lambs, an increase in "little" ACTH occurred after CRF whereas "intermediate" ACTH rose after AVP. The rise in plasma levels of different molecular forms of ACTH after stimulation by CRF or AVP could suggest that the biological pathway of ACTH synthesis, storage and release may occur in different intracellular pools or rather in different pituitary cells. Intermediate ACTH stimulated adrenal secretion of cortisol as soon as the first day of postnatal life and increased plasma aldosterone concentration in 7 and 20 day-old lambs. At these stages aldosterone level did not change after a rise in "little" ACTH.     

Impairment of renal compensatory hypertrophy by hypothyroidism in the rat

Renal compensatory hypertrophy (RCH) occurs in hypothyroid rate, but it is impaired when compared to RCH found in euthyroid controls. It is due to cellular hypertrophy as the DNA content does not change and the Protein/DNA ratio increases in the compensating kidney. RCH is enhanced by thyroxine (T4) with a rise in the DNA content of the compensating kidney, but the Protein/DNA ratio does not change indicating that hypertrophy is as important as hyperplasia. Corticotrophin (ACTH) given to eu and hypothyroid rats enhances RCH with an increase in the protein content of the compensating kidney without any change in its DNA content. In the hyperthyroid rats, the enhanced RCH is not further increased by ACTH and the rise in the kidney DNA content elicited by T4 is suppressed by ACTH. The Protein/DNA ratio is increased by ACTH in hypo, eu and hyperthyroid rats. The renotrophic action of ACTH is due to hyperadrenocorticism: it is related to an increased plasma testosterone level and to a disturbed Na+, K+ and glucose metabolism.     

Hormonal regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in the rat adrenal gland

We studied the effect of ACTH on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase enzyme. Reductase activity and reductase mass were enhanced by 22- and 6.2-fold respectively in one series of experiments, whereas in another the levels of reductase activity, reductase mass, and reductase mRNA were increased 6.6-, 3.6- and 2.2-fold respectively, following daily administration of exogenous ACTH for 3 days. Daily injection of 4-aminopyrazolopyrimidine (4-APP) to rats for 3 days increased circulating ACTH level 5.4-fold, whereas adrenal HMG-CoA reductase activity, reductase mass and reductase mRNA levels were greatly increased 36-, 10- and 16-fold, respectively. To counteract the effect of elevated plasma ACTH, dexamethasone acetate (Dex) was administered to 4-APP treated rats. At 3 h post Dex administration, plasma ACTH and corticosteroids levels were effectively decreased by 58 and 59%, respectively. The levels of adrenal HMG-CoA reductase mRNA, reductase activity and reductase mass were also diminished by 38, 31 and 40%, respectively. Our results show that rat adrenal HMG-CoA reductase can respond rapidly to hormonal changes, presumably through variations in circulating ACTH levels.     

Adrenocortical responses to adrenocorticotrophin in the rat

The time course of plasma adrenocorticotrophin (ACTH), adrenal cyclic AMP, adrenal corticosterone, and plasma corticosterone was measured in male Sprague-Dawley rats whose endogenous release of ACTH had been blocked (1) following rapid injections of 100 and 300 ng ACTH/100 g body weight, i.v., (2) during prolonged infusions at rates of 1, 2, and 4 ng ACTH/min per 100 g body weight, and (3) after termination of 30-min infusions at rates extending from 0.06 to 8 ng ACTH/min per 100 g body weight. Following injections, the time course of the variables is similar to the one simulated from our models of adrenal cortical secretion, including the simulation of an intermediate variable of our models of the adrenal cortex cell which was presumed to correspond to cyclic AMP. However, during prolonged infusions there is an unexpected overshoot of adrenal cyclic AMP content whereas adrenal and plasma corticosterone concentrations rise to a steady-state value without overshoot. The total amount of cyclic AMP gradually increases following the three increasing infusion rates of ACTH whereas similar levels of plasma corticosterone concentrations are reached at steady state; therefore the saturation of the adrenal cortical secretion is due to a step ulterior to cyclic AMP formation in the steroidogenesis. After 30-min infusions, plasma corticosterone concentration reaches its maximal value following a rate of ACTH input which evokes only a 4-fold increase in adrenal cyclic AMP content; however, there is a 250-fold increase of adrenal cyclic AMP with respect to control value following the higher rates of infusion of ACTH.     

