Brain Research 881 (2000) 204–207
www.elsevier.com / locate / bres
Short communication
Antalarmin blockade of corticotropin releasing hormone-induced
hypertension in rats
a a a b
Richard J. Briscoe , Camilo L. Cabrera , Theodore J. Baird , Kenner C. Rice ,
a,c ,
*
James H. Woods
a
Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA
b
NIDDK, National Institutes of Health, Bethesda, MD, USA
c
Department of Psychology, University of Michigan, Ann Arbor, MI 48109, USA
Accepted 18 July 2000
Abstract
Central administration of CRH results in endocrinological, cardiovascular, and behavioral effects that suggest stress or anxiety. Among these is a marked pressor response. Parenteral administration of CRH, however, results in hypotension. We used parenteral administration
of antalarmin, a novel, small molecule CRH1 receptor antagonist, and a-helical CRH9 – 41, a peptidic CRHR1 / CRHR2 antagonist to
attempt to determine the receptor mechanisms through which CRH is acting in both of these situations. Our results suggest that the hypertension produced by central CRH administration is mediated through central CRHR1 receptors, whereas the hypotension produced
by parenteral CRH administration is mediated through peripheral CRHR2 receptors. 2000 Elsevier Science B.V. All rights reserved.
Theme: Endocrine and autonomic regulation
Topic: Cardiovascular regulation
Keywords: Corticotropin releasing hormone; Corticotropin releasing hormone antagonist;a-helical CRH9 – 41; Antalarmin; Blood pressure; Rat
Corticotropin releasing hormone (CRH) has come to be produces a marked hypertension in rats [9], probably regarded as one of the most critical integrative elements in through an action on central CRH receptors. When it is the multifaceted response to stress, playing a role in given intravenously, it produces a hypotensive effect [3], initiation, modulation, and inhibition of this response, as which, because of the limited access of parenterally well as maintaining the normal rhythms of the endo- administered CRH to the central nervous system, is crinological system that are involved in stress. The role of probably through an action on peripheral CRH receptors. CRH in the behavioral, endocrinological, and physiological However, it is not known which of the subtypes of CRH effects of stress has been expanding rapidly since it was receptors might mediate the changes in blood pressure identified by Vale and colleagues in 1981 [13]. Of par- produced by CRH administration.
ticular interest is the role of CRH in stress-related diseases Three CRH receptors have been identified in rats and in including such diverse conditions as depression, drug humans: CRHR1, CRHR2aand a splice variant, CRHR2b abuse, inflammation, eating disorders, and hypertension [8,12]. The CRH1 and CRH2 receptors have similar [11] The possibility that CRH antagonists could be effec- structures and G-protein coupled mechanisms of action tive in treating any of these diseases has attracted the [4,11], but markedly different anatomical locations in the
interest of a number of investigators. brain [1]. The CRH1 receptor is thought to be the most
CRH has interesting effects on blood pressure in ro- likely mediator of the endocrinological and behavioral dents. When given introcerebroventricularly (i.c.v.), it responses to stress [2,6]. The role of the CRH2 receptor is less clearly defined, but its location on arterioles in the brain suggests a possible role in regulating blood pressure.
*Corresponding author. Tel.: 11-734-764-9133; fax: 1
1-734-764-Antalarmin is one recently developed small molecule
7118.
E-mail address: jhwoods@umich.edu (J.H. Woods). CRH antagonist which has been reported to have high
R.J. Briscoe et al. / Brain Research 881 (2000) 204 –207 205
affinity for the CRH1 receptor. Antalarmin and a close surgery prior to testing. The venous and arterial catheter structural relative, CP-154,526, have been shown to block placements were verified visually at the end of the study, CRH-induced increases in ACTH [10,14]. In some cases when the rats were euthanized. The lateral ventricular these small molecule antagonists have been shown to block cannulae placements were also verified visually on sac-some of the anxiety-like effects of administration of CRH rifice, following the injection of 10ml of a methylene blue [10], but this interaction is not always clear-cut [5]. solution. Animals were excluded from the analysis if the Although the peptide antagonist a-helical CRH9 – 41 has lateral ventricles were not stained appropriately.
