Keisuke Hattori

Role of nitric oxide from the endothelium on the neurogenic contractile responses of rabbit pulmonary artery

The effects of L-NG-nitro arginine (L-NO2Arg), a stereospecific inhibitor of nitric oxide formation, on the responsiveness of rabbit pulmonary artery to transmural electrical stimulation were studied. The contractile response evoked by electrical stimulation at 4 Hz was abolished by tetrodotoxin (10(-7) M) and depressed to approximately 10% by bunazosin (10(-6) M), an alpha 1-antagonist. Pretreatment with L-NO2Arg (10(-5) M) significantly potentiated the response to electrical stimulation without changing the resting tension. D-NO2Arg (10(-5) M) did not show such a potentiating action. In endothelium-denuded arteries, L-NO2Arg did not potentiate the response to electrical stimulation. The effect of L-NO2Arg on endogenous noradrenaline release in response to electrical stimulation was also examined by HPLC with electrochemical detection; L-NO2Arg did not affect noradrenaline release. The contractions induced by exogenous noradrenaline (10(-6)-10(-5) M) were enhanced by L-NO2Arg, but not by D-NO2Arg. These results suggest that the vasoconstriction induced by sympathetic nerve stimulation in the rabbit pulmonary artery is modulated by endogenous nitric oxide or nitric oxide-like substances released from endothelial cells.

The effects of age on the release of adenine nucleosides and nucleotides from rat caudal artery.

1. The spontaneous and alpha‐adrenoceptor‐induced release of ATP, ADP, AMP and adenosine were determined from arterial segments and from isolated endothelial cells from caudal arteries of young (5‐week‐old), adult (30‐week‐old) and old (100‐ to 110‐week‐old) Wistar rats. 2. The spontaneous (non‐evoked) release of the sum total of the four purines was significantly greater from artery segments of young rats than from adult and old rats. 3. The release of the adenine nucleotides and adenosine induced by methoxamine (10 microM), an alpha 1‐adrenoceptor agonist, was greater from artery segments from young rats than from old rats. 4. The spontaneous release of the sum total of the four purines was significantly greater from endothelial cells prepared from caudal arteries of young rats than of old rats. 5. The noradrenaline (10 microM)‐induced release of the sum total of the four purines was significantly greater from endothelial cells prepared from caudal arteries of young rats than of old rats. 6. The levels of adenine nucleotides and adenosine, determined in plasma from anaesthetized rats, were significantly higher in young rats compared with adult and old rats. 7. These findings suggest that the release of ATP from the vascular endothelial cells is reduced with advancing age.

Methoxamine enhances the release of endogenous noradrenaline from rabbit ear artery: possible involvement of ATP

SummaryThe effect of methoxamine, an α1-adrenoceptor agonist, on the electrically-evoked release of endogenous noradrenaline was examined in the isolated rabbit ear artery. Noradrenaline was quantified by high performance liquid chromatography-electrochemical detection. The release of adenine nucleotides and nucleosides by methoxamine was examined using high performance liquid chromatography-fluorescence detection.The release of noradrenaline evoked by electrical field stimulation (EFS) at 4 Hz was reduced by tetrodotoxin 0.3 μmol/l and clonidine 1 μmol/l by approximately 80% and 50%, respectively. On the other hand, methoxamine at 10 but not 1 μmol/l enhanced the release of noradrenaline to approximately twice the control, and the enhancement was prevented by prazosin 1 μmol/l. The facilitatory action of methoxamine was also abolished after desensitization of P2-purinoceptors by α,β-methylene ATP 30 μmol/l as well as by the presumed P2-purinoceptor antagonist suramin given at 10 μmol/l. Exogenous ATP 10 μmol/l significantly enhanced the EFS-evoked release of noradrenaline, and the enhancement was abolished by α,β-methylene ATP and suramin. None of the drugs changed the spontaneous outflow of noradrenaline. These results indicate that endogenous ATP, acting at prejunctional purinoceptors, may participate in the facilitatory effect of methoxamine. Indeed, methoxamine 10 μmol/l significantly enhanced the spontaneous outflow of ATP and, less so, ADP. The methoxamine evoked release of ATP and ADP was antagonized by prazosin 1 μmol/l.It is concluded that methoxamine releases endogenous ATP from postjunctional sites which then, via prejunctional purinoceptors, facilitates action potential-evoked release of noradrenaline in rabbit ear artery.

Endothelium-dependent and -independent relaxation by dopamine in the rabbit pulmonary artery

1. The relaxing response of dopamine (DA) was studied in the rabbit pulmonary artery. DA caused concentration‐related relaxation in helically cut strips of the artery contracted with prostaglandin F2α in the presence of prazosin.

