Measurement of tricyclic antidepressants. Part II. Applications of methodology

This review, together with Part 1 (Clin. Chem. 26: 5-17, 1980), summarizes progress in measurement of tricyclic antidepressants in biological fluids and the application of the methodology to clinical practice. For many of the older drugs and for all of the new-generation antidepressants, further studies are required to delineate the precise relationship between plasma concentration and clinical response in well-defined diagnostic groups. For new drugs, rigorous evaluation of a method of measurement is required before it is applied to clinical studies. Assessment of drug interactions, inter-patient variability in plasma concentrations, and determination of the plasma concentrations required for therapeutic response all depend almost entirely on the quality of the assay methodology.

Bibliometric analysis of HRC-supported biomedical publications, 1990 to 1994

AIM

To document changes in the rate and impact of publications resulting from Health Research Council of New Zealand (HRC) biomedical grants since its inception and to relate the number of publications to Health Priority Areas, fields of research and specific types of grant.

METHODS

All original papers or reviews and editorials published by HRC-supported investigators in peer-refereed journals, from 1990 to 1994, were entered into a bibliographic database.

RESULTS

In this five-year period, researchers receiving HRC biomedical grants published a total of 2094 articles in 623 peer-reviewed journals, of which 1190 (57%) derived from HRC support. Of the publications, 90.2% were original papers; the remainder were reviews or editorials. From 1990 to 1994, there was an increase in the number of HRC-supported publications (p<0.04) but not of those deriving from other support. There was no change in the quality of publications over this period, as reflected by the impact factor (a measure of the number of times that publications in a journal are cited). The majority (62.6%) of publications derived from project grants, however, the average cost per publication was 8.4% higher for project than for programme (multi-investigator) grants. Finally, nearly 40% of HRC publications directly addressed designated health priority areas.

CONCLUSIONS

The present study has examined one aspect of the value for money obtained from the public investment in biomedical research. As the HRC is the major provider of contestable biomedical research funding in New Zealand, bibliometric analysis may be of ongoing value to monitor the effects of changes to the organisation of biomedical research funding in New Zealand.

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 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.

Effects of prednisolone and deflazacort on osteocalcin metabolism in sheep

Glucocorticoids adversely affect bone and mineral metabolism through a number of mechanisms, including inhibition of bone formation. Deflazacort is a glucocorticoid which has been reported to be relatively "bone-sparing." We compared the effects in oophorectomized sheep of deflazacort and prednisolone on the metabolism of osteocalcin (OC), a marker of osteoblast function. An [125]OC infusion method was used to measure the OC plasma clearance rate (PCR) and OC plasma production rate (PPR). Six-day intravenous infusion of deflazacort and prednisolone (in the dose range 0.007-1.00 mg/hour) induced dose-dependent decreases in OC PPR which were of a similar pattern but significantly different magnitude (P < 0.02); deflazacort demonstrated a potency about 150% that of prednisolone. Both steroids decreased plasma OC levels on a dose-related basis but at the lower doses 0.05 mg/hour (P < 0.05) and 0.013 mg/hour (P < 0.0005), deflazacort caused greater decrements. OC PCR was significantly increased only by higher doses of deflazacort (1.00 mg/hour, 0.25 mg/hour; P < 0.05). Deflazacort and prednisolone increased both postabsorptive plasma glucose and plasma calcium levels, but there were no significant differences between their effects. We conclude that plasma OC levels and OC PPR in sheep were more sensitive to the effects of deflazacort than to prednisolone. At high doses, the depressive effect of deflazacort on plasma OC levels may have been due in part to an increased OC PCR which was not evident with prednisolone treatment. However, the agents appeared to have a similar dose-dependent hyperglycemic effect, and both caused a small dose-dependent increase in plasma calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemodynamic and metabolic effects of short term administration of synthetic sex steroids in humans

Synthetic sex steroid administration is a major cause of iatrogenic hypertension but little is known of the haemodynamic or metabolic consequences of these steroids. This study examined the short term blood pressure, volume and metabolic consequences of 5 day administration of synthetic androgen to normal men and synthetic oestrogen or progestogen to normal women. Healthy subjects (8 women, 6 men) on a constant diet took part in each of 3 studies. Males received testosterone undecanoate 120 mg/day (n = 6) and females either ethinyloestradiol 0.3 mg/day (n = 5) or norethisterone 15 mg/day (n = 6) for 5 days in the last week of the cycle. Norethisterone increased lying (+7 mmHg) and standing (+8 mmHg) systolic pressure but the other steroids did not alter blood pressure. All 3 treatments increased body weight. There were no consistent changes in plasma electrolytes or glucose with any steroid, and no urinary sodium retention or changes in urine Na:K ratio. Haematocrit fell on ethinyloestradiol but no steroid significantly increased plasma volume (measured as volume of distribution of 125I human serum albumin). Renin substrate and cortisol rose and renin concentration fell on ethinyloestradiol. These studies suggest that the progestogen component may contribute to the blood pressure raising effects of oral contraceptives.

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.

The effect of uninephrectomy on osteocalcin metabolism in sheep: a direct evaluation of renal osteocalcin clearance

Indirect evidence has suggested that the kidney is a major organ of clearance for osteocalcin, a circulating marker of osteoblast function. The objectives of the present study were (1) to confirm the role of the kidney in osteocalcin clearance (2) to quantify the contribution of extrarenal sites and (3) to investigate the renal mechanism(s) of osteocalcin clearance. Plasma osteocalcin levels, osteocalcin plasma clearance rate (PCR) and plasma production rate (PPR) were determined in oophorectomized (OX) and uninephrectomized oophorectomized (UOX) sheep. The osteocalcin renal extraction efficiency (REE) and the effective renal plasma flow (ERPF) were measured, and the osteocalcin renal clearance rate (RCR) was calculated. The osteocalcin PCR was reduced significantly in UOX compared with OX sheep (2.0 +/- 0.1 (n = 9) vs 2.5 +/- 0.1 litres/h (n = 44); P less than 0.0005). In UOX sheep with plasma creatinine levels less than or equal to 130 mumol/l, the osteocalcin REE was 9 +/- 1.3% and the osteocalcin RCR was 50-91% of osteocalcin PCR (n = 4). In UOX sheep with plasma creatinine levels in the range 100-440 mumol/l, there was a linear relationship between osteocalcin PCR and ERPF; the osteocalcin RCR was related to the osteocalcin PCR (RCR = 0.9 x PCR - 0.50). Intravenous infusion of the synthetic glucocorticoid triamcinolone acetonide (TA) in UOX sheep led to marked decrements in plasma osteocalcin levels and the osteocalcin PPR, and a significant increase in the osteocalcin PCR. These changes were accompanied by a 44% increase in ERPF.(ABSTRACT TRUNCATED AT 250 WORDS)

The failure of nisoldipine to prevent the hypertensive response to cyclosporine A infusion in sheep

Hypertension and nephrotoxicity are major clinical problems associated with cyclosporine A administration. Sheep rapidly develop hypertension after intravenous administration of cyclosporine A at 6 mg/kg per day over 5 days, and this is associated with a rise in peripheral resistance. Nephrotoxicity is not a feature of cyclosporine A-induced hypertension in this species. This study reports the use of nisoldipine to investigate the role of Ca2(+)-induced smooth muscle contraction in cyclosporine A-induced hypertension in conscious sheep. After 3 control days, nisoldipine at 24 mg/day was infused intravenously alone for 24h (E1), followed by 5 days of nisoldipine plus cyclosporine A (6 mg/kg per day; E2-E6). After 24 h of nisoldipine alone, mean arterial pressure (MAP) was unchanged, heart rate rose from a control value of 60 +/- 2 beats/min to 102 +/- 9 beats/min (P less than or equal to 0.001), calculated total peripheral resistance (CTPR) fell from 15.8 +/- 0.5 to 11.7 +/- 0.5 mmHg/l per min (P less than or equal to 0.001) and stroke volume fell from 73 +/- 4 ml/beat to 60 +/- 5 ml/beat (P less than or equal to 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Amiloride blocks the onset of ACTH-induced hypertension in the sheep

This study investigated the ability of two diuretics, amiloride and frusemide, to prevent the development of ACTH induced hypertension in conscious sheep. Infusion of amiloride (20 mg/day) or frusemide (50 mg/day) for three days into normotensive sheep did not have any significant effects on blood pressure. Amiloride blocked ACTH-induced hypertension and the sodium retention and hypokalemia which is usually associated with ACTH administration. Frusemide failed to completely block the hypertension and potassium loss, however it blocked the transient initial urinary sodium retention associated with ACTH-induced hypertension. As frusemide failed to completely block the hypertension it is unlikely that the amiloride effect is due primarily to effects on urinary Na excretion. It is possible that amiloride is exerting its antihypertensive effects by blocking sodium channels.

Lack of pressor response to intracerebroventricular infusion of aldosterone in sheep

1. Studies in the rat and the dog have shown that infusion of aldosterone for several weeks into the cerebral ventricles (ICV) can produce hypertension at doses that do not have an effect when infused systemically. We have previously shown that a high physiological dose of aldosterone infused intravenously at 10 micrograms/h in sheep produces an increase in blood pressure of 7 mmHg within 2 days. 2. In this paper we report the effects of ICV infusion of aldosterone at 2 micrograms/h for 6 days in conscious sheep. 3. Neither blood pressure nor heart rate were altered, and there were no consistent changes in any of the metabolic parameters measured. 4. These results do not support a role for central effects of aldosterone in the hypertension produced by systemic infusion of the steroid in sheep.