been shown to block the hypotensive effects of parenteral Cardiovascular measurements were conducted in a administration of CRH [3], no studies of the ability of standard Plexiglas rodent cage identical to the rats’ home antalarmin to modify the blood pressure effects of CRH cage. Rats were placed in the recording chamber and administration have been reported. Thus, it is not known attached to the pressure transducer (Spectromed model whether the hypotensive effect of parenteral CRH is P23XL, Grass Instruments, West Warwick, RI) and were mediated through an action on CRH1 or CRH2 receptors continuously monitored using a polygraph (Model 12RX, (but see Turnbull & Rivier, 1997 [11]; they suggest a Grass Instruments, West Warwick RI) for the duration of CRH2 receptor mechanism), or whether the hypertensive the experiment. Baseline mean arterial pressure (MAP) effect of central CRH is through an action on either type of was collected for 15 min prior to the first treatment. All
CRH receptor. i.c.v. injections were given in a volume of 10 ml. Both
The current study utilized antalarmin, which produces a CRH and a-helical CRH9 – 41 were purchased from Cal-selective blockade of CRHR1-receptors, and a-helical biochem (San Diego, CA). Antalarmin was synthesized by CRH9 – 41, which has affinity for both receptors, but does one of the authors (K.C.R.)
not readily cross the blood–brain barrier, to characterize Statistical significance was determined using repeated the diverse effects of CRH on blood pressure in awake, measures fixed effects MANOVA with Greenhouse-Geisser freely moving rats. Male Wistar rats (Harlan) were used as correction and subsequent post-hoc Duncan’s multiple subjects in this study. Prior to surgery, the rats were range tests. The drug treatment conditions were loaded as group-housed in standard plastic cages in a vivarium that the between groups factor and the time of measurement as was accredited by the American Association for Accredita- the within-group (repeated measures) factor. All statistical tion of Laboratory Animal Care. The room was maintained analysis was conducted using CSS: Statistica (Complete at 208628C on a 12 h light / dark cycle (lights on at 7:00 Statistical Systems, Tulsa, OK) software. The criterion for a.m.). The rats had ad-libitum access to food and water statistical significance was set at P,0.05.
throughout the study. Following surgery, the rats were Fig. 1 shows the group mean (6S.E.) MAP readings in singly housed in plastic cages until the termination of the each of six rats in each of the four treatment conditions
study. collected over the 45 min test session. CRH, 1.0mg i.c.v.,
206 R.J. Briscoe et al. / Brain Research 881 (2000) 204 –207
Fig. 1. Mean arterial pressure following i.c.v. CRH administration. Group
Fig. 2. Mean arterial pressure following i.v. CRH administration. Group means (6S.E.) of mean arterial pressure are plotted as a change from
means (6S.E.) of mean arterial pressure are plotted as a change from baseline for antalarmin doses over the course of 45 min. Antalarmin or
baseline for antalarmin doses over the course of 45 min. Antalarmin or vehicle was administered at time 0 and CRH or vehicle was administered
vehicle was administered at time 0 and CRH or vehicle was administered at 15 min. Each point represents the mean of six rats. *P,0.05, **P,
at 15 min. Each point represents the mean of 6 rats. *P,0.05, **P,0.01 0.01 as compared with the vehicle-treated animals. Control mean arterial
as compared with the vehicle-treated animals. Control mean arterial pressure (6S.E.) averaged over all experimental groups was 123.463.0
pressure (6S.E.) averaged over all experimental groups was 124.463.0 (n524).
(n524).
Fig. 2 shows the group mean (6S.E.) MAP in each of laboratory noted marked attenuation, by antalarmin, of the six rats in each of the four treatment conditions over the 45 increases in ACTH and corticosterone produced by re-min recording session. CRH 10 mg / kg i.v. produced a straint stress. These results indicate that CRH1 receptor statistically significant decrease in MAP as compared with blockade is in effect for at least 60 min subsequent to i.p. vehicle treatment [main treatment effect: F(1,10)540.18, injection of 32 mg / kg antalarmin. Thus, this hypertension P,0.00009; treatment3time interaction: F(44,440)5 appears to be mediated through central CRH1 receptors, 22.82, P,0.000001]. This decrease in MAP persisted although the involvement of peripheral CRH1 receptors in throughout the recording period (P,0.05 where noted in this effect cannot be absolutely ruled out by the present Fig. 2). Pretreatment with antalarmin, 32 mg / kg i.p., did experimental findings. As a peptide, CRH has limited not result in a significant antagonism of this depressor access to the central nervous system and parenterally effect of CRH, 10 mg / kg i.v., administration, as MAP in administered CRH should have direct action only on this group over the duration of the recording session was peripheral CRH receptors. These are most likely involved not significantly different from that in vehicle 1 CRH in the depressor effect of i.v. CRH administration. This is treated rats [main treatment effect: F(1,10)50.33, P,0.58; indicated by the ability of systemic administration of the treatment3time interaction: F(44,440)50.48, P50.99]. non-selective peptidic antagonist, a-CRH9 – 41, which also However, the effect of CRH was antagonized by adminis- has limited access to the brain, to block this effect. The tration of a-helical CRH9 – 41 120 mg / kg i.v., as MAP finding that antalarmin had no effect on this peripherally values in this group were not statistically different from mediated hypotensive effect suggests that the hypotension that in vehicle treated animals [main treatment effect: was probably mediated through CRH2 receptors.
