Reduced response of the hypothalamo-pituitary-adrenal axis to alpha1-agonist stimulation during lactation

To determine whether altered noradrenergic activation of the hypothalamo-pituitary-adrenal (HPA) axis contributes to the attenuated neuroendocrine response to stress observed during lactation, the effect of intracerebroventricular injection of the alpha1-agonist methoxamine (100 microg) was compared between virgin and lactating rats. Virgin rats showed significant increases in plasma corticosterone after methoxamine, reaching 317 +/- 44 ng/ml at 10 min and remaining significantly elevated for more than 120 min, but lactating rats showed no significant increase in corticosterone levels. Furthermore, methoxamine induced an increase in paraventricular nucleus (PVN) CRF messenger RNA expression in virgin, but not lactating, animals. Both groups of rats exhibited comparable elevations in plasma PRL after methoxamine treatment. Arginine vasopressin messenger RNA expression within the parvocellular PVN was greater in the lactating animals than in the virgin controls, but methoxamine injection was without further effect. Studies performed on ovariectomized virgin rats and ovariectomized rats receiving estradiol or progesterone replacement failed to reproduce the attenuated HPA responses seen after methoxamine treatment, although methoxamine-induced PRL levels were greatly increased by estradiol, probably arising from an effect on hormone synthesis. In vitro electrophysiological recordings of PVN neurons in hypothalamic slices from proestrous virgin and lactating rats showed that 45-52% of neurons in both groups exhibited excitatory responses to 10(-4) M methoxamine, but there was a differential response to 10(-5) M methoxamine, with PVN neurons from lactating animals failing to show a response. These data show a selective down-regulation of alpha1-mediated activation of the HPA axis in lactating animals. This may contribute to the attenuated stress-induced activation of the HPA axis during lactation.     

Pulsatile release of somatotropin related to meal feeding and somatotropin response to secretagogues in horses

Our goal was to establish a time of day and(or) interval from feeding that would avoid the refractory period after a somatotropin (ST) surge and optimize the responsiveness of horses to ST secretagogues. Two experiments were conducted with eight geldings conditioned to consume grain at 0800 and 1600 daily. In Exp. 1, during a 24-h period, these geldings averaged 3.2 +/- .3 pulses of ST with peak amplitude of 4.2 +/- .4 ng/mL, pulse duration of 55 +/- 6 min, and interpeak interval of 400 +/- 57 min. No ST peaks occurred within 2 h after either grain feeding. In Exp. 2, eight geldings were given 50 micrograms of ST-releasing factor (STRF) at 0800. Two geldings that had a pulse of ST between 0700 and 0800 failed to respond to STRF, but the other six responded with a pulse of ST at 37 +/- 3 min; peak amplitude was 4.6 +/- 2.2 ng/mL and duration was 123 +/- 25 min. Experiments 3 and 4 were with mares aged 20 to 26 yr and conditioned to be fed grain at 0800 daily. In Exp. 3, blood was sampled for 8 h beginning at 0500. Seven of the eight mares had a ST pulse in progress at 0500. Five additional pulses were detected, all from 0740 to 0940, but none from 0600 to 0700 or from 1000 to 1300. In Exp. 4, four of the same eight mares were given 50 micrograms of STRF at 0700 and the other four at 1300. Three of the four treated at 0700 and all four treated at 1300 responded to STRF with ST peaks at 20 +/- 5 min; peak amplitude was 12.7 +/- 9.5 ng/mL and duration was 69 +/- 6 min. In Exp. 5, nine mares aged 20 to 26 yr were fed grain at 0800 and 1600 as in Exp. 1 and 2 and given a nonpeptidal ST secretagogue (STS, Merck L-163,255) i.v. at 0, 1, or 5 mg/kg (n = 3 mares/dose) at 1300. No mare had a pulse of ST during the 1 h before treatment. All six mares given STS responded with ST pulses. The ST responses to STS at 1 and 5 mg/kg did not differ (P > .05); time to ST peak was 35 +/- 4 min, pulse amplitude was 24.0 +/- 6.3 ng/mL, and pulse duration was 100 +/- 9 min. We conclude that mares and geldings fed grain once or twice daily usually have a period of 2 to 5 h after feeding with no ST pulses. When horses are fed grain at 0800, one may give a ST secretagogue at 1300 to avoid a refractory period and improve the probability of an ST response.     

