The effects of chronic hypoxia on renal function in the rat

1. Studies were performed on rats that had been made chronically hypoxic (CH rats) in a normoxic chamber at 12% O2 for 3-5 weeks. Under Saffan anaesthesia, respiratory and cardiovascular variables, renal haemodynamics and renal function were recorded while the rats spontaneously breathed 12% O2 followed by a switch to air breathing for 20 min. Plasma renin activity was assessed by radioimmunoassay of angiotensin I. Plasma atrial natiruetic peptide (ANP) was indirectly assessed by measurement of cyclic GMP in urine. 2. When breathing 12% O2, CH rats showed hyperventilation and raised haematocrit (52%) relative to normoxic (N) rats. But arterial pressure (ABP), renal blood flow (RBF), renal vascular conductance (RVC), mean right atrial pressure (mRAtP), urine flow, glomerular filtration rate (GFR) and absolute sodium excretion (UNaV) were comparable to those recorded in N rats breathing air. Urinary cGMP was 40% greater than in N rats, but plasma renin activity was not significantly greater in CH than in N rats. 3. Air breathing in CH rats induced hypoventilation, a 12% increase in ABP, no change in mRAtP, RBF or GFR, but increases of 75 and 100% in urine flow and UNaV, respectively. Neither urinary cGMP nor plasma renin activity changed. Such increases in urine flow and UNaV were absent when renal perfusion pressure (RPP) was prevented from rising during air breathing by using an occluder on the dorsal aorta. 4. We propose that by 3-5 weeks of chronic hypoxia renal function was normalized, principally because arterial O2 content was normalized by the increase in haematocrit and because ABP and renal haemodynamics were normalized: acute hypoxia in N rats produces a fall in ABP. We suggest that plasma ANP was raised by the actions of hypoxia or erythropoietin on the atrium, rather than by atrial distension, but suggest that ANP had little direct influence on renal function and tended to limit the influence of the renin-angiotensin system. We further propose that the diuresis and natriuresis seen during air breathing were mediated by the increase in RPP; neither plasma ANP nor renin activity change in the immediate short term.

Postural vasoconstriction and leg ulceration in homozygous sickle cell disease

1. Chronic leg ulceration is a major cause of morbidity in patients with homozygous sickle cell disease; the ulcers commonly resolve on bed rest. We have therefore compared the cutaneous vascular response to dependency in three groups of eight patients with sickle cell disease (those with an active ulcer, with an ulcer scar and with no history of ulceration) and in eight subjects with normal haemoglobin and no history of leg ulceration. 2. We monitored, with a laser Doppler flowmeter, the change in red cell (erythrocyte) flux induced in the skin of the leg, at two sites proximal to the malleoli, with the leg horizontal and 5 and 10 min after moving the leg to the dependent position. 3. With the leg horizontal, mean cutaneous red cell flux was substantially higher in normal skin of patients with sickle cell disease than in normal subjects and was higher still at the site of the ulcer or scar. On dependency, red cell flux fell not only in normal subjects but also in the patients with sickle cell disease, both in the normal skin and at the site of the ulcer or scar; there was no difference in any group between the 5- and 10-min values. The fall in red cell flux in normal skin of patients with sickle cell disease was smaller than in normal subjects when considered as a percentage of the control values (32%, 36%, 30% and 61% respectively in sickle cell patients with an active ulcer, with an ulcer scar and with no history of ulceration and in normal subjects), but in absolute terms the falls in red cell flux were similar in sickle cell patients and normal subjects. By contrast, the fall in red cell flux at the ulcer or scar site was greater than in normal skin from sickle cell patients whether considered as a percentage of the control value (48% and 49% respectively in those with an active ulcer or ulcer scar) or in absolute terms. 4. We propose that high resting perfusion is important in patients with sickle cell disease to maintain normal integrity of cutaneous tissue and that pronounced vasoconstriction on dependency hinders the healing and encourages recurrence of leg ulcers.

Studies on the roles of ATP, adenosine and nitric oxide in mediating muscle vasodilatation induced in the rat by acute systemic hypoxia

