Biomedical subjects

M I Phillips

Publications and source records attributed to M I Phillips.

At least 91 records · Page 5Linked to original sources

PubMed1993

Angiotensin II receptor subtypes on adrenal adenoma in primary hyperaldosteronism.

Patients with an aldosterone-producing adenoma (APA) characteristically fail to show an increase in plasma aldosterone (PA) concentration with maneuvers that increase angiotensin II (Ang II), yet they retain a brisk response of PA to adrenocorticotrophic hormone. Therefore, adrenal Ang II receptor binding was characterized in a patient with APA who had a blocked PA response to Ang II infusion before adrenalectomy. The binding of [125I]Sar1,IIe5-Ang II in adrenal gland and tumor was fully displaced by excess Ang II. In the tumor, 98% of [125I]Sar1,IIe5-Ang II binding was displaced by the AT, receptor antagonist losartan, yet only 5% was displaced by the AT2 receptor antagonist PD-123,319. Autoradiography of the adrenal gland itself showed a predominance of AT1 receptors in the cortex and AT2 receptors in the medulla. The tumor showed a predominance of AT1 receptors, but there was some evidence of a limited population of AT2 receptors. The tumor and adjacent adrenal contained high concentrations of Ang II. In conclusion, a defect in Ang II-stimulated aldosterone secretion in APA occurs despite high concentrations of Ang II in the adrenal and the presence of specific, high-affinity Ang II receptor binding sites.

Adenoma↗

PubMed1992

Changes in skin angiotensin II receptors in rats during wound healing.

Angiotensin (AII) is associated with increased vascular smooth muscle growth and we have found increased levels of tissue AII during healing of wounded skin. Here we have determined changes in skin AII receptors during wound healing in adult male Sprague-Dawley rats. An abdominal surgical incision was made under anesthesia and rats were sacrificed at different times after wounding. Specific binding of 125I-AII was significantly decreased at 12, 18 and 24 hours in the wounded tissue compared to control tissue from the same rat. By 3 days the binding had recovered to baseline levels. Receptors were mostly AT1, with a high and a low affinity site in the skin both in control and healing tissue. The Bmax of the high affinity site was significantly decreased in healing tissue but there was no significant change in Kd. Our results demonstrate that adult rat skin contains predominantly AT1 receptors and also that these receptors are downregulated for 12-24 hours after wounding.

Angiotensin II↗

PubMed1992

Losartan potassium, a nonpeptide antagonist of angiotensin II, chronically administered p.o. does not readily cross the blood-brain barrier.

Recently several novel nonpeptide antagonists of angiotensin II (Ang II) have been identified. One of these, losartan potassium (formerly DuP 753) was developed as an orally active and highly selective antagonist for Ang II. As it is inhibited by sulfhydryl agents, it is specific for the AT1 receptor subtype. Since Ang II has both central and peripheral effects, we investigated whether losartan, given p.o. chronically, crosses the blood-brain barrier. The effects of chronic administration of losartan orally (p.o.) at 3 mg/kg per day for three days on the dipsogenic and pressor responses to a pre-established dose of Ang II i.v.t. (50 ng) were studied. Three series of experiments were carried out using conscious normotensive Sprague-Dawley rats. The rats were injected with Ang II intraventricularly (i.v.t.) before and after treatment of losartan p.o. and blood pressure and drinking responses measured. The experiments established that 3 mg/kg losartan p.o. for 3 days antagonized pressor effects of Ang II intravenously (i.v.), but did not antagonize the pressor or drinking effects of Ang II i.v.t. Daily water intake significantly increased with chronic losartan p.o.. Since chronic administration of losartan p.o. was able to block the effects of Ang II i.v. but had no effect on Ang II i.v.t. we conclude that losartan potassium does not readily cross the blood-brain barrier using this dose regimen.

Administration, Oral↗

PubMed1992

The role of angiotensin, AT1 and AT2 receptors in the pressor, drinking and vasopressin responses to central angiotensin.

