HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 296/3/R774    most recent 90466.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Skovgaard, N. Articles by Wang, T. Search for Related Content PubMed PubMed Citation Articles by Skovgaard, N. Articles by Wang, T.

COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Histamine induces postprandial tachycardia through a direct effect on cardiac H₂-receptors in pythons

¹Zoophysiology, Department of Biological Sciences, University of Aarhus, Denmark; and ²Department of Molecular Biology, University of Aarhus, Denmark

Submitted 31 May 2008 ; accepted in final form 13 December 2008

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 H₂-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 H₂- 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.

reptile; digestion; heart rate; blood flow; blood pressure