1. In Saffan-anaesthetized rats, we have further investigated the mechanisms underlying the vasodilatation induced by adenosine in skeletal muscle by acute systemic hypoxia (breathing 8% O2 for 5 min). 2. In eleven rats the nitric oxide (NO) synthesis inhibitor nitro-L-arginine methyl ester (L-NAME, 10 mg kg-1, i.v.) reduced the increase in femoral vascular conductance (FVC) induced by hypoxia by approximately 50%. L-NAME had similar effects on the increase in FVC induced by intra-arterial (I.A.) infusion of adenosine (at 1.2 mg kg-1 min-1 for 5 min via the tail artery) and by ATP (I.A., 1 mg kg-1 min-1 for 5 min). Subsequent administration of the adenosine receptor antagonist 8-sulphophenyl theophylline (8-SPT, 20 mg kg-1, i.v.) virtually abolished the adenosine- and ATP-induced increase in FVC. 3. In a further nine rats, 8-SPT reduced the increase in FVC induced by hypoxia by approximately 50%. This remaining increase in FVC was substantially reduced by L-NAME. 4. In an additional nine rats, alpha,beta-methyleneADP (160 micrograms kg-1, i.v.) which inhibits the 5'-ectonucleotidase that degrades AMP to adenosine, reduced the peripheral vasodilatation (fall in arterial blood pressure, ABP) induced by ATP infusion, but had no effect on the increase in FVC or decrease in ABP evoked by systemic hypoxia. 5. These results provide the first evidence that the muscle vasodilatation induced by adenosine during systemic hypoxia is mainly dependent on NO synthesis. They also suggest that adenosine is released as such rather than being formed extracellularly from AMP. Given evidence that extraluminal adenosine acts in an NO-independent fashion we propose that hypoxia releases adenosine from the endothelium. Our results also indicate that hypoxia induces muscle vasodilatation that is adenosine independent but NO dependent: they allow the possibility that this is partly mediated by ATP released from the endothelium.

Postnatal development of the pattern of respiratory and cardiovascular response to systemic hypoxia in the piglet: the roles of adenosine

1. In 3-day-old and 3-week-old spontaneously breathing piglets anaesthetized with Saffan, we have studied ventilatory and cardiovascular responses evoked by 5 min periods of hypoxia (breathing 10 and 6% O2). 2. In 3-day-old piglets both 10 and 6% O2 evoked an increase followed by a secondary fall in ventilation, a gradual tachycardia and a renal vasoconstriction, with an increase in femoral blood flow that was attributable to femoral vasodilatation. Arterial blood pressure rose initially but fell towards control values by the 5th minute of hypoxia. 3. The stable adenosine analogue 2-chloroadenosine (2-CA; 30 mg kg(-1) i.v.) evoked bradycardia and renal vasoconstriction, but had no effect on femoral vasculature. These responses were blocked by the adenosine receptor antagonist 8-phenyltheophylline (8-PT; 8 mg kg(-1) i.v.). 8-PT also abolished the secondary fall in ventilation evoked by 10 and 6% O2 and the renal vasoconstriction evoked by 10% O2, but had no effect on the tachycardia, or on the femoral vascular response. 4. By contrast, in 3-week-old piglets both 10 and 6% O2 evoked a sustained increase in ventilation, tachycardia and a rise in arterial pressure with renal vasoconstriction, but no change in renal blood flow and substantial femoral vasodilatation with an increase in femoral blood flow. 2-CA evoked bradycardia and renal vasoconstriction, as in 3-day-old piglets, but also evoked pronounced femoral vasodilatation. 8-PT blocked these responses and the hypoxia-induced femoral vasodilatation, but had no significant effect on other components of the hypoxia-induced response. 5. We propose that there is postnatal development of the ventilatory and cardiovascular responses evoked by systemic hypoxia and of the role of locally released adenosine in these responses: at 3 days, adenosine released within the central nervous system and within the kidney is a major contributor to the secondary fall in ventilation and renal vasoconstriction respectively, whereas at 3 weeks, adenosine makes little contribution to the ventilatory response, or renal vasoconstriction, but is largely responsible for hypoxia-induced vaso-dilatation in skeletal muscle.

The domain organization of streptokinase: nuclear magnetic resonance, circular dichroism, and functional characterization of proteolytic fragments

Streptococcus equisimilis streptokinase (SK) is a bacterial protein of unknown tertiary structure and domain organization that is used extensively to treat acute myocardial infarction following coronary thrombosis. Six fragments of SK were generated by limited proteolysis with chymotrypsin and purified. NMR and CD experiments have shown that the secondary and tertiary structure present in the native molecule is preserved within all fragments, except the N-terminal fragment SK7. NMR spectra demonstrate the presence in SK of three structurally autonomous domains and a less structured C-terminal "tail." Cleavage within the N-terminal domain generates an N-terminal fragment, SK7, which remains noncovalently associated with the remainder of the molecule; in isolation, SK7 adopts an unfolded conformation. The abilities of these fragments to induce active site formation within human plasminogen upon formation of their heterodimeric complex were assayed. The lowest mass SK fragment exhibiting Plg-dependent activator activity was shown to be SK27 (mass 27,000, residues 147-380), which contains both central and C-terminal domains, although this activity was reduced approximately 6,000-fold relative to that of full-length SK. The activity of a 36,000 mass fragment, SK36 (residues 64-380), which differs from SK27 in possessing a portion of the N-terminal domain, was reduced to 0.1-1.0% of that of SK. Other fragments (masses 7,000, 11,000, 16,000, 17,000, 25,000, and 26,000), representing either single domains or single domains extended by portions of other domains, were inactive. However, SK7 (residues 1-63), at a 100-fold molar excess concentration, greatly potentiated the activities of SK27 and SK36, by up to 50- and > 130-fold, respectively. These findings demonstrate that all of SK's three domains are essential for native-like SK activity. The central and C-terminal domains mediate plasminogen-binding and active site-generating functions, whereas the N-terminal domain mediates an activity-potentiating function.