Angiotensin II (Ang II) given centrally produces an increase in blood pressure and motivation to drink. The physiological mechanisms that mediate the pressor response include release of vasopressin (AVP) and activation of the sympathetic nervous system. Using 2 new Ang II receptor antagonists, we were able to investigate the role of AT1 or AT2 receptors in mediating these effects. Adult male Sprague-Dawley rats were cannulated in the lateral ventricle and 5 days later catheterized in the carotid artery for blood pressure measurements. All experiments were carried out in conscious rats. Three treatments were given intraventricularly (i.v.t.), in 2 microliters artificial cerebrospinal fluid (ACSF) at 30 min intervals: (1) 50 ng Ang II, (2) 0.7 micrograms AT1 antagonist Losartan or 7.0 micrograms AT2 antagonist PD123177, followed by 50 ng Ang II, and (3) 50 ng Ang II, to test for recovery. Blood pressure and drinking measurements were recorded. Also, blood samples for assay of AVP were drawn at 1 or 3 min post-injection in 2 separate groups of rats. We found that both Losartan and PD123177 significantly reduced release of AVP to Ang II 1 min post-injection. Losartan significantly blocked the pressor response (P less than 0.001), while PD123177 had no significant effect. Drinking was also antagonized by Losartan (P less than 0.05) and reduced (n.s.) by PD123177. The results suggest that the pressor response to Ang II (i.v.t.) is predominantly AT1 mediated, while the drinking and AVP responses may be mediated by both receptor subtypes.

Angiotensin II↗

PubMed1992

Angiotensin II receptor subtypes play opposite roles in regulating phosphatidylinositol hydrolysis in rat skin slices.

Among the many functions of angiotensin II (Ang II) it now appears that Ang II is a growth factor. The concentration of Ang II in rat skin has been shown to increase during wound healing. To investigate the intracellular effect of Ang II in skin we determined the levels of total cytoplasmic inositol phosphates after incubation of skin slices with different doses of Ang II. 10(-6) M of Ang II increased significantly the phosphatidylinositol (PI) hydrolysis, and the effect was dose dependent up to 10(-4) M Ang II. The majority of inositol phosphates yielded after 1 hour incubation in the presence of lithium was InsP1, with lesser amount of InsP2. Losartan, the Ang II AT1 antagonist, at a dose of 10(-4) M blocked the effect of Ang II, while PD123319, the Ang II AT2 antagonist, had no antagonistic action; PD123319 at the higher dose of 10(-3) M, however, potentiated the effect of Ang II on PI hydrolysis. The results suggest that PI hydrolysis is a second messenger system for Ang II in rat skin. Also, the two subtypes of Ang II receptors mediate opposite effects on PI hydrolysis: Ang II binding to AT1 receptors increases inositol phosphate production, while Ang II binding to AT2 receptors decreases inositol phosphate production.

Angiotensin II↗

PubMed1992

Atrial natriuretic peptide as a marker for doxorubicin-induced cardiotoxic effects.

Doxorubicin is an effective antineoplastic agent, but it frequently causes dose-related cardiotoxic effects. Because the atrial natriuretic peptide (ANP) level is elevated in children with heart defects, the authors measured the ANP levels in children to determine whether ANP might serve as a simple diagnostic indicator of cardiotoxic effects. Sixteen patients, 5 to 19 years of age, who were being treated with doxorubicin (45 mg/m2 body surface area) for various malignancies had ANP levels measured in plasma. There was a group of six children, with a significant peak of plasma ANP (pANP) levels 3 weeks after the administration of the drug. Of these six patients, five had received high cumulative doses of doxorubicin (160 to 370 mg/m2), and two of them went into congestive heart failure without a previous decline in left ventricular ejection fraction, a standard technique for monitoring cardiac function during treatment with doxorubicin. The other ten patients had normal ANP levels throughout the study, and signs of cardiac dysfunction did not develop. None of the patients in the control group who had cancer and were not treated with doxorubicin and none of the healthy volunteers had elevated ANP levels. These preliminary results suggest that pANP may be useful as an early and sensitive indicator for doxorubicin-related myocardial damage.