Effect of the growth hormone-secreting tumor StW5 on pituitary and adrenal gland function in rats

A growth hormone-secreting tumor (StW5 was implanted into male rats and resulted in a tripling of adrenal weight concomitant with a 30% decrement in pituitary weight. Plasma concentrations of corticosterone in tumor-bearing (TB) rats were significantly elevated at rest or after ACTH injections or the stress of either anesthesia. The rise in plasma concentrations of corticosterone was due mainly to the large increment in adrenal size although a significant increase in adrenal responsiveness to ACTH was demonstrated in vitro. In addition, plasma corticosterone concentrations were higher in TB rats despite both a doubling of the blood volume and a 50% increase in liver capacity to metabolize corticosterone. Pituitary ACTH content was significantly lower in TB rats, but these pituitary glands could still release near-normal quantities of ACTH as shown both by in vitro incubations and adrenal corticosterone output following ether stress.     

Pituitary and adrenal responses to ovine corticotropin releasing factor and vasopressin injected into young and adult guinea-pigs

Comparison of effects of synthetic ovine corticotropin releasing factor (oCRF), Arginine-Vasopressin (AVP) and the combination of both peptides have been tried in adult and 7-days-old guinea-pigs. On plasmas collected 15 min after interscapulary injection, cortisol, aldosterone and ACTH were measured. The different circulating forms of ACTH were isolated by Sephadex G50 column chromatography, with 1% formic acid and measured by radioimmunoassay. Thus, in the guinea-pig plasma, we detected three immunoreactive forms of ACTH: a "big" molecular form (Mr greater than 20000), an "intermediate" (Mr = 9500) and a "little" ACTH form (Mr = 4500) which was eluted in the same fractions as human 1-39 ACTH. In adult guinea-pigs, CRF increased total ACTH and the "intermediate" form and also plasma cortisol concentrations whereas AVP remained without significant effect excepted a rise in cortisol levels. Injected together, CRF and AVP enhanced plasma concentrations of total ACTH, of the three circulating forms and of cortisol. In 7-days-old guinea-pigs, both CRF and AVP increased plasma concentrations of total, of "intermediate" ACTH and of cortisol and aldosterone whereas the combination of both peptides enhanced dramatically plasma concentration of total ACTH suggesting a magnifying effect of AVP on CRF activity still more efficient in young than in adult guinea-pigs.     

Increased expression of corticotropin-releasing factor receptor mRNA in the locus coeruleus of stress-induced rat model of depression

Hypersecretion of corticotropin-releasing factor (CRF) has been hypothesized to occur in depression. To investigate CRF receptor (CRFR) response to the increased production of CRF in chronically stressed rats, we measured by in situ hybridization the expression of CRFR mRNA in the locus coeruleus (LC) concomitant with measuring plasma adrenocorticotropin (ACTH). The expression of both CRFR mRNA in the LC and the plasma level of ACTH increased significantly in "depression-model rats" which exhibit reduced activity following exposure to 14 days forced walking stress (FWS), but not in "spontaneous recovery rats" whose activity was restored after the long-term stress. These results suggest that the LC neurons continue to be stimulated by CRF, and that the hypothalamic-pituitary-adrenal (HPA) axis is hyperfunctioning in the depression-model rats.     

Effect of corticotropin and hydrocortisone on carbohydrate metabolism in skeletal muscles

The intraperitoneal administration of corticotropin (ACTH) in the rate of 1 and 2 units per 100 g of body weight and that of hydrocortisone in the rate of 1 mg and 5 mg per 100 g body weight were studied for their effects on carbohydrate metabolism rate in musculus gastrocnemius as well as on the level of 11-oxycorticosteroids in blood plasma of rats. The glycogen level in muscles was found to rise 3 hours after ACTH and hydrocortisone administration and it correlated with the hydrocortisone level increase in blood plasma (r = 0.714 and 0.863, respectively); the activity of pyruvate kinase decreased. Simultaneously ACTH did not change while hydrocortisone lowered the phosphorylase activity and the content of both fructose-6-phosphate and lactate.     

Function of hypothalamic-pituitary-adrenocortical system in hypertensive rats of ISIAH strain

Functional activity of hypothalamic-pituitary-adrenocortical axis has been studied under control and restraint stress conditions in rats with inherited stress-sensitive arterial hypertension (ISIAH strain) and in normotensive WAG (Wistar Albino Glaxo) strain. The levels of hypothalamic CRH-mRNA (in control and 2 hrs stress), pituitary and plasma ACTH and plasma corticosterone (in control and after 5, 15 or 30 min of restraint stress), were evaluated. Hypothalamic CRH-mRNA level was found to be approximately the same in the control rats of both strains. In control conditions, the pituitary and plasma ACTH content in ISIAH rats was significantly lower whereas the corticosterone level in the plasma differed from each other in both strain. The restraint stress resulted in a statistically significant increase of the CRH-mRNA in ISIAH rats and not in the WAG rats. Moreover, in spite of the lower ACTH level in stressed ISIAH rats, the corticosterone blood plasma concentration in hypetensive rats was significantly higher. The data obtained confirm the idea that the stress-dependent hypertension might be related to an enhanced sensitivity of the main endocrine links involved in the stress response organization.     

