Biomedical subjects

J X Wilson

Publications and source records attributed to J X Wilson.

At least 55 records · Page 3Linked to original sources

PubMed1989

Ascorbic acid transport in mouse and rat astrocytes is reversibly inhibited by furosemide, SITS, and DIDS.

The uptake of L-ascorbic acid (vitamin C) by astrocytes was studied using primary cultures prepared from the neopallium of newborn Swiss CD-1 mice or Sprague-Dawley rats. Initial uptake rates were significantly greater in mouse than in rat astrocytes. Exposure of cultures to 0.25 mM dibutyryl cyclic AMP for 2 weeks changed cell morphology from polygonal to stellate and stimulated ascorbate uptake, with the greatest stimulation occurring in mouse astrocytes. Uptake was specific for the vitamin since it was not diminished by the presence of other organic anions including acetate, formate, lactate, malonate, oxalate, p-aminohippurate, pyruvate and succinate. Ascorbate uptake was Na(+)-dependent but did not have a specific requirement for external Cl- (Cl-0). Substitution of Cl-0 by Br- or NO3- decreased ascorbate uptake rates by 20-31%; whereas substitution by gluconate or isethionate increased uptake by 20-31%. Ascorbate transport by astroglial cultures from both animal species was rapidly (less than or equal to 1 min) and reversibly inhibited by the anion transport inhibitors furosemide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The rapid and reversible effects of the impermeant inhibitors (SITS and DIDS) are consistent with direct inhibition of ascorbate transporters located in the astroglial plasma membrane.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1989

High-affinity sodium-dependent uptake of ascorbic acid by rat osteoblasts.

Ascorbic acid is essential for the formation of bone by osteoblasts, but the mechanism by which osteoblasts transport ascorbate has not been investigated previously. We examined the uptake of L-[14C]ascorbate by a rat osteoblast-like cell line (ROS 17/2.8) and by primary cultures of rat calvaria cells. In both systems, cells accumulated L-[14C]ascorbate during incubations of 1-30 min at 37 degrees C. Unlike propionic acid, which diffuses across membranes in protonated form, ascorbic acid did not markedly alter cytosolic pH. Initial ascorbate uptake rate saturated with increasing substrate concentration, reflecting a high-affinity interaction that could be described by Michaelis-Menten kinetics (apparent Km = 30 +/- 2 microM and Vmax = 1460 +/- 140 nmol ascorbate/g protein/min in ROS 17/2.8 cells incubated with 138 mM extracellular Na+). Consistent with a stereoselective carrier-mediated mechanism, unlabeled L-ascorbate was a more potent inhibitor (IC50 = 30 +/- 5 microM) of L-[14C]ascorbate transport than was D-isoascorbate (IC50 = 380 +/- 55 microM). Uptake was dependent on both temperature and Na+, since it was inhibited by cooling to 4 degrees C and by substitution of K+, Li+ or N-methyl-D-glucamine for extracellular Na+. Decreasing the external Na+ concentration lowered both the affinity of the transporter for ascorbate and the apparent maximum velocity of transport. We conclude that osteoblasts possess a stereoselective, high-affinity, Na+-dependent transport system for ascorbate. This system may play a role in the regulation of bone formation.

Animals↗

PubMed1989

Ascorbic acid uptake by a high-affinity sodium-dependent mechanism in cultured rat astrocytes.

Ascorbic acid (vitamin C) is synthesized in rodent liver, circulates in the blood, and is concentrated in the brain. Experiments were performed to characterize the mechanism of ascorbate uptake by rat cerebral astrocytes in primary culture. Astroglial uptake of L-[14C]ascorbate was observed to be both saturable and stereoselective. In addition, uptake was dependent on both the incubation temperature and the concentration of Na+ because it was largely inhibited by cooling to 4 degrees C, by treatment with ouabain to increase intracellular Na+, and by the substitution of K+, Li+, or N-methyl-D-glucamine for extracellular Na+. The affinity for ascorbate was relatively high in cells incubated with a physiological concentration of extracellular Na+, because the apparent Km was 32 microM in 138 mM Na+. However, the affinity for ascorbate was significantly decreased when the extracellular Na+ concentration was lowered. Treatment of astrocytes with dibutyryl cyclic AMP induced stellation and increased the maximum rate of ascorbate uptake by 53%. We conclude that astrocytes possess a stereoselective, high-affinity, and Na+-dependent uptake system for ascorbate. This system may regulate the cerebral ascorbate concentration and consequently modulate neuronal function.

Animals↗

PubMed1988

Chicken gonadotropin-releasing hormone II increases plasma catecholamines in the bullfrog.

The aim of the present experiments was to test the effects of two native neuropeptides, [His5,Trp7,Tyr8]gonadotropin-releasing hormone (chicken GnRH II) and [Trp7,Leu8]GnRH (salmon GnRH), on the sympathoadrenal system of chronically cannulated, conscious bullfrogs (Rana catesbeiana). We observed that i.v. injection of chicken GnRH II or salmon GnRH increased plasma noradrenaline and adrenaline concentrations, at doses that did not significantly affect arterial blood pressure or heart rate. Chicken GnRH II was 10 times more potent than salmon GnRH for increasing plasma adrenaline, while the two neuropeptides were equally effective in raising noradrenaline concentration. These observations are consistent with a regulatory role for chicken GnRH II in the bullfrog sympathoadrenal system.

Animals↗

PubMed1987

Reevaluation of the effect of substance P on nasal salt gland secretion in the duck (Anas platyrhynchos).

Adrenergic and osmoregulatory responses to substance P (SP) were studied in salt-loaded ducks. SP inhibited nasal salt secretion by decreasing the salt concentration of the nasal fluid, but reversed the inhibitory effect of angiotensin II (ANG II) on nasal water and K secretion. SP also stimulated salivation, urinary water excretion, and urinary salt excretion, but diminished the diuretic and saluretic responses to ANG II. The osmoregulatory effects of SP were accompanied by elevated plasma concentrations of norepinephrine and epinephrine. The data suggest that SP may contribute to adrenergic and osmotic regulation in ducks.

Angiotensin II↗

PubMed1987

Osmoregulatory actions of angiotensin II are independent of adrenergic receptor mechanisms in the duck, Anas platyrhynchos.

1. Intravenous infusion of a physiological dose of fowl angiotensin II (ANG II) in salt-loaded ducks raised systemic arterial blood pressure, inhibited nasal salt gland fluid and solute secretion, and stimulated renal-cloacal urine production. 2. Beta-adrenergic receptor blockade by propranolol lowered arterial pressure but did not prevent the effects of ANG II on salt and water excretion. 3. Alpha-adrenergic receptor blockade by prazosin decreased both arterial pressure and plasma glucose levels, but it did not impair the osmoregulatory actions of ANG II. 4. These observations indicate that redistribution by ANG II of salt and water excretion is independent of adrenergic receptor mechanisms and therefore does not depend on the sympathomimetic activity of the hormone.

Angiotensin II↗

PubMed1987

Adrenergic and osmotic responses to atrial natriuretic peptide and angiotensin II in the duck (Anas platyrhynchos).

There is evidence that analogues of atrial natriuretic peptide (ANP) and angiotensin II (ANG II) occur in birds. The present experiments studied the adrenergic and osmoregulatory responses to synthetic ANP and ANG II in salt-loaded ducks (Anas platyrhynchos). Excretion of water and salt through the nasal salt glands was abolished by ANG II. This extrarenal, salt-retaining effect of ANG II was not altered by ANP. However, ANP did augment the diuretic response to ANG II. ANP also potentiated the stimulatory effect of ANG II on plasma norepinephrine. The data are consistent with physiological roles for native analogues of ANP and ANG II in adrenergic and osmotic regulation in the duck.

Angiotensin II↗

PubMed1987

Catecholamine and blood pressure regulation by gonadotropin-releasing hormone analogs in amphibians.

Analogs of gonadotropin-releasing hormone (GnRH) occur in the brain, plasma, and sympathoadrenal system of anuran amphibians. The present experiments studied the effects of GnRH and [Trp7, Leu8]-GnRH on plasma catecholamines and cardiovascular function in conscious adult bullfrogs (Rana catesbeiana) and cane toads (Bufo marinus). Both GnRH analogs elicited dose-dependent (0.1-1 nmol.kg-1) increases in arterial norepinephrine, epinephrine, and blood pressure levels when injected intravenously into toads. In bullfrogs, [Trp7, Leu8]-GnRH (1 nmol.kg-1) increased arterial norepinephrine concentration approximately 10-fold without affecting the concentrations of norepinephrine sulfate, norepinephrine glucuronide, epinephrine, epinephrine sulfate, or epinephrine glucuronide. The noradrenergic response of bullfrogs to [Trp7, Leu8]-GnRH was specific to the neurohormone because it could be inhibited by [D-pGlu1, D-Phe2, D-Trp3,6]-GnRH. The sympathomimetic activities of the GnRH analogs did not depend on changes in temperature, which occur seasonally in natural habitats, because similar noradrenergic responses were observed at 4 and 22 degrees C. GnRH and [Trp7, Leu8]-GnRH (0.01-10 nmol.kg-1) did not raise arterial blood pressure in bullfrogs despite their pressor actions in toads. This interspecific difference was remarkable because cardiovascular responses to norepinephrine, angiotensin II, and vasotocin in bullfrogs were similar to those in toads. The parallels between catecholamine and blood pressure responses suggest that epinephrine is the principal mediator of the blood pressure response to native GnRH analogs in toads. In bullfrogs, [Trp7, Leu8]-GnRH mobilizes norepinephrine but not epinephrine, and the noradrenergic effect is insufficient to raise blood pressure. These observations are consistent with a physiological role for native GnRH analogs in the regulation of the sympathoadrenal system in anuran amphibians.

Angiotensin II↗

PubMed1986

Cardiovascular responses to neurohormones in conscious chickens and ducks.

Cardiovascular responses (cardiac frequency, fH; mean arterial pressure, Pa; ischiatic arterial blood flow; Qi; ischiatic vascular resistance, Ri) to 1-norepinephrine (NE), acetylcholine (ACH), [Asp1, Val5]-angiotensin II (ANG II), and arginine vasotocin (AVT) were studied in conscious chickens (Gallus gallus) and Pekin ducks (Anas platyrhynchos). Age-dependent changes, in the cardiovascular variables and the responses to the native avian neurohormones, were also studied in ducks. NE injection caused larger increases in Pa and Ri, and a greater associated fall in fH, in ducks than in chickens. The pressor effect of ANG II was more persistent and developed at a slower rate than the response to NE in both species, although the pressor effect was greater in ducks. Interestingly, ANG II injection caused a tachycardia in these baroreceptor-intact birds. ACH and AVT produced similar rapid falls in Pa and a corresponding tachycardia in both species, although the fH response was greater in ducks. ANG II rapidly increased NE concentration in the arterial plasma of adult ducks, while AVT increased epinephrine (E) concentration. Resting Pa and hematocrit were lower, and fH was higher, in immature ducks. Immature ducks also were less responsive than adults to the cardiovascular actions of NE, ACH, AVT, and ANG II. The results demonstrate differences in the cardiovascular responses to neurohormones in chickens and ducks consistent with a higher level of cardioinhibitory nervous tone and a greater sensitivity to sympathetic stimuli in the aquatic species, which increase during maturation.

Acetylcholine↗

PubMed1986

Alpha- and beta-adrenergic mechanisms mediate blood pressure control by norepinephrine and angiotensin in ducks.

Adrenergic mechanisms for the pressor actions of blood-borne L-norepinephrine (NE) and fowl angiotensin II (ANG II) were studied in barbiturate-anesthetized adult ducks (Anas platyrhynchos). NE (1.5-6.0 nmol X kg-1) or ANG II (0.4-1.6 nmol X kg-1) injected iv caused dose-dependent increases in mean arterial pressure (Pa) and pulse pressure (Pp) but slowed cardiac frequency (fH); higher doses of ANG II increased Pa, Pp, and fH X beta-Adrenergic blockade by propranolol lowered baseline Pa, completely blocked cardiovascular responses to isoproterenol, augmented the bradycardic effect of NE, and inhibited the stimulation of Pp by ANG II. However, the tachycardiac effect of high-dose ANG II persisted during beta-blockade. alpha-Adrenergic blockade following iv prazosin completely blocked the pressor effect of methoxamine, diminished the pressure response to NE, and decreased Pa sensitivity to ANG II injections. Combined alpha- and beta-adrenergic blockade decreased both the sensitivity and the maximal Pa response to ANG II. We conclude that (i) beta-adrenergic mechanisms predominate in the maintenance of resting Pa, (ii) NE increases Pa principally by alpha-adrenergic action while beta-adrenergic stimulation buffers the consequent bradycardia, and (iii) although the positive chronotropic effect of high doses of ANG II probably is not mediated by catecholamines, low doses of ANG II elevate Pa and Pp by alpha- and beta-adrenergic mechanisms.

Angiotensin II↗

PubMed1985

Conjugated catecholamines in rats transfused with perfluorocarbon blood substitute.

The reappearance of circulating catecholamines (CAs) after transfusion with perfluorocarbon blood substitute and the importance of blood for CA conjugation were determined in rats. Arterial plasma concentrations of unconjugated (i.e. free), sulfoconjugated and glucuronoconjugated forms of the CAs dopamine (DA), noradrenaline (NA) and adrenaline (AD) in cannulated, anesthetized, control rats remained stable during the 4.5 h long experiments. Contrarily, in parallel experiments with another group of rats, replacement of blood by the perfluorocarbon blood substitute initially lowered the arterial concentrations of DA glucuronide, free AD and AD glucuronide; subsequently, free DA, NA and AD increased, followed by delayed increases in conjugated CA levels. These changes in CA concentrations preceded a fall in systemic arterial blood pressure (pa) and thus were not the consequences of hypotension.

Animals↗

PubMed1985

Cardiovascular function in adrenalectomized Pekin ducks (Anas platyrhynchos).

Cardiovascular function was progressively impaired in Pekin ducks following surgical adrenalectomy. Diastolic and systolic arterial pressures (Pa) were respectively 45% and 28% lower in adrenalectomized (ADX) ducks than in sham-operated (SHAM) controls within 3 days after surgery. Adrenalectomy caused cardiac frequency (fH) to approximately double, diminished cardiac stroke volume, decreased body weight, and decreased plasma norepinephrine, epinephrine, osmolal, Na and Cl concentrations. Adrenalectomy did not alter blood volume, hematocrit, or plasma concentrations of Ca and Mg. Administration of a synthetic glucocorticoid, betamethasone, prevented hypotension and prolonged the survival of ADX ducks. ADX and SHAM ducks maintained with betamethasone for up to 8 days did not differ in Pa, body weight, hematocrit, or plasma concentrations of Na and K. These experiments demonstrate the critical importance of glucocorticoid activity for blood pressure, Na and Cl regulation in birds.

Adrenalectomy↗

PubMed1985

Catecholamine hormones and the control of avian salt glands.

Hypertonic saline loading (0.5 M NaCl, 15 ml.kg-1 i.v.) increased cardiac frequency and elicited nasal salt gland secretion in control ducks. Partial depletion of catecholamines by prior treatment with reserpine decreased body weight, lowered arterial pressure and abolished the tachycardiac responses to saline loading. Reserpine also increased plasma concentrations of Na, K and total osmolytes, yet altered neither the composition nor the flow rate of nasal fluid secretion. The preservation of the normal secretory responses to hypertonic stress in hypotensive, reserpine-treated ducks indicates that the nasal salt glands can function independently of changes in circulating catecholamine hormones.