Adolescent↗

PubMed1992

The effect of chronic bilateral nephrectomy on plasma and brain angiotensin.

OBJECTIVE: To prove the independence of local tissue renin-angiotensin system (RAS) in brain from classical kidney RAS, we measured local angiotensin levels in bilaterally nephrectomized rats which had been dialyzed with a dialysis technique to greatly prolong survival time. DESIGN: Two groups of animals were used: (1) bilaterally nephrectomized rats with intraperitoneal dialysis, where both kidneys were surgically removed; and (2) controls with intact kidneys and dialysis. By using this protocol, we were able to study plasma and brain angiotensins 5 days after nephrectomy (no longer periods have been attempted). METHODS: Plasma sodium, potassium and pH were monitored while rats were dialyzed four times a day. Plasma samples and brain areas were obtained and angiotensin II measured by radioimmunoassay and high-pressure liquid chromatography (HPLC). RESULTS: Plasma angiotensin II was significantly diminished in the nephrectomized rats but was still detectable, the levels being above the minimal detectable value. The identity of angiotensin I and angiotensin II detected by radioimmunoassay was confirmed by HPLC. In the brain, angiotensin II content was significantly increased in all areas studied. The highest increments were in hypothalamus and brain stem. CONCLUSIONS: Our results demonstrate that: (1) brain angiotensin II is regulated independently of peripheral angiotensin II; and (2) a reduced plasma angiotensin II persists 5 days after bilateral nephrectomy. We conclude that the angiotensin II in the plasma was derived from non-renal tissue and the results support the conclusion that tissue RAS has paracrine and autocrine functions independent of the endocrine function of circulating plasma angiotensin.

Angiotensin II↗

PubMed1992

Angiotensin II receptor activation depolarizes rat supraoptic neurons in vitro.

Functional studies indicate that hypothalamic magnocellular neurosecretory neurons are a target for angiotensin. The present investigation used intracellular recordings to characterize the nature and type of angiotensin II receptors on rat supraoptic nucleus neurons maintained in superfused hypothalamic explants. Of 68 cells transiently exposed to either Val5- or Ile5-angiotensin II (maximum peak concentration 1-25 microM), 34 responded with a gradual membrane depolarization (1-15 mV) that peaked in 2.2 +/- 0.4 (SD) min and was accompanied by a 17.6 +/- 4.8% reduction of input resistance. Responses persisted (and were actually enhanced) in media containing tetrodotoxin (0.5-1.0 microM) and/or nominally zero calcium, indicating a direct postsynaptic action. In 19 responsive cells, the mean reversal potential for the angiotensin-induced response was -26.4 +/- 2 mV. Bath application of the nonpeptide type-1 angiotensin receptor antagonist DuP753 (5-20 microM) reversibly blocked the angiotensin-induced depolarization in all of 11 cells tested. By contrast, equimolar applications of the type-2 antagonist PD123177 were ineffective in all seven angiotensin-responsive cells tested. These observations provide novel evidence for the existence of functional type-1 receptors on rat supraoptic nucleus neurons. The reversal potential for the angiotensin-induced response suggests mediation through a nonselective cationic conductance.

Angiotensin II↗

PubMed1992

Abnormal neuroendocrine responses during exercise in heart transplant recipients.

