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M I Phillips

Publications and source records attributed to M I Phillips.

At least 127 records · Page 7Linked to original sources
PubMed1988

Plasma angiotensin II levels at moment of drinking during angiotensin II intravenous infusion.

Angiotensin II (ANG II) was infused intravenously within an apparent physiological dose range of 10-200 ng.kg-1.min-1 to induce a drinking response in rats. To determine the plasma ANG II level at the moment of drinking, blood samples were collected from the femoral artery at the onset of the drinking response. Control blood samples were obtained in a similar way before infusion. The lowest dose of ANG II did not evoke drinking. Variable water intake in response to 25, 50, and 75 ng ANG II.kg-1.min-1 after a relatively long latency to drink (40-65 min) was observed. All animals showed a drinking response when 100 ng ANG II.kg-1.min-1 or higher doses of ANG II were infused. The latencies to drink were inversely correlated to the dose of ANG II and were as short as 8 min with 200 ng ANG II.kg-1.min-1. Measurement of ANG II in the plasma of drinking rats showed that all concentrations were similar with an average of 458 +/- 58.1 pg/ml. This dipsogenic plasma ANG II level is equivalent to plasma ANG II after 48 h of dehydration. The results show that drinking in response to exogenous intravenous ANG II requires a threshold level to be reached that is equivalent to levels produced by the endogenous renin-angiotensin system when dehydration is prolonged. This suggests that intravenous ANG II is not involved in moment-to-moment fluid homeostasis but operates only when dehydration is severe.

Angiotensin II↗
PubMed1988

Immunocytochemical and biochemical characterization of angiotensin I and II in cultured neuronal and glial cells from rat brain.

Neuronal and glial cells cultured from neonatal rat brains showed staining for both angiotensin I and II using the peroxidase-antiperoxidase method. In glial cell extracts of normotensive Wistar-Kyoto rats, the concentrations of angiotensin I and II were 12.47 +/- 2.71 (n = 4) and 66.73 +/- 13.28 fmol/mg protein (n = 4). Angiotensin I and II found in neuronal cell extracts of normotensive Wistar-Kyoto rats were 11.29 +/- 2.99 (n = 4) and 60.25 +/- 12.77 fmol/mg protein (n = 4). No significant difference was found in the concentration of angiotensin I and II in both cell types from the same rat strain. Angiotensin I concentrations of 16.83 +/- 3.43 fmol/mg protein (n = 5) determined in neuronal cell extracts derived from spontaneously hypertensive rats did not differ significantly from those found in neuronal cell extracts of Wistar-Kyoto rats. However, neuronal cell extracts from spontaneously hypertensive rats revealed values of 25.19 +/- 4.31 fmol angiotensin II/mg protein (n = 4). This was significantly different (p less than 0.05) and represented a 58% reduction in the angiotensin II levels in neuronal cells from spontaneously hypertensive rats compared to Wistar-Kyoto rat cultures. Angiotensin I and II measured in the growth medium containing 10% plasma-derived horse serum was below the detection limit of both radioimmunoassays. No difference in the angiotensin I and II levels was found in cells kept in serum-free medium. The angiotensin I and II immunoreactive material determined in the cell extracts could be characterized on reversed-phase high pressure liquid chromatography as (Ile5)-angiotensin I and II. (Ile5)-angiotensin III was not detectable.

Angiotensin I↗
PubMed1987

Presence of renin in primary neuronal and glial cells from rat brain.

Immunocytochemical and biochemical techniques have been utilized in the present study to characterize renin in brain cell cultures. With the use of renin-specific antibody, positive renin staining was seen in neuronal and in astrocytic glial cells using the peroxidase-antiperoxidase method. Renin concentration was pH-dependent with highest concentrations at 5.5, decreasing from pH 6.0 to 6.5. At pH 7.4 no renin was detectable in either glial or neuronal cells. The contribution of cathepsin D to the measured renin was about 10% at pH 5.5; 7% at pH 6.0 and 3% at pH 6.5. Comparison of glial with neuronal cells from WKY rats revealed significantly elevated renin at pH 5.5 in glial cells. No difference was seen between glial and neuronal renin levels in WKY rats at pH 6.0 and 6.5. At pH 5.5 and 6.0 renin was significantly increased in neuronal cells of SHR compared to WKY, whereas at pH 6.5 no difference was observed. The renin concentration in cells kept for 2 days in serum-free medium did not differ from those measured in cells kept in serum-containing medium. The generated peptide was identified as [Ile5]Angiotensin I on reversed-phase HPLC.

