Biomedical subjects

R C Speth

Publications and source records attributed to R C Speth.

At least 55 records · Page 3Linked to original sources

PubMed1991

The AT2 angiotensin receptor subtype predominates in the 18 day gestation fetal rat brain.

The angiotensin II receptor subtype-specific antagonists Dup 753 (AT1) and PD 123177 (AT2) were used to characterize the angiotensin II receptor subtypes present in 18 day gestation fetal Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rat brain using in vitro receptor autoradiography. The AT2 subtype was predominant in the brain of both rat strains, even in areas that display predominantly the AT1 subtype in the adult rat brain.

Angiotensin II↗

PubMed1991

Sulfhydryl reducing agents distinguish two subtypes of angiotensin II receptors in the rat brain.

Two angiotensin II receptor subtypes were distinguished in the rat brain using in vitro receptor autoradiography based on the differential effects of sulfhydryl reducing agents on 125I-sarcosine1,isoleucine8 angiotensin II binding in various brain nuclei. At several nuclei, e.g. the hypothalamus, circumventricular organs and the dorsal medulla, 125I-sarcosine1,isoleucine8 angiotensin II binding was strongly inhibited by 30 mM beta-mercaptoethanol or 5 mM dithiothreitol, whereas at other nuclei, e.g. the lateral septum, colliculi, locus coeruleus and medial amygdala, sulfhydryl reducing agents had either little effect on radioligand binding or enhanced the binding. The distribution of the sulfhydryl reducing agent inactivated subtype corresponds exactly with the distribution of DuP 753 sensitive (designated as AII alpha) 125I-sarcosine1,isoleucine8 angiotensin II binding sites25. The subtype not inhibited by sulfhydryl reducing agents corresponds with the DuP 753 insensitive (designated as AII beta) sites in the brain25. The sulfhydryl reducing agent effect on brain angiotensin II receptor subtypes is similar to that seen in angiotensin II receptor subtypes in peripheral tissues. These observations indicate that many previous studies of brain angiotensin II receptor binding that included 5 mM dithiothreitol in the assay medium overlooked the sulfhydryl reducing agent inactivated (AII alpha) receptor subtype.

Angiotensin II↗

PubMed1991

Discrimination of angiotensin II receptor subtype distribution in the rat brain using non-peptidic receptor antagonists.

The non-peptidic angiotensin II receptor subtype selective antagonists, DuP 753 and PD123177, were used to characterize angiotensin II receptor binding sites in the rat brain. Competitive receptor autoradiography with 125I-Sar1-Ile8 angiotensin II defined a regional distribution of binding sites that were sensitive to either DuP 753 (designated AII alpha subtype) or PD123177 (designated AII beta subtype). Whereas most brain nuclei could be assigned to a category containing a predominant subtype, a multiple receptor subtype analysis indicated that some regions are homogeneous, while others contain a mixture of both AII alpha and AII beta subtypes.

Angiotensin II↗

PubMed1991

Pertussis toxin blocks the dipsogenic actions of carbachol, but does not block the dipsogenic and pressor actions of angiotensin II.

Rats were tested for dipsogenic and pressor responses to intracerebroventricularly (icv) administered Ang II and for dipsogenic responses to icv administered carbachol in the absence and presence of pertussis toxin, also administered icv. Pertussis toxin did not inhibit the pressor or dipsogenic responses to Ang II, but did inhibit the dipsogenic responses to carbachol. This suggests that the pressor and dipsogenic responses to Ang II in the brain are not mediated by a pertussis toxin-sensitive G protein, but that the muscarinic cholinergic dipsogenic response is mediated by a pertussis toxin-sensitive G protein.

Angiotensin II↗

PubMed1991

Angiotensin II and the locus coeruleus.

The locus coeruleus (LC) is a putative site of action for angiotensin II in the brain. Immunocytochemical studies have identified angiotensin II-like immunoreactive material in nerve terminals innervating the LC, and the LC contains one of the highest densities of angiotensin II receptor binding sites in the rat brain. Recent studies using selective neurotoxins suggest that the binding sites for angiotensin II in the LC are present on noradrenergic perikarya. Angiotensin II receptors are now known to exist as two subtypes that are distinguishable both pharmacologically and biochemically. Radioligand binding studies using agonists and antagonists selective for these angiotensin II receptor subtypes indicate that the rat LC contains a mixture of the two known angiotensin II receptor subtypes, but that the PD123177-sensitive AII beta receptor subtype is predominant. Comparisons of spontaneously hypertensive rats with normotensive rats indicates that angiotensin II and its receptors in the LC are elevated in the hypertensive rat strain. Studies of the biochemical and physiological actions of angiotensin II in the LC have not yet established an agreed-upon function for angiotensin II in this nucleus.