F(1,10)50.61, P50.45; treatment3time interaction F(44,440)50.47, P,0.098].
Central administration of CRH produced a hypertensive Acknowledgements effect that was most likely mediated through central CRH
R.J. Briscoe et al. / Brain Research 881 (2000) 204 –207 207
with the CRF receptor: design of small molecule inhibitors,
References 1
receptor subtypes and clinical indications, Curr. Pharm. Des. 5 (1999) 289–315.
[1] D.T. Chalmers, T.W. Lovenberg, E.B. De Souza, Localization of [9] A. Morimoto, T. Nakamori, K. Morimoto, H. Tan, N. Murakami, novel corticotropin-releasing factor receptors (CRF2) mRNA ex- The central role of corticotropin-releasing factor (CRF-41) in pression to specific subcortical nuclei in rat brain: comparison with psychological stress in rats, J. Physiol. 460 (1993) 221–229. CRF1 mRNA expression, J. Neurosci. 15 (1995) 6340–6350. [10] D.W. Schulz, R.S. Mansbach, J. Sprouse, J.P. Braselton, J. Collins, [2] D.T. Chalmers, T.W. Lovenberg, D.E. Grigoriadis, D.P. Behan, E.B. M. Corman, A. Dunaiskis, S. Faraci, A.W. Schmidt, T. Seeger, P. De Souza, Corticotropin-releasing factor receptors: from molecular Seymour, F.D. Tingley 3rd, E.N. Winston, Y.L. Chen, J. Heym, biology to drug design, TIPS 17 (1996) 166–172. CP-154,526: a potent and selective nonpeptide antagonist of cor-[3] R. Corder, D. Turnill, N. Ling, R.C. Gaillard, Attenuation of ticotropin releasing factor receptors, Proc. Nat. Acad. Sci. USA 93
corticotropin releasing factor-induced hypotension in anesthetized (1996) 10477–10482.
rats with the CRF antagonist, alpha-helical CRF9 – 41; comparison [11] A.V. Turnbull, C. Rivier, Corticotropin-releasing factor (CRF) and with effect on ACTH release, Peptides 13 (1992) 1–6. endocrine responses to stress: CRF receptors, binding protein, and [4] K.D. Dieterich, H. Lehnert, E.B. De Souza, Corticotropin-releasing related peptides, Proc. Soc. Exp. Bio. Med. 215 (1997) 1–10.
factor receptors: an overview, Exp. Clin. Endocrinol. Diabetes 105 [12] O. Valdenaire, T. Giller, V. Breu, J. Gottowik, G. Kilpatrick, A new (1997) 65–82. functional isoform of the human CRF2 receptor for corticotropin-[5] G. Griebel, G. Perrault, D.J. Sanger, Characterization of the be- releasing factor, Biochim. Biophys. Acta 1352 (1997) 129–132.
havioral profile of the non-peptide CRH receptor antagonist CP- [13] W. Vale, J. Spiess, J. Rivier, C. Rivier, Characterization of a 154,526 in anxiety models in rodents, Comparison with diazepam 41-amino acid residue ovine hypothalmic peptide that stimulates the and buspirone, Psychopharmacology 138 (1998) 55–66. secretion of corticotropin and b endorphin, Science 213 (1981) [6] S.C. Heinrichs, J. Lapsansky, T.W. Lovenberg, E.B. De Souza, D.T. 1394–1397.
Chalmers, Corticotropin-releasing factor CRF1, but not CRF 2, [14] E.L. Webster, D.B. Lewis, D.J. Torpy, E.K. Zachman, K.C. Rice, receptors mediate anxiogenic-like behavior, Regulatory Peptides 71 G.P. Chrousos, In vivo and in vitro characterization of antalarmin, a (1997) 15–21. nonpeptide corticotropin-releasing hormone (CRH) receptor antago-[7] D.L. Mattson, Long-term measurement of arterial blood pressure in nist: suppression of pituitary ACTH release and peripheral
