Isatin (Indole-2, 3-dione) inhibits natriuretic peptide-induced hyperthermia in rats

In vivoeffects of isatin on rat platelet eicosanoids

To establish the possible influence of isatin (2,3-dioxo-indole) on the activity of platelets, the effects of isatin on platelet eicosanoid synthesis were studied in rats. Different doses (12.5-50 mg/kg) of isatin were injected intraperitoneally (i.p.) and the effects on the arachidonate cascade of isolated platelets were investigated. Cells were labeled with [(14)C]arachidonic acid, then the eicosanoids were separated with overpressure thin-layer chromatography and were quantitatively determined with a liquid scintillation analyzer. The lipoxygenase pathway was significantly inhibited by isatin (50 mg/kg) treatment and also the overall activity of the arachidonate cascade was diminished; however, the cyclooxygenase system was significantly stimulated. A 50-mg/kg i.p. dose of isatin significantly increased the production of vasoconstrictor cyclooxygenase metabolites. Among the vasodilator cyclooxygenase products, the synthesis of PGE2 and PGD2 were significantly decreased while that of 12-hydroxyheptadecatrienoic acid (HHT) increased upon isatin (50 mg/kg) administration. Our results provide further evidence on the peripheral actions of isatin and suggest that this endogenous indole may induce significant changes in the production of blood platelet arachidonic acid metabolites, which are important regulatory substances, thus isatin may potentially affect an even broader range of functions than was previously assumed.

Sedative–hypnotic profile of novel isatin ketals

Isatin (1H-indol-2,3-dione) is an endogenous compound found in many tissues and fluids. Isatin and its derivatives exert pharmacological effects on the central nervous system, including anxiogenic, sedative and anticonvulsant activities. Two new groups of isatin derivatives were synthesized (nine dioxolane ketals and nine dioxane ketals) and studied for their sedative, hypnotic and anesthetic effects using pentobarbital-induced sleeping time, locomotor activity evaluation and intravenous infusion. The dioxolane ketals were more potent than dioxane ketals for inducing sedative-hypnotic states, causing up to a three-fold increase in pentobarbital hypnosis. The dioxolane ketals produced sedation, demonstrated by decreased spontaneous locomotor activity in an open field. Hypnosis and anesthesia were observed during intravenous infusion of 5'-chlorospiro-[1,3-dioxolane-2,3'-indolin]-2'-one (T3) in conscious Wistar rats. Complete recovery from hypnosis and anesthesia required 39.1+/-7.3 and 6.8+/-2.4 min, respectively. Changes in hemodynamic parameters after infusion of 5.0 mg/kg/min were minimal. These findings suggest that these new isatin derivatives represent potential candidates for the development of new drugs that act on the central nervous system and may lead to a new centrally acting anesthetic with no toxic effects on the cardiovascular or respiratory systems.

Isatin: role in stress and anxiety

(Indoledione 2,3) isatin is an endogenous indole found both in mammalian brain and peripheral tissues. Isatin concentration in blood can exceed 1 microM and tissue concentrations vary from < 0.1 to 10 microM. Its level in the brain and periphery is increased by stress. Isatin has a wide spectrum of behavioural and metabolic effects. It is anxiogenic at lower doses and sedative at higher doses. Its most potent known in vitro actions are as an antagonist of atrial natriuretic peptide (ANP) function and NO signaling. In this review, we discuss isatin and stress in animal models, the few human studies, and also what it is known to date about the molecular mechanisms of its action. We suggest the possibility that isatin and its analogues may be interesting new pharmacological agents; Isatin antagonists may be anxiolytic, and isatin agonists may activate the HPA axis.

Natriuretic peptide interaction with [3H]isatin binding sites in rat brain

Isatin is an endogenous indole, which has a distinct and discontinuous distribution in the brain and exhibits a wide range of physiological and pharmacological effects. In the present study, we have demonstrated that atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) inhibited [3H]isatin binding to rat brain sections and isolated membrane fractions. Isatin itself antagonised not only natriuretic peptide receptor type A (NPR-A) (ANP-stimulation of guanylyl cyclase) but also NPR-C (ANP and CNP mediated inhibition of adenylyl cyclase) signalling. These results suggest that some [3H]isatin binding in the brain may be to NPR-A and NPR-C. Competitive interactions between isatin and natriuretic peptides and their receptors give a possible explanation of the known anxiogenic effect of low doses of isatin, interacting at NPR-A, and the sedative effects of higher doses, antagonising respectively the anxiolytic effect of ANP and the anxiogenic effect of CNP.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

The effects of isatin (indole-2, 3-dione) on pituitary adenylate cyclase-activating polypeptide-induced hyperthermia in rats

BACKGROUND

Previous studies have demonstrated that centrally administered natriuretic peptides and pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) have hyperthermic properties. Isatin (indole-2, 3-dione) is an endogenous indole that has previously been found to inhibit hyperthermic effects of natriuretic peptides. In this study the aim was to investigate the effects of isatin on thermoregulatory actions of PACAP-38, in rats.

RESULTS

One microg intracerebroventricular (icv.) injection of PACAP-38 had hyperthermic effect in male, Wistar rats, with an onset of the effect at 2 h and a decline by the 6th h after administration. Intraperitoneal (ip.) injection of different doses of isatin (25-50 mg/kg) significantly decreased the hyperthermic effect of 1 microg PACAP-38 (icv.), whereas 12.5 mg/kg isatin (ip.) had no inhibiting effect. Isatin alone did not modify the body temperature of the animals.

CONCLUSION

The mechanisms that participate in the mediation of the PACAP-38-induced hyperthermia may be modified by isatin. The capability of isatin to antagonize the hyperthermia induced by all members of the natriuretic peptide family and by PACAP-38 makes it unlikely to be acting directly on receptors for natriuretic peptides or on those for PACAP in these hyperthermic processes.