Endocrine and behavioural responses to noise stress: comparison of virgin and lactating female rats during non-disrupted maternal activity

The behavioural and endocrine responses to a 10 min white noise stress have been characterized in female virgin and undisturbed lactating Sprague-Dawley rats. Animals were continuously video-taped and frequent blood samples were collected using an automated sampling system. Noise stress caused hypothalamo-pituitary-adrenal (HPA) activation, as indicated by a rapid increase in plasma corticosterone and ACTH in the virgins: corticosterone concentrations peaked 20 min after initiation of the stress before declining rapidly back to basal concentrations. In contrast, noise stress had no significant effect on either plasma corticosterone or ACTH concentrations in the lactating animals. However, 72 h after weaning the corticosterone response of the ex-lactating rats was of comparable magnitude, but longer duration to that seen in the virgins. Plasma prolactin concentrations were significantly higher in the lactating animals and declined in response to the noise whereas, a transient but reproducible increase was seen in the virgin group. In situ hybridization revealed a significantly lower basal expression of CRF mRNA in the paraventricular nucleus of lactating rats as compared to the virgins, but noise stress had no further effect. Virgin animals showed behavioural responses to the stress, including an increase in the total activity, exploratory behaviours (rearing) and displacement behaviours (grooming). Lactating animals also showed behavioural responses to the noise, but their activities were principally directed towards the pups. These data show that although lactating rats showed normal behavioural reactivity to a psychological stress they showed no statistically significant activation of the HPA axis, suggesting a dissociation of behavioural and neuroendocrine responses to this mild stress.     

Hypothalamic-pituitary-adrenal axis activity in the inbred Brown Norway and Fischer 344 rat strains

We have examined the basal and the stress-induced secretion of corticosterone in relation to the expression of adrenal steroid receptors in the pituitary, hypothalamus and hippocampus of the inbred Brown Norway and Fischer 344 rat strains. Our data indicated that plasma transcortin and integrated plasma corticosterone levels were significantly higher in Fischer 344 compared to Brown Norway rats. Fischer 344 hypersecrete corticosterone during the dark phase of the diurnal cycle and during the phase of recovery following a 20 min period of restraint stress compared to Brown Norway rats. This hypersecretion of corticosterone was negatively correlated with the size of the adrenal gland but might be related to the higher density of mineralocorticoid receptors in the hippocampus of Fischer 344 rats.     

Effect of repeated immobilization on serotonin metabolism in different rat brain areas and on serum corticosterone

The effect of daily repeated 10 min immobilization on the serotoninergic neurotransmission and serum corticosterone levels was studied. Male Lewis rats were immobilized for a 10 min period daily once or on 5 consecutive days. Serotoninergic neurotransmission was followed using differential in vivo pulse voltammetry with carbon fibre electrodes measuring extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels. Recordings were performed in brain areas involved in the control of behaviour, mood, and stress response such as the frontal cortex, the hippocampal CA-3 and dentate gyrus, the striatum, and the raphe nuclei dorsalis (NRD) and medialis (MRN). The first immobilization resulted in an increase of the extracellular 5-HIAA levels in all areas under study, except the striatum where no reaction was observed. The major effect was recorded in the frontal cortex, showing an increase of about 400% as compared to control, which lasted for 3h after the end of the immobilization period. Beginning on day 2 in all areas, except the striatum, a consecutive habituation to the stressor seemed to occur, since the stress-induced increase in the voltammetric signal was found to be reduced after consecutive immobilization. Serum corticosterone levels were measured directly after a single and after 5 daily immobilization periods. After single immobilization the serum corticosterone level was found to be about 270 ng/ml. After the 5th immobilization about 300 ng/ml were detected. These differences were not found to be significant. In summary, our data indicate that the serotonin metabolism shows habituation in nearly all brain areas after repeated immobilization, though the corticosterone level at the end of the immobilization period was comparable after single and repeated immobilization.     

