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Biomedical subjects

J M Saavedra

Publications and source records attributed to J M Saavedra.

At least 19 recordsLinked to original sources
PubMed1992

The AT2 subtype of the angiotensin II receptors has differential sensitivity to dithiothreitol in specific brain nuclei of young rats.

We studied the effect of the sulfhydryl reducing agent dithiothreitol on the binding of the angiotensin II agonist [125I][Sar1]-angiotensin II to AT2 receptors in selected brain areas of young (2-week-old) rats. In the inferior olive and the hypoglossal nucleus, angiotensin II binding to AT2 receptors was insensitive to 5 mM dithiothreitol. Conversely, in the ventral and mediodorsal thalamic, medial geniculate, and oculomotor nuclei, the superior colliculus and the cerebellar cortex, incubation with 5 mM dithiothreitol significantly decreased angiotensin II binding to AT2 receptors to about 40% of control. These data suggest that brain AT2 receptors are heterogeneous with respect to their sensitivity to sulfhydryl reducing agents.

Angiotensin II↗
PubMed1992

Selective localization of C atrial natriuretic peptide receptors in the rat brain.

We studied the distribution of C atrial natriuretic peptide (C-ANP) receptors in the rat brain after incubation with 125I-rANP, and competition with the selective C-ANP receptor competitor C-ANP(4-23) (10(-6) M). C-ANP receptors were selectively localized to a few structures, the external plexiform layer of the olfactory bulb, the arachnoid mater and the choroid plexus, and their amount corresponds to 25%, 75% and 35%, respectively, of the ANP specific binding. These data suggest specialized functions for C-ANP receptors in brain.

Animals↗
PubMed1992

Angiotensin AT2 receptors regulate cerebral blood flow in rats.

LARGE cerebral arteries have been reported to contain angiotensin receptors that are exclusively of the AT2 subtype. We measured the effect of the AT2 receptor selective ligand PD 123319 on cerebral blood flow (CBF) in rats, using laser-doppler flowmetry. PD 123319 (1-10 mg kg-1) dose-dependently inhibited the increase in CBF, when the blood pressure was increased by a norepinephrine infusion. However, PD 123319 did not alter baseline CBF at normal blood pressures. Therefore PD 123319 appears to interfere with the autoregulatory mechanisms of CBF. The participation of AT2 receptors in the regulation of CBF confirms a physiological role for this receptor subtype, and may give clues for future treatment of various cerebrovascular disorders.

Angiotensin II↗
PubMed1992

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.

Animals↗
PubMed1992

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.

Angiotensin II↗
PubMed1992

Pineal muscarinic phosphoinositide responses: age-associated sensitization, agonist-induced desensitization and increase in melatonin release from cultured pineal glands.

Regulation of phosphoinositide (PI) signaling through the muscarinic cholinergic receptors (mAChRs) and their possible role were explored in the rat pineal gland. A sensitization of the PI signaling pathway was seen with advancing age. Binding of the mAChR ligand [N-methyl-3H]scopolamine to pineal sections, as detected by autoradiography, significantly decreased with advancing age and thus negatively correlated with the gland's ability to respond to cholinergic stimulus. The cholinergic agonist carbachol induced a time-dependent desensitization of the muscarinic PI signaling after 2 h of pretreatment in vitro (43 and 61% dampening of the PI response after 2 and 11 h pretreatment, respectively). This homologous desensitization was not mimicked by forskolin or phorbol esters, suggesting that proteins kinases A and C were not involved. Carbachol stimulation of the pineal glands in vitro increased melatonin release 2-fold, an effect quantitatively similar to that seen after adenylyl cyclase activation. Carbachol failed, however, to affect pineal cAMP levels. These results suggest that the PI signaling through pineal mAChRs is desensitized in young rats, possibly due to higher exposure to endogenous acetylcholine. Thus acetylcholine might play a prominent role in the developing gland. Moreover, acetylcholine could modulate melatonin release from the adult pineal gland in vivo.

Aging↗
PubMed1992

Differential expression of melatonin receptors in spontaneously hypertensive rats.

