Alicia Seltzer

Balloon angioplasty enhances the expression of angiotensin II AT1 receptors in neointima of rat aorta.

Angiotensin II is a vasoactive peptide and may act as a growth factor in vascular smooth muscle cells. Experimental injury of the rat aorta causes rapid migration of medial smooth muscle cells and their proliferation resulting in the formation of neointima. We have examined, using quantitative autoradiography, the expression of angiotensin II receptor subtypes AT1 and AT2, and angiotensin-converting enzyme, in the neointima formed in the rat thoracic aorta 15 d after balloon-catheter injury. In contrast to the normal aortic wall, which contained both AT1 and AT2 receptors (80% and 20%, respectively), neointimal cells expressed almost exclusively angiotensin II AT1 receptors. The apparent number of these receptors was fourfold higher in the neointima compared to that in the normal aortic wall. The affinities of the neointimal receptors to angiotensin II or to the AT1 receptor antagonist, losartan, were not different from those in the normal aortic wall. Angiotensin-converting enzyme binding in the neointima was not different from that in the media of the uninjured aorta. Our data suggest that angiotensin II AT1 receptors may have a significant role in injury-induced vascular smooth muscle proliferation and migration.

Estrogens regulate angiotensin-converting enzyme and angiotensin receptors in female rat anterior pituitary

We studied the effects of the estrous cycle, ovariectomy and estrogen replacement on angiotensin-converting enzyme (ACE) (kininase II, EC 3.4.15.1) and angiotensin II (AT) receptors in the pituitary gland of the female rat. Quantitative autoradiography, with the use of consecutive pituitary sections, allowed for simultaneous determination of changes in binding and in the potential AT synthetic ability of individual pituitaries, and for a correlation between these two phenomena. In the anterior pituitary, ACE activity and binding of the ACE inhibitor [125I]-351A were not changed during the estrous cycle. Ovariectomy produced a significant increase in ACE activity and binding, and both of these parameters returned to normal after estrogen replacement. There were no changes in ACE activity or binding in the posterior pituitary during the estrous cycle or after ovariectomy or hormone replacement. AT receptors were characterized as of the AT1 type, since they were displaced by the selective AT1 antagonist DuP 753 and not by the AT2 competitor PD 123177. There were marked changes in the concentration of AT1 receptors during the estrous cycle, with highest numbers in metestrus, lower in estrus and diestrus, and lowest during proestrus. Estrogen replacement in ovariectomized rats decreased AT1 receptor number in the anterior pituitary. Our results indicate a dual effect of estrogen on anterior pituitary AT, physiologically on AT receptor expression and pharmacologically on ACE activity.

Restraining Action of GABA on Estradiol-Induced LH Surge in the Rat: GABA Activity in Brain Nuclei and Effects of GABA Mimetics in the Medial Preoptic Nucleus

The relationship between GABA dynamics and LH release was studied on day 2 after subcutaneous estrogen implant in short-term ovariectomized rats. GABA accumulation, used as an index of GABA turnover, was determined in the medial preoptic nucleus (MPN), medial (MS) and lateral (LS) septal nuclei, median eminence-mediobasal hypothalamus (MBH) and locus ceruleus (LC). Measurements of GABA were performed at two different times of day (11.00 and 15.00 h), 3 h after intraperitoneal administration of gamma-vinyl-GABA (GVG), an irreversible inhibitor of GABA transaminase. Either morning or afternoon ovariectomized rats (OVX) showed a significant increase in GABA accumulation after GVG treatment in all the areas studied. Estrogen-treated OVX rats showed in the morning a lower GABA accumulation in the MPN, MBH and LC, and GABA levels remained unchanged in the LS and MS. In the afternoon, the MPN and LS showed a lower rate of GABA accumulation whereas in the MBH and LC the GABA increase was not observed. In contrast the MS showed a rate of GABA accumulation similar as in the OVX rats. Local administration in the MPN of 20 micrograms GVG, or GABA-A receptor stimulation by muscimol (50 ng), prior to the increase in plasma LH levels, prevented the occurrence of the estradiol-induced LH surge. The effect of muscimol was reversed by bicuculline (30 ng), a GABA-A receptor antagonist. Bicuculline in low doses lacked effect by itself. In conclusion, these results strongly suggest that a decreased GABAergic activity in MPN, MBH and LC precedes the estradiol-evoked LH surges in ovariectomized rats. Moreover, that in septal nuclei, a low GABAergic activity takes place well before the occurrence of plasma LH increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Restraint stress stimulation of prolactin and ACTH secretion: role of brain histamine

