Zx. Shi et al., LOCALIZATION OF THYROTROPIN-RELEASING-HORMONE MESSENGER-RNA EXPRESSION IN THE RAT-HEART BY IN-SITU HYBRIDIZATION HISTOCHEMISTRY, Pathobiology, 64(6), 1996, pp. 314-319
Our laboratory has recently detected mRNA of thyrotropin-releasing hor
mone (TRH) in the rat heart. The density of mRNA for TRH is five-fold
higher in the atria than in the left and right ventricle. We also foun
d TRH receptor mRNA and H-3-TRH-binding sites in both ventricles. Card
iac contractility was stimulated after intracoronary administration of
TRH. This study was performed to investigate the localization of TRH
in the heart. We utilized in situ hybridization histochemistry (ISHH)
to localize TRH mRNA expression in the rat heart. ISHH was performed o
n fresh frozen heart tissue sections, which were hybridized with a spe
cific S-35-TRH oligo probe and subsequently processed by autoradiograp
hy. The autoradiographic signals corresponding to TRH mRNA were analyz
ed with an image program. For positive controls, TRH mRNA was identifi
ed in the hypothalamic paraventricular nucleus. This test confirms the
specificity of the TRH oligo probe. Cardiac hybridization signals wer
e observed predominantly in the atria and localized preferentially in
atrial connective tissues, vascular adventitia and atrial cardiomyocyt
es. No hybridization signals were found in ventricular cardiomyocytes.
These observations suggest that TRH is synthesized in atrial myocytes
and atrial vascular structures. Based on studies which show synthesis
of the TRH receptors in ventricular cardiomyocytes, we hypothesize th
at atrial TRH is an endocrine source for the stimulation of ventricula
r contractility and that endothelial and adventitial TRH may play a ro
le(s) in the regulation of the growth and/or vasomotor tone of the car
diac vascular system.