Cardiovascular actions of adrenocorticotropin microinjections into the nucleus tractus solitarius of the rat.
The presence of adrenocorticotropin (ACTH) containing cells and melanocortin (MC) receptors has been reported in the nucleus tractus solitarius (NTS) of the rat. The importance of the NTS in the regulation of cardiovascular function is also well established. Based on these reports, it was hypothesized that ACTH acting within the NTS may modulate the central regulation of cardiovascular function. To test this hypothesis, cardiovascular effects of ACTH in the NTS were investigated in intact urethane-anesthetized and unanesthetized decerebrate, artificially ventilated, adult male Wistar rats. Microinjections of ACTH (0, 0.5, 1, 2, and 4 mM) into the medial subnucleus of NTS (mNTS) elicited decreases in mean arterial pressure (MAP; 0+/-0, 24.4+/-3.5, 35.7+/-4.3, 44.5+/-5.8 and 53.7+/-5.6 mm Hg, respectively) and heart rate (HR; 0+/-0, 25.7+/-5.3, 35.5+/-6.4, 47.5+/-12.1 and 55.0+/-5.6 beats/min, respectively). The onset and duration of the responses to microinjections of ACTH (0.5-4 mM) were 5-10 s and 45-120 s, respectively. Control microinjections of artificial cerebrospinal fluid (aCSF) did not elicit any response. The volume of all microinjections was 100 nl. The concentrations of ACTH that elicited depressor and bradycardic responses when microinjected into the mNTS (e.g. 1 or 2 mM, 100 nl), did not elicit a response when injected i.v. (n=5) or i.c.v. (n=2) indicating that there was no leakage of the drug from the injection site in the mNTS. Microinjections of MC3/4 receptor antagonists (acetyl-[Nle(4), Asp(5), d-2-Nal(7), Lys(10)]-cyclo-alpha-MSH amide, fragments 4-10 (SHU9119) and agouti-related protein (83-132) amide) into the mNTS blocked the responses to ACTH. Microinjections of ACTH (2 mM) into the mNTS decreased efferent greater splanchnic nerve activity. Bilateral vagotomy significantly attenuated ACTH-induced bradycardia. These results indicated that: 1) microinjections of ACTH into the mNTS elicited depressor and bradycardic responses, 2) these responses were mediated via MC3/4 receptors, 3) the depressor effects were mediated via a decrease in the activity of the sympathetic nervous system, and 4) the bradycardic responses were vagally mediated.
Brown
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Department of Neurology and Neurosciences, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
Chitravanshi
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VC
Sapru
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HN
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D054369:Agouti-Related Protein; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects*; D003655:Decerebrate State; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006728:Hormones / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D008297:Male; D008845:Microinjections / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D017552:Solitary Nucleus / Q000187:drug effects*; D013153:Splanchnic Nerves / Q000187:drug effects / Q000502:physiology; D013997:Time Factors; D014628:Vagotomy / Q000379:methods
C515197:AGRP protein, rat; D054369:Agouti-Related Protein; D006728:Hormones; D036341:Intercellular Signaling Peptides and Proteins; D018698:Glutamic Acid; D000324:Adrenocorticotropic Hormone