Suppressive effect of pentagastrin on pituitary-adrenocortical secretion.

The effect of pentagastrin on the pituitary-adrenocortical secretion was examined in male rats. In the morning the intraperitoneal injection of this peptide produced a slight, but significant, decrease in the plasma corticosterone levels, but it had no effect on the evening rise due to circadian periodicity and the stress-induced elevation of the plasma corticosterone level. Following intracerebroventricular administration of pentagastrin, plasma corticosterone tended to decrease and in in vitro incubation of rat pituitary tissue the addition of pentagastrin elicited a suppressive effect on the ACTH release from the tissue into the medium. It was suggested that gastrin-like peptide might control the secretion of ACTH.     

Vasopressin pressor receptor-mediated activation of HPA axis by acute ethanol stress in rats

The plasma arginine vasopressin (AVP), ACTH, and corticosterone levels and the hypothalamic corticotropin-releasing hormone (CRH) content were measured after oral administration of 1 ml of 75% ethanol to rats, a model known to induce acute gastric erosions and stress. Elevated plasma AVP, ACTH, and corticosterone levels were detected 1 h after ethanol administration. Treatment with the vasopressin pressor (V(1)) receptor antagonist [d(CH(2))(5)Tyr(Me)-AVP] before ethanol administration significantly reduced the ACTH and corticosterone level increases. A higher hypothalamic CRH content was measured at 30 or 60 min after ethanol administration. V(1) receptor antagonist injection, 5 min before ethanol administration, inhibited the rise in hypothalamic CRH content. The protein synthesis blocker cycloheximide prevented the hypothalamic CRH content elevation after stress. The AVP-, CRH-, and AVP + CRH-induced in vitro ACTH release in normal anterior pituitary tissue cultures was also prevented by pretreatment with the V(1) receptor antagonist. The results support the hypothesis that stress-induced AVP may not only act directly on the ACTH producing anterior pituitary cells but also indirectly at the hypothalamic level via the synthesis and release of CRH.     

Evaluation of the inhibitory effect of circulating corticosteroids on circadian stimulated and stress induced secretion of ACTH in rats

Male rats were bilaterally adrenalectomized in order to measure the extent of inhibition exerted by endogenous corticosteroids on both basal ACTH secretion along its circadian rhythm and ether-stress induced ACTH secretion. In intact controls, plasma ACTH levels at the circadian maximum exceeded by 4 times the circadian minimum, and ACTH response 15 min after ether-stress surpassed the circadian minimum by 20 times. In adrenalectomized rats, the daily minimum was 8 times that of the controls. Nevertheless the circadian maximum was 3 times above the rhythm's minimum, while the maximal stress response (15 min) surpassed the circadian minimum by 8 times. In adrenalectomized rats supplemented with a solid source of corticosterone inducing a stable plasma corticosterone level equivalent to the controls' circadian minimum (3 micrograms/100 ml), the ACTH rhythm still fluctuated twice as high as in intact controls. The tonic feed-back inhibition exerted by endogenous corticosteroids on ACTH secretion appeared thus significantly stronger than the GABAergic inhibition to the corticotropic system which was previously studied under similar standard conditions.     

Two-site immunoradiometric assay for adrenocorticotrophin: a cautionary study about the reactivity to its precursor molecules

The specificity of a "two-site" immunoradiometric assay (IRMA) has been reevaluated by examining its ability to detect heterogeneous adrenocorticotrophin-like immunoreactivity (ACTH-LI) separated by gel column chromatography. Plasma samples from patients with Addison's disease, Nelson's syndrome and ectopic ACTH syndrome and tissue extract of human anterior pituitary were subjected to ACTH-IRMA and the levels of ACTH-LI were compared with those measured by conventional ACTH-radioimmunoassay (RIA). The level of ACTH-LI measured by IRMA was considerably lower than that measured by RIA in the plasma of a case of ectopic ACTH syndrome and the ACTH-LI did not show a dilution curve parallel with that of the standard. Gel exclusion chromatography revealed that the plasma contained a relatively large quantity of "big ACTH" which was found to be poorly detected by the IRMA. In the plasma of Addison's disease or the extract of pituitary gland in which "big ACTH" constituted a small portion, whole ACTH-LI was apparently diluted in parallel with the ACTH standard, although the "big ACTH" also did not show full parallelism with the ACTH standard in the IRMA. These data suggest that "big ACTH" derived not only from an ectopic ACTH-producing tumour but also from a normal human pituitary gland cannot be detected as well as authentic ACTH by the ACTH-IRMA system. Therefore, samples which contain a relatively large proportion of "big ACTH" in the total ACTH-LI should be carefully evaluated by ACTH-IRMA.     