Animals↗

PubMed1985

Conjugated catecholamines and pressor responses to angiotensin, luteinizing hormone-releasing hormone and prazosin in conscious toads.

Synthetic angiotensin II (Ang II), mammalian luteinizing hormone-releasing hormone (LHRH) and salmon LHRH (sLHRH) were injected intravenously into conscious, adult toads (Bufo marinus) to elucidate the cardiovascular actions of the hormones. The maximal increases in pulse pressure elicited by the three peptides did not differ from each other but only Ang II increased cardiac frequency. The maximal increases in mean arterial blood pressure (MAP) caused by LHRH and sLHRH were identical, while Ang II caused a 100% greater maximal effect. The median effective doses (ED50) for both Ang II and LHRH were approximately 0.1 nmol kg-1 whereas the potency of sLHRH was 10 fold less. Pressor responses to LHRH and sLHRH were blocked completely by (D-pGlu1, D-Phe2, D-Trp3,6)-LHRH but this antagonist did not inhibit Ang II. Significant proportions of circulating, endogenous dopamine, noradrenaline (NA) and adrenaline (Ad) were found to be sulphoconjugated. Arterial plasma concentration of free NA increased simultaneously with the rise in blood pressure following Ang II injection. The magnitude of the free NA response increased with increasing Ang II dose but even a high dose failed to augment the plasma level of conjugated NA. Ang II did not alter concentrations of free or conjugated dopamine and Ad. Intraarterial injection of an alpha-adrenoceptor antagonist, prazosin, caused sustained elevation of arterial pressure and free Ad. Subsequently Ang II lowered plasma Ad concentration. Prazosin inhibited the NA response to Ang II yet the pressor effects of the alpha-adrenoceptor antagonist and Ang II were additive. Administration of a beta-adrenoceptor antagonist, propranolol, largely reversed the cardiovascular sequelae of alpha-adrenoceptor blockade. It is concluded, firstly, that the cardiovascular actions of Ang II and LHRH are mediated through different receptors. Secondly, although it had been shown that alpha- and beta-adrenoceptor mechanisms mediate the pressor effect of LHRH, the present experiments showed that mobilization of catecholamines cannot account for the pressor response to Ang II. Thirdly, both free and conjugated catecholamines circulate in toads; however the extent of conjugation can be dissociated from the changes in free NA and Ad induced by Ang II and prazosin.

Angiotensin II↗

PubMed1985

Angiotensin and converting enzyme regulate extrarenal salt excretion in ducks.

Numerous previous studies have proposed a salt-conserving role for the renin-angiotensin system in mammals, but there is little evidence of this putative role in birds. Especially interesting are marine birds, which have a relatively limited ability to regulate the osmolality and ionic composition of their urine but possess extrarenal salt glands capable of excreting a highly concentrated NaCl solution. In the present experiments, hypertonic saline, angiotensin I (ANG I), and captopril were infused iv into chronically cannulated ducks to study the neuroendocrine, cardiovascular, renal, and extrarenal excretory responses to osmotic stress. Infusion of hypertonic saline elicited nasal salt excretion, which could be stopped completely by coadministration of ANG I. The effective dose of ANG I increased the plasma norepinephrine (NE) concentration, but did not alter heart rate or arterial blood pressure. Captopril enhanced extrarenal salt excretion in the saline-loaded ducks. The converting enzyme inhibitor also blocked the noradrenergic and NaCl-retaining actions of ANG I; conversely, coadministration of captopril and ANG I increased the plasma epinephrine (E) concentration. These findings indicate that the renin-angiotensin system, in addition to effects on the sympathoadrenal system, regulates NaCl and water metabolism in birds with extrarenal salt glands.

Angiotensin I↗

PubMed1984

Conjugated catecholamines in birds.

