Biomedical subjects

C Sernia

Publications and source records attributed to C Sernia.

At least 73 records · Page 4Linked to original sources

PubMed1992

Angiotensinogen secretion by single rat pituitary cells: detection by a reverse haemolytic plaque assay and cell identification by immunocytochemistry.

A reverse haemolytic plaque assay (RHPA) for angiotensinogen was developed in rat hepatoma H4 cells and applied to investigate the possible secretion of angiotensinogen from rat pituitary cells in primary culture. Over a 24-hour incubation period in Cunningham chambers plaques with a mean area of 2,800 +/- 430 and 590 +/- 220 microns2/plaque (SD, n = 6) formed around all viable H4 cells and 2.8 +/- 0.59% of viable pituitary cells respectively. As a positive control PRL secretion from lactotrophs was routinely checked by the RHPA and shown to form plaques with a mean area of 4,050 +/- 1,850 microns2/plaque after a 4-hour incubation. By comparing plaque size in H4 cells with angiotensinogen release in cell culture, as quantified by radioimmunoassay, the secretion rate of angiotensinogen from pituitary cells was calculated as 22 +/- 8 ng/10(6) cells/24 h. Plaque-forming cells consisted of two morphologically distinct populations; 78% being small cells (less than 6 microns diameter) containing little cytoplasm and 22% were large (greater than 9 microns diameter) cells with an abundant cytoplasm. Immunocytochemical staining of pituitary cells after formation of plaques with anti-angiotensinogen, anti-LH and anti-PRL antiserum showed that the large plaque-forming cells were gonadotrophs and none were lactotrophs. All plaque-forming cells stained for angiotensinogen but only 44% of the viable cells which stained for angiotensinogen actually formed plaques. The possibility that cellular angiotensinogen was imported from extracellular sources was investigated by incubation of pituitary cells with pure 125I-angiotensinogen for periods up to 24 h. No uptake of the radiolabelled protein was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensinogen↗

PubMed1992

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.

Animals↗

PubMed1991

Oxytocin receptors in the mammary gland and reproductive tract of a marsupial, the brushtail possum (Trichosurus vulpecula).

Previous studies of marsupial lactation have shown that the milk-ejection reflex changes in sensitivity, being greater in small mammary glands sucked by small pouch young and lesser in larger glands supplying milk to larger young. The involvement of oxytocin receptors in these changes was examined in the brushtail possum Trichosurus vulpecula. Oxytocin receptors were measured in the mammary glands, uterus, and medial vaginal sacs by radioreceptor assay, using [3H]oxytocin as radioligand. In the mammary gland, a single oxytocin binding site was found with an affinity and receptor concentration of 0.81 +/- 0.41 l/nmol and 10.2 +/- 4.8 pmol/g tissue respectively (SD, 10 possums). Competitive displacement curves with related peptides and analogs showed the following order of specificity: d(CH2)5[Tyr(Me)2,Thr4,Tyr9-NH2]-vasotocin much greater than vasotocin greater than oxytocin = Arg-vasopressin greater than mesotocin greater than [Thr4,Gly7]-oxytocin = Lys-vasopressin greater than [deamino-Pen1, O-methyl-Tyr2, Arg8]-vasopressin greater than isotocin much greater than [d(CH2)5, D-Phe2, Ile4, Ala9-NH2]-AVP. [3H]Oxytocin did not bind to vasopressin receptors in the thoracic aorta. The concentration of oxytocin receptors was very high in small mammary glands (18.6 pmol/g tissue in a 2-g gland) and decreased logarithmically as the size of the mammary gland increased. It is suggested that the changes in the sensitivity of milk ejection to oxytocin is related to the concentration of mammary oxytocin receptors. The presence of oxytocin receptors in both uterus and median vaginal sacs extends previous observations and supports the hypothesis that in marsupial parturition, the uterus and medial vaginal sacs respond as a single functional unit to oxytocin.

Animals↗

PubMed1991

Comparison of inotropic and chronotropic responses in rat isolated atria and ventricles.