The possible role of brain histamine in the release of prolactin, ACTH and corticosterone following acute restraint, was pharmacologically evaluated in adult male rats. Fifteen min of restraint caused marked increases in the plasma levels of these hormones. alpha-Fluoromethyl histidine (FH), a histidine decarboxylase inhibitor which depleted hypothalamic histamine, inhibited the enhancement of plasma prolactin levels. In contrast, plasma ACTH levels were not modified. FH treatment decreased plasma corticosterone concentrations in animals submitted to stress or in rest; this suggests a direct action of FH on the adrenal. Intraventricular (IVT) injection of ranitidine (H2 antagonist) blunted the prolactin response to restraint stress whereas its systemic administration had no effect. On the contrary, pyrilamine (H1 antagonist) given systemically decreased slightly, but significantly, the prolactin rise but when injected IVT it was ineffective. Pyrilamine was also unable to affect the ranitidine action. ACTH and corticosterone levels in plasma of restrained rats were not modified by the histamine antagonists. It is concluded that histamine is involved, mainly through central H2 receptors, in the enhancement of plasma prolactin levels produced by an acute stress. The failure of both antihistaminic compounds and a histamine depletor to alter the ACTH stimulation suggest that histamine has no participation in the hypophysio-corticoadrenal response to acute restraint.

Angiotensin II receptor subtypes and angiotensin-converting enzyme in the fetal rat brain

Angiotensin II (ANG II) receptor subtypes (AT1, displaced by losartan, and AT2, displaced by CGP 42112A) were characterized by quantitative autoradiography after incubation with the ANG II agonist [125I]Sar1-ANG II, in specific brain nuclei of 19-day-old rat embryos. Binding to AT1 receptors, located in the subfornical organ, paraventricular nucleus, nucleus of the solitary tract and choroid plexus, was sensitive to incubation with GTP gamma S. The sensitivity of AT2 receptors to GTP gamma S was heterogeneous. In the ventral thalamic, rostral hypoglossal and medial geniculate nuclei, and in the locus coeruleus, binding to AT2 receptors was sensitive to GTP gamma S and these areas belong to the AT2A subgroup. Conversely, in the inferior olive, medial (fastigial) cerebellar nucleus and caudal part of the hypoglossal nucleus, areas belonging to the AT2B subgroup, binding was insensitive to GTP gamma S. AT2 receptors were also present in cerebral arteries. In the fetal anterior pituitary, AT1 receptors predominated. The angiotensin-converting enzyme (ACE; EC 3.4.15.1) was studied by autoradiography with the selective inhibitor [125I]351A. In 19-day-old embryos, ACE was highly expressed in choroid plexus, with high concentrations in subfornical organ, posterior pituitary and cerebral arteries. No ACE binding was detected in extrapyramidal structures or anterior pituitary in 19-day-old embryos.

Inflammatory responses of the substantia nigra after acute hypoxia in neonatal rats.

The neocortex and the striatum are the brain regions most known to be particularly vulnerable to acute insults like hypoxia or ischemia. In this work, we assess the possibility of cellular damage to the substantia nigra (SN) after hypoxia-reoxygenation in the new born rat. The aim of the present paper was to evaluate the expression of growth factor IGF-I, and growth factor binding proteins IGFBP-3 and IGFBP-5 genes and induction of NOS family members (nNOS, eNOS and iNOS) and TNF-alpha genes together with glia activation, in the SN at 5 and 48 h after severe hypoxia in the 7 day-old rat, a model for the term human fetus. At early time, while IGFs remain unchanged, we found a transient increase in eNOS and nNOS. Two days after the injury, nNOS expression remained high, iNOS and TNF-alpha increased and also GFAP protein expression was observed together with a profusion of reactive astrocytes distributed throughout the SN. This study on the acute effects of hypoxia on the developing brain provides additional insights into the vulnerability of the SN, a brain region involved in neurodegenerative pathologies.

Stress and angiotensin II: novel therapeutic opportunities.

