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Biomedical subjects

R C Speth

Publications and source records attributed to R C Speth.

At least 73 records · Page 4Linked to original sources
PubMed1988

Neuronal localization of specific angiotensin II binding sites in the rat inferior olivary nucleus.

Adult male Sprague-Dawley rats were treated with 3-acetylpyridine, a neurotoxin selective for the inferior olivary nucleus. Following treatment, the rats exhibited deficits in locomotor behavior indicative of destruction in the inferior olivary nucleus. The rats were sacrificed 3 weeks later, and the binding of 125I-sarcosine, isoleucine angiotensin II to brain homogenates and slide-mounted sections of brainstem was determined. Treatment with 3-acetylpyridine significantly decreased specific 125I-sarcosine, isoleucine angiotensin II binding in homogenates of posteroventral brainstem (containing the inferior olivary nucleus) by approximately 50%. Homogenates of dorsal brainstem and hypothalamus-thalamus-midbrain showed no significant changes in specific binding. Treatment with 3-acetylpyridine did not significantly alter the radioligand binding affinity which was determined in the hypothalamus-thalamus-midbrain. Autoradiographic analysis of 125I-sarcosine, isoleucine angiotensin II binding in the brainstem sections indicated that specific angiotensin II binding sites in the inferior olivary nucleus were virtually eliminated by the 3-acetylpyridine treatment. In addition, a comparatively small, but significant, decrease in specific 125I-sarcosine, isoleucine angiotensin II binding occurred in the solitary tract nucleus/dorsal vagal motor nucleus complex. These results indicate that specific angiotensin II binding sites in the inferior olivary nucleus occur exclusively on neuronal perikarya and/or dendrites.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1987

Localization of angiotensin II receptors in ovarian follicles and the identification of angiotensin II in rat ovaries.

Specific, high-affinity (Kd approximately equal to 0.6 nM), and saturable (3.3 fmol/mg of tissue, wet weight) binding of 125I-labeled [Sar1,Ile8]angiotensin II to rat ovarian membranes was observed. Displacement of 125I-labeled [Sar1,Ile8]angiotensin II binding to rat ovarian membranes by angiotensin II analogs and fragments resembled the potency order of these compounds on angiotensin II receptors in other tissues: [Sar1,Ile8]angiotensin II greater than angiotensin II greater than des-Asp1-angiotensin II greater than angiotensin I greater than des-Asp1,Arg2-angiotensin II. Several unrelated peptides, including follicle-stimulating hormone at 10 microM, did not displace ovarian 125I-labeled [Sar1,Ile8]angiotensin II binding. Autoradiograms of 125I-labeled [Sar1,Ile8]angiotensin II binding to ovarian sections indicated that the angiotensin II receptor binding sites were localized exclusively to a subpopulation of follicles, occurring on the granulosa and theca interna cells. Other follicles were devoid of 125I-labeled [Sar1,Ile8]angiotensin II binding sites. Angiotensin II immunoreactive material was also identified in the ovary. The concentration of ovarian Ang II immunoreactivity was 8- to 75-fold greater than that of plasma, was not reduced in bilaterally nephrectomized rats, and was shown by high-pressure liquid chromatographic analysis to be the native angiotensin II octapeptide. The presence of angiotensin II and its receptor binding sites in the ovary suggests a role for angiotensin II as a regulator of ovarian function.

Angiotensin II↗
PubMed1987

Regulation of angiotensin II in rat adrenal gland.

Levels of angiotensin II immunoreactivity in the rat adrenal gland are over one hundredfold higher than those in plasma. It is unclear, however, whether the major source of adrenal angiotensin II immunoreactivity is intracellular synthesis by a local renin-angiotensin system, uptake by angiotensin II receptors, or both. Our studies show that angiotensin II immunoreactivity in the adrenal gland is predominantly attributable to angiotensin II (greater than 75%). Angiotensin III (16%) and other angiotensin II fragments are also present. The majority of angiotensin II immunoreactivity (73%), renin activity (73%), and angiotensin II receptor binding activity (66%) in the adrenal gland is located in the capsular glomerulosa cell layers. Dehydration produced by 2% NaCl imbibition decreased these activities in the capsular-glomerulosa. In the fasciculata-medullary regions of the adrenal gland, dehydration decreased renin activity but not angiotensin II immunoreactivity or angiotensin II receptor binding activity. Combined data from control and dehydrated rats showed a close correlation of the capsular-glomerulosa angiotensin II immunoreactivity with angiotensin II receptor binding activity (r = 0.94, p less than 0.001) and a weaker, nonsignificant correlation with renin activity (r = 0.66, p less than 0.1). In the fasciculata-medullary cell layers, no significant correlations were found between angiotensin II immunoreactivity and either renin or angiotensin II receptor binding activity. These data demonstrate that functionally distinct layers of the rat adrenal gland differentially regulate angiotensin II receptors and the renin-angiotensin system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1986

Effect of intraventricular infusion of an angiotensin II antagonist on 125I-angiotensin II binding in rats.

