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The effects of acetylcholine and nitric oxide on the smooth and cardiac muscle of the paced cranial vena cava of the rat
Author(s) -
Buffini Maria Anne,
Jones James,
Mifflin Steve
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.2_supplement.55
Subject(s) - inotrope , cardiac muscle , acetylcholine , sodium nitroprusside , medicine , nitric oxide , contraction (grammar) , venae cavae , endocrinology , nitric oxide synthase , cardiology , anesthesia
Rat venae cavae contain both smooth and cardiac muscle tunics. Our aims were to examine the effects of acetylcholine (ACh) and nitric oxide (NO) on the smooth and cardiac muscle of the rat cranial vena cava, and to determine whether the negative inotropic action of ACh is mediated partially or wholly by NO. The effect of exogenous NO was examined using the NO donor sodium nitroprusside (SNP). This had little effect on either muscle type. The effects of ACh were examined with and without nitric oxide synthase (NOS) inhibition (L‐NNA 10 −4 M). ACh (10 −7 M) caused vasoconstriction of the smooth muscle raising the baseline by 22.9 ± 9.7 %, p=0.034. It also had a negative inotropic action on the cardiac muscle contraction (decreased in force by 25.9 ± 4.3 %, p=0.012). 10 −4 M L‐NNA abolished the vasoconstrictor effect of ACh and reduced its negative inotropic effect (p=0.003), so that cardiac contractions decreased in force by only 3.86 ± 1.29 %. Histochemical experiments showed that NOS is located in the cardiac muscle of the cranial vena cava. These results suggest that ACh acts partially through the release of NO. Based on this finding and the localisation of NOS in the cardiac muscle, it is proposed that in the cranial vena cava, NO release is regulated by cardiac muscle contraction which in turn regulates smooth muscle contraction. This may provide a vis a fronte suction mechanism to aid venous return and facilitate right atrial filling.