1. The positive inotropic and chronotropic responses to adrenoceptor agonists (noradrenaline, phenylephrine), to compounds which increase cAMP by post-adrenoceptor mechanisms (forskolin, theophylline and dibutyryl cAMP) and to calcium chloride were measured in isolated rat atria and papillary muscles from both ventricles. 2. Noradrenaline produced similar maximal inotropic responses to calcium chloride in all tissues. Forskolin gave similar responses to calcium chloride in atrial but not ventricular tissues; the reverse was observed with dibutyryl cAMP. Phenylephrine and theophylline produced significantly smaller inotropic responses than calcium chloride in all tissues, especially in ventricular tissues. 3. Maximal chronotropic responses to noradrenaline, theophylline and dibutyryl cAMP were similar. Forskolin produced significantly greater responses while calcium chloride and phenylephrine produced significantly smaller responses than noradrenaline. 4. These results show that the maximal positive inotropic response of some agonists is markedly dependent on the tissue chosen. Further, chronotropic responses in right atria do not mimic inotropic responses in left atria.

Animals↗

PubMed1991

Effect of intra-ovarian infusion of oxytocin on plasma progesterone concentrations in pregnant ewes.

The function of oxytocin receptors in the corpus luteum of pregnant ewes was investigated by infusing saline or oxytocin (100 ng/min) into the utero-ovarian artery of pregnant ewes (62 +/- 5 days, n = 12). During a 4-h infusion, plasma oxytocin (OT) concentration increased to 268 +/- 80 pg OT/ml in the OT-infused group and remained unchanged at 2.5 +/- 1.5 pg OT/ml in the saline-infused group. Progesterone concentration in jugular venous plasma (17 +/- 9 ng/ml) rapidly decreased during oxytocin infusion to 59 +/- 10% and 26 +/- 9% of control at 1.5 and 2 h, respectively; the utero-ovarian venous concentration of 64 +/- 38 ng/ml decreased by a similar magnitude during oxytocin infusion. Electron microscopy of corpora lutea, removed at the end of the experiments, showed no indication of luteolytic changes following oxytocin infusion. It was concluded that oxytocin markedly and rapidly reduces progesterone secretion in pregnant ewes.

Animals↗

PubMed1990

The immunocytochemical localization of angiotensinogen in the rat ovary.

The present study examined the presence and cellular distribution of angiotensinogen, the precursor to the angiotensin peptides, in the ovary of the normal cycling rat by immunocytochemistry. Angiotensinogen staining was present in the granulosa cells of maturing follicles and to a lesser extent in those undergoing atresia. Staining was not seen in the granulosa cells of primordial or early primary follicles. In maturing follicles intense staining for angiotensinogen was confined to the antral cell layers, cells of the cumulus oophorus and in the follicular fluid. Strong immunostaining was also seen in the germinal epithelium covering the ovary. Lighter angiotensinogen staining was observed in some parts of the cortical and medullary stroma and occasionally in corpora lutea. No variation in the intensity or pattern of angiotensinogen staining was observed throughout the estrous cycle. Comparison of the distribution of angiotensinogen with the previously described localization of renin, AII, angiotensin converting enzyme and AII receptors, suggests that there are a number of intra-ovarian sites at which AII could be produced.

Angiotensin II↗

PubMed1990

Angiotensin receptors in an Australian marsupial, the brushtail possum Trichosurus vulpecula.

