Cardiac inotropic actions of urocortin in conscious sheep

Urocortin (Ucn) is a recently isolated peptide related to the corticotropin-releasing factor (CRF) family, which can produce hemodynamic and hormonal actions in conscious rats. This study examined in detail the cardiovascular actions of Ucn and CRF after intravenous injection in chronically instrumented, conscious sheep. Injection of Ucn produced dose-dependent changes in cardiac contractility [rate of increase of aortic flow (dF/dt)], maximum aortic flow (Fmax), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), and coronary blood flow (CF). Ucn injected at 100 micrograms produced a potent increase in dF/dt, from 909 +/- 44 to a maximum of 1,849 +/- 901.min-1.s-1, and in Fmax, from 25.5 +/- 0.8 to 36.6 +/- 1.4 l/min. Cardiac contractility increased within 30 min of injection and remained significantly elevated for up to 24 h. MAP increased from 78 +/- 2 to 90 +/- 3 mmHg, and HR increased from 73 +/- 4 to 103 +/- 9 beats/min. CO rose from 5.0 +/- 0.1 to 5.8 +/- 0.2 l/min, whereas central venous pressure, total peripheral conductance, and stroke volume were unchanged. All Ucn-induced cardiovascular effects were inhibited by prior treatment with the CRF antagonist alpha-helical CRF-(9-41). Equimolar doses of CRF produced little change in any hemodynamic parameter. Both peptides increased plasma levels of adrenocorticotropin and cortisol, with Ucn having a more potent effect than CRF. We have shown for the first time that Ucn can produce potent and long-lasting actions to elevate cardiac contractility in conscious animals.

Direct cardiac and vascular actions of adrenomedullin in conscious sheep

1. Adrenomedullin (ADM) is a recently characterized circulating hormone which affects haemodynamic, renal and pituitary function in mammals. We have shown previously that in sheep, ADM produces vasodilatation together with increases in cardiac output and contractility. However, whether these effects are direct or mediated by autonomic reflexes is unclear. The present study examined the cardiovascular actions of an intravenous infusion of ADM in conscious, chronically instrumented sheep with either sympathetic, parasympathetic or autonomic ganglion blockade, to determine the role of the autonomic nervous system in mediating these cardiovascular changes. 2. Human ADM (1-52) was infused for 60 min at 2 micrograms kg-1 h-1 following: (1) saline control, (2) combined alpha/beta-adrenoceptor (sympathetic) blockade (proporanolol 0.4 mg kg-1 h-1 + phentolamine 0.15 mg kg-1 h-1 for 20 h), (3) muscarinic (parasympathetic) blockade (methscopolamine 0.05 mg kg-1 h-1 for 20 h) or (4) ganglion blockade (hexamethonium 3 mg kg-1 h-1 for 4 h). Measurements were made of mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral conductance (TPC), maximal aortic flow (Fmax) and maximal rate of change of aortic flow (dF/dt). 3. ADM reduced MAP by 3 +/- 1 mmHg, and increased CO (1.2 +/- 0.2 l min-1), HR (14 +/- 2 beats min-1), TPC (21 +/- 3 ml min-1 mmHg-1). Fmax (2.3 +/- 0.8 l min-1) and dF/dt (86 +/- 21 l min-1 s-1) in normal sheep. In animals with alpha/beta blockade, similar changes were observed with ADM. However, during muscarinic blockade, the increases in HR (32 +/- 4 beats min-1), CO (2.1 +/- 0.4 l min-1), TPC (31 +/- 4 ml min-1 mmHg-1). Fmax (4.0 +/- 0.6 l min-1), and dF/dt (150 +/- 12 l min-1 s-1) produced by ADM were enhanced. During ganglion blockade, ADM produced a greater reduction in MAP (-10 +/- 2 mmHg) compared to controls (-3 +/- 1 mmHg). However, there was no increase in HR. The changes in CO, TPC and contractility were similar to those observed in control animals. 4. These results suggest that the vasodilator effects of ADM on the periphery and its ability to increase CO and cardiac contractility are not mediated by the autonomic nervous system, but are probably the result of direct actions of ADM on the heart and vasculature.

Diuretic and natriuretic actions of melanin concentrating hormone in conscious sheep

