Beta-adrenergic stimulation induces an increase of the plasma levels of immunoreactive alpha-MSH, beta-endorphin, ACTH and of corticosterone

Infusion of I-isoproterenol in anesthetised rats induced a dose-dependent increase of the plasma levels of immunoreactive α-MSH (α-MSHi), β-endorphin (β-ENDi), ACTH (ACTHi) and of corticosterone (B). Steady state levels of all of these substances were reached within 20 min after the start of the infusion. The ED₅₀ values of I-isoproterenol for the increase of plasma α-MSHi, β-ENDi, ACTHi and B were similar (42, 86, 84 and 48 ng/kg. min, respectively). Infusion of I-epinephrine also induced a dose-dependent increase of plasma α-MSHi, β-ENDi, ACTHi and B with similar ED₅₀ values (89, III, 110 and 46 ng/kg. min, respectively). The I-epinephrine-induced increase of plasma α-MSHi, β-ENDi, ACTHi and B was blocked by I-propranolol but not by d-propranolol.Pretreatment of rats with dexamethasone (2.0 mg/kg s.c., 16 hr) completely prevented the I-epinephrine-induced increase of plasma ACTHi and B, without affecting the increase of plasma α-MSHi and β-ENDi.We conclude that catecholamines can stimulate the secretion of peptides from the intermediate lobe (e.g. α-MSH, β-END) as well as from the anterior lobe (e.g. ACTH) of the pituitary gland via interaction with one or more β-adrenergic receptor mechanisms.     

New embedding medium for sectioning undecalcified bone

Methylmethacrylate (MMA) is the most commonly used embedding medium for sectioning undecalcified bone; however, a number of problems exist with its use in a research laboratory. MMA requires a long infiltration time and temperature control, and it reacts with many polymers. We used Kleer Set resin™ as an alternative embedding medium for sectioning undecalcified bone specimens. Fluorochrome labeled bone specimens were sectioned transversely using a ground section technique and longitudinally on a sledge macrotome. The slides were viewed using both transmitted light and epifluorescence microscopy. High quality sections were obtained using Kleer Set resin™ for both sectioning techniques. We have shown that this new embedding medium is simpler, safer, quicker to use and does not interfere with visualization of fluorochromes.     

CHRONIC STIMULATION OF THE HYPOTHALAMUS–PITUITARY–ADRENAL AXIS IN RATS BY INTERLEUKIN 1β: CENTRAL AND PERIPHERAL MECHANISMS

The authors have studied mechanisms which could be involved in the sustained activation of the hypothalamus–pituitary–adrenal (HPA) axis during continuous infusion of rats with recombinant human interleukin-1β (IL-1β). First, the effects of 3 days of intracerebroventricular (i.c.v.) infusion of rats with IL-1 on plasma adrenocorticotropin (ACTH) and corticosterone (B) levels were investigated. Thereafter, changes in plasma ACTH and B levels were followed in rats intraperitoneally (i.p.) infused with IL-1β after immunoneutralization of corticotropin-releasing hormone (CRH), hypophysectomy (HPX), macrophage depletion using dichloromethylene diphosphonate (Cl₂MDP)-containing liposomes, adrenalectomy (ADX) and dexamethasone (DEX) administration, respectively. Infusion of IL-1β i.c.v., even in doses as low as 0.1 μg/day, induced significant increases in plasma ACTH and B levels. HPX and ADX rats died within 18 h after starting the IL-1β infusion (0.5 μg/day). Immunoneutralization of CRH significantly decreased and macrophage depletion significantly increased the stimulation of the HPA axis by IL-1 (4.0 μg/day). Administration of high doses of DEX completely abolished the stimulation of the HPA axis by IL-1β (2.0 μg/day). The present study demonstrates that lower doses of IL-1β were able to activate the HPA axis when infused i.c.v. compared with i.p. Regarding stimulation of the HPA axis by chronic i.p. infusion of IL-1β the present study: (1) provides evidence that the CRH system is involved; (2) provides no evidence for a direct stimulatory effect of IL-1β on the release of B by the adrenal gland which is of sufficient magnitude to resist the stress of chronic i.p. IL-1β infusion; (3) shows that endogenous macrophage-derived mediators, induced by i.p. IL-1β infusion, express an overall inhibitory rather than a stimulatory effect on the activity of the HPA axis; (4) demonstrates that exogenous administration of DEX blocks the effect of IL-1β, which fits well in the concept of an immunoregulatory feedback between IL-1β and glucocorticoids.