Quantitative autoradiography was used to compare melatonin receptors in brain areas and arteries of young (4 weeks old) and adult (14 weeks old) spontaneously hypertensive rats (SHR) to those in age-matched normotensive controls, Wistar-Kyoto (WKY) rats. Age and strain influenced the number of melatonin receptors in an anatomically selective manner, and the most striking changes occurred in arterial receptors. Melatonin receptors were not detectable in the anterior cerebral arteries of adult SHR. In the caudal artery, melatonin receptors decreased with age in both strains, but the decrease was more pronounced in SHR. When compared to age-matched WKY rats, the number of caudal artery receptors was higher in young and lower in adult SHR. The number of melatonin receptors was higher in the area postrema of adult SHR when compared to adult WKY rats, but in the suprachiasmatic nucleus, no such differences between the two strains were present. Alterations in receptor density were not accompanied by changes in binding affinity. Our results indicate that in the rat melatonin receptors show different developmental patterns according to location and that the receptors may be expressed differentially in genetic hypertension.

Age Factors↗
PubMed1992

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.

Angioplasty, Balloon↗
PubMed1992

Differential regulation of the rat melatonin receptors: selective age-associated decline and lack of melatonin-induced changes.

To gain some understanding of the factors regulating high affinity melatonin (MT) receptors in the rat, we conducted a series of studies using quantitative autoradiography of [2-125I]iodo-MT binding in vitro with validated assay conditions. MT receptor status and the relative protein content of the autoradiographic sections were assessed in the anterior pituitary gland, the area postrema, the caudal (tail) artery (CA), the anterior cerebral artery (ACA), and the suprachiasmatic nuclei (SCN) of 9-, 96-, and 306-day-old Wistar rats. When age-associated changes in protein content were taken into account, MT receptor expression in the area postrema and the SCN remained relatively constant between 9-306 days of age. On the contrary, a dramatic loss of MT receptors was observed in the arteries of 306-day-old rats (98% and 89% loss compared to the 9-day-old rats in the ACA and CA, respectively). In the anterior pituitary gland, MT receptors were expressed only in the 9-day-old rats. The above changes reflected major changes in binding capacity and minor changes in binding affinity. Neither removal of endogenous circulating MT (acute light exposure for 24 h, pinealectomy, or superior cervical ganglionectomy) nor MT injections (1 mg/kg for 10 days 6 h after lights on) affected MT receptor status in the ACA, CA, area postrema, or SCN. Our data suggest that MT receptor expression is differentially regulated during development and that permanent alterations in MT levels do not affect rat MT receptor status.

Age Factors↗
PubMed1992

Melatonin-binding sites in brain and caudal arteries of the female rat during the estrous cycle and after estrogen administration.

Melatonin-binding sites were studied by quantitative autoradiography in brain and caudal (tail) arteries and in selected brain areas of cycling female rats, ovariectomized rats, and ovariectomized rats treated with estradiol. In the caudal artery, the number of melatonin-binding sites was significantly lower during proestrus, estrus, and metestrus than during diestrus. In ovariectomized rats, melatonin binding to the caudal artery was similar to that found during proestrus, estrus, and metestrus, and a further decrease in the receptor number was produced by estradiol replacement. Similarly, melatonin binding in anterior cerebral arteries was higher during diestrus than at other stages of the estrous cycle. In ovariectomized rats, estradiol replacement also resulted in decreased melatonin binding in anterior cerebral arteries. Conversely, no changes in the number of melatonin-binding sites were observed in the suprachiasmatic nucleus or the area postrema during the estrous cycle, in ovariectomized rats, or after estradiol replacement. The present results suggest that in the female rat, reproductive hormones modulate the expression of cerebral and caudal arterial melatonin-binding sites.

Animals↗
PubMed1992

Chemical lesion of the circumventricular organs with monosodium glutamate reduces the blood pressure of spontaneously hypertensive but not of one kidney-one clip hypertensive rats.