Renal actions of atrial natriuretic factor: modulation of effect by changes in sodium status and aldosterone

To examine the effect of changes in Na status on the renal response to atrial natriuretic factor (ANF), human ANF-(99-126) was infused into the renal artery of conscious sheep while Na replete, Na depleted, or Na loaded. The natriuretic response to ANF was attenuated during Na depletion and enhanced in Na-loaded animals. To demonstrate that the enhancement or attenuation of response was related to Na status rather than to the initial level of Na excretion, aldosterone was infused into the renal artery for 2 h to decrease Na excretion to a level inappropriately low for the animal's Na status (and not different from Na-depleted animals), and they were again challenged with ANF. Their response to ANF, however, was not significantly different from that in normal Na-replete animals but was significantly greater than that observed in Na-depleted animals. Similarly, Na-loaded animals treated with aldosterone had control Na excretion in the Na-replete range; however, their response to ANF was not significantly different from that of Na-loaded animals. The response to ANF was enhanced in sheep treated with aldosterone for 48 h, consistent with Na retention and hypervolemia, secondary to aldosterone treatment. The study demonstrates that Na status or some associated physiological parameter is an important determinant of the natriuretic response to ANF. The present series of experiments demonstrate that changes in aldosterone levels per se are not a determinant of the natriuretic response to ANF.

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.

A 'hypertensinogenic' class of steroid hormone activity in man?

1. Studies in sheep have led to the concept of a 'hypertensinogenic' (HT) steroid hormone activity, whereby the blood pressure (BP) raising effects of adrenocortical steroids can be separated from their in vivo glucocorticoid (GC) or mineralocorticoid (MC) activities. 2. The three main lines of evidence are as follows: (i) BP raising effects of ACTH cannot be reproduced by appropriate rates of infusion of steroids with GC and MC activities; (ii) certain steroids e.g. 9 alpha-fluorocortisol can increase BP at rates of infusion below threshold for in vivo GC or MC actions and for many steroids there is no correlation between GC, MC and HT effects; (iii) demonstration of differential antagonism of HT, MC and GC effects. 3. Studies in man show that the BP effects of ACTH are due to cortisol (F) at levels which have both MC and GC activity. However, BP effects of ACTH cannot be blocked by MC and GC antagonists. 4. Although complete separation of in vivo GC, MC and HT activities has not been possible in man, our own studies show a degree of dissociation. Taken together, these data suggest that steroids may raise BP by a HT mechanism distinct from classical in vivo MC or GC activities in man as well as 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).

Adrenocorticotrophin-induced hypertension in the rat: haemodynamic, metabolic and morphological characteristics

Adrenocorticotrophin (ACTH) administration has been systematically studied in man and sheep. It raises systolic blood pressure (SBP) in the rat, but this has been little studied. ACTH was injected once daily at 0.5 mg/kg for 12 days in male Sprague-Dawley rats (n = 19). Sham-injected animals were studied in parallel (n = 15). ACTH increased SBP from 94 +/- 4 to 121 +/- 4 mmHg (P less than 0.001), significantly greater (P less than 0.02) than sham injection. The SBP of ACTH-treated rats was significantly higher than that of sham-injected rats when the same animals were measured by both the tail-cuff method (ACTH, 126 +/- 3 mmHg; sham, 99 +/- 3 mmHg) and direct arterial cannulation (ACTH, 137 +/- 2 mmHg; sham, 123 +/- 3 mmHg): P less than 0.005 and P less than 0.001, respectively. There was a loss of body weight, and increased water intake and urine output in ACTH-treated animals compared with both control (P less than 0.001) and sham treatments (P less than 0.02). ACTH increased plasma [Na] (sham, 140 +/- 1 mmol/l; ACTH, 145 +/- 1 mmol/l; P less than 0.001) and urinary Na excretion compared with control (P less than 0.01) and sham injection (P less than 0.05), and also decreased plasma [K] (sham, 4.6 +/- 0.2 mmol/l; ACTH, 3.3 +/- 0.8 mmol/l; P less than 0.01) and increased urinary K excretion (P less than 0.01) compared with control. SBP in adrenalectomized animals (n = 10) was unchanged by ACTH. ACTH increased adrenal, renal, cardiac and brain weights compared with sham injection (P less than 0.05). There were no significant changes in vascular morphology, although ACTH treatment increased glomerular epithelial cell droplets and abolished the adrenal zona glomerulosa.

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.

Studies on spirolactone steroid antagonists in ACTH-induced hypertension in sheep

This study investigated the anti-mineralocorticoid potency and haemodynamic effects of a series of mineralocorticoid antagonists of the spirolactone type (RU 28318, spironolactone, K-prorenoate, K-canrenoate and canrenone), for their ability to prevent the development of ACTH-induced hypertension in conscious sheep. In vivo bioassay, using aldosterone dependent changes in parotid salivary [Na+]/[K+] of sodium depleted adrenalectomized sheep, showed spironolactone was the most potent anti-mineralocorticoid tested. Infusions of the antagonists at equal doses alone for 4 days demonstrated that none affected mean arterial pressure, except for K-prorenoate which exhibited slight pressor activity. All the antagonists produced a natriuresis. Some of the steroid antagonists of the spirolactone group blocked the development of ACTH hypertension in sheep, spironolactone being the most effective. This study provides additional evidence for an essential mineralocorticoid component in ACTH-induced hypertension.

