PubMed Health⌕ Search

Biomedical subjects

R C Speth

Publications and source records attributed to R C Speth.

At least 37 records · Page 2Linked to original sources
PubMed1996

Pituitary lactotrope expresses transforming growth factor beta (TGF beta) type II receptor mRNA and protein and contains 125I-TGF beta 1 binding sites.

Transforming growth factor beta 1 (TGF beta 1) has recently been shown to be produced in the prolactin (PRL)-secreting lactotropes of the pituitary gland. TGF beta 1 inhibits lactotropic secretion and proliferation, and the production of TGF beta 1 in lactotropes is reduced during lactotropic growth following estrogen treatment in ovariectomized rats. In many estrogen-responsive tissues, TGF beta 1 has been shown to exert its effect by binding to TGF beta 1 type II receptors (T beta R II) at the cell surface. In this study, we sought to ascertain whether T beta R II is involved in TGF beta 1 action on lactotropes by determining the changes of T beta R II mRNA and protein levels and specific 125I-TGF beta 1 binding sites on the lactotropes during estrogen-induced proliferation of lactotropes in Fischer 344 rats. Double immunohistochemical procedures were employed to identify immunoreactive T beta R II in PRL-reactive cells. The majority of T beta R II-reactive cells in the anterior pituitary were observed to be lactotropes. Dual immunohistochemistry and in situ hybridization procedures also indicated that lactotropes were the major cell types containing T beta R II mRNA hybrids. Both the levels of immunoreactive T beta R II protein and in situ T beta R II mRNA hybrids in the pituitary were significantly decreased in ovariectomized rats after 15 days of estrogen treatment. Determination of 125I-TGF beta 1 binding sites in lactotropes by double immunohistochemistry and receptor autoradiography also revealed specific binding sites of 125I-TGF beta 1 in lactotropes in the anterior pituitary. 125I-TGF beta 1 binding in the anterior pituitary was also reduced following estrogen treatment in ovariectomized rats. These data suggest that down-regulation of T beta R II may be an important mechanism of estrogen action on lactotropic cell growth and PRL secretion, and further support the notion that TGF beta 1 controls lactotropic function by autocrine/paracrine mechanisms.

Animals↗
PubMed1995

Angiotensin-(1-7) binding at angiotensin II receptors in the rat brain.

Angiotensin-(1-7) (Ang-(1-7)) is reported to be equipotent with angiotensin II (AII) in producing some central biological effects but the receptors responsible for these actions have not been defined. Three classes of receptor have been proposed: AT1, AT2, and a putative Ang-(1-7) selective receptor. This study specifically evaluates Ang-(1-7) competition at AII binding sites (AT1 and AT2) in the rat brain. 125I Sar1 Ile8 AII (269-312 pM) was used to conduct receptor autoradiographic binding assays in brain sections. Competition with Ile5 AII and Val5 AII was similar at nuclei in which either AT1 or AT2 receptor subtypes predominate (Ki = 11-18 nM). Ang-(1-7) competed 150-fold less effectively than native AII at AT1 predominant brain nuclei (Ki = 2.4 microM). At brain regions where AT2 receptors predominate, Ang-(1-7) showed a very low affinity (Ki = 104 microM) for the majority of the 125I Sar1 Ile8 AII binding sites (AT2). A small proportion of 125I Sar1 Ile8 AII binding sites showed an affinity of 2.0 microM, presumably AT1 receptors present in those brain regions. For biological responses where Ang-(1-7) is reported to be equipotent with AII, it is unlikely that these actions are mediated by the widely distributed AT1 or AT2 receptor subtypes which recognize 125I Sar1 Ile8 AII.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1995

Brain angiotensin and the female reproductive cycle.