Angiotensin I↗
PubMed1987

Distinct angiotensin II receptor in primary cultures of glial cells from rat brain.

Angiotensin II (Ang-II) has profound effects on the brain. Receptors for Ang-II have been demonstrated on neurons, but no relationship between glial cells and Ang-II has been established. Glial cells (from the hypothalamus and brain stem of 1-day-old rat brains) in primary culture have been used to demonstrate the presence of specific Ang-II receptors. Binding of 125I-Ang-II to glial cultures was rapid, reversible, saturable, and specific for Ang-II. The rank order of potency of 125I-Ang-II binding was as follows: Ang-II = [sarcosine1,Ala8]Ang-II greater than [sarcosine1,Ile8]Ang-II much greater than Ang-III greater than Ang-I. Scatchard analysis revealed a homogeneous population of high-affinity (Kd = 1.1 nM) binding sites with a Bmax of 110 fmol/mg of protein. Light-microscopic autoradiography of 125I-Ang-II binding supported the kinetic data, documenting specific Ang-II receptors on the glial cells. Ang-II stimulated a dose-dependent hydrolysis of phosphatidylinositols in glial cells, an effect mediated by Ang-II receptors. However, Ang-II failed to influence [3H]norepinephrine uptake, and catecholamines failed to regulate Ang-II receptors, effects that occur in neurons. These observations demonstrate the presence of specific Ang-II receptors on the glial cells in primary cultures derived from normotensive rat brain. The receptors are kinetically similar to, but functionally distinct from, the neuronal Ang-II receptors.

Angiotensin II↗
PubMed1987

Functions of angiotensin in the central nervous system.

In this review, the emerging functional roles of the brain angiotensin system have been considered. The major effects of Ang II can be classified into three groups, which imply three possible functions: The first, and largest, group is actions associated with the regulation of body fluid volume in response to hypovolemia. These include thirst, blood pressure increase, vasopressin release, sodium appetite and excretion, and ACTH and aldosterone release. This function alone has important implications for the control of blood pressure and the disease of hypertension. Another possible function is a role for angiotensin in the activity of gonadotropic hormone releasing hormones and pituitary hormones during the reproductive cycle and pregnancy. A third group of functions is the synaptic, neurotransmitter interactions of Ang II with catecholamines, serotonin, prostaglandins, and other peptides, not all of which could be reviewed here due to space limitations. This interaction is significant for all functions mentioned and leads to alterations in motivation (thirst, pain), memory (and possibly learning), and motor control. The amount of data available, however, is so limited that to claim angiotensin plays any major role in the latter functions would be premature. Throughout this review, we compared the central and peripheral effects of Ang II. We suggest that normally, a blood-CVO barrier prevents diffusion of peripheral Ang II to brain receptors inside the BBB. Because of this mechanism, the responses to the two routes of administration are distinctly different. When systemic peptide levels are low, Ang II activates only receptors in the CVOs; however, when these levels are high, the peptide diffuses to receptors that are normally activated only by brain Ang II.

Angiotensin II↗
PubMed1987

Angiotensin II does not alter ACTH responses to hypoglycemia in conscious dogs.

These experiments were designed to test for an interaction between angiotensin II (ANG II) and stress in the control of plasma adrenocorticotropin hormone (ACTH), corticosteroids, and aldosterone. The stimulus to ACTH used in this study was insulin-induced hypoglycemia, a stimulus that does not increase plasma ANG II concentrations. Five trained dogs with exteriorized carotid arteries were studied. Each dog was infused with ANG II intravenously (10 ng X kg-1 X min-1) or into the carotid artery (1 ng X kg-1 X min-1) or with saline (iv) for 80 min. Twenty minutes after the start of the infusion, insulin (0.10 U/kg iv) was injected. Intravenous infusion of ANG II increased mean arterial pressure (MAP) and plasma aldosterone concentrations but did not increase ACTH or corticosteroid responses to hypoglycemia. Intracarotid infusion of ANG II did not increase MAP and also failed to increase ACTH and corticosteroid responses to hypoglycemia. Since ANG II infusions did not increase basal corticosteroids, the failure of ANG II to stimulate ACTH is not a result of steroid negative feedback. Thus it appears that increased plasma ANG II concentrations do not increase ACTH responses to hypoglycemic stress.