Pulsatile release of LH and secretion of ovarian steroids in sheep during the luteal phase of the estrous cycle

The concentration of LH and progesterone in jugular venous plasma and the secretion of steroids by the ovary were measured every 10 minutes for 2 hours on days 12, 14, and 16 of the estrous cycle in 5 ewes with utero-ovarian autotransplants. A pulse of LH occurred about once every 2 hours, when the concentration rose from a basal level of 0.57 +/- 0.08 ng/ml to a peak of 2.97 +/- 0.57 ng/ml. Within 5 minutes of the pulse of LH, the secretion of estradiol (an exclusive product of the follicle) rose rapidly from a basal level of 0.75 +/- 0.12 ng/min to reach a peak value of 2.16 +/- 0.33 ng/min in about 30 minutes. In contrast, the secretion of progesterone from the corpus luteum, and the concentration of progesterone in the peripheral plasma changed very little following the pulse of LH. The secretion of androstenedione, which arises from the follicle and corpus luteum, increased from 3.03 +/-0.75 ng/min to 7.85 +/- 1.78 ng/min by 30 minutes after the pulse of LH. These findings indicate that the follicle, and possibly the stroma, respond rapidly to episodic fluctuations in the concentration of LH and are probably involved in the negative feedback loop between the ovary and the hypothalamic pituitary system. The fluctuations in the secretion of progesterone from the corpus luteum, on the other hand, are unrelated to pulses of LH.     

Effect of feed restriction and season on LH and prolactin secretion, adrenal response, insulin and FFA in group housed pregnant gilts

A trial was designed to determine the effect of season and feed restriction on LH and prolactin secretion, adrenal response, insulin and FFA in the early pregnant gilt. Groups of cross bred gilts (n = 24) were mated and allocated to two feeding levels; a non-restricted group received close to ad libitum feeding of 3.6 kg whereas, the restricted group received 1.8 kg as recommended by the NRC. The trial was carried out in winter-spring and repeated in summer-autumn to investigate the effects of season. The feeding regimen were fed to the group housed animals for the first two weeks of pregnancy. A 12 h period of blood sampling every 15 min thereafter revealed higher amplitude LH pulses with larger area under the curve in winter compared with summer (1.17 +/- 0.03 vs. 0.69 +/- 0.03 ng ml(-1) and 65.09 +/- 1.46 vs. 33.60 +/- 1.25, P < 0.05). Overall, feed restriction reduced LH pulse frequency (2.5 +/- 0.1 and 1.6 +/- 0.1 pulses/12 h for high and low feeding levels, P < 0.05), but the difference was large in winter and no difference was detected in summer. An ACTH challenge test carried out the day after the frequent sampling revealed greater response to the ACTH challenge in winter in comparison with summer. Plasma prolactin values were generally very low and ranged from 1 to 4.5 ng/ml with highest values detected in the feed restricted group in summer. Plasma FFA and insulin concentrations showed greater pre- versus post-prandial variation in the feed restricted groups. It was concluded, that feed restriction and season affected LH secretion and those effects appeared to be related to the metabolic changes in the early pregnant group housed gilt.     

Effect of corticotropin releasing hormone on the pituitary-adrenocortical activity under basal and social stress conditions

The effect of social crowding stress on the CRH-induced hypothalamic-pituitary-adrenocortical (HPA) responsiveness was assessed in rats crowded for 3 days, when the HPA response to neurotransmitter receptors stimulation was powerfully reduced. CRH given systemically dose-dependently increased the secretion of corticosterone. The increase was not affected by pretreatment with prazosin or propranolol, an alpha 1- or beta-adrenergic receptor antagonist, indicating the lack of involvement of adrenergic receptors in that stimulation. In the corticosterone response to CRH administered icv, a moderate involvement of hypothalamic alpha 1-adrenergic receptors and neuronal noradrenaline seems possible. The corticosterone responses to CRH given by either route to rats exposed to social crowding stress were identical with the responses of unstressed controls. Our results for the first have time shown that social crowding stress does not impair the HPA responsiveness to CRH stimulation.     

Hypoxia effects on hypothalamic corticotropin-releasing hormone and anterior pituitary cAMP