Melanin concentrating hormone (MCH) is a 19 amino-acid peptide expressed in high concentrations within the dorso-lateral hypothalamus of rats, sheep and man. MCH regulates skin colour and ACTH release in teleost fish, however, its physiological relevance in mammals is unclear. The present study examined the cardiovascular and metabolic actions of intracerebroventricular (i.c.v.) infusion of MCH, and the pro-MCH derived peptide Neuropeptide-E-I (NEI), in conscious, chronically instrumented sheep. Human MCH (1-19) or NEI (1-13) was infused i.c.v. for 24 h into 6 sheep, and measurements were made every 10 min of arterial pressure, heart rate, cardiac output, stroke volume and peripheral blood flow/conductance. Recordings of water intake (H2Oin), urine volume (Uv), urinary Na (UNaV) and K excretion (UKV) were made, as well as hematocrit, plasma Na, K, osmolality, protein, glucose, ACTH, vasopressin, renin, endothelin, ANF, cortisol and aldosterone concentrations. After 24 h of infusion at 10 microg/h, MCH produced a significant increase in Uv from 0.8 +/- 0.2 to 1.4 +/- 0.3 l/day, together with an increase in UNaV from 56 +/- 8 to 107 +/- 14 mmol/day, and in UKV from 202 +/- 18 to 369 +/- 38 mmol/day. H2Oin was unchanged. Similar renal changes were observed during i.c.v. infusion of NEI. There was no change in any cardiovascular parameter, although hematocrit showed a large decrease with infusion of both peptides after 24 h infusion. Plasma osmolality increased from 291 +/- 1 to 295 +/- 1 mOsm/kg during MCH infusion, whereas total protein and plasma Na and K were unchanged. MCH increased plasma glucose from 3.4 +/- 0.2 to 3.8 +/- 0.2 mmol/l. Plasma aldosterone exhibited a 30-40% decrease following MCH or NEI infusion, whereas all other plasma concentrations remained unchanged. This study has shown that i.c.v. infusion of MCH or NEI can produce diuretic, natriuretic and kaliuretic changes in conscious sheep, triggered by a possible increase in plasma volume as indicated by the changes in hematocrit. These results, together with anatomical data reporting the presence of MCH/NEI in fluid regulatory areas of the brain, indicate that MCH/NEI may be an important peptide involved in the central control of fluid homeostasis in mammals.

ACTH-suppressive and vasodilator actions of adrenomedullin in conscious sheep

Adrenomedullin (ADM) is a 52 amino-acid peptide which is a potent vasodilator in rats, and suppresses basal and CRF-induced ACTH release from cultured pituitary cells. The present study examines the hemodynamic and hormonal actions of human ADM (1-52) infusion in conscious, chronically instrumented sheep. Five sheep were infused intravenously (IV) or intracerebroventricularly (ICV) with ADM at 100 micrograms/h for 60 min, and mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral conductance (TPC), coronary blood flow (CF), coronary conductance (CC), peak aortic flow (Fmax), and left ventricular dF/dt were monitored by a computer-based data collection system every 2 min. Plasma concentrations of adrenocorticotropin (ACTH), arginine vasopressin (AVP) and renin were measured after 60 min of infusion. IV ADM produced a small fall in MAP of 3 +/- 1 mmHg, associated with a reflex increase in HR of 14 +/- 3 b/min. CO increased by 1.3 +/- 0.3 l/min, whereas SV remained unchanged. TPC was markedly increased by 20 +/- 3 ml/min/mmHg. Changes in CF were also seen with an increase of 10 +/- 2 ml/min, and CC increased in parallel by 0.15 +/- 0.02 ml/min/mmHg. Fmax and dF/dt showed small increases of 2.1 +/- 0.5 l/min and 85 +/- 20 l/min/sec respectively. Plasma concentrations of ACTH and cortisol were reduced by 58% and 55% respectively, whereas plasma renin concentration increased by 106%. There was no change in plasma levels of AVP. ICV infusion of ADM had no effect on any parameter measured. These data suggest that systemic ADM produces a sustained vasodilator action to lower blood pressure in sheep, and this is the first study to report the ACTH-suppressor action of ADM in conscious animals. ADM may therefore be an important hormone involved in the regulation of pituitary/adrenal function, in addition to its cardiovascular and fluid regulatory actions in mammals.

Preferred room temperature of young vs aged males: the influence of thermal sensation, thermal comfort, and affect

BACKGROUND

While research has demonstrated that aged persons may show impaired thermoregulatory control, we do not know whether dysthermia in the aged results from altered behavioral or autonomic responses. Consequently, we investigated age-related differences concerning the ability to regulate room temperature.

METHODS

Two groups of matched healthy males (22.9 yr and 66.9 yr) were subjects of this study. After equilibration at 24 degrees C (rh 50%), chamber temperature controllers were set into cooling mode. Using a dual position switch, subjects adjusted this temperature when air temperature moved outside their preferred range. Switch operation resulted in maximal cooling or heating, without a steady state. Subjective ratings of thermal sensation, discomfort, and affect were provided at each activation.

RESULTS

Both groups controlled temperature equivalently: 24.9 degrees C (+/- 1.3, young) and 24.5 degrees C (+/- 1.5, elderly; p > .05). At cold-induced change points, the skin temperatures of the calf, thigh, chest, and hand were significantly lower in the elderly subjects. During the heat-induced changes, chest, hand, upper arm, and mean skin temperatures were also lower (p < .05). At cold-induced change points, the elderly group felt colder (p < .05), were less uncomfortable (p < .05), and felt better than the young subjects (p < .05). During heat-induced changes, thermal sensation was equivalent, the elderly were more comfortable (p < .05), and felt better (p < .05).