The effects of chronic (six day) intracerebroventricular (i.c.v.) infusion of an angiotensin II antagonist, sarcosine1, isoleucine8 angiotensin II ([Sar1, Ile8]Ang II), (500 ng/microliter per hour) was studied. Specific 125I-Ang II binding site density and binding affinity in the hypothalamus-thalamus-septum-midbrain (H-T-S-M) region of the brain and the adrenal medulla did not differ significantly between [Sar1, Ile8]Ang II treated and control (0.9% saline) rats. However, 125I-Ang II binding to the adrenal cortex was significantly reduced by i.c.v. infusion of [Sar1, Ile8]Ang II. The drinking response to microinjection of Ang II was blunted for up to seven days of [Sar1, Ile8]Ang II infusion. Thus, although [Sar1, Ile8]Ang II effectively blocked the central Ang II receptors, chronic infusion of this Ang II antagonist did not appear to cause alterations in brain H-T-S-M Ang II receptors, suggesting that brain Ang II receptors in normal rats do not undergo homologous regulation.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1986

Distribution of [125I]angiotensin II binding sites in the rat brain: a quantitative autoradiographic study.

Angiotensin II receptors have been localized by quantitative autoradiography in the rat central nervous system after labeling with [125I]angiotensin II. A highly discrete distribution of these receptors was found throughout the rat brain. The highest density was seen in regions of the medulla, hypothalamus and circumventricular organs where angiotensin II could potentially produce cardiovascular, dipsogenic and neuroendocrine responses. The distribution of angiotensin II receptors correlates relatively well with the previously reported distribution of angiotensin immunoreactive nerve terminals as well as areas determined by various physiological techniques to be sensitive to angiotensin II. Finally, the anatomical localization of angiotensin II receptor populations has revealed several areas of the brain where the effects of this peptide have not been investigated. Many of these nuclei are involved in the transmission and processing of somatic and visceral sensory information. These results suggest a broader role for the central renin-angiotensin system in modulating several types of sensory input.

Animals↗
PubMed1986

Monoiodinated angiotensin II is a potent, full agonist analog of angiotensin II.

Mono 125I-angiotensin II (Ang II) has been used extensively as a radioligand to identify Ang II receptors whereas its receptor binding properties are well characterized, its biological activity has been less well studied. To examine this issue, nonradioisotopic monoiodo-Ang II was prepared and compared to Ang II. Monoiodo-Ang II was found to be a potent, full agonist in in vivo bioassays and a more potent (2.5-fold) pressor agent than the native hormone Ang II in the pithed rat. In eliciting dipsogenic responses monoiodo-Ang II was equipotent to Ang II, but was less potent (2.7-fold) than Ang II in contracting rat aortic strips. These results suggest that the well characterized binding affinity of monoiodo-Ang II is representative of its biological activity (40-250% of the activity of Ang II). The variation in relative peptide potency is consistent with the hypothesis of a heterogeneity of Ang II receptors. Most importantly, the similar efficacies between Ang II and monoiodo-Ang II indicate that the monoiodinated Ang II is a suitable ligand for the study of Ang II receptors.

Angiotensin II↗
PubMed1985

Angiotensin II receptor localization in the canine CNS.

Specific binding of [125I]angiotensin II [(125I]Ang II) to sections of dog brain was determined by in vitro receptor autoradiography. Highly discrete, dark images representing specific binding of [125I]Ang II were observed in areas corresponding to the nucleus of the solitary tract, dorsal motor nucleus of the vagus, area postrema, ventrolateral medulla, pineal, subfornical organ, nucleus medianus, septum, organum vasculosum of the lamina terminalis and the anterior pituitary. The specific binding was frequently present either as a narrow band or tiny spot within a small portion of the nuclei to which the binding corresponded. The location of these Ang II recognition sites in regions associated with regulation of autonomic and neuroendocrine function provides further evidence for a role of this peptide within the central nervous system.

Angiotensin II↗
PubMed1985

Angiotensin II receptor binding sites in brain microvessels.

We assessed the specific binding of 125I-labeled angiotensin II (125I-Ang II) to particulate fractions of the cerebral cortex and cerebellum and to microvessels obtained by bulk isolation from these two brain regions in the dog. 125I-Ang II binds to cerebral and cerebellar microvessels in a specific, saturable, and reversible manner and with high affinity (dissociation constant about 1 nM). Maximal binding of 125I-Ang II to brain microvessels was about 2-fold higher than the maximal binding to particulate fractions of the cerebellum and more than 15-fold higher than that of the cerebral cortex. No significant differences were noted between cerebral and cerebellar microvessels in their specific binding of Ang II. Furthermore, our finding that analogues of Ang II displace specific 125I-Ang II binding to brain microvessels in a rank order that correlates with their pharmacological activities confers biological relevance on the ligand-binding studies. These results strongly suggest that specific Ang II receptor binding sites are present in brain microvessels. Such Ang II receptors may have an important role in regulating the microcirculation of the brain.