AIM: To study the effects of acute and chronic hypoxia on hypothalamus-anterior pituitary-adrenocortex axis. METHODS: Rats and pikas were exposed to different altitude and periods. Animals were injected with CRH, Arg and NE in the third ventricle of the brain of rats. RESULTS: Anterior pituitary cAMP and plasma corticosterone levels of rats obviously increased during 1 h of hypoxia. cAMP was increased from 2.23 +/- 0.13 of control group to 7.7 +/- 0.7 of 5 km and 13.4 +/- 1.9 nmol/g wet tissue of 8 km, respectively. i.c.v. CRH, Arg and NE all activated HPA axis. The effects of CRH were most potent. CRH 2 microL 0.75 nmol i.c.v increased anterior pituitary of cAMP from 3.5 +/- 0.4 of control to 22.4 +/- 2.2 nmol/kg wet tissue. Stimulating altitude of 5000 m resulted in a 16.9% decrease in corticosterone level (P < 0.05), 8000 m resulted in a 47.5% decrease (P < 0.01) after hypoxia for 25 d. Hypoxia did not activate HPA axis in pikas. CONCLUTION: 1) Hypoxia stress activates the secretion of corticotrophin (ACTH) via cAMP; 2) Adrenocotical function of rats decays during chronic hypoxia; 3) Arg and NE regulate the secretion of plasma corticosterone and synthesis of pituitary cAMP at the hypothalamus level; 4) Hypoxia tolerance of the pika was high.     

Induction of macrophage migration inhibitory factor messenger ribonucleic acid in rat forebrain by reperfusion

To evaluate the impact of uremia and associated caloric restriction on physiologically pulsatile growth hormone (GH) release, we used deconvolution analysis of spontaneous plasma GH profiles in 5/6-nephrectomized male rats (NX, N = 9). Three different normal renal function sham-operated groups were used: rats fed a normal diet ad libitum (SAL, N = 9); NX pair-fed rats (SPF, N = 6); NX rats pair-fed for protein ingestion but calorically supplemented up to the energy intake of SAL (SPF+, N = 8). Severe renal failure was confirmed by much higher (P < 0.001) BUN in NX than sham groups. NX rats were growth retarded as shown by reduced (P < 0.01) weight and length gains as compared with sham animals. Deconvolution analysis (mean +/- SEM) of plasma samples obtained every 10 minutes over 6 hours, and 14 to 16 days after second stage nephrectomy showed that NX rats had a longer GH t(1/2) (17.0 +/- 1.8 vs. 11.6 +/- 0.8 min), less GH mass secreted per burst (48 +/- 15 vs. 95 +/- 16 ng/ml/pulse), lower secretory pulse amplitude (1.9 +/- 0.5 vs. 5.8 +/- 0.9 ng/ml/min), and a reduced total GH secretion (240 +/- 69 vs. 400 +/- 56 ng/ml/6 hr) than SAL rats. Corresponding data were not significantly different between NX and SPF, or between SAL and SPF+ groups. In summary, stunted rats with chronic renal failure exhibit a prolonged GH t(1/2) and suppression of GH secretory pattern burst mass. Control data from rats with normal renal function suggest that the amplitude-specific depression of GH secretion may be attributed, at least in part, to chronic renal failure-associated calorie deficiency.     

Analysis of pulsatile secretion of thyrotropin and growth hormone in the hypothyroid rat

To characterize the role of TRH in the generation of TSH pulsatility as well as the effect of hypothyroidism on episodic GH secretion, blood was constantly withdrawn (30-60 microliters/min) from rats treated with 0.02% methimazole in the drinking water for 8-10 days. This treatment significantly reduced circulating levels of both T3 and T4 and elevated plasma TSH; however, since thyroid hormone titers were still detectable (T3, 39.6 +/- 5.3 vs. 89.8 +/- 5.3 ng/dl in euthyroid animals), methimazole-treated rats were referred to as being mildly hypothyroid. TSH was found to be secreted in secretory bursts, consisting of one to several peaks in these rats. Pulsar analysis of TSH secretory profiles revealed a mean pulse frequency of 2.8 pulses/h, a mean pulse amplitude of 10 ng/pulse, and a mean pulse duration of 0.2 h. Euthyroid rats exhibited similar fluctuations of circulating TSH levels; however, due to the variability of the TSH RIA in the range of euthyroid TSH titers, no significant pulsatility was detected by Pulsar. Mean plasma TSH levels in eu- and hypothyroid rats were 2.3 +/- 0.3 and 14.6 +/- 1.8 ng/ml, respectively. To confirm that the TRH antiserum (TRH-AS) used in the present study for passive immunization had sufficient binding capacity to absorb endogenous TRH release, euthyroid rats were pretreated with either normal rabbit serum or TRH-AS, followed by the injection of clonidine (100 micrograms/kg BW, iv). This alpha 2-adrenergic agonist caused a significant (P < 0.01) 12.7-fold rise in plasma TSH levels in normal rabbit serum-treated animals, which was completely abolished by TRH-AS pretreatment, indicating that clonidine stimulates TSH secretion via activation of hypothalamic TRH release. When TRH-AS was slowly infused into hypothyroid rats that were sampled frequently for the detection of TSH pulsatility, it caused a significant (60.3%; P < 0.01) decrease in mean TSH levels, with TSH titers approaching euthyroid concentrations 1 h after the infusion of TRH-AS. The antiserum treatment also caused the disappearance of statistically significant (Pulsar) TSH secretory pulses. Mild hypothyroidism shifted the GH secretory profiles from a low frequency, high amplitude in euthyroid animals to a high frequency, low amplitude pattern in hypothyroid rats. Mean GH levels in hypothyroid rats were 76% lower than those in euthyroid controls. These findings show that TSH is secreted in a pulsatile fashion in the hypothyroid rat and that TRH is predominantly responsible for the generation of TSH pulsatility.(ABSTRACT TRUNCATED AT 400 WORDS)     