Adrenal Cortex Hormones↗
PubMed1986

Isolation and purification of angiotensin II using affinity and high-pressure liquid chromatography.

Peptides have been found in a variety of tissues including brain. To purify the peptide angiotensin II, a three-step method for the isolation and purification has been developed using extraction, affinity chromatography, and high-pressure liquid chromatography. Angiotensin II antiserum purified by affinity chromatography was covalently coupled to Affi-gel 10 (Affi-gel 10-AB). The efficiency and usefulness of this column for the purification of angiotensin II from biological sources were tested with 125I- and 3H-labeled (Ile5)-angiotensin II added to rat brains prior to extraction. After extraction, the recoveries for both peptides were 74 and 75%, respectively. Recovery after the purification on Affi-gel 10-AB was 84 and 82%. Thirty-two percent of the radioactivity was not retained and 50% of the radioactivity could be eluted with 0.1 M Na citrate buffer containing 1 M NaCl using a stepwise pH gradient. Characterization by HPLC of the unretained radioactivity from the Affi-gel 10-AB column showed one peak for [125I]angiotensin II, coeluting with the [125I]angiotensin II standard and two minor peaks. Only 30% of unretained [3H]angiotensin II could be identified as intact [3H]angiotensin II on HPLC. Both [125I]angiotensin II and [3H]angiotensin II elutable at pH 5.0 and 4.0 on Affi-gel 10-AB could be demonstrated as highly purified [125I]angiotensin II and [3H]angiotensin II on HPLC with a purity of more than 90%. On HPLC, the recovery was 81% for [125I]angiotensin II and 99% for [3H]angiotensin II. The recovery for the entire three-step procedure was about 60%. The loading capacity of the Affi-gel 10-AB column for (Ile5)-angiotensin II was 550 ng.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1986

A constant perfusion slice chamber for stable recording during the addition of drugs.

A new design for a brain slice chamber is described. This chamber has the following features: slices are maintained in a stable condition for long-term (3-4 h) intracellular recording; drugs may be injected into the flowing perfusion medium in known concentrations without disturbing intracellular penetration; a wide range of concentrations may be used to test a single cell, highly repeatable results may be obtained; only minute amounts are required of substances to be tested, and the apparatus is easy to use and clean since all parts are removable. The chamber may also be easily modified to allow for the requirements of different experiments. The chamber has been used successfully to test the effects of Ang II, carbachol, insulin and gonadotropin releasing hormone.

Action Potentials↗
PubMed1986

Angiotensin II attenuates baroreflexes at nucleus tractus solitarius of rats.

Microinjection of angiotensin II (ANG II) into the nucleus tractus solitarius (NTS) has been shown to produce a dose-dependent increase in blood pressure and heart rate. We have tested the effect of subpressor infusions of ANG II (10 ng . kg-1 . min-1) in the NTS on reflex bradycardia after intravenous administration of the vasoconstrictor phenylephrine (1-12 micrograms) in normotensive urethan-anesthetized rats. ANG II within the brain is thought to contribute to the decreased baroreflex sensitivity in spontaneously hypertensive rats (SHR). The sensitivity of the baroreflex was significantly decreased by the infusion of ANG II (1.01 +/- 0.08) compared with control (2.41 +/- 0.51) in the normotensive animals. Baroreflex sensitivity was significantly decreased in SHR (0.40 +/- 0.21) compared with normotensive animals. We conclude that ANG II within the NTS can inhibit the function of baroreceptor reflexes in normotensive animals, suggesting that the endogenous peptide may perform an inhibitory role in the baroreflex arc, and this is further evidence that central ANG II is involved in blood pressure of SHR.

