Synthesis and biological activity of oxo-7H-benzo[e]perimidine-4-carboxylic acid derivatives as potent, nonpeptide corticotropin releasing factor (CRF) receptor antagonists.

A novel series of derivatives of oxo-7H-benzo[e]perimidine-4-carboxylic acid (I) potently displaced radioligand binding of 125I-CRF to both CRF1 and CRF2 receptors. The members of this series antagonized CRF-stimulated cAMP formation and CRF-stimulated corticotropin release from rat pituitary in vivo. These are the first nonpeptide antagonists to show activity at both CRF1 and CRF2 receptors.

Locus coeruleus electrophysiological activity and responsivity to corticotropin-releasing factor in inbred hypertensive and normotensive rats.

The spontaneously hypertensive rat (SHR) and its normotensive progenitor, the Wistar-Kyoto rat (WKY), have been shown to be differentially responsive to the behavioral and endocrine effects of both stress and corticotropin-releasing factor (CRF), both of which increase locus coeruleus (LC) electrophysiological activity. However, the effect of central administration of CRF in these rat strains has yet to be examined. In the present studies, LC electrophysiological responsivity to intracerebroventricular infusions of CRF was assessed in SHR, an inbred strain of WKY rats (the WKY[LJ] rat), and an outbred normotensive rat strain, Sprague-Dawley (SD) rats. Spontaneous LC discharge rate, mean arterial blood pressure and heart rate were also examined. LC activity was increased to the same extent in the three rat strains in response to a 3 microg dose of CRF. However, WKY(LJ) rats showed an exaggerated LC in response to a 1 microg dose of CRF in comparison to the other rat strains tested at this dose. Spontaneous discharge rates of individual LC neurons were lower in both SHR and WKY[LJ] rats than in SD rats. Further, the variability of the discharge rates of LC neurons was greater in WKY[LJ] rats than in the other two strains. These results indicate that the WKY[LJ] rat may provide a useful model for assessing the role of sensitivity to CRF in stress responsiveness.

Spinal nicotinic receptor expression in spontaneously hypertensive rats.

Intrathecal administration of nicotinic agonists previously has been shown to result in exaggerated pressor and heart rate responses as well as greater nociceptive behavior in adult (12-week-old) spontaneously hypertensive rats (SHR) than in age-matched normotensive Wistar-Kyoto rats (WKY). Paradoxical to these augmented responses to nicotinic agonists in SHR, nicotinic receptor number in the spinal cord as measured by cytisine binding sites is lower in adult SHR than normotensive WKY and Sprague-Dawley rats. Using the high-affinity agonist epibatidine, we found similar differences in receptor number between strains in both in vitro ligand binding experiments with spinal cord membranes and in situ autoradiographic analyses. Spinal nicotinic receptor number did not differ in 5-week-old prehypertensive SHR and age-matched WKY; however, receptor numbers were higher in young rats of both strains than in their adult counterparts. Antihypertensive treatment (25 mg/kg per day hydralazine PO) in 6-week-old SHR from 6 to 12 weeks of age markedly reduced the progressive rise in blood pressure yet did not alter nicotinic receptor number compared with untreated rats. Similar treatment of WKY with hydralazine produced a slight fall in blood pressure but no change in receptor number. Thus, normalization of blood pressure by hydralazine in SHR does not result in a return of receptor expression to levels seen in normotensive rats. Higher centrally mediated pressor activity or augmented postcoupling events after neuronal nicotinic receptor stimulation may slowly downregulate expression of spinal nicotinic receptors in this genetically hypertensive rat strain.

Peripheral beta adrenergic blockade modifies airpuff startle-induced heart rate responses.

Prior studies showed that repeated airpuff startle-reaction stimuli applied to normotensive inbred Wistar-Kyoto rats bred in La Jolla or Sprague-Dawley rats elicit pressor responses on all trials except trial-dependent bradycardia or tachycardia. However, hypertensive inbred spontaneously hypertensive rats bred in La Jolla exhibited no bradycardia. Peripheral methylatropine blocked bradycardia and unmasked tachycardia, which implies concurrent autonomic discharges on early trials. As shown here, vendor inbred Wistar-Kyoto rats from Charles River Laboratories (WKYCR) fail to show bradycardia. Because stress-induced parasympathetic responses are important to understanding arrhythmogenesis, we tested whether (WKYCR) and inbred spontaneously hypertensive rats from Charles River Laboratories (SHRCR) exhibit any parasympathetic activation by blunting sympathetic chronotropic responses with cardioselective beta-adrenoceptor antagonists. WKYCR or SHRCR were pretreated with either nonselective propranolol, beta 1-selective metoprolol, beta 1-selective celiprolol (with beta 2-receptor agonist activity) or ICI 118,551, a selective beta 2-receptor antagonist. Neither propranolol nor metoprolol affected resting HR in WKYCR, but both decreased HR in SHRCR, whereas celiprolol raised resting HR only in WKYCR. Although control WKYCR nor SHRCR exhibited bradycardia, bradycardia was unmasked in both by all beta 1-selective agents but not by ICI 118,551. However, ICI 118, 551 reduced tachycardia responses over all trials in WKYCR, which suggests beta 2-adrenoceptor involvement in the stress-induced tachycardia. Significant cardiac contributions to the pressor responses in both WKYCR and SHRCR were found.(ABSTRACT TRUNCATED AT 250 WORDS)