title: Diurnal and seasonal changes in sympathetic signal transduction in cardiac ventricles of European hamsters.
abstract: This investigation of the relationship between cardiac beta-adrenoceptors and adenosine 3',5'-cyclic monophosphate (cAMP) formation in cardiac ventricles of the nocturnally active European hamster both during euthermia under a 12:12-h dark-light cycle and during hibernation under constant-darkness conditions showed that neither the densities, affinities, nor distribution of the beta 1- and beta 2-receptor subtypes differed between the dark phase, light phase, and hibernation. Basal formation of cAMP by the cardiac adenylyl cyclase of euthermic hamsters was higher in ventricles obtained at night [core temperature (Tcore) = 37.8 degrees C] than in ventricles obtained during the day (Tcore = 36.4 degrees C). Basal formation of cAMP was also significantly lower in hibernating hamsters (Tcore = 7.0 degrees C) than in euthermic hamsters. When adenylyl cyclase activity was stimulated by isoprenaline, guanylylimidodiphosphate [Gpp(NH)p], or forskolin, the rank order of potency was the same in euthermic hamsters and hibernating hamsters: isoprenaline < Gpp(NH)p < forskolin. Functional competition curves indicated that in the euthermic hamsters beta 1-receptors were responsible for 67% of the response to isoprenaline at night and 62% of the response during the day. In hibernating hamsters, in contrast, most of the response to isoprenaline (58%) was mediated via beta 2-receptors. This shift in the relative importance of the receptor subtypes may facilitate arousal from hibernation by making the heart more sensitive to circulating epinephrine.
authors.affiliation: Max-Planck-Institut für Physiologische und Klinische Forschung, W. G. Kerckhoff-Institut, Bad Nauheim, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Pleschka
authors.forename: A
authors.initials: A
authors.lastname: Heinrich
authors.forename: K
authors.initials: K
authors.lastname: Witte
authors.forename: B
authors.initials: B
authors.lastname: Lemmer
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002940:Circadian Rhythm; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae / Q000502:physiology*; D000242:Cyclic AMP / Q000096:biosynthesis; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006329:Heart Conduction System / Q000502:physiology*; D006605:Hibernation; D007545:Isoproterenol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D012621:Seasons; D015398:Signal Transduction; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol