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M I Phillips

Publications and source records attributed to M I Phillips.

At least 163 records · Page 9Linked to original sources
PubMed1982

A micromethod for the measurement of renin in brain nuclei: its application in spontaneously hypertensive rats.

The aim of this study was to develop a method for the measurement of renin activity in small tissue samples obtained from rat brains by the micropunch technique and to investigate the activity of brain renin in spontaneously hypertensive rats. The assay satisfied sensitive and specificity requirements. Angiotensin I was generated at a pH of 6.0; complete recovery of angiotensin I and kinetic studies supported the specificity of the method. Angiotensinase and cathepsin D-like acid protease activity were measured in parallel with renin. Renin was present in all brain regions studied and decreased with the age of the animals. An increased activity of renin was measured in several nuclei of the brain stem and in the neurohypophysis of young hypertensive rats when compared with age-matched normotensive control animals. These differences disappeared in older rats. There was a dissociation between renin and cathepsin D-like acid protease activity. No correlation existed between the distribution of renin and angiotensinase activity. The increased renin activity in brain stem nuclei of spontaneously hypertensive animals is in agreement with previous findings that the brain renin-angiotensin system contributes to the maintenance of high blood pressure in these rats.

Aging↗
PubMed1982

Uptake of prolactin from cerebrospinal fluid in rat brain.

The fate of prolactin in the cerebrospinal fluid was studied by the use of fluorescein labelled prolactin. The distribution was compared to the immunocytochemical distribution of endogenous prolactin. High intensity fluorescence was found in the ependyma of the area postrema, rostral dorsolateral cerebral aqueduct close to the subcommissural organ, and in some cells of the floor of the cerebral aqueduct. This distribution was not seen when excess unlabelled prolactin was injected. The results suggest prolactin uptake from CSF at specific sites which correspond to sites of localization of immunoreactive prolactin.

Animals↗
PubMed1982

Studies on the presence of angiotensin II in rat brain.

Angiotensin II-like immunoreactivity was extracted from brains of bilaterally nephrectomized rats with several different extraction procedures (90% methanol, distilled water, 6 M urea, 0.1 N HCl, and 2 M acetic acid). The activity was measured with radioimmunoassays using three different antisera, two of which had been used previously for immunocytochemical studies. With none of the extraction procedures or antisera employed was more than 80 pg/g wet weight of angiotensin II-like immunoreactivity found. Analysis was undertaken with two different reverse-phase high-pressure liquid chromatography systems; in one of these the immunoreactivity did not coelute with angiotensin II or III. On the basis of its elution pattern from a molecular sieving column, the immunoreactivity seems to have a higher molecular weight than angiotensin II. It is concluded that neurons in the brain do not synthesize and store angiotensin II.

Angiotensin II↗
PubMed1982

Dehydration and fluid balance: central effects of angiotensin.

Central effects of dehydration are stimulated by osmotic stimuli, the reduced input of volume receptors, and angiotensin II. The subfornical organ (SFO) and organum vasculosum laminae terminalis (OVLT) have become accepted as putative receptor sites for angiotensin II in the brain. The exact quantitative relationship between the hours of water deprivation and the amount of angiotensin generated peripherally and whether that amount is sufficient to induce thirst centrally have not been established, but there is no question that when animals are dehydrated their angiotensin levels rise and the animals are thirsty. Attempts to block centrally the contribution of angiotensin II to thirst have been variable and cholinergic inputs have to be blocked at the same time. Various stimuli for thirst interact in a parallel fashion, and when one stimulus is blocked the other stimuli are still effective. Plasma angiotensin II may induce natural thirst, but how it enters the brain still remains to be explained. Although the SFO and OVLT have no blood-brain barrier, the blood supply to these organs acts as a limited perfusion system whereby blood-borne proteins cannot diffuse far from the capillary bed. A second set of receptors is found on the ventricular surface of the OVLT, as shown by fluorescence labeled angiotensin II. The connection between the SFO and OVLT was cut by discrete knife cuts. Drinking to angiotensin II intraventricularly was not significantly altered but the pressor response was reduced by 50%. These results can be explained by a circuit for drinking passing down below the level of the knife cut and a separate pressor pathway passing dorsally through the area that was cut by the knife. Thirst and pressor neural circuits beginning with angiotensin receptors could explain some of the data accumulated with the AV3V syndrome that occurs when the OVLT and nucleus medianas are destroyed.