Expression of leukocyte integrins and tissue factor in mononuclear phagocytes

Histocompatible Fischer 344 and Lewis rats have been shown to differ on a wide variety of behavioral, chemical, and molecular measures. This investigation aimed to clarify strain differences in unconditioned motor behavior with respect to the amount and patterns of movements. Twenty female Fischer 344, Lewis, and Sprague-Dawley were tested in the Behavioral Pattern Monitor for 30 min. The locomotor activity and movement patterns, quantified by counts of photobeam breaks and the spatial scaling exponent, d, were assessed. The level of locomotor activity did not differ significantly between Fischer, Lewis, and Sprague-Dawley rats. In contrast, movement patterns differed significantly between the strains. Specifically, Sprague-Dawley rats exhibited significantly more straight movements than both Fischer and Lewis rats. Moreover, Lewis rats showed significantly more straight movements compared to Fischer rats during the first 10 min in the enclosures. Differences in movement patterns across strains may provide an important behavioral variable to further explore the genetic and developmental aspects of behavior.     

Characterization of phenytoin-resistant kindled rats, a new model of drug-resistant partial epilepsy: comparison of inbred strains

PURPOSE: Previous work from our laboratory showed that amygdala-kindled Wistar outbred rats can be selected according to the increase of afterdischarge threshold (ADT) after phenytoin application. Animals that consistently do not respond to phenytoin (PHT) with an ADT increase (non-responders) are the first animal model of pharmacoresistant complex partial seizures. In this study, we determined the ability to respond to PHT in male kindled rats of different inbred strains. METHODS: The experiments were performed in fully kindled rats of five different inbred strains, Wistar-Kyoto, Lewis, Fischer 344, ACI, and Brown Norway. The response type of each rat was revealed by four consecutive PHT applications (75 mg/kg, i.p.) in fully kindled rats. RESULTS: PHT application resulted in plasma concentrations ranging from some 16 microg/ml in Lewis rats to 35 microg/ml in Fischer 344 rats, and in slight ataxia, most strongly in Fischer 344 rats. The rats of each strain did not show a homogeneous response to PHT. A significant increase of ADT was found after 86-97% of applications in Lewis, Wistar-Kyoto, and Fischer 344 rats. In contrast, Brown Norway rats responded in only 34% of experiments. This led to a considerable number of responders (i.e., consistent ADT increase by >20%) in Fischer 344, Wistar-Kyoto, and Lewis rats. The only strain revealing nonresponders (i.e., consistent lack of ADT increase by >20% with PHT treatment) was Brown Norway. CONCLUSIONS: Inbred strains, although genetically more homogenous than outbred strains, differ in their response to PHT. Brown Norway rats can offer advantages for further detailed investigation of the resistance to PHT in the kindling model of complex partial seizures.     

