Histamine induces postprandial tachycardia through a direct effect on cardiac H2-receptors in pythons.
The intrinsic heart rate of most vertebrates studied, including humans, is elevated during digestion, suggesting that a nonadrenergic-noncholinergic factor contributes to the postprandial tachycardia. The regulating factor, however, remains elusive and difficult to identify. Pythons can ingest very large meals, and digestion is associated with a marked rise in metabolism that is sustained for several days. The metabolic rise causes more than a doubling of heart rate and a fourfold rise in cardiac output. This makes the python an interesting model to investigate the postprandial tachycardia. We measured blood pressure and heart rate in fasting Python regius, and at 24 and 48 h after ingestion of a meal amounting to 25% of body wt. Digestion caused heart rate to increase from 25 to 56 min, whereas blood pressure was unchanged. The postprandial rise in heart rate was partially due to a doubling of intrinsic heart rate. The H(2)-antagonist did not affect heart rate of fasting snakes but decreased heart rate by 15-20 min at 24 h into digestion, whereas it had no effects at 48 h. Thus, the histaminergic tone on the heart rose from none to 30% at 24 h but vanished after 48 h. In anesthetized snakes, histamine caused a systemic vasodilatation and a marked increase in heart rate and cardiac output mediated through a direct effect on H(2)- receptors. Our study strongly indicates that histamine regulates heart rate during the initial phase of digestion in pythons. This study describes a novel regulation of the vertebrate heart.
Skovgaard
Nini
N
Dept. of Biological Sciences, Univ. of Aarhus, Denmark. nini.jensen@biology.au.dk
Møller
Kate
K
Gesser
Hans
H
Wang
Tobias
T
D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D017821:Boidae / Q000502:physiology*; D005260:Female; D006632:Histamine / Q000097:blood / Q000494:pharmacology*; D017442:Histamine Agonists / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008297:Male; D019518:Postprandial Period / Q000187:drug effects* / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000187:drug effects; D011970:Receptors, Histamine H2 / Q000187:drug effects*; D012039:Regional Blood Flow / Q000187:drug effects; D012849:Sinoatrial Node / Q000187:drug effects; D013610:Tachycardia / Q000139:chemically induced* / Q000503:physiopathology
D017442:Histamine Agonists; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D006632:Histamine