Angiotensin II↗
PubMed1986

Interaction between CRF and angiotensin II in control of ACTH and adrenal steroids.

These experiments were designed to test for interactions between plasma angiotensin II (ANG II) and corticotropin-releasing factor (CRF) in the control of plasma adrenocorticotropin (ACTH), aldosterone, and corticosteroids, mean arterial pressure (MAP), and heart rate (HR) in conscious dogs. Five trained dogs with exteriorized carotid arteries were studied. Each dog was infused with saline and with CRF at three rates (2.5, 5, and 10 ng X kg-1 X min-1) and ANG II at three rates (5, 10, and 20 ng X kg-1 X min-1) for 60 min. The same animals were also coinfused with 10 ng X kg-1 X min-1 ANG II at each rate of CRF infusion and with 10 ng CRF X kg-1 X min-1 at each rate of ANG II infusion. Infusion of ANG II alone caused dose-related increases in aldosterone, corticosteroids, and MAP but did not alter ACTH or HR. Infusion of CRF alone increased ACTH, aldosterone, and corticosteroids but not MAP or HR. Coinfusion of CRF and ANG II caused ANG II dose-related ACTH responses but did not alter the sensitivity of the ACTH responses to CRF. Thus it appears that ANG II alone does not stimulate ACTH release but requires increased CRF concentrations to effect ACTH release.

Adrenal Cortex Hormones↗
PubMed1986

A biphasic excitatory response of hippocampal neurons to gonadotropin-releasing hormone.

Central gonadotropin-releasing hormone (GnRH) injected intraventricularly (IVT) has been shown to facilitate rat sexual behavior. To elucidate the brain mechanisms of GnRH action, we have applied GnRH to hippocampal brain slices in vitro. Using intracellular recording from 40 hippocampal CA1 pyramidal neurons, we have found GnRH to elicit predominantly excitation. There are two types of excitatory responses. One is a short-latency, short-duration response and the second a long-latency, long-duration response. These responses were characteristic of GnRH and not peptides generally because angiotensin II, which also had an excitatory effect, had only long-latency, short-duration effects. The neural response to GnRH may be involved in the initiation of the behavioral response since the termination of the long-duration response coincides with the onset of the behavior.

Action Potentials↗
PubMed1986

Converting enzyme inhibitors and brain angiotensin.

The spontaneously hypertensive rat (SHR) has many characteristics indicative of an overactive brain-angiotensin system. Since converting enzyme inhibitors are powerful hypotensive agents, the SHR was used to study the mechanisms of blood pressure reduction with MK421, MK422, Hoe498, and ramiprilat. A comparison of intraventricular (i.v.t.) to intravenous (i.v.) routes of administration showed that with MK421 the i.v.t. route was far more potent than the i.v. area. MK421 i.v.t. produced a profound and prolonged lowering of blood pressure in SHR. The blood pressure was reduced for a longer period than angiotensin II (ANG II) formation was inhibited. Ramiprilat decreased blood pressure in SHR for a prolonged period but was not significantly effective in the Wistar-Kyoto rats (WKY). The inhibition of ANG I pressor action correlated to the depressor effect. Brain ANG II was measured in different parts of the brain and plasma. With Hoe498 i.v. 50 micrograms/kg, there was an increase in hypothalamic angiotensin and plasma angiotensin. With MK422 i.v.t., there was a decrease in brain ANG II. Ramiprilat i.v.t. increased plasma ANG II and the variability of brain ANG II in different brain regions. In the SHR, ramiprilat decreased brainstem ANG II but did not change hypothalamic ANG II. High-pressure liquid chromatography characterization showed that the ANG II measured was authentic. In the SHR brain, ANG II was significantly higher in certain regions than in WKY. The results showed an increase of brain ANG II in normotensive animals with angiotensin converting enzyme inhibitor but a reduction of brainstem ANG II in the SHR. This may indicate the mechanism of lowering blood pressure in SHR is by disinhibition of the baroreflex.

Angiotensin II↗
PubMed1986

Levels of brain angiotensin in the spontaneously hypertensive rat and treatment with ramiprilat.