The results consistently show from experiment to experiment that there is a surge of brain Ang II prior to the well known preovulatory LH surge. It should be pointed out that these experiments have been carried out by two different laboratories and with the help of different experimenters and some of the experiments have been repeated. Therefore, the consistency of the results is reassuring. It does appear that Ang II increases in the brain, specifically in the hypothalamus, probably in cells of the paraventricular nucleus about 1 hour before the LH levels in plasma rise to a peak. Since LH release from the anterior pituitary gland is stimulated by the release of LHRH from the arcuate nucleus into the median eminence, the results would suggest that Ang II stimulates the release of LHRH. The peak in the OVX of Ang II treated rats is sharp and short-lasting with a second, later peak. The LH surge follows the first peak and a second rise in LH follows the second Ang II peak. These data suggest that brain Ang II synthesized and stored in the brain plays a critical role in the female reproductive cycle by initiating the LH surge. The regulation of Ang II may be by estrogen and progesterone, but as the increase in angiotensinogen mRNA was not marked, the surge of Ang II appears to result more from the sudden release of stored Ang II than its synthesis. Thus, the question is what releases Ang II. Earlier studies showed that catecholamines release Ang II from neurons and not from glia involving alpha 2 receptor blockade to increase norepinephrine by inhibiting reuptake (7). An interaction between catecholamines, Ang II and LH had also been suggested earlier (18, 19). Therefore, a series of events triggered by steroids in proestrus may begin with increases in norepinephrine activating neuronal alpha 2 receptors and precipitating release of brain Ang II. This is represented diagrammatically in Figure 15. The Ang II surge stimulates the cells containing GnRH (gonadotropin releasing hormone) in the arcuate nucleus. The effect of Ang II on multiple GnRH cells amplifies the effect and GnRH is released into the portal vessels of the pituitary to stimulate the large LH release, from gonadotrope cells in the anterior pituitary, into the plasma that produces the LH surge. The effect of the LH surge is ovulation which ends the estrogen build up.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II↗
PubMed1995

Fosinopril treatment of pregnant rats: developmental toxicity, fetal angiotensin-converting enzyme inhibition, and fetal angiotensin II receptor regulation.

Pregnant women are advised against using angiotensin-converting enzyme (ACE) inhibitors due to reports of adverse effects on human fetuses. This study examined ACE binding and angiotensin II (Ang II) receptor binding in fetuses of rats treated with the ACE inhibitor fosinopril (16 mg/kg/day fosinopril, p.o. in 4 divided doses, from gestational day (gd) 13 to gd 18). Binding of the potent radiolabeled ACE inhibitor 125I-351A to ACE in the lung and aorta of gd 19 fetuses of fosinopril-treated dams was reduced by 56 and 44%, respectively, compared to fetuses from vehicle-treated dams, indicating that fosinopril or its active metabolite, fosinoprilat, crosses the placental barrier and inhibits fetal ACE. Fetal Ang II receptor binding of 125I-Sar1,Ile8 Ang II was not altered in most of the tissues examined, although reductions in binding in the adrenal of fetuses of fosinopril-treated dams approached statistical significance.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1995

Influence of tissue freezing on the binding of 125I-sarcosine1, isoleucine8 angiotensin II to angiotensin II receptor subtypes in the rat.

Evaluation of angiotensin II (AII) receptor binding often necessitates freezing of the tissue of interest prior to assay of radioligand binding. This study evaluated the effects of freezing of various rat tissues at different rates on 125I-sarcosine1, isoleucine8 angiotensin II (125I-SI AII) binding to AII receptor subtypes. Slow freezing in a -20 degrees C compartment significantly reduced 125I-SI AII binding to AT1 receptors in the adrenal (51%), epididymis (34%), and liver (22%). Binding of 12tI-SI AII to the AT1 receptor in the brain was not significantly reduced. In the adrenal, both the Bmax and affinity of AT1 receptors were decreased by freezing. But in the epididymis, only the affinity of AT1 receptors was decreased. Binding of 125I-SI AII to AT2 receptors in the adrenal, epididymis, and brain was also not significantly reduced by freezing. Further evaluation of the mechanism of the reduction in 125I-SI AII binding to AT1 receptors in the adrenal indicated that both the receptor density and affinity for 125I-SI AII were decreased by freezing. Rapid freezing in a dry-ice bath caused even greater reductions in 125I-SI AII binding to AT1 receptors in the adrenal. Snap freezing in liquid nitrogen decreased 125I-SI AII binding in adrenals to a similar extent as did slow freezing. These results suggest that studies of AII receptors subtypes that involve freezing of the tissues underestimate the density and affinity of the AT1 receptor subtype.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1995

Urethral pressure response to smooth and skeletal muscle relaxants in anesthetized, adult male cats with naturally acquired urethral obstruction.