In this study, the binding properties of angiotensin receptors were examined in the liver, adrenal, brain, and vascular tissue of the brushtail possum, Trichosurus vulpecula. With 125I-Ile5-angiotensin II as the radioligand, the binding affinity (Ka) and receptor number (R0) were estimated for the liver (Ka = 3.60 +/- 0.31 liters/nmol; R0 = 23.8 +/- 1.30 pmol/g tissue; n = 8) and adrenal (Ka = 1.68 +/- 0.29 liters/nmol; R0 = 1.67 +/- 0.23 pmol/g tissue; n = 8). Specific binding was not found in any of seven areas of the possum brain (n = 6), whereas the expected binding was present in similar areas of the rat brain. Using angiotensin III or the antagonist Sar1-Ala8-angiotensin II as radioligands or changing the composition of the incubation buffer did not alter the outcome. Moreover, the intracerebroventricular injection of 1 and 5 nmol of angiotensin II did not elicit an increase in blood pressure which could be attributed to brain angiotensin II (AII) receptors. Ligand affinities of the adrenal and liver receptors were found to be in the following decreasing order: Val5-AII greater than Ile5-AII = Ile5-AIII greater than Sar1-Ala8-AII greater than Sar1-Gly8-AII greater than Sar1-Leu8-AII greater than Ile5-AI greater than hexapeptide greater than Phe3-Tyr8-AII. The cardiovascular AII receptor was investigated by generating dose-response curves of the pressor activity of Ile5-AII and six AII analogs infused intravenously. It was concluded that liver, adrenal, and vascular AII receptors in the marsupial possum have characteristics similar to those in eutherian mammals. However, the failure to find brain AII receptors raises the possibility that those functions mediated by such receptors in the eutherian brain are absent in the possum and perhaps other marsupials.

Adrenal Glands↗

PubMed1990

Mesotocin in the brain and plasma of an Australian marsupial, the brushtail possum (Trichosurus vulpecula).

Oxytocic peptides extracted from the brain and plasma of the brushtail possum, Trichosurus vulpecula, were separated by reverse-phase high pressure lipid chromatography (HPLC) and quantified by specific radioimmunoassays for oxytocin (OT) and mesotocin (MT). The pituitary, hypothalamus and cerebral cortex were found to contain MT only in quantities of 3.9 +/- 0.2 (SE) ug, 17.6 +/- 0.6 ng and 21.0 +/- 2.6 ng respectively. The plasma concentration of MT varied according to the degree of stress of the possum. In anaesthetized animals values of 39.7 +/- 9.7 pg/ml (11 males) and 31.5 +/- 12.9 pg/ml (6 females) were obtained; in four conscious catheterized animals, 9.4 +/- 6.3 pg/ml. Samples taken from three anaesthetized animals during exsanguination contained 271 +/- 102 (SD) pg MT/ml. It was concluded that hypothalamic and extra-hypothalamic MT is present in the marsupial brain and that as in placental mammals, stress stimulates the secretion of mesotocin.

Animals↗

PubMed1990

Uterine oxytocin receptors in an Australian marsupial, the brushtail possum, Trichosurus vulpecula.

1. Oxytocin receptors in the uterus of the brushtail possum (T. vulpecula) were characterized by radioreceptor assay and compared with those of the sheep and rat uterus. 2. A single oxytocin binding site was found with an affinity (Kd) and receptor concentration (Ro) of 3.0 +/- 0.8 nmol/l and 200 +/- 60 fmol/mg protein, respectively (SEM; n = 5). The receptor was stable at -20 degrees C; divalent ions were required for optimum binding. 3. Competitive displacement curves with related peptides showed the following order of specificity: vasotocin greater than oxytocin greater than mesotocin = arginine-vasopressin = [Thr4, Gly7]-oxytocin greater than lysine-vasopressin = isotocin much greater than [d(CH2)5, D-Phe2, Ile4, Ala9-NH2]-AVP. 4. It was concluded that oxytocin receptors in the possum have similar characteristics to those of placental mammals.

Animals↗

PubMed1989

Immunocytochemical location of oxytocin and mesotocin within the hypothalamus of two Australian marsupials, the bandicoot Isoodon macrourus and the brushtail possum Trichosurus vulpecula.

The presence of oxytocin and mesotocin in the hypothalamus of two Australian marsupials, the bandicoot (Isoodon macrourus) and the brushtail possum (Trichosurus vulpecula), was examined by immunocytochemistry. Tissue was fixed in paraformaldehyde in phosphate buffer and immunoreactive cells were detected using highly specific rabbit antioxytocin and sheep anti-mesotocin as primary antisera. Immunoreactive oxytocin cells were demonstrated in the paraventricular and supraoptic nuclei of bandicoot and possum hypothalami, with greater density being observed in paraventricular nuclei. Immunoreactive mesotocin cells were also found in both hypothalamic nuclei of the possum but not of the bandicoot. The same cells appeared to stain for both peptides.

Animals↗

PubMed1989

The localization of oxytocin and mesotocin in the reproductive tract of the male marsupial bandicoot Isoodon macrourus.

The cellular localization of oxytocin and mesotocin within the testis and prostate of the Northern brown bandicoot, Isoodon macrourus, was examined. Tissues were fixed in 4% paraformaldehyde and immunoreactive cells and tissues were detected with antibodies to oxytocin and mesotocin. Immunoreactive oxytocin was present in the Leydig cells and in the spermatids of the adult and the 263-day bandicoots and there was faint staining in the 123-day bandicoot. Mesotocin was not present in the testes of the bandicoot. Immunoreactive oxytocin and mesotocin were present in the ventral portion of the prostate. The oxytocin within the testis may play a role in spermatogenesis and in seminiferous tubule contractility whereas the hormones present in the accessory glands may have a role in sperm transport in the female reproductive tract.

Animals↗

PubMed1989

Regulation of liver angiotensinogen mRNA by glucocorticoids and thyroxine.

This study examines the immediate and longer-term changes in angiotensinogen mRNA and in plasma angiotensinogen which follow the withdrawal and replacement of glucocorticoids or thyroxine. RNA from rat liver was analysed by Northern blot and dot-blot hybridization with a 40-mer oligodeoxynucleotide probe specific for angiotensinogen mRNA. Adrenalectomy decreased plasma angiotensinogen and angiotensinogen mRNA to 55 and 50% of control values respectively over a period of 16 days. Similar decreases were obtained after propylthiouracil (1 mg/kg for 16 days) treatment, except when injected simultaneously with T3 (3 micrograms/kg/day). Over the same period plasma renin activity increased in adrenalectomized rats from 4.1 +/- 0.8 to 7.0 +/- 1.5 pmol angiotensin I (AI)/ml/h, and decreased in propylthiouracil-treated rats from 3.8 +/- 0.4 to 1.6 +/- 0.4 pmol AI/ml/h. Approximate half-times of 2-3 days were calculated for both plasma angiotensinogen and angiotensinogen mRNA post-adrenalectomy or after propylthiouracil treatment. Dexamethasone (400 micrograms/kg, i.m.) given to intact rats rapidly increased angiotensinogen mRNA to a maximum of 250% of control by 8 h and with a half-maximal response of 2.8 h. Plasma angiotensinogen responded similarly, apart from an initial delay of 2 h. Treatment with different doses of propylthiouracil and dexamethasone showed that responses were dose-related. We conclude that changes in plasma angiotensinogen and angiotensinogen mRNA are closely correlated, and that under various physiological circumstances angiotensinogen mRNA has a rapid rate of accumulation but a slow rate of decay.

Adrenalectomy↗

PubMed1989

Oxytocin receptors in the ovine corpus luteum.

There is inconclusive evidence that oxytocin acts directly on the corpus luteum and affects steroidogenesis. Since any such action would probably be mediated by oxytocin receptors, these should be present in luteal tissue. In this study, homogenates of corpora lutea from both pregnant and non-pregnant ewes were examined for oxytocin receptors by radioreceptor assay. Specific oxytocin binding was not observed in luteal tissue during the oestrous cycle. However specific binding was found in the corpora lutea of pregnant ewes; appearing at a fetal head length of approximately 0.65 cm (about 30 days of pregnancy) and persisting to a head size of 11 cm, the largest size examined in this study. The affinity (Kd) of the receptor was calculated as 2.9 +/- 0.3 nmol/l (S.E.M.; n = 9), a value similar to that obtained for the uterus. The receptor number ranged from a low of 8.7 +/- 3.2 fmol/mg protein (n = 6) at a head size of less than 0.65 cm, to a maximum of 40.1 +/- 6.5 fmol/mg protein (n = 25) at a head size of 2.5-3.75 cm. These values were lower than our estimate of 588 +/- 39 fmol/mg protein (n = 5) for the uterus. It is concluded that a direct action of oxytocin on the corpus luteum is possible but only after the first month of pregnancy and not in the corpus luteum of the oestrous cycle.