Angiotensin II↗

PubMed1991

Angiotensin II receptors in the ventral portion of the bed nucleus of the stria terminalis.

In vitro receptor autoradiography, using the radiolabeled angiotensin II (Ang II) antagonist 125I-sar1,ile8 Ang II (125I-SI Ang II; 250 pM) in the absence or presence of 1 microM Ang II, was used to identify Ang II receptor binding sites in the preoptic-anterior hypothalamic (POAH) brain region of cycling female rats. A nucleus within this region, lateral to the organum vasculosum of the lamina terminalis and ventral to the anterior commissure, displayed a discrete locus of 125I-SI Ang II binding sites (385 fmol/g tissue). This nucleus, which corresponds to the area of the POAH from which Ang II is most effective at eliciting luteinizing hormone release, has been identified as the ventral portion of the bed nucleus of the stria terminalis (BSTV) by the rat brain atlas of Paxinos and Watson. The selective nonpeptidic Ang II alpha receptor antagonist Dup 753 completely inhibited the binding of 125I-SI Ang II to the BSTV and other hypothalamic nuclei, suggesting that these receptors are of the Ang II alpha subtype.

1-Sarcosine-8-Isoleucine Angiotensin II↗

PubMed1990

Novel angiotensin II binding sites in the mesopontine area of the rat brain.

Angiotensin II (AII) immunoreactivity in the mesopontine area of the rat brain is distributed through several areas where co-localization of AII receptors has not been established. The current in vitro receptor autoradiography study re-examined the distribution of AII binding using 125I-Sar1,Ile8-AII ([125I]SIAII). When incubations were conducted without sulfhydryl reducing agents, [125I]SIAII binding was observed in the locus coeruleus, inferior colliculus, superior colliculus and the central gray in agreement with previous reports. Novel [125I]SIAII binding sites were detected in the parabrachial nucleus, pedunculopontine tegmental nucleus and the caudal linear raphe nucleus, corresponding with previously reported localization of AII immunoreactivity in these nuclei. [125I]SIAII binding was also found in the paragenual nucleus where the peptide has not been detected. Thus, the observation of novel AII receptors which are sensitive to sulfhydryl reducing agents, resolves several AII-AII receptor mismatches.

Angiotensin II↗

PubMed1990

Angiotensin II receptor subtypes in the rat brain.

The non-peptide angiotensin II (AII) receptor subtype selective antagonist, DuP 753, was used to characterize AII receptor binding sites in the rat brain. DuP 753 competed for specific 125I-[Sar1,Ile8]AII (125I-SIAII) binding in many brain nuclei (IC50 = 20-30 nM), but was a weak competitor at remaining sites (IC50 greater than 10(-4) M). DuP 753 sensitive binding sites (designated AII alpha subtype) correspond with areas where binding is inhibited by sulfhydryl reducing agents, whereas DuP 753 insensitive sites (AII beta) correspond with areas where binding is not inhibited by sulfhydryl reducing agents.

1-Sarcosine-8-Isoleucine Angiotensin II↗

PubMed1990

Discrimination of two angiotensin II receptor subtypes with a selective agonist analogue of angiotensin II, p-aminophenylalanine6 angiotensin II.

Angiotensin II receptor binding sites in rat liver and PC12 cells differ in their affinities for a nonpeptidic antagonist, DuP 753, and p-aminophenylalanine6 angiotensin II. In liver, which primarily contains the sulfhydryl reducing agent-inhibited type of angiotensin II receptor, which we refer to as the AII alpha subtype, DuP 753 displays an IC50 of 55 nM, while p-aminophenylalanine6 angiotensin II displays an IC50 of 8-9 microM. In PC12 cells, which primarily contain the angiotensin II receptor type whose binding affinity is enhanced by sulfhydryl reducing agents (AII beta), DuP 753 displays an IC50 in excess of 100 microM, while p-aminophenylalanine6 angiotensin II displays an IC50 of 12 nM. p-Aminophenylalanine6 angiotensin II binding affinity in liver is decreased in the presence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) suggesting that this analogue is an agonist.

Adrenal Gland Neoplasms↗

PubMed1990

Loss of striatal angiotensin-converting enzyme following intrastriatal AF64A is not related to destruction of cholinergic interneurons.