The effects of the skeletal muscle-relaxing drug dantrolene sodium alone, and in combination with the alpha 1-adrenergic antagonist prazosin, on the urethral pressure profile were investigated in male cats with obstructive lower urinary tract disease. Decreases in mean segmental intraurethral pressure induced by dantrolene (n = 3) or dantrolene in combination with prazosin (n = 3) were evaluated statistically, using a paired design. Statistical analysis was applied to absolute (mm of Hg) pressure values. Intravenous administration of dantrolene alone (1 mg/kg of body weight, n = 3) significantly decreased pressure in the postprostatic/penile urethral segment, but did not decrease prostatic urethral pressures. Dantrolene in combination with prazosin (0.03 mg/kg IV) caused a 20% pressure decrease in the prostatic segment (P = 0.060). Preprostatic urethral pressure was not significantly affected by either treatment regimen in the small pool of cats studied. There was no difference in baseline pressures (mm of Hg) in the 3 intraurethral segments of these 6 recently obstructed male cats, compared with historic baseline pressures (mm of Hg) in the 3 intraurethral segments of 28 healthy male cats. These results indicate that dantrolene and prazosin may be effective in relaxing intraurethral skeletal and smooth musculature in male cats clinically afflicted with obstructive lower urinary tract disease. However, it is not certain that administration of muscle relaxants would facilitate urethral catheterization and removal of the obstruction in male cats with blockage of the lower urinary tract. Strikingly, results of this study suggest that urethral muscle spasm had a minor role in these cats.

Animals↗
PubMed1994

Variations in angiotensin-II release from the rat brain during the estrous cycle.

To investigate the hypothesis that the release of angiotensin-II (AII) in the rat brain increases on the day of proestrus, samples of cerebrospinal fluid (CSF) and interstitial fluid from the general region of the bed nucleus of the stria terminalis pars ventralis in the preoptic-anterior hypothalamic area were monitored for AII-immunoreactive material (AII-ir) using push-pull cannulas. Samples of CSF were obtained on the day of proestrus and diestrus day 1 at 30-min intervals from 1200-1600 h. Samples of interstitial fluid were obtained at 25-min intervals from 0930-1600 h. The rate of release of AII-ir into CSF was significantly greater on proestrus compared to diestrus day 1, and in the early afternoon of proestrus compared to the late afternoon. In five of seven rats and in the overall comparison of AII-ir release from the preoptic-anterior hypothalamic area, significantly more AII-ir was released on the day of proestrus vs. diestrus day 1. These observations are consistent with previous studies suggesting that brain AII may play a role in the regulation of LH release on the day of proestrus.

Angiotensin II↗
PubMed1994

Effect of succinylcholine, diazepam, and dantrolene on the urethral pressure profile of anesthetized, healthy, sexually intact male cats.

Effects of the neuromuscular blocking agent succinylcholine (n = 9), the centrally acting skeletal muscle relaxant diazepam (n = 11), and the directacting skeletal muscle relaxant dantrolene sodium (n = 8) on the urethral pressure profile were evaluated in anesthetized, healthy, sexually intact, adult male cats. Intravenous administration of succinylcholine (0.075 mg/kg of body weight) significantly decreased mean absolute pressure in the prostatic and post-prostatic/penile intraurethral segments by -9.5 and -6.5 mm of Hg, respectively (P = 0.0002 and P = 0.0006, respectively). Dantrolene (1.0 mg/kg, IV) significantly decreased mean prostatic and postprostatic/penile intraurethral segmental pressures by -3.5 and -2.8 mm of Hg, respectively (P = 0.005 and P = 0.0181, respectively). Diazepam (0.8 mg/kg, IV) did not significantly alter mean intraurethral segmental pressures. None of the drugs caused a change in segmental lengths of the urethra. These results indicate that skeletal muscle makes a substantial contribution to intraurethral tone in anesthetized, healthy, sexually intact male cats and that skeletal muscle relaxation may be successful in reducing prostatic and post-prostatic/penile urethral segmental tone in male cats. These results also suggest that dantrolene sodium may be valuable for the pharmacologic management of urethral disorders in male cats.

Anesthesia, General↗
PubMed1993

Angiotensin II and non-angiotensin II displaceable binding sites for [3H]losartan in the rat liver.

By virtue of the more than 1000-fold selectivity of losartan (DuP 753) for the AT1 angiotensin II (AII) receptor subtype compared with the AT2 subtype, [3H]losartan may be a useful radioligand for studies of the AT1 receptor subtype. Comparison of Bmax values in the liver obtained from saturation isotherms using [3H]losartan (Bmax = 194 pmol/g tissue) and [125I]sarcosine1,isoleucine8 angiotensin II (Bmax = 20 pmol/g tissue) indicated that the AII receptor concentration was approximately 10% that of the [3H]losartan binding sites. In addition, AII at concentrations as high as 10 microM displaced less than one-third of specific [3H]losartan binding in the liver and less than 80% in the whole adrenal. The presence of non-AII displaceable [3H]losartan binding in the liver did not appear to result from metabolism of the radioligand since HPLC analysis of free and bound 3H revealed that greater than 90% of the 3H eluted at the same time as the parent [3H]losartan. This suggests that [3H]losartan binds with high affinity to a site(s) other than angiotensin II receptors in the rat liver.