Uptake of noradrenaline by the adrenergic fibers of the submaxillary and sublingual glands of the rat

Abstract The uptake of noradrenaline by the submaxillary and sublingual glands of the rat was investigated histochemically and quantitatively. The administration of noradrenaline increased the noradrenaline fluorescence surrounding the serous acini of the submaxillary gland. The fluorescence in the walls of arterioles of both the submaxillary and sublingual glands was also intensified. On the denervated side, practically no fluorescence was seen after the injection of noradrenaline, although the quantitative determinations revealed a slight increase in noradrenaline levels. After the administration of noradrenaline to the animals treated with monoamine oxidase inhibitor, definite fluorescent fibers appeared among the mucous cells of the sublingual gland, where otherwise little fluorescence was seen. Such fluorescent fibers were never obtained on the denervated side. It was concluded lhat the mucous acini of the sublingual gland are innervated by adrenergic fibers, but normally the amount of noradrenaline in the fibers is too small or its distribution is too diffuse for it to be detected histochemically. A distinction between histochemical and biochemical findings is discussed.

L‐NITROARGININE INCREASES BLOOD PRESSURE IN THE RAT

1. Effects of administration of NG‐nitro‐L‐arginine (NO2Arg), a guanidino nitroarginine derivative, for 1 week on blood pressure and some vascular responses of rats were studied.

Evidence for Elevated Levels of Dopamine in the Rabbit Pulmonary and Carotid Artery

Catecholamine levels in six arteries, two aortae, and atria of rabbits were determined by high-performance liquid chromatography (HPLC) coupled with electrochemical detection. An appreciable concentration of dopamine (DA) was found in the pulmonary and carotid arteries. The content in these two arteries was >200 ng/g, although the mesenteric, celiac, renal, and femoral arteries had <55 ng/g. The ratio of DA to norepinephrine (NE) in the pulmonary artery was 32.2 ± 6.3%, and that in the carotid artery was 9.0 ± 3.8%. These values are equivalent to the ratio in the canine paw pad and kidney, which are considered to be innervated by a dopaminergic system among peripheral tissues. The presence of DA in the pulmonary artery was confirmed by gas chromatography and mass spectrometry. In addition, uptake and distribution of [3H]DA and significant enhancement of [3H]DA release by transmural stimulation in the pulmonary artery were observed. These results suggested the possibility of dopaminergic innervation in the rabbit pulmonary and, possibly, carotid arteries.

Human urinary trypsin inhibitor (urinastatin)-like substance in mouse liver

Mouse liver contains a human urinary trypsin inhibitor (urinastatin, UT)-like immunoreactive substance with trypsin inhibitory activity. Northern blot analysis demonstrates the presence of the appropriate 1.3 kb mRNA band in liver tissue but not in kidney or other tissues examined. Administration of hydrocortisone, which is known to increase the urinary excretion of the UT-like substance, increased the levels of UT-like substance in serum and in the liver tissue. In contrast, deoxycorticosterone acetate did not have such an effect. These results suggest that the gene encoding UT-like substance is primarily expressed in the liver of the mouse, and that glucocorticoids play an important role in regulating the hepatic synthesis of UT-like substance. Furthermore, these findings indicate that the mouse is a suitable species for research on the biological function of UT or UT-like substances.

Effect of extracellular calcium on vascular contraction induced by phorbol ester

In rat thoracic aorta, 12-0-tetradecanoyl-phorbol-13-acetate (TPA) caused a slowly onset, sustained vascular contraction. The contraction was markedly reduced in the absence of extracellular Ca2+, although small tension development was still observed. The tension developed by TPA in the presence of Ca2+ was decreased by serial addition of a Ca2+-channel blocker, verapamil in a concentration-dependent manner. TPA could cause vascular contraction to almost maximum level at lower concentration of extracellular Ca2+, compared with KCl- or norepinephrine-induced contraction. These results suggest that extracellular Ca2+ which influxes through Ca2+-channels into cytoplasm is necessary for full tension development by TPA, and that TPA increases sensitivity of contractile mechanisms coupling with Ca2+.

COMPARISON OF VASOPRESSOR EFFECTS OF NITRO ARGININE IN STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS AND WISTAR-KYOTO RATS

1. NG‐nitro‐L‐arginine (NO2Arg) is a guanidine nitro arginine derivative and an inhibitor of endothelium‐dependent vascular relaxation. Significant rise of the systolic blood pressure was observed after 1 week administration of NO2Arg in food (0.023% in weight, about 2.8 mg of NO2Arg/rat per day) in female rats of stroke‐prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar‐Kyoto rats (WKY). The rises were not different between SHRSP (21 mmHg) and WKY (23 mmHg).