A neuromodulatory role for neuronal nitric oxide in the rabbit renal artery.

1. The effects of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on vasoconstrictor responses to transmural electrical nerve stimulation and noradrenaline were examined in the rabbit isolated renal artery with and without an intact endothelium. In addition, the effect of removing the endothelium from the renal artery on vasoconstrictor responses to transmural electrical nerve stimulation and noradrenaline was also investigated. Immunohistofluorescence techniques were carried out to determine if there were any nitrergic nerves supplying the renal artery. 2. The vasoconstriction produced in response to transmural electrical nerve stimulation (2-64 Hz) was significantly enhanced in the presence of L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M). 3. L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M) did not significantly affect the maximum vasoconstriction produced in response to noradrenaline. However, the noradrenaline dose-response curve was significantly shifted to the left by the addition of L-NAME (3 x 10(-6), 10(-5), 3 x 10(-5) and 10(-4) M). 4. The increase in the amplitude of the vasoconstriction, produced in response to transmural electrical nerve stimulation (16 Hz) and noradrenaline (10(-5) M) in the presence of L-NAME (10(-5) M) was not observed when L-arginine (10(-3) M) was added in addition to L-NAME (10(-5) M). 5. Removing the endothelium did not significantly affect the response to transmural electrical nerve stimulation (1-64 Hz). The maximum vasoconstriction in response to noradrenaline was also unaffected by the removal of the endothelium. The pD2 value for noradrenaline obtained from vessels with no endothelium was significantly greater than the pD2 value obtained from vessels with an intact endothelium (5.90 +/- 0.11 and 5.16 +/- 0.03, respectively). 6. On renal artery segments with no endothelium L-NAME (3 x 10(-5) M) significantly enhanced the response to transmural electrical nerve stimulation (2-64 Hz). L-NAME did not affect the maximum response to noradrenaline. However, there was a significant shift to the right of the noradrenaline doseresponse curve in the presence of L-NAME (3 x 10(-5) M). 7. Both nitric oxide synthase-containing and NADPH-diaphorase stained nerves were located on the adventitial-medial border of the rabbit renal artery. 8. The present study has suggested a presynaptic inhibitory action for nitric oxide (probably derived from identified perivascular nitrergic nerves), on perivascular sympathetic vasoconstrictor nerve mediated responses of the rabbit renal artery. In contrast, the enhancement of the response to noradrenaline by L-NAME can be attributed to inhibition of the synthesis of endothelium-derived nitric oxide.

Release of vasoactive agents from the isolated perfused human ovary.

OBJECTIVE: To investigate local vascular control in the isolated perfused premenopausal human ovary by measuring flow-induced release of vasoactive substances. DESIGN: Release of adenosine 5' triphosphate (ATP), substance P (SP), endothelin (ET), and vasopressin (AVP) from the ovarian vascular endothelium was estimated in perfusate under basal conditions and during two periods of increased flow. MAIN OUTCOME MEASURES: Vascular resistance; ATP, SP, ET and AVP release. RESULTS: The mean ratio (pressure/flow during increased flow):(pressure/flow at basal flow) was 1.27 +/- 0.04 for the first, and 1.15 +/- 0.05 for the second period of increased flow (n = 10), indicating significant vasoconstriction (P < 0.01 and 0.05, respectively), present to a greater extent during the first period of increased flow compared to the second (P < 0.05). ATP release was seen in response to increased flow (n = 8, P < 0.05). From 12 ovarian bed preparations, five released ET and SP and three of these released AVP. Four of the five perfused ovaries that released peptides contained either a developing follicle or a corpus luteum while all those that showed no peptide release were inactive. CONCLUSIONS: ATP release may play a role in the local control of the human premenopausal ovarian vasculature independent of ovulatory status. Peptides may also contribute to local vascular control in the ovary and their release from predominantly active ovaries suggests a relationship between ovulation and vascular endothelial function.

ATP release from the isolated perfused guinea pig heart in response to increased flow.

The Langendorff heart preparation was used to investigate the release of ATP from the guinea pig heart in response to increased coronary flow. The lucifer-in-luciferase firefly technique was used to determine levels of ATP in the perfusate. During periods of increased flow, ATP release was rapidly and significantly increased by at least tenfold the basal release. The pressure/flow ratio was reduced in increased-flow conditions suggesting that coronary vasodilatation had occurred. It is concluded that ATP release from the guinea pig heart is increased under raised-flow conditions. It is suggested that this ATP release induces coronary vasodilatation.

Differential effects of ATP- and 2-methylthioATP-induced relaxation in guinea pig coronary vasculature.