The potent angiotensin-converting enzyme (ACE) inhibitor 351A was radioiodinated (125I-351A) and used to quantitate ACE in the striatum of rats treated with the cholinergic neurotoxin AF64A. Unilateral administration of 4 nmol of AF64A into the striatum, which caused a 42% reduction in striatal choline acetyltransferase (ChAT) activity, reduced binding of 125I-351A in the lesioned striatum by 37% relative to the untreated striatum. The AF64A treatment also reduced the dopamine (DA) concentration by 59% in the lesioned striatum, but did not significantly reduce the serotonin (5-HT) concentration. Despite the reductions in ACE and these neurochemical markers, there was no significant correlation between the extent of reduction of the specific neurochemical markers and ACE. These results suggest that the AF64A treatment caused non-specific damage to striatal non-cholinergic neurons as well as destroying cholinergic neurons, and that ACE is contained in non-cholinergic neurons.

Animals↗

PubMed1990

Autoradiographic localization of angiotensin II receptor binding sites on noradrenergic neurons of the locus coeruleus of the rat.

The locus coeruleus (LC) of the rat was lesioned by microinjection of selective neurotoxins into the brainstem. 6-Hydroxydopamine (6-OHDA), 3 micrograms/microliter, given unilaterally at two sites 0.6 mm apart on the rostro-caudal axis of the LC, was used to lesion catecholamine-containing neuronal elements. Ibotenic acid, 2.5 micrograms/0.5 microliters, administered similarly was used to lesion nerve cell bodies. Two weeks after administration of the neurotoxin, lesion efficacy was determined based on the norepinephrine content of the cerebral cortex ipsi- and contralateral to the lesion. 6-OHDA lesions of the LC caused a 46% reduction in ipsilateral cortical norepinephrine and a 60% reduction in specific 125I-[Sar1, Ile8]-angiotensin II (125I-SIAII) binding in the LC. Ibotenic acid lesions of the LC caused a 73% reduction in ipsilateral cortical norepinephrine and a 81% reduction in specific 125I-SIAII binding in the LC. These results indicate that AII receptor binding sites in the LC are localized on noradrenergic nerve cell bodies or their dendritic and axonal ramifications within the LC.

1-Sarcosine-8-Isoleucine Angiotensin II↗

PubMed1989

Monoamine depletion does not alter angiotensin II binding sites in the rat brain.

6-Hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT) was administered in the lateral cerebral ventricles of rats. These respective treatments caused reductions in norepinephrine (NE) and 5-hydroxytryptamine (5-HT) levels in the hypothalamus-thalamus-septum-midbrain (HTSM; 62% and 44%) and brainstem (57% and 26%), respectively. Catecholamine depletion in 6-OHDA-treated rats resulted in a 55% decrease in the pressor response to ICV Ang II which was not associated with any significant change in the binding of 125I-sarcosine1, isoleucine8 Ang II to Ang II binding sites in the HTSM or brainstem. The radioligand binding was not significantly affected by the 5,7-DHT treatment. These results indicate that brain Ang II binding sites are not predominantly localized on NE- or 5-HT-containing nerve terminals. They do not, however, preclude the existence of a small proportion of Ang II binding sites on these neuronal populations.

5,7-Dihydroxytryptamine↗

PubMed1989

Topographic probes of angiotensin and receptor: potent angiotensin II agonist containing diphenylalanine and long-acting antagonists containing biphenylalanine and 2-indan amino acid in position 8.

A series of phenylalanine-mimicking amino acids with increasing conformational restraint were prepared and incorporated into angiotensin II, in order to develop topographic probes of angiotensin useful for probing receptor boundaries by molecular graphics analysis and for conformational analysis of the ligand by NMR. In binding studies, all analogues displayed high affinity for rat uterus (Ki of 0.74-6.08 nM) and brain (0.46-1.82 nM) receptors. In smooth muscle (rat uterus) contraction assay, the diphenylalanine-containing [Sar1,Dip8]AII and [Sar1,D-Dip8]AII were potent agonists with respectively 284% and 48% activity of [Asn1]AII. In contrast, the biphenylalanine-containing [Sar1,Bip8]AII, [Sar1,D-Bip8]AII, and the 2-indan amino acid containing [Sar1,2-Ind8]AII were potent inhibitors, approximately 9, 2, and 1.4 times more effective than a standard antagonist, [Sar1,Leu8]AII. Their respective pA10 values in rat uterus assay were 8.87, 8.70, and 8.82. By comparison, the pA10 value for [Sar1,Leu8]AII was 8.35. In rats, a single dose of 10 micrograms of [Sar1,2-Ind8]AII or [Sar1,Bip8]AII produced prolonged blockade of the pressor response toward angiotensin II for over 90 min. The very different pharmacological profiles of these rigid aromatic analogues suggest that the angiotensin receptor activation site consists of a relatively wide and elongated pocket with a narrow opening.

Affinity Labels↗

PubMed1989

Low-calcium diet increases blood pressure and alters peripheral but not central angiotensin II binding sites in rats.