Previous studies have indicated that brain angiotensin II (ANG II) in the spontaneously hypertensive rat (SHR) may play an important role in the maintenance of hypertension. Preventing the synthesis of ANG II leads to a reduction in blood pressure and, therefore, brain ANG II levels in the SHR should be higher or have increased turnover than in the Wistar-Kyoto (WKY) rat. To investigate this issue we have dissected discrete areas of the brain from SHR and WKY and extracted, purified and quantified brain ANG II. Significantly higher levels were found in the hypothalamus, striatum, cortex and cerebellum in SHR compared to WKY. The new converting enzyme inhibitor, ramiprilat, injected centrally lowered blood pressure by synthesis inhibition but measurements of brain ANG II after ramiprilat did not indicate increased turnover. Further analysis of the peptide fragments needs to be done before turnover rates can be fully understood.

Angiotensin I↗
PubMed1985

[125I]Tyr-bradykinin binding in primary rat brain cultures.

Kinins bind to specific, high affinity recognition sites in rat brain cell culture. Studies in these cultures minimize non-specific binding and degradation of the ligand. Binding of [125I]Tyr-bradykinin to intact cultured brain cells from neonatal rats was time- and pH-dependent. Scatchard analysis of saturation experiments yielded two affinity components with dissociation constant and maximum binding site concentration averaging 1 nM and 100 fmol/mg protein, and 16 nM and 1000 fmol/mg protein, respectively. The binding sites were specific for kinins and kinin analogues, and the order of potency in competing for [125I]Tyr-bradykinin binding was Lys-bradykinin greater than bradykinin greater than Tyr-bradykinin greater than Tyr8-bradykinin much much greater than Des-Arg9-bradykinin. Monovalent and divalent cations inhibited kinin binding. Comparison of competition curves performed in glial-enriched vs neuron-enriched cultures suggested that the kinin binding sites resided primarily on neurons. These data enhance the existing evidence suggesting kinins as neurotransmitters or neuromodulators.

Animals↗
PubMed1985

The mechanism of guanosine triphosphate depletion in the liver after a fructose load. The role of fructokinase.

A Sephadex G-25 filtrate of a 100 000g supernatant of rat liver homogenate was shown to be able to phosphorylate fructose, with GTP as the phosphate donor. Attempts to separate ATP- and GTP-dependent fructokinase activities failed, indicating that there is a single enzyme able to use both nucleotides. With a partially purified enzyme, Km values for fructose of 0.83 and 0.56 mM were found with ATP and GTP as substrates respectively. Km values of 1.53 and 1.43 mM were found for GTP and ATP respectively. Both ADP and GDP inhibited the GTP- and ATP-dependent fructokinase activity. We conclude that the depletion of hepatic GTP caused by intravenous administration of fructose to mice and rats can be explained simply by the utilization of the nucleotide by fructokinase.

Adenosine Diphosphate↗
PubMed1985

Neuropeptide action in nucleus tractus solitarius: angiotensin specificity and hypertensive rats.

We have reported that microinjection of angiotensin II (ANG II) into the nucleus tractus solitarius of urethan-anesthetized normotensive rats produces an increase in mean arterial pressure (MAP) over the dose range 50-500 pmol. The effect in spontaneously hypertensive rats (SHR) is now reported. Over the range 100-500 pmol SHR exhibit increases in MAP and heart rate greater than Wistar-Kyoto or Sprague-Dawley rats. SHR did not exhibit exaggerated responses to intravenous phenylephrine, suggesting a central site of increased responsiveness to ANG II. We also found depressor effects in Sprague-Dawley at lower doses (0.1 and 1 pmol). The decreases in MAP were extremely variable and not dose related. A selected dose of additional neuropeptides identified in the NTS was tested. Somatostatin, bradykinin, and vasoactive intestinal peptide (0.5 nmol) were without cardiovascular effects. Oxytocin and vasopressin, however, produced significant increases in MAP. Substance P produced a very small but significant increase in heart rate and MAP. Interaction between the vasopressin and ANG II pressor effects was studied, and each proved to be independent.

Angiotensin II↗