Adrenocortical steroid requirements for initiation of ACTH-dependent hypertension in sheep

1. Previous studies demonstrated that the combined infusion of cortisol (F), aldosterone (ALDO), deoxycorticosterone (DOC), corticosterone (B), 11-deoxycortisol (S), 17 alpha-hydroxyprogesterone (17 alpha OHP) and 17 alpha, 20 alpha- dihydroxy-4-pregnane-3-one (17 alpha 20 alpha OHP), at rates equivalent to their production during adrenocorticotrophic hormone (ACTH) treatment, reproduced the pressor and metabolic responses to ACTH administration in sheep. 2. This study examined which of these adrenocortical steroids were necessary for the initiation of the hypertension produced by these steroids in sheep. 3. Infusion of F, ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP together, increased MAP by 19 mmHg, similar to both complete steroid cocktail (+25 mmHg) or ACTH administration (+21 mmHg). Infusion of F, 17 alpha OHP and 17 alpha 20 alpha OHP increased MAP by +7 mmHg. Infusion of ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP had no effect on MAP. Thus F and ALDO were essential for the pressor effects of the steroid infusion. 4. To determine the role of glucocorticoid activity in the MAP rise, prednisolone, a non-pressor glucocorticoid, was substituted for cortisol. Combined prednisolone, ALDO, 17 alpha OHP and 17 alpha 20 alpha OHP infusion did not raise blood pressure. This suggested that the mineralocorticoid component rather than glucocorticoid component of cortisol's activity was involved in the pressor response. 5. Aldosterone (7 micrograms/h) was substituted for cortisol, giving a total of 10 micrograms/h aldosterone. High dose ALDO (10 micrograms/h), 17 alpha OHP and 17 alpha 20 alpha OHP infusion raised blood pressure by 18 mmHg. Thus, the essential role of cortisol appeared to be due to its occupancy of mineralocorticoid receptors, rather than glucocorticoid receptors. 6. Given that ACTH produces a transient initial increase in aldosterone secretion of up to 10 micrograms/h, it appears that aldosterone and not cortisol is essential for the pressor effects of ACTH. 7. Hypertension resulting from the combined steroid infusion in the sheep appears to be produced by a mechanism which involves a complex interaction between ALDO, F, 17 alpha OHP and 17 alpha 20 alpha OHP. Therefore, the putative 'hypertensinogenic' receptor may be multivalent with binding sites for F, ALDO and 17 alpha 20 alpha OHP, or is a site of single interactive receptors for these steroids and that F exerts its permissive action by occupying the same site as ALDO on the hypertensinogenic receptors.

Renal effects of atrial natriuretic factor (99-126) in potassium loaded sheep

1. The renal response to renal arterial infusion of synthetic atrial natriuretic factor (ANF 99-126) was examined in conscious sheep following dietary K loading, and compared with the response in normal sheep. 2. Renal arterial infusion of ANF in K loaded sheep increased the excretion of Na and Ca, but did not affect the excretion of K. 3. The natriuretic effect of ANF was attenuated in K loaded animals, possibly as a consequence of the reduction in Na status which is associated with K loading.

Progesterone antagonizes development but not maintenance of ACTH-induced hypertension in sheep

1. This study investigated the effect of progesterone, which, under certain circumstances, can antagonize both the mineralocorticoid and glucocorticoid activities of steroid hormones, on the development and maintenance of adrenocorticotrophic hormone (ACTH)-induced hypertension in conscious sheep. 2. Progesterone (500 mg/day) alone, for 5 days, had no effect on blood pressure, but increased urinary Na excretion by 38 +/- 10 mmol/day (P less than 0.05) during the first 24 h. 3. Infusion of ACTH (5 micrograms/kg per day), alone, for 3 days, increased arterial pressure by 21 +/- 2 mmHg (P less than 0.001) associated with hypernatraemia, hypokalaemia, urinary Na retention, and increased fasting plasma glucose concentration. 4. Progesterone (500 mg/day) concurrently with ACTH blocked the rise in mean arterial pressure and the mineralocorticoid (urinary Na retention) but not the glucocorticoid (increase in plasma glucose concentration) effects associated with ACTH administration. 5. Progesterone (500 and 1000 mg/day) failed to reverse the hypertension and hypokalaemia in sheep pretreated for 3 days with ACTH. 6. Thus, progesterone blocked the onset but did not affect established ACTH hypertension. The mechanism by which progesterone blocked the development of ACTH hypertension appears to be related to the ability of progesterone to block the essential mineralocorticoid component of the adrenocortical steroids involved in the development of ACTH hypertension.

