N-substituted adenosines as novel neuroprotective A(1) agonists with diminished hypotensive effects.

The synthesis and pharmacological profile of a series of neuroprotective adenosine agonists are described. Novel A(1) agonists with potent central nervous system effects and diminished influence on the cardiovascular system are reported and compared to selected reference adenosine agonists. The novel compounds featured are derived structurally from two key lead structures: 2-chloro-N-(1-phenoxy-2-propyl)adenosine (NNC 21-0041, 9) and 2-chloro-N-(1-piperidinyl)adenosine (NNC 90-1515, 4). The agonists are characterized in terms of their in vitro profiles, both binding and functional, and in vivo activity in relevant animal models. Neuroprotective properties assessed after postischemic dosing in a Mongolian gerbil severe temporary forebrain ischemia paradigm, using hippocampal CA1 damage endpoints, and the efficacy of these agonists in an A(1) functional assay show similarities to some reference adenosine agonists. However, the new compounds we describe exhibit diminished cardiovascular effects in both anesthetized and awake rats when compared to reference A(1) agonists such as (R)-phenylisopropyladenosine (R-PIA, 5), N-cyclopentyladenosine (CPA, 2), 4, N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR 79236, 26), N-cyclohexyl-2'-O-methyladenosine (SDZ WAG 994, 27), and N-[(2-methylphenyl)methyl]adenosine (Metrifudil, 28). In mouse permanent middle cerebral artery occlusion focal ischemia, 2-chloro-N-[(R)-[(2-benzothiazolyl)thio]-2-propyl]adenosine (NNC 21-0136, 12) exhibited significant neuroprotection at the remarkably low total intraperitoneal dose of 0.1 mg/kg, a dose at which no cardiovascular effects are observed in conscious rats. The novel agonists described inhibit 6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate-induced seizures, and in mouse locomotor activity higher doses are required to reach ED(50) values than for reference A(1) agonists. We conclude that two of the novel adenosine derivatives revealed herein, 12 and 5'-deoxy-5'-chloro-N-[4-(phenylthio)-1-piperidinyl]adenosine (NNC 21-0147, 13), representatives of a new series of P(1) ligands, reinforce the fact that novel selective adenosine A(1) agonists have potential in the treatment of cerebral ischemia in humans.

Effect of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in the rat aorta.

1. This study sought to evaluate whether the effects of acute and long-term treatment with 17-beta-estradiol on the vasomotor responses in rat aortic rings are mediated through the same mechanism. 2. Ovariectomized rats were treated daily with either 17-beta-estradiol-3-benzoate (100 microg kg(-1)) or vehicle for 1 week. 3. The effect of long-term 17-beta-estradiol treatment on the responses to cumulative doses of phenylephrine, 5-HT, calcium, potassium and 17-beta-estradiol was determined in aortic rings. In the same rings, the effect of acute exposure to 17-beta-estradiol (5 and 10 microM) on the dose response curves for phenylephrine, 5-HT, calcium, potassium and acetylcholine were estimated. The measurements were made in rings with and without intact endothelium. The tone-related basal release of nitric oxide (NO) was measured in rings with intact endothelium. 4. Long-term 17-beta-estradiol treatment reduced the maximum developed contraction to all contracting agents studied. This effect was abolished in endothelium denuded vessels. Acute 17-beta-estradiol treatment also reduced maximal contraction. This effect, however, was independent of the endothelium. 5. Long-term 17-beta-estradiol treatment significantly increased the ability of the rings to dilate in response to acetylcholine whereas acute exposure to 17-beta-estradiol had no effect. The tone-related release of NO was significantly increased after long-term exposure to 17-beta-estradiol. 6. In conclusion, this study indicate that the acute and long-term effects of 17-beta-estradiol in the rat aorta are mediated through different mechanisms. The long-term effect is mediated through the endothelium most likely by increasing NO release. In contrast, the acute effect of 17-beta-estradiol seems to be through an effect on the vascular smooth muscle cells.

Atriopeptin III improves renal functions in a ureter-obstructed rat kidney model.

The renal hemodynamic and excretory effects of atriopeptin III were studied in normal rat kidneys and in kidneys made dysfunctional by the application and release of a 24 h unilateral ureteral obstruction (UO24h), which decreased baseline glomerular filtration rate (GFR) by 80%. Atriopeptin III (0.5 nmol/kg i.v.) decreased blood pressure (10-15%) for more than 30 min, and increased urine flow rate and sodium excretion in normal and diseased kidneys for ca. 15 min. An initial enhancement of renal blood flow (ca. 20%) was apparent for less than 5 min. Atriopeptin III (bolus injection) temporarily enhanced the GFR 2-3-fold in the diseased (UO24h) kidneys, whereas no changes of GFR were noted in control kidneys. When atriopeptin III was continuously infused at a rate of 0.1 nmol/kg per min, GFR in UO24h kidneys increased from 0.28 +/- 0.08 ml/g per min to a stable level of 0.82 +/- 0.10 ml/g per min. Again, GFR in the control kidneys remained unaffected (1.25 +/- 0.08 ml/g per min). The enhancement of GFR in the UO24h kidney was associated with large increases of urine flow rate and sodium excretion.

Dissociation of the spasmolytic and metabolic effects of glucagon.

Glucagon and glucagon-(1-21)-peptide were equipotent with regard to inhibitory effect on the amplitude of electrically evoked contractions of the isolated guinea-pig ileum. The effect was not potentiated by isobutylmethylxanthine (IBMX) nor inhibited by phentolamine or propranolol. Both peptides inhibited intestinal motility in rabbits in vivo. Glucagon and equimolar doses of glucagon-(1-21)-peptide exerted a relaxing effect on the rabbit gall bladder in vitro and in vivo and increased bile flow in rats. Both peptides inhibited pentagastrin stimulated gastric acid secretion in cats. However, contrary to glucagon, glucagon-(1-21)-peptide did not increase blood glucose and plasma IRI levels after intravenous administration to rats in vivo. Whereas the entire glucagon molecule was required for the metabolic effects, the amino acid sequence (1-21) of glucagon exerted a full spasmolytic action on the enteric muscles and the biliary tree. The spasmolytic effects on these organs are therefore likely to be mediated via a mechanism that does not involve the activation of adenyl cyclase.