Functional transplantation of the rat pituitary gland

OBJECTIVE: These studies evaluated the ability of transplanted pituitary cells to restore pituitary function in hypophysectomized rats. METHODS: The pituitary glands of neonatal Lewis rats were rapidly removed, enzymatically dispersed, and stereotactically introduced into the third ventricle of hypophysectomized adult male Lewis rats. Four weeks after implantation, plasma levels of anterior pituitary hormones in implanted animals were compared with those of sham-transplanted control animals. RESULTS: Plasma levels of prolactin, growth hormone, thyroid-stimulating hormone, and beta-endorphin were below the range of detection in 14 sham-operated animals. In implanted animals, restitution of serum prolactin occurred in 100% of the animals tested, with levels of 2.6 +/- 1.0 ng/ml (mean +/- standard error of the mean; normal, 2-4 ng/ml). Growth hormone was assayable in 71% of the animals, with a mean value of 29 +/- 13 ng/ml over all animals (normal, 1-100 ng/ml); thyroid-stimulating hormone was restored in 68%, with mean resting levels of 79 +/- 13 ng/ml (normal, 100-400 ng/ml); luteinizing hormone levels were found in 53%, with mean levels over all animals of 0.2 +/- 0.1 ng/ml (normal, 0.5-1.0 ng/ml); and beta-endorphin was restored in 45% to high resting levels of 163 +/- 31 pg/ml (normal, 20-30 pg/ml). A challenge with hypothalamic releasing factor and a cold stress test were performed on the animals that had received transplants. Positive hormone responses to both of these tests suggested sensitivity of the pituitary grafts to both endogenous and exogenous sources of stimulation. Histological sections of paraformaldehyde-fixed brains from implanted animals clearly demonstrated survival of clusters of grafted pituitary cells. Positive immunohistochemical staining for adrenocorticotropic hormone and thyroid-stimulating hormone was demonstrated in sections of the grafted tissue. CONCLUSION: These data suggest survival of neonatal pituitary transplants in the third ventricle of adult hypophysectomized rats with concomitant restoration of anterior pituitary hormone function.     

Effects of endothelin-1 on the rat pituitary-adrenocortical axis under basal and stressful conditions

Endothelins (ETs) and their receptor subtypes A and B (ETA and ETB) are expressed in the various components of the mammalian hypothalamo-pituitary-adrenal (HPA) axis, but their involvement in the functional regulation of HPA is controversial. To gain insight into this topic, we have investigated the effects of ET-1 and/or the specific antagonists of ETA and ETB receptors (BQ-123 and BQ-788, respectively) on the plasma concentrations of ACTH, corticosterone and aldosterone of non-stressed (control) and ether- or cold-stressed rats. The study of the effects of the administration of the two ET-receptor antagonists alone could provide informations about the possible action of endogenous ETs on the HPA axis. Exogenous ET-1 increased ACTH, corticosterone and aldosterone blood levels in control rats, as well as evoked a sizable enhancement of the HPA axis response to ether stress and a marked depression of the response to cold stress. BQ-123 and BQ-788 did not prevent the stimulatory effect of exogenous ET-1 in control rats, but when administered alone, raised the plasma concentrations of ACTH, corticosterone and aldosterone. Both ET-receptor antagonists magnified the HPA axis response to ether and cold stresses, but their effect was not counteracted by exogenous ET-1. Although very difficult to interpret, our present findings allow us to conclude that endogenous ETs play a role in the maintenance of the basal activity of rat HPA axis acting through ETA and ETB receptor subtypes, which are partially insensitive to BQ-123 and BQ-788. Conversely, the involvement of ETs in the modulation of the HPA axis responses to various stresses is very doubtful.     

Kinetics and quantitation of eosinophil and neutrophil recruitment to allergic lung inflammation in a brown Norway rat model

We quantitated neutrophil and eosinophil migration into lung parenchyma using specific peroxidase enzyme assays, and into the bronchoalveolar compartment by bronchoalveolar lavage (BALF), in sensitized brown Norway (BN), Fischer, and Lewis rats and also assessed the lungs by histopathology. Fourteen days after sensitization with ovalbumin (OA in alum [given subcutaneously] and OA with Bordetella pertussis [given intraperitoneally]), rats were challenged with an OA aerosol for 1 h. In BN rats, there was marked perivascular and peribronchial edema, focal hemorrhages, and increase in lung wet weight and BALF protein content, accompanied by neutrophilic infiltration at 3-14 h postchallenge. Few eosinophils were seen at 14 h in lung tissue or in BALF. Neutrophils peaked at 24 h in parenchyma ([94 +/- 7] x 10[6]) and in BALF ([2.7 +/- 0.4] x 10[6]) and declined rapidly thereafter. Marked eosinophil infiltration into parenchyma was apparent by 24 h. Eosinophil accumulation peaked at 48 h in parenchyma ([127 +/- 18] x 10[6]) and at 72 h in BALF ([10 +/- 2.4] x 10[6]), comprising up to 85% of lavage cells at this time. Lung eosinophilia persisted for at least 6 d with only a slow decline or clearance, not approximating baseline until day 13 after challenge. Histopathology showed peribronchial and interstitial eosinophilic pneumonia, most severe on day 3. In contrast to the BN rats, essentially no pulmonary inflammation was observed in Lewis and Fischer rats. This model in the BN rat, and the specific peroxidase assays for quantitating tissue eosinophils and neutrophils, should be useful for investigating the regulation of allergen-induced eosinophil and neutrophil migration into and clearance from the lung.     