Angiotensin II was initially described as a hormone of peripheral origin, the active end product of the Renin-Angiotensin System. The subsequent discovery that Angiotensin II was locally formed and selectively regulated in most organs indicated that tissue Angiotensin II systems might play additional important roles. After initial controversy, the presence of an Angiotensin II system in the brain is now universally accepted. Brain Angiotensin II is probably involved in the regulation of many brain functions. Angiotensin II AT1 receptors are localized not only in areas related to the regulation of autonomic and endocrine control, but also in many other areas of the brain involved in emotional, sensory and motor functions. Angiotensin II AT2 receptors are more abundant in brain areas related to sensory and motor control. The roles of brain Angiotensin II appear to be multiple and complex. In addition to a regulatory role in the control of the autonomic and hormone systems, the peptide participates in brain development, sensory processes, cognition and in the regulation of cerebrovascular flow. Recent developments indicate that blockade of the brain Angiotensin II AT1 receptors not only contributes to a significant blood pressure decrease in hypertension, but that simultaneous antagonism of peripheral and brain AT1 receptors reduces the sympathoadrenal and hormonal responses to stress and prevents stress-induced gastric injury. A novel role emerges for the use of peripheral and centrally acting AT1 receptor antagonists as therapeutically advantageous for the treatment of stress-related disorders.

Characterization of brain angiotensin II AT2 receptor subtype using [125I] CGP 42112A

Recently two subtypes of angiotensin receptors have been described, AT1 and AT2. Currently used radiolabeled agonists and antagonists are not able to discriminate between these receptors subtypes. Here we characterize the use of [125I] CGP 42112A, a novel, specific ligand for AT2 receptors, in a membrane binding assay and in autoradiography of brain sections of 2 week old rats. [125I] CGP 42112A bound with high affinity and autoradiography revealed binding selectively localized to areas known to express the AT2 receptor subtype only. CGP 42112A, angiotensin II, angiotensin III and PD 123177 competed for [125I] CGP 42112A binding, with potencies consistent with high affinity and specific binding to AT2 receptors. Thus [125I] CGP 42112A will be a useful new tool to study AT2 receptors.

Enhanced angiotensin converting enzyme binding in arteries from spontaneously hypertensive rats.

Aim: To localize and measure angiotensin converting enzyme (ACE) in different vascular beds of genetically hypertensive rats Methods: Quantitative autoradiography using the angiotensin converting enzyme (E.C. 3.4.15.1) inhibitor [125I]351A Results: [125I]351A binding was significantly increased in the ascending aorta (both adventitia and intima), descending (abdominal) aorta, carotid artery and coronary arteries of adult, 12-week-old spontaneously hypertensive rats (SHR) compared with Wistar—Kyoto (WKY) rats. Increased [125I]351A binding was also present in the descending aorta of 1-week-old SHR compared with age-matched WKY rats, and both groups of young rats had much higher binding than adult rats. No difference in [125I]351A binding was found in the caudal (tail) artery of adult SHR compared with WKY rats. In both the atria and the ventricles of adult SHR, [125I]351A binding was very significantly reduced. Conclusions: Our results indicate that higher ACE concentrations occur in some arteries of genetically hypertensive rats, and support the hypothesis that local arterial concentrations of ACE affect the development and maintenance of genetic hypertension

Histamine-Induced Prolactin Release: Pharmacological Characterization of Receptors in Male Rats

Studies were undertaken to investigate the nature of receptors involved in the prolactin-releasing action of histamine in male rats. The increase of plasma prolactin levels induced by third-ventricle injection of histamine was blocked by intraventricular injection of ranitidine, an H2-antagonist, but not by systemic administration of mepyramine, an H1-antagonist. The H2-histamine agonists 4-methylhistamine and Dimaprit, given intraventricularly in unrestrained and ether-anesthetized rats, enhanced prolactin release. The effect of 4-methylhistamine was dose-dependent, whereas Dimaprit had opposite effects depending on the dose. In low doses, Dimaprit decreased whereas in higher doses it increased plasma prolactin levels. The stimulatory effects of both agonists, similar to those produced by histamine itself, were blocked by metiamide (H2-antagonist), but not by intraventricular mepyramine. High doses of mepyramine only partially decreased the effects of 4-methylhistamine. Ranitidine was able to prevent the prolactin response to 4-methylhistamine. The selective H1-histamine agonist 2,2-pyridylethylamine had no action on prolactin release. 2-Methylhistamine, which exhibits predominantly H1-mediated actions, increased the release of prolactin. Its effect, however, was blocked by low doses of metiamide and was obtained at higher concentrations than 4-methylhistamine. Mepyramine prevented 2-methylhistamine action only at high doses. It is concluded that the increased release of prolactin evoked by histamine in male rats is mainly due to its action on H2-receptors. In addition, the results altogether indicate that H1-receptors have not a significant participation.