BACKGROUND: Osmotic and neural factors stimulate neuroendocrine activity during exercise. In contrast to excitatory mechanisms, afferent information from cardiac mechanoreceptors inhibits integrative centers in the hypothalamus and medula oblongata, which serves to buffer neuroendocrine activity. Orthotopic cardiac transplantation results in the loss of afferent information from cardiac mechanoreceptors. Thus, transplantation possibly results in exaggerated neuroendocrine responses when patients are physically active. METHODS AND RESULTS: We measured the neuroendocrine response to moderate and strenuous exercise performed at the same relative intensity in 11 heart transplant recipients (50 +/- 14 years old) 18 +/- 12 months after transplantation and 11 control subjects matched with respect to sex, age, and body size. Plasma levels of norepinephrine, vasopressin, renin activity, atrial natriuretic peptide, angiotensin II, and aldosterone were measured at rest, during a maximal graded exercise test, and during submaximal exercise at 40% and 70% of peak power output on a cycle ergometer (W). Plasma renin activity and atrial natriuretic peptide were elevated at rest in heart transplant recipients (p < or = 0.05). Heart rate (%HRmax reserve), rating of perceived exertion, and reductions in plasma volume (% delta from rest) at the conclusion of the three exercise conditions did not differ between heart transplant recipients and control (p > or = 0.05). Relative changes in neuroendocrine hormones were similar (p > or = 0.05) in heart transplant recipients and control during exercise at 40% of peak power output. Relative changes in plasma norepinephrine, vasopressin, atrial natriuretic peptide, and plasma renin activity were greater (p < or = 0.05) in heart transplant recipients during exercise at 70% of peak power output and the graded exercise test. CONCLUSIONS: We interpret these data as a possible indication of ablation of cardiac mechanoreceptor afferents and unopposed neuroendocrine stimulation in heart transplant recipients. Furthermore, chronic neuroendocrine hyperactivity is likely in ambulatory heart transplant recipients. Although cyclosporine nephrotoxicity is implicated in the development of hypertension, our data suggest that chronic neuroendocrine hyperactivity, which alters renal volume regulation, also contributes to the incidence and severity of hypertension in heart transplant recipients.

Afferent Pathways↗

PubMed1992

White blood cell and lymphocyte populations following interleukin-2 administration in the spontaneously hypertensive rat.

The immune system has been linked to the pathogenesis of hypertension in the spontaneously hypertensive rat (SHR). Recently interleukin-2 has been reported to inhibit the development of hypertension in the SHR, but no measures of different lymphocyte populations were made. To test the effect of interleukin-2 we repeated the protocol in the report by injecting forty two day old, male SHR and WKY rats, and in addition, analyzed lymphocyte subpopulations. Untreated, age matched rats of the same strain were used as a control. At three and four months of age blood was drawn from all animals. Monoclonal antibodies were used to fluorescently label different lymphocyte subpopulations. The populations examined were the total T-cells, T-nonhelper cells, T-helper cells and B-cells. Total numbers of lymphocytes and white blood cells were also examined. Blood pressures were measured in conscious, restrained animals at two and four months of age. The results showed no attenuation of blood pressure in the interleukin-2 treated SHR at either age. The interleukin-2 treated SHR had a decrease in the percentage of B-cells and an increase in the percentage of T-nonhelper cells relative to the control SHR. Both treated and untreated SHR had increased numbers of white blood cells and lymphocytes compared to both groups of WKY. We conclude that the interleukin-2 used was active but failed to have any effect on blood pressure or absolute numbers of white blood cells and lymphocytes in the treated animals.

Aging↗

PubMed1992

Alterations of lymphocyte populations during development in the spontaneously hypertensive rat.

OBJECTIVE: Immune system abnormalities have been linked to hypertension in the spontaneously hypertensive rat (SHR). The goal of our study was to examine different lymphocyte subpopulations in the prehypertensive and developmental phases of hypertension in the SHR. DESIGN: Blood samples were obtained from SHR and Wistar-Kyoto (WKY) rats at the following time-points: 2 weeks and 1, 2, 3 and 4 months. Lymphocytes were separated from the whole blood. METHODS: Monoclonal antibodies were used to fluorescently label the following lymphocyte subpopulations; total T cells, T non-helper cells, T helper cells and B cells. Fluorescence-activated cell sorting (FACS) analysis was used to quantify the percentages of the different subpopulations examined. RESULTS: The T non-helper cell population was depressed in SHR from 2 weeks of age. This finding persisted throughout the entire 4-month study period. At the 4-month time-point, the total T cell percentage was also depressed in the SHR. CONCLUSIONS: These results demonstrate that immune system abnormalities are present in the prehypertensive and developmental phases of hypertension in the SHR. This supports the hypothesis that the immune system is involved in the development and maintenance of hypertension in the SHR, preceding not adapting to this state.