Subcutaneous injection of monosodium glutamate (MSG) on days 1, 5 and 9 of the experiment (5 g/kg per day) significantly reduced the blood pressure of a group of 10 spontaneously hypertensive rats (SHR) measured 7 and 14 days after treatment (200 +/- 7 mmHg vs 172 +/- 8 mmHg or 185 +/- 3 mmHg, respectively), without affecting that of 11 age-matched Wistar Kyoto (WKY) rats (127 +/- 7 mmHg vs 123 +/- 5 mmHg and 119 +/- 5 mmHg, respectively). Using autoradiographic methods and 125I-Sar1-angiotensin II, receptor binding was shown to be higher in the subfornical organ (SFO) of SHR (332 +/- 31 fmol/mg protein) when compared to WKY rats (240 +/- 30 fmol/mg protein) and similar (222 +/- 21 vs 170 +/- 14 fmol/mg protein) in the paraventricular nucleus (PVN). Binding to angiotensin-converting enzyme (ACE) was evaluated using the ACE inhibitor 125I-351A as ligand. Binding to ACE was lower in SHR in the PVN and the globus pallidus (GP) of SHR when compared to WKY rats (PVN: 111 +/- 9 vs 172 +/- 13 and GP: 163 +/- 2 vs 213 +/- 7 fmol/mg protein) and similar in the SFO, choroid plexus (ChP) and caudate nucleus (CD) of both strains (SFO: 779 +/- 107 vs 805 +/- 169; ChP: 2,780 +/- 210 vs 3,140 +/- 360 and CD: 461 +/- 42 vs 424 +/- 18 fmol/mg protein). No changes in angiotensin II (Ang II) receptor number or binding to ACE were detected in these brain areas after MSG treatment of SHR or WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Heterogeneity of angiotensin II AT2 receptors in the rat brain.

Angiotensin II (AT) receptor subtypes (AT1, selectively displaced by DuP 753, and AT2, selectively displaced by PD123177 and CGP42112A) were characterized by quantitative autoradiography after incubation with the AT agonist 125I-Sar1-AT, in specific brain nuclei of young (2-week-old) rats. Binding to AT1 receptors was sensitive (decreased affinity) to incubation in the presence of guanosine 5'-O-(3-thio)triphosphate (GTP gamma S). Only the AT1 receptors in the paraventricular nucleus were sensitive to pertussis toxin, indicating the possibility of the existence of AT1 receptor subtypes. The sensitivity of AT2 receptors to GTP gamma S was heterogeneous. In the ventral thalamic and medial geniculate nuclei and in the locus coeruleus, binding to AT2 receptors was sensitive to GTP gamma S and to pertussis toxin pretreatment. Conversely, in the inferior olive, binding was insensitive to GTP gamma S and to pertussis toxin pretreatment. We propose the nomenclature of AT2A receptors for those receptors sensitive to guanine nucleotides and pertussis toxin and that of AT2B receptors for those showing no sensitivity to guanine nucleotides or pertussis toxin treatment.

Angiotensin II↗
PubMed1991

Angiotensin II AT1 receptors in rat superior cervical ganglia: characterization and stimulation of phosphoinositide hydrolysis.

Angiotensin II receptor number was higher in superior cervical ganglia of 2-week-old when compared to 8-week-old rats. In both young and adult rats, specific binding of [125I][Sar1]angiotensin II was displaced competitively by the AT1-receptor antagonist DuP 753 but not by the AT2-receptor competitor PD 123177. In ganglia from adult rats, DuP 753 competed with an IC50 of 113 nM. The stable guanine nucleotide GTP gamma S inhibited binding of [125I][Sar1]angiotensin II in young and adult rats by approximately 50% with IC50 values of 105 and 120 nM, respectively, suggesting that the angiotensin receptor is G-protein linked. Angiotensin II at a dose of 1 microM stimulated inositol phosphate formation 58% over control values in superior cervical ganglia from 8-week-old rats. This effect was totally blocked by 10 microM DuP 753 but not by 10 microM PD 123177. Our findings demonstrate that rat superior cervical ganglia contain AT1-type angiotensin receptors that are probably G-protein linked, and their stimulation results in increased inositol phospholipid metabolism.