2-Amino-7-Phosphonoheptanoic Acid Inhibits Insulin-Induced Convulsions and Striatal Aspartate Accumulation in Rats with Frontal Cortical Ablation

Pretreatment of rats with the excitatory amino acid antagonist 2-amino-7-phosphonoheptanoic acid (2-APH; 0.5 mmol/kg, i.p.) protected against insulin-induced clonic seizures. Complete protection was observed in 38% of the rats and partial protection in an additional 50%. Lesioning of the corticostriatal pathway by frontal cortical ablation caused decreases in the striatal levels of aspartate (-28%) and glutamate (-18%), an increase in striatal glutamine level (45%), and decreased high-affinity uptake of D-[3H]aspartate (-27%) in the lesioned dorsal neostriatum. Insulin-induced hypoglycemia caused a predicted sharp increase in aspartate level (165%) and decreased glutamate (-20%) and glutamine (-38%) levels in the intact striatum. Pretreatment of rats with 2-APH significantly reversed the insulin-induced changes in striatal aspartate, glutamate, and glutamine levels, especially in the intact hemisphere. In normoglycemic control rats, the "metabolic," i.e., concentration in the lesioned hemisphere, aspartate pool constituted 72% and the "synaptic," i.e., the concentration difference between the intact and lesioned hemispheres, 28% of the total striatal aspartate pool. 2-APH had no effect on the level of "metabolic" aspartate in the striata of normoglycemic rats but caused an almost complete suppression of "synaptic" aspartate. Following insulin-induced hypoglycemia, the "metabolic" aspartate pool doubled, whereas the "synaptic" aspartate pool increased 3.5-fold in the absence of 2-APH. The insulin-induced rise in "synaptic" aspartate level was almost completely blocked by 2-APH (a 5% rise instead of a 3.5-fold rise).(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuroendocrine and immunological mechanisms in stress-induced immunomodulation

Here, we report that emotional stressors (restraint, footshock) can affect humoral immune responses as well as the capacity of immune and accessory cells to secrete interleukins. Acute restraint stress (5 min) caused a 4- to 6-fold enhancement of splenic antibody responses to sheep red blood cells. In an attempt to study endocrine mechanisms, we administered antibodies raised in rats to corticotropin releasing factor (CRF). Intravenous administration of these antibodies prior to stress-exposure and immunization prevented the stress-induced increase in the humoral response. In a parallel experiment, we observed that CRF-immunoneutralization prevented the restraint stress-induced increase in plasma ACTH concentrations, but was without effect on plasma prolactin, melanocyte stimulating hormone, adrenaline and noradrenaline responses. These data suggest the presence of an indirect pathway involving ACTH and related peptides by which CRF controls humoral responses to stress. A pathway involving a direct mechanism of CRF at the level of the immune cells will be discussed. In a set of other experiments, we addressed the question of whether interleukin-1 and interleukin-6 plasma levels induced by injection of endotoxin could be modulated by emotional stress. Exposure to prolonged footshock stress (20 min) prior to endotoxin injection resulted in a blunted plasma ACTH and interleukin-1 response, without affecting the endotoxin-induced plasma interleukin-6 respose. These data suggest that at least one level at which emotional stress may influence immune function is by changing the capacity of immune cells to produce and/or secrete immune regulatory interleukins.     

Effect of hydrocortisone on ACTH, growth hormone, insulin and glucose in the blood of bilaterally adrenalectomized patients

This study is aimed at elucidating the mechanism of paradoxical rise in plasma ACTH levels in response to glucocorticoids, observed by several authors in bilaterally adrenalectomized patients with Cushing's disease. Six control subjects and fourteen patients bilaterally adrenalectomized for Cushing's disease were given a dose of 200 mg hydrocortisone sodium succinate by 3-5 mm i.v. injection. Plasma ACTH (in 6 patients), serum cortisol, growth hormone (GH) and insulin and blood glucose levels were estimated at 0, 30, 60, 90, and 120 minutes. The administration of hydrocortisone significantly suppressed plasma ACTH levels only at 60 min. In one case a slight rise in ACTH level during the test was observed. A significant fall in blood glucose levels was found only in the adrenalectomized patients. No significant changes in serum insulin and GH levels were noted. The possible mechanisms are discussed, especially the potential role of transient glucose deficiency in the pathophysiology of plasma ACTH increase in response to hydrocortisone in the bilaterally adrenalectomized patients.