Animals↗

PubMed1992

Presence of angiotensin peptides in human urine.

Immunoreactive angiotensin I and angiotensin II were found in human urine that was purified on octadecasilylsilica cartridges. The daily excretion of angiotensin I and II in healthy volunteers was 189.00 (SE 38.36) and 17.54 (SE 3.07) pmol/24 h or 148.09 (SE 32.22) and 12.82 (SE 2.34) pmol/L, respectively (n = 12). No circadian rhythm was observed in the excretion patterns of angiotensin I and II. In vitro degradation of angiotensin I or II could not be detected in acidified urine samples. A marked increase in the excretion of angiotensin I and II could be demonstrated in patients with anaphylactoid reactions to drugs and food additives after oral challenge. Immunoreactive angiotensin I and II could be characterized by HPLC as Ile5-angiotensin I, Ile5-angiotensin II, and angiotensin II metabolites.

Adult↗

PubMed1991

Chronic ICV infusion of neuropeptides alters lymphocyte populations in experimental rodents.

The sympathetic nervous system has been shown to influence immune function. Angiotensin II and substance P are two neurally active peptides that have been shown to increase sympathetic nervous system activity when injected centrally. Using osmotic minipumps, we chronically infused angiotensin II (1 microgram/h) and substance P (2 micrograms/h) into the brains of intact Sprague-Dawley rats for a period of 1 month and 2 weeks, respectively. Age-matched control animals were infused with artificial cerebrospinal fluid. We then examined the effect of this infusion on the percentage of different lymphocyte populations in the peripheral blood. The angiotensin II infused animals showed an increase in the percentage of total T-cells and a decrease in the percentage of B-cells relative to controls. The substance P treated animals also showed an increase in the percentage of T-cells present, but failed to show the decrease in the B-cell population seen with the angiotensin II infused group. This study shows that the central nervous system can influence the immune system. As shown in this study, these effects are most likely mediated via the sympathetic nervous system. These results add to the expanding body of data suggesting an important role of the central nervous in regulating immune function and our susceptibility to disease.

Angiotensin II↗

PubMed1991

Effect of exercise training on blood pressure in 70- to 79-yr-old men and women.

Men and women 70-79 yr of age (N = 49) were studied to assess the effect of 6 months of resistance or endurance exercise training on their blood pressure, hemodynamic parameters, and pressor hormone levels. Resistance training consisted of one set of 8-12 repetitions on ten Nautilus machines three times per week. The endurance training group progressed to training at 75-85% VO2max for 35-45 min three times per week for the last 2 months of training. No changes in body weight or estimated lean body mass occurred; however, the sum of seven skinfolds, as an index of percent body fat, decreased in both exercise groups. Upper and lower body strength increased with resistance training, while VO2max increased by 20% in the endurance training group. Blood pressure did not change with resistance training in individuals with normal or somewhat elevated blood pressures. Diastolic and mean blood pressure decreased significantly, by 5 and 4 mm Hg, with endurance training. Subjects with blood pressure greater than 140/90 reduced their systolic, diastolic, and mean blood pressure by 8, 9, and 8 mm Hg, respectively, with endurance exercise training. Cardiac output, peripheral vascular resistance, and plasma levels of angiotensin I and II and epi- and norepinephrine did not change in any of the groups. Thus, resistance exercise training does not adversely affect, or reduce, blood pressure, while endurance exercise training produces modest reductions in blood pressure in 70-79-yr-old individuals with somewhat elevated blood pressures.