Angiotensin II↗
PubMed1991

Differential development of insulin-like growth factor-I binding in the hypothalamus of hamster and rat.

We investigated the binding of [125]insulin-like growth factor-I ([125I]IGF-I) within the hamster suprachiasmatic nucleus (SCN) and median eminence (ME) by quantitative autoradiography and compared the development of binding to the same regions in the rat. Binding in the hamster SCN was to a single class of sites (estimated Kd = 6 x 10(-10) M). Binding in the ME was approx. 1.5-fold that of the SCN. Full displacement of binding from the SCN and ME of adults and neonates was achieved by 10(-8) M IGF-I, 10(-8) M IGF-II or 10(-6) M insulin. Binding within the hamster SCN was evident by E15, peaked between P5 and P7 and decreased to adult levels by P20 while binding in the rat SCN peaked perinatally and declined to adult levels by P6. Binding in the hamster ME was evident at P4, peaked by P12 and decreased to adult levels by P20 while binding in rat ME was present by P2, peaked by P7 and declined to adult levels by P9. These results demonstrate a different developmental time course for [125I]IGF-I binding between the SCN and ME of hamster and rat. The peak binding in the SCN of each species correlates with previously reported time courses for onset of retinohypothalamic innervation of the SCN. Further study of IGFs in these regions may help elucidate the developmental role of brain IGFs.

Animals↗
PubMed1991

Changes in expression of angiotensin receptor subtypes in the rat aorta during development.

Quantitative autoradiography was used to characterize angiotensin AT1 and AT2 receptors, in the rat aorta at three developmental ages; embryonic day 18 (E18), and postnatal weeks 2 and 8. The expression of angiotensin receptors was higher in the aorta of E18 and 2-week-old rat. A major proportion of the angiotensin receptors expressed in the aorta at these two ages was AT2 (84 and 81% respectively). Conversely, in the aorta of 8-week-old rats, AT1 was the predominant angiotensin receptor subtype (71%). In 8-week-old rats, the AT2 subtype was also present (28%). In pre- and postnatal rats, [125I]Sar1-angiotensin II binding to AT1 receptors was sensitive to GTP gamma S whereas binding to AT2 receptors was not. AT2 receptors may serve an important role during stages of rapid growth of the aorta, and also have a significant function in the adult vasculature.

Aging↗
PubMed1991

Different effects of chronic K+ depletion on forebrain and peripheral angiotensin II receptors in young rats.

K+ depletion stimulates the circulating renin-angiotensin system and affects the regulation of peripheral angiotensin II receptors. The effects of K+ depletion on the regulation of central angiotensin II receptors are unknown. We studied the effects of selective K+ depletion (less than 0.05% in diet for 16 days) on angiotensin II receptor number in kidneys, adrenal glands, and selected brain areas of young rats. K+ depletion caused a significant increase in plasma renin activity and significantly decreased angiotensin II receptor number in the kidney glomeruli and medulla, and in the adrenal zona glomerulosa and adrenal medulla. In the brain, the angiotensin II receptor number was unchanged in the subfornical organ and the hypothalamic paraventricular nucleus after 16 days of K+ depletion. An additional NaCl supplementation (0.02% in the drinking water) to K(+)-depleted rats produced a decrease in plasma renin activity but failed to affect subfornical organ or paraventricular angiotensin II receptor number. Our results suggest that in young animals, K+ depletion has a significant impact on the peripheral renin-angiotensin system without affecting the density of forebrain angiotensin II receptors.

Adrenal Glands↗
PubMed1991

Type-1 and type-2 angiotensin II receptors in fetal rat brain.

Brain angiotensin II receptors were located in 18-day-old rat embryos by quantitative autoradiography. In the nucleus of the solitary tract and choroid plexus, binding was displaced by the type-1 antagonist DuP 753. In the inferior olive, paratrigeminal and hypoglossal nuclei, binding was displaced by the type-2 antagonist CGP 42112 A. Meninges and cephalic soft tissues contained predominantly type-2 angiotensin II receptors. Our results indicate a role for type-1 and type-2 angiotensin II receptors during brain development.

Angiotensin II↗