The Langendorff heart preparation was used to investigate the mechanism of action of vasodilatation evoked by ATP and its analogues in guinea pig coronary vasculature. The relative order of potency of ATP and its analogues in causing a reduction in perfusion pressure was 2-methylthioATP (2-meSATP) > ATP > beta, gamma-methyleneATP (beta,gamma-meATP) > or = alpha,beta-methyleneATP (alpha,beta-meATP), thus establishing the presence of P2y-purinoceptors in this preparation. L-NG-nitroarginine methyl ester (L-NAME, 3 x 10(-5) M) significantly attenuated both the area under the flow-time curve and the maximum decrease in perfusion pressure of the vasodilatation produced in response to 2-meSATP (5 x 10(-12)-5 x 10(-9) mol). However, for ATP (5 x 10(-7)-5 x 10(-10) mol), L-NAME 3 x 10(-5) M significantly attenuated the area under the flow-time curve of the response but did not reduce the maximum decrease in perfusion pressure except at one low dose (5 x 10(-10) mol). L-Arginine 1.5 x 10(-3) M significantly reversed inhibition of the area under the flow-time curve of the response to 2-meSATP 5 x 10(-10) mol and ATP 5 x 10(-8) mol by L-NAME 3 x 10(-5) M. The maximum decrease in perfusion pressure of the response to ATP 5 x 10(-10)-5 x 10(-7) mol was significantly attenuated in the presence of indomethacin 10(-6) M.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of suramin on vasodilator responses to ATP and 2-methylthio-ATP in the Sprague-Dawley rat coronary vasculature.

The effect of suramin, a P2 purinoceptor antagonist, on the vasodilator response to adenosine 5'-triphosphate (ATP), 2-methylthio-ATP (2-meSATP) and adenosine were examined in the Sprague-Dawley rat coronary vasculature using the Langendorff heart preparation. Relaxation induced by 2-meSATP was significantly inhibited by suramin. Only responses to low doses of adenosine and ATP were inhibited by suramin. 8-(p-Sulphophenyl)theophylline (8-PSPT) did not affect the relaxant response to ATP and 2-meSATP at a concentration that significantly inhibited the response to adenosine. It is concluded that 2-meSATP acts via P2Y purinoceptors while ATP appears to be acting largely through a different mechanism. It is not acting via a P1 purinoceptor because ATP was not inhibited by the P1 purinoceptor antagonist 8-PSPT.

Effects of pyrimidines on the guinea-pig coronary vasculature.

1. The effects of the pyrimidines, uridine 5'-triphosphate (UTP), thymidine 5'-triphosphate (TTP) and cytidine 5'-triphosphate (CTP), were examined in the guinea-pig coronary bed, by use of a Langendorff technique. Comparisons were made with the actions of the purines adenosine 5'-triphosphate (ATP), inosine 5'-triphosphate (ITP) and guanosine 5'-triphosphate (GTP). The effect of, the nitric oxide synthase inhibitor, L-NG-nitroarginine methyl ester (L-NAME) and, the prostaglandin synthesis inhibitor, indomethacin on the vasodilator response to these purines and pyrimidines was examined. The effects of these inhibitors were assessed on their ability to inhibit both the amplitude and the area of the vasodilator response. 2. The relative order of potency of the purines and pyrimidines studied was ATP > UTP > ITP >> GTP, TTP, CTP. 3. The maximum amplitude and area of the vasodilator response to the pyrimidines, UTP (5 x 10(-10)-5 x 10(-7) mol), TTP (5 x 10(-8)-5 x 10(-7) mol) and CTP (5 x 10(-7) mol), and purines, ITP (5 x 10(-9)-5 x 10(-7) mol) and GTP (5 x 10(-8)-5 x 10(-7) mol), were significantly reduced by L-NAME (3 x 10(-5) and 10(-4) M). 4. The inhibition of the response to ATP (5 x 10-8 mol), UTP (5 x 10-8 mol), ITP (5 x 10-8 mol), TTP(5 x 10-7 mol), CTP (5 x 10- mol) and GTP (5 x 10- mol) by L-NAME (3 x 10-5 M) was significantly reversed by L-arginine (1.5 x 10-3 M).5. L-NAME (3 x 10-5 and 10-4 M) only inhibited the amplitude of the vasodilator response to a low dose of ATP (5 x 10-mol), although the area of vasodilator response to ATP(5 x 10-11-5 x 10-7 mol) was significantly reduced by L-NAME (3 x 10-5 and 10-4 M).6. The maximum amplitude of the vasodilator response to ATP (5 x 10-10-5 x 10-7 mol) was significantly reduced by indomethacin (10-6 M), although the area of the vasodilator response to ATP was only significantly reduced at one intermediate dose (5 x 10-9 mol). Indomethacin (10-6 M) did not affect the maximum amplitude or area of the vasodilator responses to UTP (5 x 10-11-5 x 10-7 mol),ITP (5 x 10-10-5 x 10-7 mol), CTP (5 x 10-7 mol), TTP (5 x 10-8-5 x 10-7 mol) and GTP(5 x 10-8-5 x 10-7 mol).7. It is concluded that in the guinea-pig coronary vasculature, the vasodilatation evoked by the pyrimidines, UTP, TTP and CTP, was mediated in large part via nitric oxide, as were the vasodilatations evoked by the purines ITP and GTP. The vasodilatations evoked by ATP, however, appear to involve prostanoids in addition to the release of nitric oxide.