Animals↗

PubMed1988

Immunocytochemical localization of angiotensinogen in the rat brain.

The distribution of angiotensinogen-like immunoreactivity in the rat brain was investigated using specific antisera against pure rat plasma angiotensinogen in conjunction with the sensitive streptavidin-biotin peroxidase method. Angiotensinogen antisera were shown by radioimmunoassay and Western blotting to recognize angiotensinogen from both rat plasma and cerebrospinal fluid, and to cross-react with des-AI-angiotensinogen (100%) but not with angiotensin I and II, tetradecapeptide, luteinizing hormone-releasing hormone, rat albumin and angiotensinogen from eight other species. Angiotensinogen-like immunoreactivity was detected throughout the rat brain in both neuroglia and neurons. The highest concentration of neuroglial angiotensinogen-like immunoreactivity was in the hypothalamus and preoptic areas, with moderate to heavy concentrations in the mesencephalon and myelencephalon. The cerebellum demonstrated neuroglial staining in the granular layer and fibre tracts. Very little neuroglial staining was noted in the cerebral cortex or olfactory bulbs. Neuronal immunostaining was observed throughout the globus pallidus and the caudate putamen, in various parts of the thalamus and the supraoptic nucleus of the hypothalamus. In the midbrain moderate immunostaining was observed in periaquaductal central gray, the deep mesencephalic nucleus, the inferior colliculus and in scattered cells in the anterior mesencephalon. In the medulla, neuronal staining was localized to the vestibular nuclei and to other cell bodies mainly in the dorsolateral regions. In the cerebellum, staining was noted mainly in the deeper cerebellar nuclei and in the Purkinje cells. Immunostaining in the cerebral cortex was localized to the cingulate cortex and the primary olfactory cortex. Light staining was present in the endopiriform cortex and in scattered neurons adjacent to the external capsule. In the olfactory bulbs light neuronal staining was mainly associated with the mitral cell layer. The widespread distribution of angiotensinogen-like immunoreactivity supports the view that it is synthesized in the central nervous system and forms part of a brain renin-angiotensin system. In addition, its presence at sites other than those normally associated with the control of blood pressure and fluid and electrolyte homeostasis suggests that its involvement may not be limited to these regulatory functions.

Angiotensinogen↗

PubMed1987

Production and metabolic clearance of angiotensinogen in conscious rats as measured by steady-state isotope dilution.

Previous studies on the hormonal regulation of hepatic angiotensinogen relied on in-vitro liver preparations and on the measurement of changes in plasma concentration. In this study 125I-labelled angiotensinogen was used to measure simultaneously the production rate (PR) and metabolic clearance rate (MCR) in conscious rats by the constant-rate infusion and single-injection methods. Male rats received daily s.c. injections of isotonic saline (as control), 1 mg corticosterone acetate (CA), 25 micrograms 17 beta-oestradiol benzoate (OB) or 20 micrograms thyroxine (T4) per 100 g body weight. On day 7 of treatment 125I-labelled angiotensinogen was infused into a jugular vein at a rate of 1 microliter/h by osmotic minipumps and blood samples taken 4, 5 and 6 days later. The PR of angiotensinogen increased from 576 +/- 28 (S.E.M.; n = 9) to 954 +/- 63 (n = 9), 1010 +/- 84 (n = 9) and 2359 +/- 150 (n = 10) micrograms/h per kg following treatment with CA, OB and T4 respectively. In contrast, the PR of rat albumin did not change significantly from 218 +/- 8 (n = 7) mg/h per kg. All three hormones increased MCR from 13 +/- 1 (n = 17) ml/h per kg to 17 +/- 1 (n = 9), 18 +/- 2 (n = 9) and 27 +/- 2 (n = 9) ml/h per kg for CA, OB and T4 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensinogen↗

PubMed1986

Purification of rat angiotensinogen.