CONCLUSIONS

Assuming thermal discomforture drives behavior, it is possible that elderly people may require a more intense thermal stimulus to elicit the appropriate behavioral responses in the home. It is also possible that such stimuli will result in a greater heat flow, elevating the risk of dysthermia in the aged.

Pyrogenic stimulation of vascular resistance in conscious sheep

Increased arterial blood pressure following a pyrogenic reaction has been reported in previous studies, however the mechanism of this hypertension has not been examined in detail. The present study investigated the effects of both intravenous (IV) and intracerebroventricular (ICV) injection of lipopolysaccharide (LPS) from E. coli on body temperature (Tb), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), calculated total peripheral resistance (CTPR), stroke volume (SV) and plasma levels of adrenocorticotropin (ACTH) and arginine vasopressin (AVP) in conscious, chronically instrumented sheep. IV injection of LPS (1 microgram) increased Tb in a biphasic manner from 38.7 +/- 0.1 to 39.5 +/- 0.2 degrees C after 50 min and to 39.9 +/- 0.2 degrees C after 130 min, and MAP increased biphasically from 64 +/- 1 to 70 +/- 4 mmHg after 40 min and to 78 +/- 3 mmHg after 130 min. CO initially decreased from 4.4 +/- 0.1 to 3.5 +/- 0.1 after 40 min followed by a secondary rise to 4.8 +/- 0.1 l/min after 100 min. This occurred together with a large, biphasic increase in CTPR from 14.5 +/- 1.0 to 22.0 +/- 2.0 mmHg/l/min at 40 min, and to 18.1 +/- 0.1 mmHg/l/min at 120 min. HR increased from 68 +/- 4 to 97 +/- 4 b/min and SV decreased from 65 +/- 2 to 41 +/- 4 ml/beat during the first phase of activation. Plasma ACTH increased from 22 +/- 9 to 1043 +/- 175 pg/ml after 80 min, and plasma AVP increased from 0.7 +/- 0.2 to 12 +/- 4.0 pg/ml after 60 min. ICV injection of LPS produced a long-lasting increase in Tb and MAP, but had no effect on HR or plasma AVP. Plasma ACTH increased from 30 +/- 12 to 427 +/- 110 pg/ml. These changes suggest that intravenous pyrogenic infection produces a potent vasoconstrictor action in sheep to increase blood pressure, possibly mediated by the actions of AVP within the CNS, or other pyrogenically released vasoconstrictor factors. Furthermore, the duration of activation of the cardiovascular system following peripheral and central LPS administration is different, which together with the contrasting effects on ACTH and AVP, indicate the involvement of several hypertensive mechanisms.

Cardiovascular actions of adrenomedullin in conscious sheep

Adrenomedullin (Adm) is a 52-amino acid peptide that promotes a potent vasodilator action in rats and elevates adenosine 3',5'-cyclic monophosphate levels in isolated vascular tissue preparations. To date, the cardiovascular activity of Adm has been examined only in anesthetized animals, hence the present study examines in detail the hemodynamic actions of human Adm-(1-52) in conscious, chronically instrumented sheep. Five sheep were injected intravenously with 0.1, 1, 10, 50, or 100 micrograms Adm, and mean arterial pressure, heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral conductance (TPC), coronary blood flow (CF), coronary conductance (CC), peak aortic flow (Fmax), and left ventricular dF/dt were monitored by a computer-based data collection system. Adm produced dose-dependent changes in all parameters measured, with the threshold dose being 10 micrograms. Adm injected at 100 micrograms rapidly and significantly decreased blood pressure by 10 +/- 1 mmHg, accompanied by an increase in HR of 35 +/- 4 beats/min. CO increased by 1.6 +/- 0.3 l/min, whereas SV exhibited a small reduction of 11 +/- 4 ml/beat. TPC was markedly increased by 35 +/- 7 ml.min-1.mmHg-1. CF showed an increase of 27 +/- 4 ml/min, and CC increased in parallel by 0.45 +/- 0.06 ml.min-1. mmHg-1. Fmax and dF/dt showed small increases of 3.8 +/- 0.8 l/min and 104 +/- 12 l.min-1.s-1, respectively. All hemodynamic parameters had returned to control values by 40 min postinjection.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of corticotropin-releasing factor secretion and synthesis in the human neuroblastoma clones- BE(2)-M17 and BE(2)-C

The BE(2)-M17 and BE(2)-C human neuroblastoma cell lines have been shown to synthesize and secrete corticotropin-releasing factor (CRF) following retinoic acid treatment. It has been demonstrated that CRF secretion and intracellular synthesis increases in response to forskolin treatment. In this report, we have further characterized these cells in response to protein kinase C activators, dexamethasone, interleukin-1 alpha, as well as various neurotransmitters and peptides. Nanomolar concentrations of the phorbol ester--phorbol 12 myristate 13--acetate (TPA), increased intracellular CRF content in both cell lines while increasing secretion only in the BE(2)-M17 cell. Nanomolar concentrations of dexamethasone were not able to alter basal levels of secretion and content in either cell type. However, in the BE(2)-M17 cell but not the BE(2)-C cell, the same concentrations of dexamethasone added to 30 microM forskolin augmented levels of CRF secretion and content. Likewise, the same augmented response in CRF secretion and content was seen only in the BE(2)-M17 cell line when nanomolar concentrations of dexamethasone were added to 20 nM TPA. Furthermore, only in the BE(2)-M17 cell line were micromolar levels of the biogenic amine serotonin able to increase levels of CRF secretion and content. No effects on CRF in both cell lines were demonstrable with picomolar levels of interleukin-1 alpha as well as micromolar levels of acetylcholine, norepinephrine, arginine-vasopressin, oxytocin, and angiotensin-II. The potential usefulness of these cells as models of central nervous system or placental CRF-containing neurons is discussed.

