Dexamethasone and forskolin synergistically increase [Met5]enkephalin accumulation in mixed brain cell cultures.

Possible synergistic effects of the glucocorticoid dexamethasone (DEX, 10(-7) M) and the adenylate cyclase agonist forskolin (FSK, 10(-5) M) on [Met5]enkephalin (ME) accumulation were examined in enriched rat glial cultures and in mixed neuronal/glial cultures. In enriched glial cultures, DEX and FSK each stimulated the accumulation of ME 2-3-fold over basal media levels, but there was little additional stimulation when these agonists were combined. In contrast, mixed neuronal/glial cultures showed only weak responses to DEX or FSK alone, but the combination of these agonists produced a pronounced synergistic effect on media ME accumulation (6-10-fold over basal levels). The DEX effect was mediated via a classical glucocorticoid receptor, since DEX was potent (acting over a concentration range of 10(-11)-10(-7) M), mimicked by corticosterone (10(-6) M), and blocked by the glucocorticoid receptor antagonist RU486. There was a pronounced time lag (2 days) for the synergistic effects of DEX + FSK to develop. In situ hybridization and immunocytochemical studies suggested that astrocytes were the major source for the increased ME production in all mixed neuronal/glial cultures examined. Creating a mixed culture by plating fetal neurons onto confluent, enriched P7 glial cultures inhibited accumulation of ME in the media. DEX + FSK, but neither agonist alone, overcame this neuronal inhibition and increased accumulation of media ME to levels identical to levels in stimulated enriched glial cultures. The net effect was a 6-fold increase in ME accumulation in the mixed neuronal/glial cultures relative to a 2.5-fold increase in the enriched glial cultures. Neuronal inhibition of basal glial ME production could explain the similar synergistic effects of DEX + FSK observed in all mixed neuronal/glial cultures examined, and may be important in suppressing ME production by astrocytes in the brain.

Acute repeated nicotine injections increase enkephalin and decrease AP-1 DNA binding activity in rat adrenal medulla.

Previously we reported that a single injection of nicotine decreased AP-1 DNA binding activity in adrenal medullae, although chronic bidaily nicotine (and saline) injections increased this binding activity [15]. Repeated acute nicotine injections (3 mg/kg i.p., 7 injections equi-spaced over a 3 h period) effectively increased adrenal tyrosine hydroxylase [3] and [Met5]enkephalin levels and also profoundly decreased adrenal medulla AP-1 DNA binding activity for over 8 h.

Attempts to accelerate glucagon absorption: effects of adding a vasodilator and of injection using a 'sprinkler' needle.

Glucagon injected subcutaneously or intramuscularly may take up to 30 min to reverse hypoglycaemia. We investigated whether glucagon absorption could be accelerated by two manoeuvres known to enhance insulin absorption: addition of a powerful local hyperaemic agent (10 nmole alpha-calcitonin gene-related peptide; CGRP), and injection using a multihole 'sprinkler' needle. Glucagon (1 mg) given by conventional injection to six normal subjects produced peak plasma glucagon concentrations of 1.48 +/- 0.23 (SEM) ng ml-1 after 20 min and a peak glycaemic response of 7.8 +/- 0.8 mmol l-1 at 25 min. Glucagon injected with CGRP or using the sprinkler needle did not produce any significant differences in plasma glucagon or glycaemia profiles, compared with conventional injection. Further studies demonstrated that glucagon is itself a powerful vasodilator, causing a 300-500% increase in local blood flow, comparable to that induced by CGRP. Because of its intense local hyperaemic action, the absorption of subcutaneously-injected glucagon may be optimal and seems unlikely to be accelerated by pharmacological or other means.