Centrally mediated increased sympathetic activity is not important in the genesis of ACTH-induced hypertension in sheep

1. Adrenocorticotrophin (ACTH) administration to sheep produces a rapid adrenally dependent hypertension which is maximal after 3 days and associated with increased cardiac output (CO) and heart rate (HR), while calculated total peripheral resistance remains unchanged. 2. This study investigated the proposal that a centrally mediated increase in sympathetic activity is important in the development of ACTH-induced hypertension. 3. Concomitant intravenous infusions of either clonidine (60 micrograms/kg per day) or methyldopa (60 mg/kg per day) with ACTH (5 micrograms/kg per day) failed to inhibit the increase in mean arterial pressure (MAP) observed with ACTH. 4. In a separate experiment clonidine abolished the increase in CO and HR but not the pressor response associated with ACTH administration. 5. These results do not support a role for centrally mediated increase in sympathetic activity in the genesis of ACTH-induced hypertension.

The hypertensive effect of synthetic glucocorticoids in man: role of sodium and volume

In previous studies, administration of adrenocorticotrophin (ACTH; 0.5 mg i.m. b.d. for 5 days) to normal subjects produced an adrenally dependent rise in blood pressure (BP) of some 20 mmHg, accompanied by an increase in cardiac output and an increase in plasma volume. The BP and metabolic effects of ACTH (increase in plasma glucose, fall in eosinophils, increase in body weight and urine sodium retention) were reproduced by infusion of the glucocorticoid (GC) cortisol at rates (6-8 mg/h) which reproduced the blood concentrations of the steroid achieved with ACTH administration. Oral administration (hydrocortisone 200 mg daily) produced similar changes qualitatively, although the cortisol concentrations and increase in pressure (12 mmHg) were less. Plasma volume was increased. To determine the role of urine sodium retention and plasma volume expansion in the hypertension, we gave synthetic steroids to six normal subjects for 5 days, at doses which were calculated to be similar for GC activity, but which had little or no mineralocorticoid (MC) activity. Prednisolone (40 mg/day), methylprednisolone (32 mg/day), triamcinolone (40 mg/day) and dexamethasone (8 mg/day) all produced equivalent GC effects (increase in plasma glucose, increase in total white cell count, fall in direct eosinophil count). There were no MC effects with any of the steroids. Body weight did not increase and urinary sodium excretion increased rather than decreased. Plasma volume (125I human serum albumin) and haematocrit were unchanged. BP rose with all four steroids: systolic BP rose by 13 mmHg with prednisolone, by 9 mmHg with methylprednisolone, by 10 mmHg with triamcinolone, and by 6 mmHg with dexamethasone. Diastolic BP increases were 8, 11, 8 and 7 mmHg, respectively. Thus, neither MC activity nor an increase in plasma volume is essential for steroids to induce an increase in blood pressure. Therefore, screening of synthetic GCs to minimize MC activity will not prevent hypertensive complications.

Hormonal regulation of osteocalcin plasma production and clearance in sheep

The plasma osteocalcin (OC) concentration correlates with histological parameters of bone formation and has been used as an index of osteoblast activity. Although the rate of OC synthesis is likely to be a major determinant of the plasma OC level, the contribution of other processes, for example, OC plasma clearance, should be evaluated if changes in the plasma OC concentration are to be interpreted meaningfully. We have treated oophorectomized sheep with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and glucocorticoids to alter the plasma OC concentration and used an 125I-OC infusion method to measure changes in the OC plasma clearance (PCR) and to calculate production (PPR) rates. 1,25-(OH)2D3 (8 micrograms/day by iv injection) increased plasma OC levels from 15.8 +/- 2.1 to 52.7 +/- 5.3 ng/ml (n = 10; P less than 0.0005) and the OC PPR from 0.9 +/- 0.08 to 2.6 +/- 0.17 mg/day (n = 5, P less than 0.0005). There was no effect on the OC PCR. Both triamcinolone acetonide (TA) and cortisol, administered by iv infusion, decreased the plasma OC concentration to less than 4 ng/ml and the OC PPR to less than 0.4 mg/day when infused in the doses 0.05-1.0 mg/h (TA) and 2.0 mg/h (cortisol). TA (0.05 mg/h) decreased plasma OC to an undetectable level within 24 h. The effect of cortisol infusion on the plasma OC level and the OC PPR was dose dependent in the range 0.2-2.0 mg/h. TA, infused at the rates of 0.25 and 1.0 mg/h, increased the OC PCR from 3.0 +/- 0.10 to 4.0 liters/h (P less than 0.005; n = 4) and from 2.6 +/- 0.10 to 3.9 +/- 0.10 liters/h (P less than 0.01; n = 3), respectively. It is concluded that the OC PPR and the plasma OC concentration in sheep are responsive to treatment with 1,25-(OH)2D3 and glucocorticoids. Although the changes in plasma OC concentration were attributable largely to effects on OC production, high infusion rates of the glucocorticoid TA led to a highly significant increase in OC plasma clearance. These findings suggest that alterations in OC clearance may contribute to the changes in plasma OC levels seen in some disease states, for example, glucocorticoid excess.