Large concentrations of dopamine (DA) glucuronide were measured in the plasma of chronically cannulated adult chickens (Gallus gallus), adult ducks (Anas platyrhynchos) and 1-month-old ducklings. Glucuronides of norepinephrine (NE) and epinephrine (E) also were present but at much lower concentrations. Sulfoconjugated DA, NE and E could be detected only in chickens. There were quantitative differences between chicken and duck catecholamine metabolism: (i) glucuronoconjugates and sulfoconjugates comprised large portions of the total DA, NE and E in chicken plasma; (ii) the predominant form of DA in duck plasma was DA glucuronide while most of the NE and E circulated in unconjugated (i.e. free) form. Catecholamine levels did not differ between adult and immature ducks. Angiotensin II injection into adult ducks elicited simultaneous increases in arterial blood pressure (Pa) and free NE but did not alter conjugated catecholamine levels.

Angiotensin II↗

PubMed1984

Gonadotropin-releasing hormone increases plasma catecholamines and blood pressure in toads.

Synthetic gonadotropin-releasing hormone (GnRH) was injected intravenously into conscious, adult toads (Bufo marinus) to elucidate the nervous and cardiovascular actions of the hormone. GnRH (0.001-1.0 nmol X kg-1) produced dose-dependent increases in mean arterial blood pressure and pulse pressure, beginning within 3 min after injection. These pressor responses to GnRH were specific to the hormone since they could be inhibited reversibly by [D-pGlu1, D-Phe2, D-Trp3,6]-GnRH. Arterial plasma concentrations of unconjugated catecholamines increased simultaneously with the rise in blood pressure following GnRH injection: the half-maximal pressor dose of GnRH (0.1 nmol X kg-1) caused a 3-fold increase in plasma noradrenaline and a 20-fold increase in plasma adrenaline concentrations. Pretreatment of toads with an alpha-adrenergic antagonist, prazosin, and a beta-adrenergic antagonist, propranolol, abolished the pressor responses to GnRH. We conclude that GnRH mobilizes catecholamines, which act through alpha- and beta-adrenergic mechanisms to raise blood pressure. Thus, endogenous GnRH or GnRH-like peptides may coordinate the pituitary, nervous and cardiovascular mechanisms which prepare toads for seasonal reproductive activity.

Animals↗

PubMed1984

The renin-angiotensin system in nonmammalian vertebrates.

The most primitive components of the RAS appeared early in the phylogenetic history of vertebrate animals. It is probable that renin granules were present in the kidneys of ancestral chordates before divergence in the evolution of actinopterygian fish and tetrapods occurred. Granulated juxtaglomerular cells similar to the renin-containing cells of the mammalian nephron are found in most extant vertebrate species although not in agnathan and elasmobranch fish. A macula densa occurs in amphibians, birds and mammals; and an extraglomerular mesangium, only in birds and mammals. Renin-like activity and angiotensin-like pressor material have been demonstrated in all classes of vertebrates. The amino acid sequences of native ANG I have been determined for representative species of teleost fish, amphibian, reptile and bird. These peptides differ from mammalian angiotensins at positions 1, 5 and 9. The RAS appears to be involved in osmoregulation, ionoregulation and the control of blood circulation. Prolonged hypovolemic hypotension or sodium depletion increases renin levels. Angiotensins elicit drinking and stimulate transepithelial ion transport. However, direct steroidogenic and antidiuretic hormone-releasing activities, which would promote mineral and fluid conservation, have not been demonstrated unambiguously in nonmammalian vertebrates. ANG II raises blood pressure by direct vasoconstrictor action on arteriolar muscles in some animals, but perhaps more generally by acting on the nervous system and adrenal paraneurons. In birds the hormone also has a hypotensive effect. ANG II stimulates the SNS in agnathans, elasmobranchs, teleosts, amphibians, reptiles, birds and mammals. Thus, modulation of sympathetic activity may be one of the most primitive and conservative functions of the RAS. For this reason, nonmammalian vertebrates are valuable models for studying the neurogenic actions of angiotensin II relevant to hypertensive disease.

Amphibians↗