Cardiovascular actions of atrial natriuretic factor in sheep with cardiac failure

The present study examines in detail the short-term cardiovascular actions of atrial natriuretic factor (ANF) in sheep with experimental low-output cardiac failure. Five conscious sheep, surgically implanted with a ventricular pacing wire, were paced at 220 beats/min for 14 days. Most clinical symptoms of congestive heart failure (CHF) were apparent after the 14 days, characterized by low cardiac output, high venous pressure, increased total peripheral resistance, increased plasma levels of ANF, noradrenaline, arginine vasopressin and renin, and marked fluid retention. On day 14 of pacing, intravenous infusion of ANF at 100 micrograms/h for 60 min restored cardiac output to prepacing values and reduced both total peripheral resistance and right atrial pressure. These effects were sustained throughout the infusion period. No change was seen in blood pressure, plasma renin, or noradrenaline levels. These hemodynamic changes, produced by short-term infusion of ANF, contrasted with those seen in normal sheep, where there was a fall in cardiac output with increased total peripheral resistance. These changes reflect a return toward normal of the left ventricular function curve. This is the first study to report that ANF improves cardiac function in conscious sheep with CHF, primarily by a vasodilator action to reduce cardiac preload, and suggests that ANF may be useful in treating the hemodynamic effects associated with cardiac failure.

The BE (2)-M17 neuroblastoma cell line synthesizes and secretes corticotropin-releasing factor

The BE (2)-M17 human neuroblastoma has previously been shown to express corticotropin-releasing factor (CRF) mRNA following retinoic acid treatment. It is demonstrated in this report that both cell extracts and cell incubation medium of retinoic acid-treated BE (2)-M17 cells were shown to contain CRF-like immunoreactivity (CRF-LI) by RIA. CRF-LI secretion and content were also dose-dependently increased by forskolin. In addition, cell extracts were applied to a C18 Vydac column and peak CRF-LI from the collected fractions was shown to coincide in time of elution with peak immunoreactivity seen with oxidized synthetic CRF standard. Thus, in containing the CRF peptide, the BE (2)-M17 cells are useful models for further study of CRF cellular and genetic regulation.

Characterization and regulation of corticotropin-releasing factor in the human hepatoma NPLC-KC cell line

Corticotropin-releasing factor (CRF) has a broad distribution throughout the brain and periphery and has been shown to be present in certain human tumors. We have identified a human hepatoma cell line, NPLC-KC, that contains and secretes immunoreactive CRF (irCRF). Cyclohexyl-silica extracted supernatant from these cells displaced iodinated human CRF (hCRF) in our CRF radioimmunoassay in a manner parallel to the hCRF standard, stimulated release of ACTH from cultured primary rat anterior pituitary cells in a dose-responsive manner. In addition, multiple bioactive and immunoreactive forms of CRF were secreted from these cells as determined by gel permeation chromatography. To determine if irCRF secretion and synthesis could be modulated in the NPLC-KC cells, we tested the ability of factors and hormones to regulate CRF release from and synthesis in these cells. Phorbol 12-myristate 13-acetate (PMA) and forskolin stimulated irCRF release and synthesis, implicating calcium/phospholipid- and cAMP-dependent protein kinases in the regulation of these cells. The cytokine, interleukin-1, was a potent secretagogue of irCRF and this was effect-additive with the increase observed with forskolin, but not with PMA. The glucocorticoid dexamethasone exhibited negative regulation of both basal and stimulated secretion and synthesis of irCRF from the NPLC-KC cell line. Thus, the control of irCRF production by the NPLC-KC human hepatoma cell line exhibits distinct similarities to regulation of CRF in the rat hypothalamus. This cell line should therefore be useful for studying regulation of the synthesis, processing and secretion of mammalian CRF in vitro.

The effect of hypovolemia on the renal and cardiovascular responses to atrial natriuretic factor (ANF) infusion

The renal and cardiovascular effects of ANF infusion have been examined in separate series of experiments; in conscious instrumented sheep following either hemorrhage (10 mL/kg body weight) or removal of 500 mL of plasma by ultrafiltration. Renal arterial infusion of hANF (99-126) at 50 micrograms/h increased sodium excretion from 99 +/- 30 to 334 +/- 102 (p less than 0.05) in normal animals, and from 77 +/- 31 to 354 +/- 118 mumol/min in hemorrhaged animals. Similarly in sheep following ultrafiltration, cardiac output and stroke volume were reduced by intravenous infusion of ANF (100 micrograms/h), although these effects were less marked than those observed in normal animals. The rapid modulation of natriuretic responses to ANF observed in volume expanded animals is not seen in this model of acute volume depletion suggesting that the mechanism through which the renal response to ANF is modulated in low sodium or volume states is not simply the reverse of that which produces rapid enhancement of response following blood volume expansion.