Angiotensin II↗
PubMed1981

Horseradish peroxidase study in rat of the neural connections of the organum vasculosum of the lamina terminalis.

Using highly localized injections by a transbuccal approach a study of the afferent and efferent connections of the organum vasculosum laminae terminalis (OVLT) with horseradish peroxidase (HRP) methods was carried out. The results showed that the OVLT has direct connections to several hypothalamic nuclei (anterior, preoptic, lateral preoptic, ventromedial nucleus) and to extrahypothalamic (central gray, locus coeruleus, subfornical organ) regions. There was not a direct projection from the supraoptic nucleus. Some of these connections may be involved in the functional actions of the OVLT observed after central injections of angiotensin II.

Afferent Pathways↗
PubMed1981

Rat brain cells in primary culture: characterization of angiotensin II binding sites.

The binding kinetics of angiotensin II (ANG II) have been studied in primary cultures from fetal rat brain. Binding of [125I]ANG II to rat brain cells in culture is time-, pH- and cell concentration-dependent. The binding is saturable, reversible, and 90--95% specific. Binding follows first-order kinetics, with values for K1 and K-1 of 4.9 x 10(6)M-1 S-1 and 3.33 x 10(4)S-1 respectively. Scatchard analysis reveals the presence of a single class of binding sites with Ka of 1.0 x 10(9)M-1 and an average of approximately 6 x 10(3) sites per cell. [125I]ANG II recovered from incubation medium under the conditions of the binding assay or after dissociation from cells is not significantly degraded as judged by gel filtration on Sephadex G-25 and radioreceptor assay. ANG II analogs compete with [125I]ANG II for binding, with potencies in general paralleling previously established biological activities. Of 5 analogs tested, (Ile8)-ANG II was almost equipotent with ANG II while (Dval3)-ANG II was least potent in the competitive binding assay. These data fulfill criteria for the identification of specific angiotensin II receptors in cells from mammalian brain.

Angiotensin II↗
PubMed1981

Separation of drinking and pressor responses to central angiotensin by monoamines.

This study investigated the neurotransmitters involved in the increase in blood pressure and drinking produced when angiotension II is injected intraventricularly (ivt). Using pharmacologic manipulations of the monoamines norepinephrine, dopamine, and serotonin it has been possible to separate the pressor response from dipsogenic responses to angiotension II. Alpha-adrenergic blockade with phentolamine restricted to the brain blocked the pressor response to angiotensin II in a dose-related manner, while drinking remained unaffected. Norepinephrine alone, injected into the ventricles elevated blood pressure, but did not produce drinking. The norepinephrine effect was also blocked by phentolamine by the same ventricular route. Other monoamines were not involved. Dopamine alone did not produce thirst. Cardiovascular effects with dopamine were observed only with large doses. The dopaminergic agonist apomorphine produced no change in blood pressure or drinking. Reduction of central serotonin stores by p-chlorophenylalanine intraperitoneally or 5,7-dihydroxytryptamine intraventricularly had no effect on the pressor or dipsogenic effects of angiotensin II. The serotonin agonist N,N-dimethyl-5-methoxytryptamine ivt did not produce a rise in blood pressure or drinking. It is concluded that the pressor effect of angiotensin II, but not the drinking effect is mediated by noradrenergic stimulation of alpha-receptors. The drinking response does not appear to be mediated by the monoamines.

Angiotensin II↗
PubMed1980

Visualization of specific angiotensin II binding sites in the brain by fluorescent microscopy.