The mechanism by which low-calcium (Ca) diet causes hypertension is unknown. We investigated angiotensin II (Ang II) receptor binding in brain, adrenals and urinary bladders in male Sprague-Dawley rats pair-fed a low-Ca (0.005% Ca; 0.5% P) and normal-Ca (1.4% Ca) diet for 8 weeks beginning at 4 weeks of age. The Ang II receptor sites in hypothalamus-thalamus-septum (HTS), adrenal glands and urinary bladder smooth muscle were measured by saturation isotherm binding using 125I-sarcosine1isoleucine8 Ang II (125I-SI Ang II). Systolic blood pressure was determined at 2-week intervals by tail-cuff method. Serum total Ca, Na+, K+ aldosterone and Ang II and bone density and mineral content were determined at the time of sacrifice. Chronic Ca deficiency in rats raised blood pressure and decreased Ang II receptor density in bladder smooth muscles and tended to increase adrenal Ang II receptors. Serum Ca. bone density and mineral content were significantly lower in the Ca-deficient rats, while serum Na+ was elevated in this group. Serum Ang II and aldosterone were unaltered after the 8-week dietary regimen. Possible mechanisms for the hypertensive actions of reduced dietary Ca intake involving the renin-angiotensin-aldosterone system are discussed.

Adrenal Glands↗

PubMed1989

Rat epididymis contains functional angiotensin II receptors.

Specific angiotensin II (Ang II) binding and functional responses have been studied in a number of male and female reproductive structures, but to date have not been characterized in the epididymis. Some epididymal functions, including smooth muscle contraction and regulation of fluid and electrolyte balance, are mediated by Ang II in other tissues. This study demonstrates specific, saturable (63 fmol/mg protein), high affinity (Kd, less than 1 nM) Ang II-binding sites in the epididymis. These binding sites, localized in the circumference of the epididymal tubule and most concentrated within the proximal cauda, are present throughout the caput, corpus, and remaining cauda epididymis. Ang II caused powerful expulsions of spermatozoa in segments of epididymis in situ. These results suggest Ang II involvement in epididymal function.

1-Sarcosine-8-Isoleucine Angiotensin II↗

PubMed1988

Reduction of CCK-8 binding in the nucleus of the solitary tract in unilaterally nodosectomized rats.

Cholecystokinin octapeptide (CCK-8) binding sites were examined in the caudal hindbrain of unilaterally nodosectomized and intact rats by in vitro autoradiography with 125I-CCK-8. Unilateral nodosectomy caused a significant reduction in CCK-8 binding in the caudal medial nucleus of the solitary tract (NST) on the side ipsilateral to the nodose ganglionectomy. Examination of other caudal hindbrain regions exhibiting CCK-8 binding did not reveal changes in binding in nodosectomized animals compared to controls. These findings suggest that the CCK receptors in this brain region may be located on terminals of vagal afferent neurons.

Animals↗

PubMed1988

Angiotensin II receptors in the lumbar spinal cord of the rat.

Locations of cells responsive to microiontophoretically applied angiotensin II (AII) were compared to distributions of AII receptor binding sites identified by autoradiography in the lumbar enlargement region of the rat spinal cord. Angiotensin II receptor binding sites were densely concentrated in the superficial layers of the dorsal horn. Considerably lower densities of binding sites were present in the remaining gray matter. Effects of microiontophoretically applied AII on lumbar spinal cord cells did not vary with location within the gray matter. AII facilitated firing of most cells in the lumbar cord whether the cells were in superficial or deeper laminae of the dorsal horn or in the ventral horn. The distribution of AII binding sites and the distribution of cells that were responsive to AII suggest that AII may play a role in modulating both sensory and motor functions of the spinal cord.

Angiotensin II↗

PubMed1988

Distribution of angiotensin-converting enzyme and angiotensin II-receptor binding sites in the rat ovary.

Recent reports of the presence of components of the renin-angiotensin system (RAS) in the mammalian ovary suggest that angiotensin II (Ang II) may be elaborated by this structure. In this study, angiotensin-converting enzyme (ACE), a key enzyme in the synthesis of Ang II, was identified enzymatically and localized to the germinal epithelium surrounding corpora lutea, granulosa cells of some--but not all--follicles, and blood vessels of the rat ovary using a potent and specific radiolabeled ACE inhibitor, 125I-351A. Follicles that bound 125I-351A also contained Ang II-receptor binding sites. Co-localization of RAS components to the follicular granulosa cells and the ability of Ang II to promote estrogen formation suggest that the ovarian RAS may promote follicular development and assertion of dominance.

Animals↗