Effects of calcium channel blockade on the hemodynamic responses to endothelin infusion in conscious sheep

The hemodynamic responses to bolus injection of endothelin I (ET) at 5, 15, and 50 micrograms were examined in conscious sheep (n = 5) before and after infusion of nisoldipine at 25 micrograms/kg/h. Endothelin produced dose-dependent increases in mean arterial pressure (MAP + 87 +/- 6 mm Hg at 50 micrograms) and calculated total peripheral resistance (CTPR + 54 +/- 15 mm Hg/L/min at 50 micrograms) and decreases in heart rate (HR - 34 +/- 6 beats/min at 50 micrograms) and cardiac output (CO - 2.6 +/- 0.3 L/min at 50 micrograms) but no change in stroke volume (SV). Nisoldipine attenuated (P less than .05) the endothelin-induced changes in MAP (+26 +/- 3 mm Hg at 5 micrograms) and CTPR (+13.0 +/- 2.1 mm Hg/L/min at 50 micrograms), but not the fall in heart rate or cardiac output. These data are compatible with the hypothesis that vasoconstrictor effects of ET in sheep are in part dependent on influx of calcium through L-type channels.

Hemodynamic effects of atrial natriuretic factor clearance receptor occupancy in conscious sheep

The present study examined the hemodynamic actions of a non-guanylate cyclase linked or "clearance" atrial natriuretic factor (ANF) receptor ligand--des[Gln116Ser117Gly118Leu119Gly120] ANF 102-121 (C-ANF 4-23)--in conscious sheep. The effect of this peptide on the duration and potency of the hypotensive action of ANF (99-126) was also studied. C-ANF (4-23), infused at 400 micrograms/h for 2 h, reduced blood pressure, cardiac output and stroke volume, and increased total peripheral resistance slightly. These changes were similar to those previously observed with infusion of 20 micrograms/h ANF (99-126) in sheep. Endogenous ANF concentration increased from 28 +/- 13 to 85 +/- 18 pg/mL after 80 min infusion of C-ANF (4-23). The duration of hypotensive action from injection of ANF (99-126) was increased almost two-fold during infusion of C-ANF (4-23), however the hypotensive potency of ANF (99-126) was similar both prior to and during infusion of C-ANF (4-23). These studies support the concept of the metabolism of ANF via clearance receptors, suggesting that long-term hemodynamic actions of endogenous ANF may be achieved via prolonged blockade of these clearance receptors.

Haemodynamic effects of long-term endothelin infusion in conscious sheep

1. Synthetic human endothelin-1 was infused intravenously at 15 micrograms/h for 24 h to examine its cardiovascular actions in five conscious sheep. 2. Endothelin produced a maximum increase in mean arterial pressure (MAP) of +8 mmHg at 8 h, with an increase in calculated total peripheral resistance (CTPR) of +2.6 mmHg/L per min, whilst cardiac output (CO) was unchanged. At 24 h MAP was not significantly elevated, however CTPR had increased by +2.8 mmHg/L per min and CO had decreased by 0.9 L/min. 3. This study shows that long-term administration of endothelin produces sustained arterial vasoconstriction in sheep.

Effects of atrial natriuretic factor on pressor responsiveness to angiotensin II, norepinephrine, and vasopressin in conscious sheep

The effects of pretreatment with atrial natriuretic factor (ANF) on the pressor responsiveness to injections of angiotensin II (ANGII), arginine vasopressin (AVP), and norepinephrine (NE), as well as the effect of pretreatment with ANGII on the hypotensive responses to ANF injection were studied in conscious sheep. The hemodynamic effects of ANF infusion (100 micrograms/h for 60 min) were also examined in animals pretreated with the angiotensin-converting enzyme (ACE) inhibitor, captopril. Infusion of ANF attenuated the pressor responsiveness to exogenous AII and NE, but caused no significant change in the blood pressure increases produced by vasopressin. In contrast, infusion of AII had no effect on the immediate hypotensive response to ANF injection. Infusion of ANF for 60 min produced similar hemodynamic actions in sheep during ACE inhibition as compared with the responses observed in normal sheep, although the reduction in cardiac output and increase in calculated total peripheral resistance was attenuated. Infusion of captopril increased plasma concentration of renin (PRC), and infusion of ANF produced no further change in PRC. In conclusion, the short-term cardiovascular responses to ANF infusion in conscious sheep are not mediated solely by inhibition of the renin-angiotensin system. However, ANF attenuates the pressor actions of pharmacologic doses of exogenous ANGII and NE. In contrast, the vasodepressor response to exogenous ANF injection was not altered in animals receiving ANGII infusion. This study suggests that ANF may be important in regulating the effects of endogenous vasoconstrictor hormones on blood pressure (BP).