Renal effects of atrial natriuretic factor (99-126) in water-deprived sheep

1. The renal response to renal arterial infusion of synthetic human atrial natriuretic factor (ANF) (99-126) at 50 micrograms/h was examined in conscious sheep dehydrated by 48 h water deprivation and was compared with the response of normally hydrated animals. 2. Renal arterial infusion of ANF produced increases in the excretion of Na, K, Ca and urine in both dehydrated and normally hydrated animals, although the effect was significantly blunted in dehydrated animals compared with normally hydrated animals. 3. The attenuation of renal effects of ANF in dehydrated animals is probably due to the negative sodium and/or fluid balance of the dehydrated animals.

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.

Digoxin enhances the pressor response to aldosterone administration in conscious sheep

1. This study examined the hypothesis that inhibition of Na,K ATPase with digoxin would enhance the pressor response to aldosterone infusion in conscious sheep. 2. While intravenous infusion of digoxin (10 micrograms/kg per day for 5 days) had no effect on blood pressure and aldosterone infusion (6 micrograms/kg per day for 5 days) increased blood pressure by 7 mmHg, combined infusion of digoxin and aldosterone increased blood pressure by 17 mmHg. 3. The metabolic effects of the combined digoxin and aldosterone infusion were similar to those for aldosterone alone, suggesting that digoxin did not enhance the mineralocorticoid action of aldosterone. 4. The results of this study suggest that changes in Na influx (aldosterone-dependent) and efflux (digoxin-dependent) are important in the genesis of aldosterone-induced hypertension.

Central effect of the enkephalin analogue FK-33824 on vasopressin secretion in conscious sheep

The role of opioids in the regulation of arginine vasopressin release from the posterior pituitary is a subject of controversy. In the present study, we examined the effects of central administration of met-enkephalin, leu-enkephalin, the enkephalin analogue FK-33824, and the opiate antagonist naloxone, and the effects of systemic administration of met-enkephalin and FK-33824 on AVP secretion in conscious normal sheep. Intracerebroventricular infusion of FK-33824 significantly increased the plasma concentration of immunoreactive AVP in a dose-dependent manner, but met-enkephalin, leu-enkephalin and naloxone failed to change plasma concentration of AVP. Intravenous infusion of met-enkephalin and FK-33824 also failed to change plasma concentration of AVP. The opiate antagonist naloxone given both centrally and systemically attenuated the increase in plasma concentration of AVP induced by FK-33824. We conclude that basal AVP release is stimulated by central administration of FK-33824.

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.

Dexamethasone suppression in essential hypertension: effects on cortisol and blood pressure

Hypothalamic-pituitary-adrenal axis (HPA) function was examined in normotensive (n = 20) and hypertensive (n = 16) men, by measurement of basal cortisol levels, diurnal variation and the response to dexamethasone suppression. Comparison between groups did not reveal any differences in basal cortisol concentrations, in their diurnal variation, or in response to dexamethasone suppression. In separate studies, treatment with dexamethasone did not alter blood pressure in normal men (n = 6) but produced a small fall in pressure in hypertensive subjects (n = 8), compatible with the notion that the HPA might contribute to blood pressure elevation in some subjects with essential hypertension.

Effects of enkephalins and the analogue FK-33824 on mean arterial pressure and heart rate in conscious sheep

Experiments were designed to evaluate the central and systemic effects by enkephalins and the enkephalin analogue FK-33824 on mean arterial pressure (MAP) and heart rate (HR) in conscious sheep. Intracerebroventricular infusion of FK-33824 increased both MAP and HR in a dose-dependent manner in normal sheep. The increases in MAP and HR were attenuated by naloxone administered centrally, but not systemically. Intracerebroventricular infusion of met-enkephalin, leu-enkephalin and naloxone failed to change both MAP and HR significantly. However, intravenous infusion of met-enkephalin, leu-enkephalin and FK-33824 resulted in bradycardia. Haemorrhage alone decreased both MAP and HR. Intracerebroventricular infusion of FK-33824 blunted the reduction in MAP in response to haemorrhage. The increases in MAP and HR following FK-33824 were also accompanied by elevated levels of plasma renin concentration. It is suggested that the tachycardia and pressor effect produced by the intracerebroventricular administration of FK-33824 in normal conscious sheep may result from a combined action of both neural and chemical pathways which are involved in cardiovascular control, and are mediated via the mu-opioid receptors. Opioids may have opposite effects on cardiovascular control depending on the route of administration.