Aged↗

PubMed1990

Dopamine synthesis and release in LLC-PK1 cells.

A porcine-derived renal epithelial cell line, LLC-PK1, was used to examine dopamine (DA) synthesis from L-dopa and DA release into the media. DA synthesis and release were elevated by increasing either L-dopa concentration or incubation time. DA synthesis was shown to be entirely due to conversion of L-dopa to DA by aromatic amino acid decarboxylase. DA release from LLC-PK1 cells was stimulated by NaCl and other Na+ or Cl- salts. DA release by LLC-PK1 cells was not dependent on extracellular Ca2+ or significantly stimulated by the depolarizing actions of KCl. LLC-PK1 cells which are devoid of any neural contributions to renal DA production can synthesize DA from L-dopa and release DA in response to stimulation by either Na+ or Cl-.

Animals↗

PubMed1990

Alpha-1-adrenergic receptors in the nucleus tractus solitarii region of rats with experimental and genetic hypertension.

The binding of the alpha 1-adrenergic receptors antagonist, 125I-HEAT, to membranes of nucleus tractus solitarii (NTS) regions of the brains of neurogenic hypertensive, spontaneously hypertensive (SH), and deoxycorticosterone (DOCA)/salt hypertensive rats and their respective controls was studied to quantitate the expression of alpha 1-adrenergic receptors. Scatchard analysis of the binding studies revealed a 1.8-fold increase in the Bmax of alpha 1-adrenergic receptors in NTS region membranes of SH rats when compared to their Wistar-Kyoto (WKY) control without significant difference in the Kd for 125I-HEAT. A decrease in the Kd with no difference in Bmax of receptors for 125I-HEAT was observed in the NTS region membranes of neurogenic hypertensive rats when compared with their sham-operated controls. In contrast, comparison of the Bmax and Kd values for 125I-HEAT binding in NTS region membrane of the DOCA/salt hypertensive rats and its sham-operated control showed no significant differences. We suggest that alterations in baroreceptor afferent activity may be related to alterations in central alpha 1-adrenergic receptors binding in SH rats and rats with neurogenic hypertension.

Adrenergic alpha-Antagonists↗

PubMed1990

High-performance liquid chromatography for the separation of angiotensin and its metabolites in human plasma and sweat.

A reversed-phase high-performance liquid chromatography (HPLC) method with gradient elution for the separation of angiotensin peptides is described. The highly reproducible method allows the base-line separation of angiotensin peptides with UV detection at 225 nm. This chromatographic methodology in combination with radioimmunoassay (RIA) is used for the characterization of angiotensin peptides in human plasma and sweat.

Acetonitriles↗

PubMed1990

Immunoreactive atrial natriuretic peptide in neuronal and glial cells of spontaneously hypertensive rat brain.

Neuronal and glial cultures from the hypothalamic-brain stem areas of 1-day-old normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rat brains stained positively with atrial natriuretic peptide (ANP)-specific antibodies. The endogenous levels of the ANP immunoreactivity in WKY neuronal and glial cultures were 17.0 +/- 2.2 and 14.3 +/- 2.7 pg/mg, respectively. Comparable neuronal and glial cultures from SH rat brains contained a 48 to 70% decrease in the endogenous ANP immunoreactivity levels. Culture media from both brain cell types also contained ANP immunoreactivity, the levels of which are significantly higher than those found in the cells. However, similar to endogenous levels, the media levels of immunoreactive ANP in SH neuronal and glial cultures were significantly reduced compared with WKY brain cultures. These observations demonstrate that endogenous ANP-like immunoreactivity is found in neuronal and glial cells and is released into the media. The levels of peptide are reduced in cultures of SH compared with WKY cultures, suggesting a genetically controlled difference between the hypertensive and normotensive rat strains long before hypertension develops.

Animals↗