Hemodynamic interactions of atrial natriuretic factor with the sympathetic nervous system in sheep

The hemodynamic effects of short-term infusion of atrial natriuretic factor (ANF) were observed in sheep with combined alpha/beta adrenoceptor pharmacological blockade. The effect of ANF on the sympathetically-mediated baroreflex system was observed in conscious sheep in which aortic and vena caval balloon occluders had been surgically implanted. ANF infused at 100 micrograms/h for 60 min produced similar effects on blood pressure, cardiac output and stroke volume during alpha/beta-adrenoceptor blockade, compared to the responses seen in normal sheep, however the increases in heart rate and total peripheral resistance were reduced. ANF markedly enhanced the gain of the baroreceptor-heart rate reflex in the sheep. This effect may mediate the large increase in heart rate which is associated with a small fall in blood pressure during short-term infusion of ANF. In conclusion, the sympathetic nervous system plays an important role in regulating the reflex cardiovascular responses to short-term infusion of ANF in sheep. The large species variation in the hemodynamic responses to ANF may be related to differing degrees of stimulation or inhibition of the baroreceptor system to affect heart rate and/or peripheral resistance.

Rapid haemodynamic response to adrenocorticotrophin and the role of peripheral resistance in adrenocorticotrophin-induced hypertension in conscious sheep

The haemodynamic effects associated with the onset of hypertension induced by infusion of adrenocorticotrophin (ACTH) were investigated in sheep. Analysis of haemodynamic data collected over 24 h by a computer-based monitoring system revealed that mean arterial pressure (MAP) was significantly increased after 4 h. Cardiac output was significantly raised after 1 h. The increased cardiac output was initially offset by a fall in calculated total peripheral resistance (CTPR) and MAP did not begin to rise until CTPR had returned to control values. This suggested that the return of CTPR to control values was essential for the development of hypertension. The development of ACTH-induced hypertension was prevented by both nisoldipine, a calcium channel blocker, and minoxidil, a vascular smooth muscle relaxant. Nisoldipine administration was also found to reverse established ACTH hypertension. A greater fall in MAP and CTPR occurred in the onset and established phase of ACTH hypertension sheep compared with normotensive controls. These results indicate that constriction of the peripheral vasculature is essential for the onset and maintenance of ACTH-induced hypertension in the sheep, and that the vasoconstriction does not involve a specific Ca21+-dependent mechanism because minoxidil was as effective as nisoldipine in abolishing the pressor response to ACTH. The onset of ACTH-induced hypertension in sheep is characterized by very rapid haemodynamic changes with an increase in cardiac output and a relative increase in CTPR after an initial peripheral vasodilatation.

Cardiovascular actions of human endothelin in conscious sheep

1. Synthetic human endothelin was injected intravenously over the range 1.5-50 micrograms to examine its cardiovascular actions in conscious sheep. 2. Mean arterial pressure increased by 9-21 mmHg within 30-120 s over the range 5-50 micrograms endothelin. The increase in blood pressure was associated with increased calculated total peripheral resistance and a fall in cardiac output and heart rate. Stroke volume was increased. 3. Injection of endothelin into ganglion blocked sheep produced vasoconstriction and an increased blood pressure response associated with an attenuation of the effects on cardiac output, heart rate and stroke volume. 4. This study suggests that endothelin produces potent arterial vasoconstriction and reflex mediated effects on the heart in conscious sheep.

Comparative hemodynamic actions of ANF-related peptides in conscious sheep

The rapid hemodynamic effects of several N- and C-terminal deleted fragments of ANF, a potent ANF analogue and the recently characterised brain natriuretic peptide (BNP) were investigated in conscious sheep, and compared to the rapid hemodynamic actions of ANF 1-28. The hypotensive potency of all peptides studied was as follows: ANF 1-28 = PLO58 greater than 5-27 = ANF 5-28 = BNP greater than ANF 7-28 greater than ANF 13-28 = ANF 5-25. All peptides reduced blood pressure via a decrease in total peripheral resistance, excluding ANF 5-25 and 13-28 which were without effect on any parameter measured. These changes were associated with reflex increases in both heart rate and cardiac output, and a slight reduction in stroke volume. The duration of hypotensive/vasodilator action of ANF 1-28, 5-27, 5-28, 7-28 and BNP was approximately 3-4 minutes, whereas that of PLO58 was 7-8 minutes. In conclusion, amino acid deletions from the C- and N-terminal of the ANF molecule reduced the hypotensive/vasodilator potency of the peptide in conscious sheep. BNP produced similar rapid hemodynamic changes to ANF 1-28, suggesting that the two peptides may co-regulate blood pressure and possibly body fluids to promote fluid and cardiovascular homeostasis.