A method of purifying rat angiotensinogen in three chromatography steps with a yield 3-4 times better than previous methods is described. Using chromatofocusing media for two steps and DEAE-affigel blue for the third step it was possible to separate angiotensinogen into three major peaks with pI of 5.25 (peak B), 4.80 (peak C) and 4.50 (peak D). Peaks B and C were completely purified with recoveries of 12% and 17% and specific activities of 21.8 and 20.0 micrograms AI/mg protein respectively. Analytical SDS-PAGE showed a 53,000 dalton band in both peaks with additional 51,000 and 57,000 dalton bands in peak C.

Angiotensinogen↗

PubMed1985

Regulation of rat brain angiotensin II (AII) receptors by intravenous AII and low dietary Na+.

Previous studies have shown the presence of specific AII receptors at several areas of the brain. The purpose of this study was to examine by radioreceptor assay the effect of intravenous AII infusion (5 or 25 ng/kg/min) and low dietary Na+ (less than 8 mmol/100 g) on AII receptors in five brain regions: the olfactory lobes (OLF), hypothalamus/thalamus/septum (HTS), midbrain (MID), cerebellum (CER) and medulla (MED). Scatchard analysis of binding data from control rats showed significant (P less than 0.01 ANOVA) differences between brain areas in both Ka (1.54 OLF, 1.87 HTS, 1.25 MID, 1.33 MED, 0.77 CER x 10(9) M-1) and Ro (321 OLF, 224 HTS, 203 MID, 145 MED, 41 CER fmol/g tissue). Following the i.v. infusion of AII for 4-7 days, marked changes were observed in the areas with a porous BBB, the HTS and MED. Both the Ka [3.20 (HTS) and 0.67 (MED) x 10(9) M-1] and Ro [116 (HTS) and 249 (MED) fmol/g tissue] changed. In addition, decreases in Ro were also observed in the OLF (241 fmol/g tissue) and CER (21 fmol/g tissue), areas which have not been considered as being accessible to blood-borne AII. A low Na+ diet for 21-30 days changed the Ka and Ro in all five regions but not in similar directions. Furthermore, with the exception of the OLF the direction of change was not similar to that caused by i.v. infusion of AII. It was concluded that AII receptor sites in the rat brain differ from each other in both receptor properties in their response to such regulatory factors as AII Na+ depletion.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1985

Liver angiotensin II receptors in the rat: binding properties and regulation by dietary Na+ and angiotensin II.

Recent evidence suggests that angiotensin II (AII) acts on the liver via specific receptors. The aims of this study were to examine the general binding properties of these receptors in the rat and to determine the role of dietary Na+ and AII in the regulation of AII receptors. Binding of 125I-labelled Ile5-AII to liver membranes was saturable and behaved as a single class of sites with an affinity (Ka) of 2.9 l/nmol and a Hill coefficient of 0.99. Kinetic analysis of AII binding gave estimates for the rates of association and dissociation of 42 l/mumol per min and 1.5 X 10(-2)/min respectively. The binding of analogues exhibited the following order of potency: Val5-AII greater than Ile5-AII greater than AIII greater than Sar1-Ala8-AII greater than Sar1-Gly8-AII greater than AI greater than des-Asp-AI greater than C4-C8 pentapeptide greater than Phe1-Tyr8-AII greater than neurotensin greater than luteinizing hormone-releasing hormone. Binding was enhanced by Mg2+ and Ca2+ and inhibited by EDTA and the reducing agent dithiothreitol. Low dietary Na+ affected in a biphasic manner both the Ka and concentration (Ro) of liver AII receptors. Initially, Ro decreased from 25.9 +/- 3.8 (control) to 16 +/- 1.9 (S.E.M.) pmol/g tissue by 1.5 days but thereafter it rapidly increased to 47.3 +/- 8.7 pmol/g tissue (3.5 days) and remained elevated to the end of the experiment, 8.5 days later. The Ka initially increased from 2.7 +/- 0.3 (control) to 4.3 +/- 0.5 l/nmol (1.5 days) and then decreased steadily to 1.2 +/- 0.1 l/mol (8.5 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