Understanding the mechanism of adrenocortical steroid hypertension

Studies of the mechanism of ACTH induced hypertension in sheep have led to the hypothesis that adrenocortical steroids may raise blood pressure by a "hypertensinogenic" action which can be distinguished from effects mediated by occupancy of classical mineralocorticoid or glucocorticoid receptors. This concept is supported by recent structure-activity studies using synthetic and naturally occurring steroids. Development of steroid hypertension is rapid (4-6 h) and although associated with an increase in cardiac output, changes in total peripheral resistance are important. Many different mechanisms have been proposed to explain how steroids raise blood pressure. In sheep it has been shown that the autonomic nervous system and vasoactive prostanoids appear to buffer, rather than cause, the rise in blood pressure. The renin-angiotensin system, AVP and serotonin are also unlikely to be involved. Further, the effects of steroids on blood pressure are not simply related to effects on Na status and changes in body fluid volumes. A direct involvement of the central nervous system remains to be established. In understanding how ACTH raises blood pressure, studies in sheep have shown that it is important to try and dissociate the effects of steroids involved in development of hypertension from the many other actions of steroids.

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 cardiovascular effects of human calcitonin gene-related peptide in conscious sheep

Calcitonin gene-related peptide (CGRP) is localized in nerve fibres in close association with the vasculature. The in vivo effect of human CGRP upon the cardiovascular system was investigated by intravenous infusion of CGRP into seven conscious sheep at doses of 1.5 and 10-pmol/kg per min for 75 min. CGRP at the 5- and 10-pmol/kg per min infusions decreased mean arterial pressure (maximal decrease of 10 mmHg) and stroke volume (maximal decrease of 42 ml/min), and increased heart rate by 60 beats/min. No changes in cardiac output were observed and total peripheral resistance only fell with the 5-pmol/kg per min infusion. Increases in both plasma arginine vasopressin and plasma renin concentration and a decrease in total and ionized plasma calcium were also observed. CGRP appears to be a potent vasodilator acting upon both arterioles and capacitance vessels in vivo.

Met-enkephalin and the enkephalin analogue FK-33824 centrally inhibit adrenocorticotrophic hormone secretion in sheep

1. The effects of central administration of met-enkephalin, leu-enkephalin, the enkephalin analogue FK-33824 and the opiate antagonist naloxone on plasma concentration of adrenocorticotrophic hormone (ACTH) were examined in conscious sheep. 2. Intracerebroventricular infusion of met-enkephalin and FK-33824 significantly decreased the basal plasma concentration of ACTH. 3. Intracerebroventricular infusion of FK-33824 inhibited the haemorrhage-induced increase in plasma concentration of ACTH. 4. Intracerebroventricular infusion of naloxone attenuated the central inhibition of plasma concentration of ACTH induced by FK-33824, but intravenous infusion of naloxone had no effect on the reduction in plasma concentration of ACTH induced by FK-33824. 5. These studies suggest that in sheep met-enkephalin may play a central inhibitory role in the control of ACTH secretion.

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.

Effect of potassium loading on bone sodium and total exchangeable sodium in sheep

1. The effect of potassium (K) loading for 10 days on bone sodium (Na) and total exchangeable Na in sheep was examined. 2. There were no significant changes in Na space or exchangeable Na after K loading. 3. Bone Na concentration decreased by approximately 20% after K loading. 4. The degree of mobilization of Na from both the non-exchangeable and exchangeable pools in bone is sufficient to account to a large degree for the observed increase in extracellular fluid volume and the net negative sodium balance which is observed during K loading.

Renal effects of atrial natriuretic factor (99-126) in conscious sodium-replete sheep

1. The effect of renal arterial infusion of synthetic human atrial natriuretic factor (ANF (99-126] on renal function in the conscious euvolaemic sheep was characterized. ANF (99-126) was infused for 2 h at 5 and 50 micrograms/h into the renal artery of crossbred Merino ewes with chronically indwelling cannulae inserted in the renal artery. The effect on absolute and fractional excretion of Na, K, Ca, Cl and HCO3, glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and free water clearance (CH2O) were measured. 2. Infusion at 50 micrograms/h produced a fourfold increase in Na and Cl excretion. Ca excretion increased eightfold, while K and HCO3 increased by small amounts. At the lower dose only Na, Cl and Ca excretion increased significantly. The changes in absolute excretion of each ion were closely mirrored by changes in fractional excretion. CH2O became more negative at both levels of infusion. Small changes in GFR were measured at both rates of infusion. No changes in ERPF or renin secretion were observed. 3. ANF (99-126) infusion at 50 micrograms/h for 1 h increased the excretion of Li, such that more than 70% of the change in Na excretion was associated with the changes in Li clearance. Changes in GFR accounted for less than 10% of change in Na excretion. 4. Following either long-term (50 micrograms/h for 6 h) or repeated short-term (20 micrograms/h for 30 min) infusions of ANF (99-126), the response of Na excretion was not sustained. The mechanisms of the tachyphylaxis remains undetermined. 5. ANF (99-126) is a powerful stimulus to the absolute and fractional excretion of Na, K, Ca, Cl and HCO3. The mechanism of action is not known, but appears to be related to changes in tubular function and/or a change in glomerulotubular balance.