Enhancement of renal but not haemodynamic effects of atrial natriuretic peptide (1-28) in sheep treated with ACTH

1. The haemodynamic and renal effects of short-term infusion of human atrial natriuretic peptide (ANP) (1-28) were examined in sheep treated with ACTH and compared with the responses previously observed in normotensive sheep. 2. Infusion of ANP at 100 micrograms/h for 60 min in ACTH-treated sheep (5 micrograms/kg per day for 5 days) decreased blood pressure and produced a fall in both cardiac output and stroke volume. No changes were seen in heart rate and total peripheral resistance. 3. ANP produced large increases in urine volume, urinary sodium and chloride excretion, and further decreased plasma potassium concentration in the ACTH-treated sheep. Compared with normal sheep studied previously under the same conditions, the ACTH-treated sheep showed a much greater diuretic and natriuretic response to ANP, although the blood pressure response to ANP was similar in both states. 4. The change in renal responsiveness to ANP in sheep may be related to the increased blood volume of the ACTH-treated animals because volume expansion is known to enhance the renal effects of ANP.

The effects of intracerebroventricular administration of biologically active peptides in conscious sheep

The present study records the physiological effects of 24-hour intracerebroventricular infusion of a variety of biologically active peptides in conscious sheep. A number of peptides including AVP and TRH produced increases in mean arterial pressure, heart rate and body temperature. There was an overall positive correlation between peptide-induced changes in body temperature and changes in either mean arterial pressure or heart rate. TRH and beta-endorphin had marked effects on behaviour and several peptides reduced food and water intake. Several peptides increased urinary sodium excretion, however, few peptides changes plasma electrolyte concentrations. TRH produced small effects on plasma ACTH and plasma glucose concentrations. The peptides in this study produced physiological changes which were probably mediated by their actions on the central nervous system.

The effects of intracerebroventricular infusion of atrial natriuretic factor in conscious sheep

The effects of 24-hour intracerebroventricular infusion of human atrial natriuretic factor (ANF) and two related fragments were studied in conscious sheep. ANF (1-28) had no effect on either mean arterial pressure (MAP) or heart rate (HR) when infused at 3 or 10 micrograms/hr, however a small diuresis and an increase in urinary sodium (Na) excretion was observed. The smaller fragment, ANF (5-27) infused at 10 micrograms/hr, increased MAP, HR and body temperature, although the same rate of infusion of ANF (5-28) was without effect. All peptides increased plasma sodium concentration and plasma osmolality. None of the peptides affected plasma ACTH, glucose or renin concentration. ANF (1-28) had no effect on either Na intake or water intake in Na-depleted sheep. These studies suggest that members of the ANF family can influence a number of physiological functions following central administration.

Long-term hemodynamic actions of atrial natriuretic factor (99-126) in conscious sheep

The hemodynamic and metabolic effects of long-term (5 day) infusion of human atrial natriuretic factor (ANF) were examined in conscious chronically instrumented sheep. Infusion of ANF at 20 micrograms/h, a rate below the threshold for an acute natriuretic effect, decreased blood pressure by 9 +/- 1 mmHg on day 5, associated with a fall in calculated total peripheral resistance. On day 1, ANF reduced cardiac output, stroke volume, and blood volume, effects that were associated with an increase in heart rate and calculated total peripheral resistance and a small decrease in blood pressure. On days 4 and 5 there was a small increase in urine volume and sodium excretion. On day 5 an increase in water intake and body weight was observed. No change was seen in plasma concentrations of renin, arginine vasopressin, glucose, adrenocorticotropic hormone, or protein. This study suggests that the short-term hypotensive effect of ANF results from a reduction in cardiac output associated with a fall in both stroke volume and effective blood volume. However, after 5 days of infusion, ANF lowers blood pressure via a reduction in total peripheral resistance.

Rapid haemodynamic responses to atrial natriuretic factor (99-126) in conscious sheep

1. Haemodynamic effects of 20 micrograms and 100 micrograms injection of atrial natriuretic factor 99-126 (ANF) were studied in conscious sheep. 2. ANF injection rapidly decreased blood pressure associated with a fall in total peripheral resistance, increased heart rate and cardiac output. These parameters returned to normal within 5 min of injection. 3. This study shows that ANF has an initial vasodilatory action to decrease blood pressure, which is different from the hypotensive mechanism seen with short-term infusion (60 min) of ANF in sheep.

Hemodynamic and renal effects of atrial natriuretic factor (99-126) in volume expanded sheep

The renal and hemodynamic effects of atrial natriuretic factor 99-126 (ANF) were examined in hypervolemic sheep and the results compared to responses previously observed in normal isovolemic sheep. Infusion of 500 ml dextran over 60 min increased blood pressure by 6 +/- 2 mmHg, associated with increases in cardiac output and stroke volume. No change was seen in heart rate nor total peripheral resistance. Subsequent infusion of ANF at 100 micrograms/h for 60 min reduced blood pressure by 6 +/- 1 mmHg and decreased stroke volume and cardiac output. There was no change in heart rate. Total peripheral resistance decreased slightly, to a similar degree to that seen after control infusion of 500 ml dextran. Moderate increases in urine volume, sodium and chloride excretion were seen after infusion of dextran and subsequent infusion of ANF markedly enhanced these renal effects. The renal changes produced by ANF in volume expanded sheep were significantly greater than those observed in normal sheep. Although normal sheep are more sensitive to the hemodynamic than to the renal effects of ANF, after dextran pretreatment there was enhancement of the renal responses with little change in the effects on blood pressure.