Angiotensin II↗
PubMed1985

Quantitative autoradiography of angiotensin II receptors in brain and kidney: focus on cardiovascular implications.

Quantitative techniques of receptor autoradiography have been applied to localize [125I]-angiotensin II binding sites in brain and kidney. High densities of autoradiographic grains, indicating the presence of angiotensin II receptors, have been localized to several rat brain nuclei including the dorsal motor nucleus of the vagus, nucleus of the solitary tract, anterior pituitary, locus coeruleus and several hypothalamic nuclei. Cat thoracic spinal cord exhibited a high density of sites over the intermedio-lateral cell column. In sections of rat kidney, angiotensin II receptors were detected in the glomerulus, vasa recta and ureter. The cardiovascular implications of these results are apparent and relate angiotensin II to hypertensive mechanisms. Thus, angiotensin II represents an endocoid which is involved in control of blood pressure through its effects on peripheral organs as well as the central nervous system.

Angiotensin II↗
PubMed1984

Rat brain angiotensin II receptors: effects of intracerebroventricular angiotensin II infusion.

Angiotensin II (Ang II) was infused into a lateral cerebral ventricle of male Sprague-Dawley rats and its effects on blood pressure, water balance and specific [125I]Ang II binding to brain and adrenal tissues were studied. The infusion was maintained at a rate of 500 ng/microliter/h for 6 days using subcutaneously implanted osmotic minipumps. A control group was infused intracerebroventricularly (i.c.v.) with 0.9% saline at a rate of 1 microliter/h for 6 days. Angiotensin II treated rats showed a four-fold increase in water intake and urine volume and a moderate increase in blood pressure; these effects were not observed in rats given saline i.c.v. There was no significant difference in [125I]Ang II binding site density or binding affinity in either the hypothalamus-thalamus-septum-midbrain (HTSM) or the brainstem between Ang II-treated and saline-treated groups. In addition, [125I]Ang II binding sites in the adrenals were also unaffected by i.c.v. infusion of Ang II. The results suggest that brain Ang II receptors are unresponsive to increased Ang II levels in cerebrospinal fluid.

Adrenal Glands↗
PubMed1984

Autoradiographic localization of angiotensin II receptors in the rat brainstem.

The microscopic localization of angiotensin II receptors in the rat brainstem has been accomplished utilizing in vitro receptor autoradiographic techniques. These receptors are highly localized to discrete nuclear regions of the brainstem. Significant densities of autoradiographic grains, indicating the presence of specifically bound [125I]-angiotensin II, were observed in regions of the film corresponding to the nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve, nucleus intercalatus, nucleus commissuralis, substantia gelatinosa of the trigeminal nerve and the inferior olivary nucleus. Previous immunohistochemical studies have indicated the presence of immunoreactive angiotensin II in several of these regions, especially those concerned with central cardiovascular regulatory mechanisms. These results provide additional evidence in support of the hypothesized role of angiotensin II as a central neuromodulator in the regulation of systemic blood pressure.

Animals↗
PubMed1984

Preparation and one-step purification of mono-125I-angiotensin II for radioligand binding assays.

A one-step purification of mono-125I-angiotensin II prepared by the chloramine T procedure is described. The purification is effected on a cellulose cation exchange column with isocratic elution by 50 mM sodium acetate, pH 5.0. The purity of the mono-125I-angiotensin II was determined by thin layer chromatography, high pressure liquid chromatography, enzymatic digestion, radioreceptor assay, and radioimmunoassay. Preparation and purification of mono-125I-angiotensin II by this procedure offers significant advantages over existing methods for its preparation in terms of purity, simplicity, efficiency, and cost.

Adrenal Glands↗
PubMed1984

Restricted dietary sodium intake alters peripheral but not central angiotensin II receptors.

Male Sprague-Dawley rats were maintained on either a normal or low-sodium diet for 5 weeks to examine whether dietary sodium restriction alters angiotensin II (Ang II) receptors. The receptor sites in the hypothalamus-thalamus-septum (H-T-S) region of the brain, the adrenal glands and bladder visceral smooth muscle were measured by saturation isotherm binding assays using 125I-Ang II. Compared to control rats, the low-sodium diet group showed a smaller weight gain, reduced water intake, elevated hematocrit, and decreased urinary sodium concentration. In addition, sodium-depleted rats had a 10-fold elevation in plasma renin activity. However, neither binding affinity of 125I-Ang II to the brain H-T-S region nor its density was significantly different between the two groups. In contrast, both the 125I-Ang II binding density and dissociation constant in the adrenal gland were significantly elevated, while the binding density of 125-I-Ang II in the bladder smooth muscle was significantly decreased in the sodium-restricted group. These results suggest that dietary sodium depletion does not alter Ang II receptors in the rat brain areas wherein Ang II exerts the majority of its central actions.

Adrenal Glands↗