Cyclosporin A and pressor responsiveness in sheep

Pressor response to graded infusion of angiotensin II, noradrenaline, arginine-vasopressin, and serotonin and blood pressure change following indomethacin, an inhibitor of cyclooxygenase, were examined in conscious sheep, before and during the development of cyclosporin A-induced hypertension. Cyclosporin caused an increase in mean blood pressure from 68 +/- 2 to 82 +/- 3 mm Hg (p less than 0.001) and in heart rate from 67 +/- 4 to 91 +/- 4 beats/min (p less than 0.001). Pressor and heart rate responses to all substances tested were not changed by cyclosporin treatment suggesting that changes in pressor responsiveness are unlikely to be involved in the development of cyclosporin hypertension in sheep.

Dihydrocyclosporin D in sheep: haemodynamic and renal effects

1. This study was designed to test the haemodynamic and renal effects in sheep of dihydrocyclosporin D (dCyD), an immunosuppressant agent derived from the fungus Tolypocladium inflatum Gams. 2. dCyD was infused for 5 days at 12 mg/kg per day. Mean arterial pressure (MAP) was elevated after 24 h, but thereafter returned to control levels. Heart rate was significantly elevated throughout the infusion and was still high 24 h postinfusion. Cardiac output rose after 5 days, but total peripheral resistance was unchanged during the infusion. 3. Glomerular filtration rate, renal blood flow and effective renal plasma flow remained unchanged, although urine sodium excretion rose for the first 48 h. 4. Infusion of the castor oil-based vehicle for cyclosporin, Cremaphore EL, for 5 days in four sheep did not produce any sustained changes in any of the parameters measured.

Role of Ca2+ in response of aldosterone to stimulation by angiotensin II in vivo

The role of Ca2+ in stimulation of aldosterone secretion (ASR) has been evaluated in vivo using conscious sheep with an adrenal cervical autotransplant. The calcium antagonists verapamil, nisoldipine, and lanthanum and the calcium ionophore BAY K 8644 were infused into the adrenal arterial supply before or concomitantly with angiotensin II. Nisoldipine reversed stimulation of ASR (n = 4) from 13.6 +/- 3.2 to 4.8 +/- 1.2 nmol/h (P less than 0.01; control 2.3 +/- 0.6 nmol/h), as did verapamil. Lanthanum had an intermediate effect. In contrast, pretreatment with nisoldipine (n = 5) did not affect the response to angiotensin II, with ASR being 3.8 +/- 0.9 nmol/h after nisoldipine alone and 12.8 +/- 1.3 nmol/h after nisoldipine plus angiotensin II. In response to graded infusion of angiotensin II, nisoldipine blunted (P less than 0.01) to a small degree the response at all doses of the peptide. Close adrenal arterial infusion of the ionophore BAY K 8644 similarly reversed stimulation of ASR by angiotensin II. It also blocked the initiation of response to the peptide. These data are consistent with the involvement of two pools of calcium in the zona glomerulosa response to angiotensin II, an intracellular pool that is primarily responsible for the initiation of response and a transmembrane extracellular pool that is primarily involved in the "sustained" response to angiotensin II.

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.

Effects of indomethacin on steroid-induced changes in pressor responsiveness in man

1. It has been shown previously that hydrocortisone (F) increases pressor responsiveness in normal subjects. The present study examined the role of vasodilator prostanoids in determining these changes. 2. Pressor responsiveness to angiotensin II (AII) (1-8 ng/kg per min) and phenylephrine (PE) (0.3-0.9 microgram/kg per min) was examined in six normal men receiving: no treatment (day 1); 100 mg indomethacin p.o. (INDO) in three divided doses over 20 h (day 2); 200 mg F for 5 days, 50 mg 6 hourly p.o. (day 6); F plus 100 mg INDO (day 7). 3. Blood pressure, body weight and plasma glucose rose with F and plasma potassium fell. F alone produced significant increases in response to AII at 2 ng/kg per min, for systolic pressure (SBP), diastolic pressure (DBP) and mean arterial pressure (MAP), and at 1 ng/kg per min for DBP. The threshold for SBP, DBP and MAP rises with AII was decreased by F. Responses to PE following F were greater at 0.6 microgram/kg per min for SBP, DBP and MAP and the threshold for all parameters fell. 4. INDO alone had no significant blood pressure or metabolic effects and no effect on the magnitude of the blood pressure rise with AII, but decreased the threshold dose for effects on MAP. INDO had no effect on the magnitude of the pressure rise with PE, but decreased the threshold dose for effects on SBP. 5. INDO did not modify responsiveness or threshold to AII following F. Responsiveness to PE was unchanged and threshold fell for SBP only during INDO.(ABSTRACT TRUNCATED AT 250 WORDS)