Hemodynamic effects of atrial natriuretic peptide in conscious sheep

The present study examines the effects of intravenous infusion of atrial natriuretic peptide (ANP) on blood pressure, heart rate, cardiac output, sodium excretion and urine output in conscious, chronically instrumented sheep. Human ANP (1-28) was infused into the jugular vein (I.V.) for 60 min at 20, 50, 100 and 500 micrograms/h. ANP caused a decrease in blood pressure at all doses which was associated with a reduction in stroke volume and cardiac output. There was also a decrease in right atrial pressure. At the two higher rates of infusion an increase in both heart rate and calculated total peripheral resistance was observed. These data are consistent with ANP acting on the venous side of the circulation to produce venodilatation, and a reduction in venous return, stroke volume and cardiac output. The increases in urinary sodium excretion and urine output observed when ANP was infused I.V. at 100 micrograms/h for 60 min were small. The data suggest that the minimum dose for effects on the cardiovascular system (20 micrograms/h) is less than that required to produce renal effects (100 micrograms/h). ANP has potent effects on the cardiovascular system in conscious sheep, exerting its effect on blood pressure primarily by its action on the venous circulation and on cardiac output.

The effect of intracerebroventricular infusions of CRF, sauvagine, ACTH (1-24) and ACTH (4-10) on blood pressure in sheep

This study reviews the effects of intracerebroventricular (i.c.v.) infusion of corticotrophin releasing factor (CRF) and adrenocorticotrophic hormone (ACTH) (1-24) on blood pressure in conscious sheep. The effects of sauvagine, a peptide with 50% homology with CRF and ACTH (4-10) and other analogues of ACTH were studied. Intracerebroventricular infusion of CRF for 24 h at 10 and 100 micrograms/h increased blood pressure and heart rate. Sodium (Na) excretion also increased. Sauvagine at 10 micrograms/h also increased blood pressure. Both peptides raised body temperature and produced 'arousal' behaviour. ACTH (1-24) at 0.8 microgram/h for 48 h raised blood pressure and body temperature but had no significant effect on Na excretion or behavior. ACTH (4-10) and other related analogs (alpha-MSH, alpha gamma 1-MSH) at up to 10 micrograms/h for 48 h had no effects. These studies show that neuropeptides involved in the physiological response to 'stress' may have central effects on blood pressure.

A simple gas chromatographic method for the analysis of trace organics in ambient air

A simple method using adsorption, heat desorption, and F.I.D. gas chromatography to determine ppb quantities of various organic vapors in air is described. Laboratory results with chemicals such as bischloromethyl ether, vinyl chloride monomer and volatile ketones are discussed.

The influence of environmental agents on prostaglandin biosynthesis and metabolism in the lung. Inhibition of lung 15-hydroxyprostaglandin dehydrogenase by exposure of guinea pigs to 100 per cent oxygen at atmospheric pressure

Enzymes in the 100 000g supernatant fraction of guinea-pig lungs, in the presence of NAD-+, converted PGF-2 alpha (prostaglanding F-2 alpha) into a less-polar compound. The u.v. spectrum of this metabolite showed a strong absorption band at 230 nm, which is characteristic of a carbonyl group in conjugation with a double bond. Reduction of this metabolite with NaBH4 resulted in a compound that behaved like PGF2 ALPHA on t.l.c. and g.l.c. From this evidence we concluded that PGF2alpha is metabolized in vitro to 15-oxo-PGF2 alpha by the NAD-+-dependent prostaglandin dehydrogenase system of guinea-pig lung. The effect of exposure of the animal to SO-2 and O2 on the rate of prostaglanding biosynthesis and catabolism by lung fractions in vitro was studied. Exposure of guinea pigs to 500 p.m. of SO2 for 5h or to 50p.p.m for 9 days (6h/day) did not alter the production or degradation of prostaglandings by lung fractions in vitro. In contrast, exposure of guinea pigs to 100% O2 for 48 h inhibited the rate of prostaglanding metabolism in vitro by 60-70% without significantly altering the rate of biosynthesis by lung fractions. Inhibition of prostaglandin dehydrogenase activity in vitro by lung fractions after exposure of the animal to O2 was dependent on the duration of exposure. Gluthathione S-aryltransferase and catechol O-methyltransferase activites of guinea-pig lung 100 000g supernatant were unaltered by exposure of the animal to O2. Thus it appears that inhibition of pulmonary prostaglandin dehydrogenase by exposure of the animal to O2 is not the result of a general toxic response. It was postulated that the inhibition of prostaglanding dehydrogenase may occur after exposure of the animal to other oxidant gases.