The organum vasculosum of the lamina terminalis has been implicated as the site of receptors mediating central responses of angiotensin II. Up to now, this had been based on indirect evidence, but direct visualization of angiotensin II at its site of action has now been achieved by the use of a biologically active fluorescent angiotensin II agonist. The ventricular surface of the organum vasculosum lamina terminalis showed intense fluorescence, which was virtually eliminated by an excess of unlabeled angiotensin II.

Angiotensin II↗
PubMed1980

Increased specific binding of angiotensin II in the organum vasculosum of the laminae terminalis area of the spontaneously hypertensive rat brain.

Three localized sites, the organum vasculosum, lamina terminalis (OVLT) subfornical organ (SFO) and cortex in the brains of spontaneously hypertensive (SH) rats and normotensive Wistar-Kyoto (WKY) rats were micro-dissected out. The membranes were assayed for 125I-labelled angiotensin II specific binding. The only significant difference was a 129% greater specific binding in the OVLT in SH compared to WKY rats. Specific binding of 125I-labelled angiotensin II in the SFO and the cerebral cortex was not significantly different between the two strains. SH rats are known to have a greater sensitivity to centrally administered angiotensin II, which may contribute to the hypertension. This data suggests that a difference in central angiotensin II receptors is at least partially responsible for the increased sensitivity.

Angiotensin II↗
PubMed1980

Presence of angiotensin II in neurons cultured from fetal rat brain.

By means of a specific antiserum to angiotensin II (ANGII), it has been possible to demonstrate the existence of ANGII immunoreactivity in cells cultured from fetal rat brain. Dissociated cells cultured from the whole brains of 20-day-old fetuses were stained according to the peroxidase antiperoxidase method. Immunoreactive ANGII was observed in less than 1% of the total cell population. These cells have been identified as neurons on the basis of morphological criteria. Positively stained neuronal processes with localized concentrations of ANGII immunoreactivity were visualized in association with ANGII-containing soma. The presence of ANGII in cultured brain cells provides an experimental model for investigating the role of angiotensin in the CNS.

Angiotensin II↗
PubMed1980

The area postrema plays no role in the pressor action of angiotensin in the rat.

The area postrema has been shown to have a major role in mediating the pressor effects of peripheral angiotensin in the dog, cat, and rabbit. The purpose of this study was to ascertain the function of the medullary circumventricular structure in the conscious rat. The pressor potency of angiotensin administered into the vertebral and carotid arteries was compared with intra-aortic infusions of angiotensin. Although no difference in pressor activity of angiotensin could be detected between intraaortic and intravertebral administration, greater sensitivity was observed during intracarotid infusion. No difference in the course of one-kidney renal hypertension was observed between sham-lesioned rats and animals with an area postrema lesion. In addition, lesioned and sham-lesioned animals showed equivalent responses to graded doses of angiotensin administered either intravenously or into the lateral ventricle. It was concluded that in the rat the area postrema plays no role in mediating the central nervous system actions of angiotensin whether the peptide reaches the brain via the blood or the cerebrospinal fluid.

Angiotensin II↗
PubMed1980

Effects of apomorphine on ventilation in the neonate rat.

Systemic administration of apomorphine (APO) to anesthetized adult rats can influence breathing pattern, and several studies suggest that dopaminergic pathways are involved. To evaluate whether ventilatory responses to APO were already present in the neonate rat, animals between 3 and 9 days of age, with sectioned vagal and sympathetic trunks, were tested. Results showed that subcutaneously administered APO (1 mg/kg) decreased breathing frequency and increased tidal volume. In addition, an instability in inspiratory off-switching was sometimes obtained. Effects on breathing with APO were antagonized by the dopaminergic blocking agent, haloperidol (2 mg/kg). Except for changes in inspiratory off-switching, these results in neonate rats are qualitatively comparable to effects obtained with APO in similarly prepared adult animals.

Animals↗