Angiotensin II↗
PubMed1993

Differences between perinatal angiotensin binding in the brains of SHR and WKY rats.

A growing body of evidence suggests that angiotensin may have a functional role in growth and development, in addition to its classical role in the maintenance of body water homeostasis. Components of the renin-angiotensin system have been identified in the rat fetus. Because of the association between the renin-angiotensin system and hypertension, we quantified angiotensin receptor binding sites in the brains of spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats during perinatal development. Using in vitro receptor autoradiography we identified specific 125I-Sar1,Ile8 AII binding in several areas of the brains of perinatal rats of both strains and observed significant differences in the concentration of binding sites, at different ages in several brain nuclei. With the knowledge that components of the renin-angiotensin system appear early in development and are known to have an association with cellular growth, it is possible that an irregularity in this system occurring during neurogenesis could contribute to developmental abnormalities, as well as subsequent hypertension.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Effects of peptidase inhibitors on binding at angiotensin receptor subtypes in the rat brain.

Sulfhydryl reducing agents affect angiotensin II (AII) receptor binding differentially at AT1 and AT2 sites. Consequently, sulfhydryl reducing agents are now used infrequently in AII receptor binding assays. In this regard, the present autoradiographic study evaluates the effects of additional peptidase inhibitors on AII receptor binding and radioligand integrity. EDTA at 5 mM enhanced binding similarly, by about 70%, at both AT1 and AT2 binding sites, whereas bacitracin (10(-4) M) did not affect binding at either site. In contrast, addition of phenanthroline and bovine serum albumin (BSA) increased binding at AT1 sites 2.3-fold, whereas binding at AT2 sites was affected minimally. Degradation of 125I-[Sar1,Ile8]-AII (125I-SIAII) was determined by HPLC analysis of samples before and after incubation with tissue in each buffer. Omission of bacitracin from buffers reduced the recovery of intact radioligand to 83-87%, while recovery exceeded 94% in the presence or absence of all other buffer constituents. These results suggest that degradation of 125I-SIAII is minimal in large volume in vitro receptor autoradiography studies of rat brain AII receptors. Further, the beneficial effects on radioligand binding caused by buffer constituents such as EDTA, phenanthroline, and BSA were not due to their ability to protect the radioligand from enzymatic degradation. Because these constituents (and possibly others) had differential effects on binding with respect to receptor subtypes, caution should be used when interpreting or comparing binding data obtained from various laboratories utilizing different buffer components.

Angiotensin II↗
PubMed1993

[125I]CGP 42112 binding reveals differences between rat brain and adrenal AT2 receptor binding sites.

The AT2 angiotensin II receptor selective ligand CGP42112 was radioiodinated and used to study AT2 receptor binding sites in the rat brain (combined olfactory bulb, septum, thalamus and midbrain) and whole adrenal. The [125I]CGP 42112 binding was of high affinity, saturable and specific in both tissues. Competition studies with nonselective and angiotensin II receptor subtype selective ligands, and evaluation of the effects of the sulfhydryl reducing agent beta-mercaptoethanol, confirmed that [125I]CGP 42112 bound selectively to the AT2 angiotensin II receptor subtype. [125I]CGP 42112 bound with higher affinity in the brain than in the adrenal. beta-Mercaptoethanol enhanced [125I]CGP 42112 binding in the brain, but did not alter its binding in the adrenal. A similar difference in binding affinity for [125I]sarcosine, isoleucine angiotensin II and enhancement of binding affinity by beta-mercaptoethanol was observed in the rat brain and adrenal. These observations suggest that the AT2 angiotensin II receptor subtypes in the brain and adrenal may differ.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Central angiotensin IV binding sites: distribution and specificity in guinea pig brain.

Our laboratory has reported previously that a unique binding site specific for the hexapeptide angiotensin (A)II(3-8), now referred to as AIV, is present in a number of tissues including bovine adrenal gland, rabbit and guinea pig heart and guinea pig kidney, liver, lung, uterus and brain. The present results extend previous findings in the guinea pig brain and identify binding sites for AIV in the neocortex, paleocortex, hippocampus, medial habenula, superior and inferior colliculi, caudate putamen, thalamus, dorsal tegmentum, central gray, red nucleus, inferior olivary, oculomotor and hypoglossal nuclei and cerebellum. Binding of [125I]AIV in selected regions was shown to be of high affinity (Kd = 0.60-1.47 nM), saturable (maximal number of binding sites = 181-449 fmol/mg of protein) and specific. This binding site was shown to be distinct from the AT1 and AT2 sites with Ki values > 10(-4) M for DuP 753, CGP42112A and PD123177. Changes at the N-terminal of the peptide, either by removal of the valine or by extension of the peptide, resulted in a large decrease in binding affinity. In contrast, C-terminal extensions resulted in little change in affinity for the binding site. Guanosine 5'-0-(3-thiotriphosphate) was shown to have no effect on binding, suggesting that the guinea pig brain binding site is not G-protein-linked. Potential functions associated with this newly discovered A binding site are discussed.

