Effect of Interleukin-1β on Plasma ACTH, β-Endorphin, and Corticosterone Levels in Infant and Prepubertal Rats

Abstract

IL-1P is known to enhance ACTH release from the anterior pituitary in the adult rat, mainly by simulating the hypothalamic ACTH-releasing hormone (CRH) release, but it seems to have a direct effect on the pituitary and on the adrenal hormone secretion, too. The effect of IL-1P on the P-endorphin (PE) secretion from the intermediate lobe is less well studied. There is very little information on the effect of IL-1P on the hypothalamic-pituitaryadrenal axis (HPAA) in the postnatal rat, which is a special period, because the reactivity of the HPAA is blunted. The effect of IL-1P in this period seemed to be of special interest, because neither the immune nor the endocrine system is fully developed.In the present study we tested the 30-and 120-min effect of intraperitoneally administered 0.5 and 100 ng/g body weight IL-1P on the plasma immunoreactive (ir) ACTH, PE, and corticosterone (CS) levels in the 10-d-old (infant) and 30-d-old (prepubertal) rat. Generally, the ir-ACTH, ir-PE, and ir-CS levels were significantly higher in prepubertal than in infant rats. Hormone levels were more enhanced by the higher dose of IL-1P, and changes were more pronounced at 120 min than at 30 min. The relative increase of ir-ACTH and ir-PE was smaller in the infant than in the prepubertal rat. In contrast, the relative increase of ir-CS was more pronounced in the infant rat. Changes in plasma ir-PE and ir-ACTH levels were not parallel, suggesting different responsiveness of the anterior pituitary Abbreviations CRH, ACTH-releasing factor PE, P-endorphin CS, corticosterone ir, immunoreactive HPAA, hypothalamic-pituitary-adrenal axis i.p., intraperitoneally IL-1P is a 17,500-D hormone-like polypeptide synthesized and released predominantly by macrophages and monocytes. It acts as a primary mediator in the acute phase of the response to microbial infection and physical stressors (1, 2). In addition to its role in the host defense mechanism, a growing body of evidence has accumulated indicating that IL-1P is a putative mediator between the immune and neuroendocrine systems (3)(4)(5)(6)(7)(8)(9)(10). Interactions between the immune system and the HPAA are of particular interest, because they are both associated in the adaptive response to stress. The main target of the IL-1P effect on the HPAA is believed to be the stimulation of Received July 12, 1994; accepted December 19, 1994 C R H secretion (11-13), but it has been shown to exert a direct effect on the pituitary and on adrenal hormone secretion as well (14,15). It is to be elucidated if activation of the HPAA by IL-1P is a specific effect or if it represents a nonspecific stress reaction.In the neonatal rat responsiveness of the HPAA to stressful stimuli is reduced. During this stress-hyporesponsive period, the ACTH response to a variety of nonspecific stressors as ether inhalation or electroshock (16,17), hypoglycemia (18), histamine, and cold (19) is blunted. Additionally, after cold or ether stress plasma PE levels were unchanged in the 10-d-old but enhanced in older rats (20). In co...

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“…The sensitivity of the assay was 0.2 fmol/tube, using 125 I‐h‐ACTH 1−39 as labelled hormone. For iodination, the chloramine‐T method was used (Barna et al ., 1995).…”

lnterleukin-1α Upregulates the Expression of Surfactant Protein-A in Rabbit Lung Explants

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