Neuroendocrine changes in luteal function in patients with premenstrual syndrome

The present study evaluates the luteal progesterone (P) and LH secretions in 14 patients affected by premenstrual syndrome (PMS) and in 14 asymptomatic controls through the evaluation of their episodic release. PMS was prospectively confirmed in two consecutive menstrual cycles using Moos' Menstrual Distress Questionnaire. A pulsatility study was performed during the luteal phase. Blood samples were drawn every 10 min for 12 h, beginning at 0800 h. Statistically significant pulses were detected using the Detect program, and the degree of concordance of LH and P pulses was estimated. Similar mean 12-h P levels were found in controls (mean +/- SD, 13.9 +/- 9.3 nmol/L) and patients (14.2 +/- 10.1). LH levels were also similar in the two groups. Patients showed a higher P pulse frequency (13.4 +/- 1.8 vs. 11.4 +/- 2.3; P < 0.02) and a reduced amplitude of secretory episodes (126.5 +/- 61.6% vs. 187.1 +/- 126.7%; P < 0.03) than controls. Similarly, PMS patients showed pulsatile LH release of increased frequency and reduced amplitude than controls. A significant degree of concordance between LH and P pulses was observed in both groups, with a time lag of 0-10 min; that is, P secretory episodes follow LH with a delay of 0-10 min. These findings demonstrate that despite the fact that integrated P levels in PMS patients are similar to those in control subjects, the episodic secretion of the hormone is characterized by pulses of increased frequency and reduced amplitude. This phenomenon is temporally related to LH secretion, thus reinforcing the concept of PMS as a neuroendocrine disorder.     

Leukemia inhibitory factor modulates interleukin-1beta-induced activation of the hypothalamo-pituitary-adrenal axis

We have shown that leukemia inhibitory factor (LIF) is expressed in corticotroph cells and stimulates POMC gene expression and ACTH secretion in vivo and in vitro. We therefore examined the regulation of in vitro and in vivo pituitary LIF expression by cytokines known to stimulate the hypothalamo-pituitary-adrenal axis. In the corticotroph cell line AtT-20/D16v-F2, recombinant murine interleukin-1beta (IL-1beta; 0.1-10.0 ng/ml) caused a 5- to 10-fold increase in LIF messenger RNA (mRNA) levels. LIF mRNA expression was induced as early as 1 h, peaked at 2 h, and still persistently elevated above the baseline after 8 h. This effect of IL-1beta on LIF mRNA expression was abolished by preincubation with human IL-1 receptor antagonist (100 ng/ml) or antimurine IL-1beta antibody (10 microg/ml). Tumor necrosis factor-alpha (20 ng/ml) only modestly increased LIF mRNA, but was synergistic with IL-1beta (up to 2.5-fold). In contrast, IL-2 and IL-6 did not alter LIF mRNA. In C57BL/6 mice, i.p. injection of 100 ng IL-1beta increased plasma ACTH and corticosterone levels after 1 h (P < 0.02). In addition, pituitary LIF mRNA content was increased for up to 2 h in response to IL-1beta. In comparison to wild-type (+/+) B6D2F1 mice, LIF knockout mice with a deleted LIF gene (-/-) exhibited decreased plasma ACTH (631 +/- 61 vs. 376 +/- 50 pg/ml; P < 0.01) and corticosterone (783 +/- 85 vs. 433 +/- 51 ng/ml; P < 0.01) levels 1 h after i.p. IL-1beta administration. In conclusion, corticotroph LIF mRNA expression is specifically stimulated by IL-1beta and tumor necrosis factor-alpha. The attenuated hypothalamo-pituitary-adrenal response to IL-1beta in LIF knockout mice indicates that the effect of IL-1beta on ACTH secretion is modulated by LIF. Thus, LIF appears to function as an immune-neuroendocrine modulator signaling the hypothalamo-pituitary-adrenal axis.