Amino Acid Sequence↗
PubMed1992

Analysis of angiotensin II receptor subtypes in individual rat brain nuclei.

Previous studies have used new angiotensin II (AII) receptor subtype selective compounds to localize AII receptor subtypes within discrete rat brain nuclei. The purpose of this autoradiographic study was to extend these preliminary findings and provide a comprehensive analysis of AII binding sites in 22 rat brain nuclei and the anterior pituitary, to include estimates of the binding affinity for 125I sar1 ile8 AII (125I SIAII) at each nucleus, and determine the fractional distribution of each subtype at each nucleus. Estimates of KD in separate experiments revealed that AT1 nuclei had a consistently higher affinity for 125I SIAII than AT2 nuclei (0.66 vs. 2.55 nM). Displacement of subsaturating concentrations of 125I SIAII by 10(-8)-10(-4) M DuP753 (selective for the AT1 subtype) or PD123177 (selective for the AT2 subtype) indicated that approximately half of the brain regions surveyed contained predominantly AT1 sites and half contained predominantly AT2 sites. Binding was partially displaced by both compounds in several regions and two site analyses were performed to estimate the distribution of subtypes within each nucleus. The data were then corrected for differential occupancy by 125I SIAII. Brain nuclei associated with cardiovascular or dipsogenic actions of AII, e.g., subfornical organ, organum vasculosum of the lamina terminalis, median preoptic nucleus, nucleus of the solitary tract and area postrema, contained pure, or almost pure, populations of AT1 receptors. The functions of AII in brain regions containing predominantly AT2 binding sites, e.g., thalamus, colliculi, inferior olive and locus ceruleus, remain undefined. Thus, AII binding sites in the rat brain have been differentiated into two subtypes with similar characteristics to those reported in peripheral tissues. However, the unexpected finding that they can be differentiated on the basis of their affinity for 125I SIAII raises questions concerning their coidentity with peripheral receptor subtypes.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1992

Angiotensin II receptor development in the bed nucleus of the stria terminalis and other perihypothalamic brain regions of the female and male rat.

Brain angiotensin II (AII) receptors play a role in the regulation of luteinizing hormone release. This action is thought to involve luteinizing hormone-releasing hormone containing neurons in the preoptic-anterior hypothalamic (POAH) area of the brain. Previous studies have demonstrated a discrete locus of AII receptor binding sites and responsiveness within the POAH to microinjections of AII in the adult female rat, corresponding to the ventral portion of the bed nucleus of the stria terminalis (BSTV). To further characterize the age- and sex-dependent AII receptor binding in the BSTV and other brain regions, in vitro receptor autoradiography using 125I-sarcosine1, isoleucine8 AII (125I-SI AII) was performed on 2-, 4- and 10-week-old female and male rat brains. Rats of both sexes displayed an age-dependent increase in 125I-SI AII binding in the BSTV, as well as in the suprachiasmatic nucleus (SCh). There was no detectable difference in binding within the BSTV between the female and male of any age group. Prepubertal ovariectomy did not impair the expression of 125I-SI AII binding in the BSTV or the SCh of adult female rats. The developmental expression of AII receptors in the BSTV and SCh may therefore play a role in sexual maturation and regulation of sexual function in the rat.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1992

Urethral pressure response to alpha-adrenergic agonist and antagonist drugs in anesthetized healthy male cats.

Urethral smooth muscle tone in response to treatment with phenylephrine, a selective alpha 1-adrenergic receptor agonist, and prazosin a selective alpha 1-adrenergic receptor antagonist, was evaluated in 12 anesthetized healthy adult sexually intact male cats. Intravenous administration of prazosin (20 to 30 micrograms/kg of body weight) decreased the average preprostatic and prostatic intraurethral pressure, compared with baseline and postphenylephrine (20 to 30 micrograms/kg) administration, values. Neither prazosin nor phenylephrine administration had an effect on functional urethral length. Results have implications for the pharmacologic management of lower urinary tract disorders in male cats.

Analysis of Variance↗