Nitric oxide inhibits the release of norepinephrine and dopamine from the medial basal hypothalamus of the rat.

A. SEILICOVICH; M.LASAGA,; M.BEFUMO,; B.DUVILANSKI,; M.C. DÍAZ,; V RETTORI,; S.M.MCCANN,

Proceedings of the National Academy of Sciences of the United States of America

NATL ACAD SCIENCES

Año: 1995 vol. 92 p. 11299 - 11302

0027-8424

Previous research indicates that norepinephrine and dopamine stimulate release of luteinizing hormohe (LH)-releasing hormone (LHRH), which then reaches the adenohypophysis via the hypophyseal portal vessels to release LH. Norepinephrine exerts its effect via ol-adrenergic receptors, which stimulate the release of nitric oxide (NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.via the hypophyseal portal vessels to release LH. Norepinephrine exerts its effect via ol-adrenergic receptors, which stimulate the release of nitric oxide (NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.Norepinephrine exerts its effect via ol-adrenergic receptors, which stimulate the release of nitric oxide (NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.(NO) from nitricoxidergic (NOergic) neurons in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.in the medial basal hypothalamus (MBH). The NO activates guanylate cyclase and cyclooxygenase, thereby inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.inducing release of LHRH into the hypophyseal portal vessels. We tested the hypothesis that these two catecholamines modulate NO release by local feedback.two catecholamines modulate NO release by local feedback. MBH explants were incubated in the presence of sodium nitroprusside (NP), a releaser of NO, and the effect on release of catecholamines was determined. NP inhibited release of norepinephrine. Basal release was increased by incubation of the tissue with the NO scavenger hemoglobin (20 ,ig/ml).were incubated in the presence of sodium nitroprusside (NP), a releaser of NO, and the effect on release of catecholamines was determined. NP inhibited release of norepinephrine. Basal release was increased by incubation of the tissue with the NO scavenger hemoglobin (20 ,ig/ml).was determined. NP inhibited release of norepinephrine. Basal release was increased by incubation of the tissue with the NO scavenger hemoglobin (20 ,ig/ml).hemoglobin (20 ,ig/ml). Hemoglobin also blocked the inhibitory effect of NP. In the presence of high-potassium (40 mM) medium to depolarize cell membranes, norepinephrine release was increased by aalso blocked the inhibitory effect of NP. In the presence of high-potassium (40 mM) medium to depolarize cell membranes, norepinephrine release was increased by ato depolarize cell membranes, norepinephrine release was increased by amembranes, norepinephrine release was increased by a factor of 3, and this was significantly inhibited by NP. Hemoglobin again produced a further increase in norepinephrine release and also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitor3, and this was significantly inhibited by NP. Hemoglobin again produced a further increase in norepinephrine release and also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitora further increase in norepinephrine release and also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitorand also blocked the action of NP. When constitutive NO synthase was inhibited by the competitive inhibitorwas inhibited by the competitive inhibitor NG-monomethyl-L-arginine (NMMA) at 300 ,iM, basal release of norepinephrine was increased, as was potassium-evoked(NMMA) at 300 ,iM, basal release of norepinephrine was increased, as was potassium-evokednorepinephrine was increased, as was potassium-evoked release, and this was associated in the latter instance with awas associated in the latter instance with a decrease in tissue concentration, presumably because synthesis did not keep up with the increased release in the presence of NMMA. The results were very similar with dopamine, except that reduction of potassium-evoked dopamine releasetissue concentration, presumably because synthesis did not keep up with the increased release in the presence of NMMA. The results were very similar with dopamine, except that reduction of potassium-evoked dopamine releasenot keep up with the increased release in the presence of NMMA. The results were very similar with dopamine, except that reduction of potassium-evoked dopamine releasewere very similar with dopamine, except that reduction of potassium-evoked dopamine releasethat reduction of potassium-evoked dopamine release by NP was not significant. However, the increase followingNP was not significant. However, the increase following incubation with hemoglobin was significant, and hemoglobin, when incubated with NP, caused a significant elevation inwith hemoglobin was significant, and hemoglobin, when incubated with NP, caused a significant elevation ina significant elevation in dopamine release above that with NP alone. In this case, NPrelease above that with NP alone. In this case, NP increased tissue concentration of dopamine along with inhibitingiting release, suggesting that synthesis continued, thereby raising the tissue concentration in the face of diminished release. When the tissue was incubated with NP plus hemoglobin, which caused an increase in release above that obtained with NP alone, the tissue concentration decreasedsuggesting that synthesis continued, thereby raising the tissue concentration in the face of diminished release. When the tissue was incubated with NP plus hemoglobin, which caused an increase in release above that obtained with NP alone, the tissue concentration decreasedwas incubated with NP plus hemoglobin, which caused an increase in release above that obtained with NP alone, the tissue concentration decreasedan increase in release above that obtained with NP alone, the tissue concentration decreased significantly compared with that in the absence of hemoglobin,with that in the absence of hemoglobin, indicating that, with increased release, release exceededthat, with increased release, release exceeded synthesis, causing a fall in tissue concentration. When NOa fall in tissue concentration. When NO synthase was blocked by NMMA, the release of dopamine,was blocked by NMMA, the release of dopamine, under either basal or potassium-evoked conditions, was increased.either basal or potassium-evoked conditions, was increased. Again, in the latter instance the tissue concentration declined significantly, presumably because synthesis did notin the latter instance the tissue concentration declined significantly, presumably because synthesis did notsignificantly, presumably because synthesis did not match release. Therefore, the results were very similar withTherefore, the results were very similar with both catecholamines and indicate that NO acts to suppressand indicate that NO acts to suppress release of both amines. Since both catecholamines activate theof both amines. Since both catecholamines activate the release of LHRH, the inhibition of their release by NO serves as an ultra-short-loop negative feedback by which NO inhibits the release of the catecholamines, thereby reducing the activation of the NOergic neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.ultra-short-loop negative feedback by which NO inhibits the release of the catecholamines, thereby reducing the activation of the NOergic neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.reducing the activation of the NOergic neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.neurons and decreasing the release of LHRH. This may be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.be an important means for terminating the pulses of release of LHRH, which generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.generate the pulsatile release of LH that stimulates gonadal function in both male and female mammals.