A2-purinoceptor-mediated relaxation in the guinea-pig coronary vasculature: a role for nitric oxide.

1. The Langendorff heart preparation was used to investigate the mechanism of action of the endothelium-dependent vasodilatation evoked by adenosine and its analogues in the guinea-pig coronary vasculature. 2. The relative order of potency of adenosine and its analogues in causing a reduction in perfusion pressure was D-5'-(N-ethylcarboxamide)adenosine (NECA) = 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N- ethylcarboxamidoadenosine (CGS 21680)> R-N6-(2-phenylisopropyl)adenosine (R-PIA) = adenosine = 2-chloroadenosine (2-CA) > S-N6-(2-phenylisopropyl)adenosine (S-PIA) = N6-cyclopentyl-adenosine (CPA); thus suggesting the presence of A2-purinoceptors in this preparation. 3. 8-(p-Sulphophenyl)theophylline (8-PSPT; 3 x 10(-5) M) significantly reduced both the maximum amplitude and area of the vasodilatation produced in response to adenosine (5 x 10(-10) -5 x 10(-8) mol) without having any effect on the response to the P2-purinoceptor agonist, 2-methylthioATP. The relaxation induced by adenosine (5 x 10(-12) -5 x 10(-8) mol) was unaffected by the selective A1-purinoceptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 10(-8) M). This antagonist profile suggests that only A2-purinoceptors are present in the guinea-pig coronary vasculature. 4. The areas of the vasodilator response to adenosine (5 x 10(-10) -5 x 10(-7 mol), NECA (5 x 10(-12) -5 x 10(-7) mol) and CGS 21680 (5 x 10(-12) -5 x 10(-10) mol) were significantly reduced by NG-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) M). The amplitude of the responses to low concentrations of adenosine (5 x 10-10-5 x 10-9mol), NECA (5 x 1011 mol) and CGS 21680 (5 x 1011-5 x 10-9mol)were significantly reduced by L-NAME (3 x 10-5 M).5. L-Arginine (1.5 x 10-3 M) significantly reversed the inhibition, by L-NAME (3 x 10-5 M), of the relaxant response to adenosine (5 x 10-8 mol), NECA (5 x I0- mol) and CGS 21680 (5 x 10-11 mol).6. Indomethacin (10-6 M) did not inhibit the response to adenosine, except at low doses (5 x 10-11-5 x 10-10 mol).7. It is concluded that in the guinea-pig coronary vasculature, while a major part of the vasodilator action of adenosine is probably directly via A2-receptors on the smooth muscle, activation of a subpopulation of A2-purinoceptors on endothelial cells by adenosine and its analogues induces relaxation via production of nitric oxide; prostanoids appear to play a minimal role in the relaxation induced by adenosine as in most other preparations.

Effects of nitric oxide synthase inhibitors, L-NG-nitroarginine and L-NG-nitroarginine methyl ester, on responses to vasodilators of the guinea-pig coronary vasculature.

1. The effects of L-NG-nitroarginine (L-NOARG) and L-NG-nitroarginine methyl ester (L-NAME) on vasodilatation induced by ATP, substance P, 5-hydroxytryptamine (5-HT), bradykinin and sodium nitroprusside (SNP) were examined in the guinea-pig coronary bed, by use of a Langendorff technique. The effects of these inhibitors of nitric oxide synthesis were assessed on their ability to inhibit both the amplitude and the area of the vasodilator response. 2. The vasodilator responses evoked by low doses of 5-HT (5 x 10(-10)-10(-8) mol) were almost abolished by L-NAME and L-NOARG (both at 10(-5), 3 x 10(-5) and 10(-4) M), although L-NOARG (3 x 10(-5) M) was significantly less potent than L-NAME (3 x 10(-5) M) as an inhibitor of vasodilator responses to 5-HT (5 x 10(-8) mol). 3. The vasodilator responses evoked by substance P (5 x 10(-12)-5 x 10(-9) mol) were reduced in the presence of L-NAME and L-NOARG (both at 10(-5) and 3 x 10(-5) M). The response to substance P was almost abolished by L-NAME and L-NOARG (both at 10(-4) M). 4. The amplitude of the vasodilator responses to ATP (5 x 10(-11) and 5 x 10(-9)-5 x 10(-7) mol) was little affected by either L-NAME or L-NOARG (both at 10(-5), 3 x 10(-5) and 10(-4) M).7. It is concluded that in the guinea-pig coronary vasculature, the vasodilatation evoked by substance P and low doses of 5-HT is mediated almost exclusively via nitric oxide, whereas the vasodilatations evoked by ATP and bradykinin appear to involve other mechanisms in addition to the release of nitric oxide. L-NAME was a more effective agent than L-NOARG in inhibiting the vasodilator actions of 5-HT and ATP in this preparation.