Diurnal and seasonal changes in sympathetic signal transduction in
the cardiac ventricle of the european hamster (cricetus
cricetus).
Pleschka, Klaus, Angela Heinrich, Klaus Witte, and Bj[diaeresis]orn
Lemmer.
Max-Planck-Institut f[umlaut]ur Physiologische und Klinische
Forschung, W.G.Kerckhoff-Institut, Parkstr1, D-61231 Bad Nauheim,
Germany., Institute of Pharmacology and Toxicology Mannheim,
Heidelberg University, Maybachstr 14-16, D-68169 Mannheim,
Germany
APStracts 2:0268R, 1995.
This investigation of the relationship between cardiac-adrenoceptors
and 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 1 and 2 receptor subtypes differed between the dark phase, light
phase, and hibernation. Basal formation of cAMP by the cardiac adenyl
cyclase of euthermic hamsters was higher in ventricles obtained at
night (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 adenyl cyclase activity was
stimulated by isoprenaline, 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 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 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 adrenaline.
Received 17 January 1995; accepted in final form 27 September
1995
APS Manuscript Number R035-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95