The behaviour of muscle microcirculation in chronically hypoxic rats: the role of adenosine

1. In rats housed in a hypoxic chamber at 12% O2 for 3-5 weeks (CH) and in normal rats housed in air (N), we directly observed responses of arterial and venous vessels of the spinotrapezius muscle to changes in O2 concentration in the inspirate. Both CH and N rats were anaesthetized with Saffan. They had haematocrits of 55.0 +/- 0.9% (mean +/- S.E.M.) and 41.9 +/- 0.5%, respectively. 2. In CH rats breathing 12% O2 and N rats breathing air, arterial and venous vessels from comparable anatomical positions in the vascular tree were of similar internal diameter. They also showed similar maximum dilator responses to topical adenosine (10(-3) M); 14.1 +/- 1.1 and 16.3 +/- 1.7% in all arterioles, 15.5 +/- 1.2 and 11.5 +/- 0.6% in all venules in CH and N rats, respectively. 3. In CH rats, the change from 12% O2 to air for 3 min induced constriction in all arterioles and venules (-12.9 +/- 1.0 and -14.3 +/- 1.7%, respectively), whereas in N rats, the change from air to 12% O2 for 3 min induced net dilatation (3.9 +/- 1.8% in arterioles and 4.7 +/- 0.8% in venules). Topical application of the adenosine receptor antagonist 8-sulphophenyltheophylline (8-SPT, 10(-3) M) had no effect on control diameters in CH or N rats, nor on constrictor responses to air in CH, but reversed or reduced dilator responses to 12% O2 in N rats (to -2.4 +/- 1.3% in arterioles and 2.0 +/- 0.9% in venules). 4. In CH rats, the change from 12 to 8% O2 produced net dilatation as great as that induced in N rats by the larger change from air to 8% O2: 8.5 +/- 2.6 and 5.0 +/- 3.7% in arterioles and 10.3 +/- 1.8 and 6.4 +/- 1.9% in venules, respectively. These responses were similarly reduced by 8-SPT to -4.3 +/- 1.9 and -5.2 +/- 2.7% in arterioles and to -6.9 +/- 2.0 and -1.5 +/- 2.0% in venules, respectively. 5. These results indicate that CH rats were acclimated to 12% O2 such that the resting tone of arterial and venous vessels of muscle was comparable to that of N rats breathing air. They also suggest that adenosine had little tonic dilator influence in CH rats breathing 12% O2 despite its contribution to the dilatation induced in N rats by acute exposure to 12% O2. This may reflect the greater haematocrit in CH rats which normalized the O2 supply to muscle. However, CH rats were more sensitive than N rats to the dilator influence of acute systemic hypoxia and this was largely mediated by adenosine.

Skeletal Muscle Vasculature and Systemic Hypoxia

Studies involving recordings of gross muscle blood flow and intravital microscopy have been used to analyze the behavior of muscle vasculature during systemic hypoxia. The roles of sympathetic nerve activity, circulating hormones (e.g., catecholamines, angiotensin, vasopressin), and locally released adenosine and K+ in determining the behavior of arterial and venous vessels are considered.

The role of adenosine in mediating vasodilatation in mesenteric circulation of the rat in acute and chronic hypoxia

1. We have compared the roles of adenosine in mediating dilator responses to acute hypoxia in mesenteric microcirculation of control, normoxic (N) rats and in chronically hypoxic (CH) rats kept in an hypoxic chamber at 10% O2 for 3-4 weeks. 2. In fifteen N rats, acute hypoxia (breathing 6% O2 for 3 min) induced mean increases in the diameter of arterial vessels of mesentery (whose internal diameter was 10-350 microns) of 8.0 +/- 1.9% (mean +/- S.E.M.) and of venous vessels (whose internal diameter was 12-360 microns) of 10.4 +/- 2.6%. These diameter changes were reduced by approximately 30% when the adenosine receptor antagonist 8-sulpho-phenyltheophylline (8-SPT, 10(-3) M) was applied topically to the mesentery. 3. In a further six N rats, topical application of graded concentrations of adenosine (10(-7)-10(-3) M) to the mesentery evoked graded increases in the diameter of all arterial and venous vessels, maximum increases with 10(-3) M being 12.5 +/- 3.3 and 8.4 +/- 4.3%, respectively; these responses were abolished by 8-SPT. 4. By contrast, in fourteen CH rats, the smaller change in inspirate from 10 to 8% O2 induced increases in diameter of arterial and venous vessels which had control diameters that were comparable to those of N rats, of 14.1 +/- 2.4 and 12.9 +/- 2.7%, respectively, and which were virtually equivalent to the responses induced by topical application of 10(-3) M adenosine (13.3 +/- 1.3 and 16.3 +/- 2.0% in arterial and venous vessels, respectively). The changes induced by acute hypoxia were abolished by 8-SPT, as were those induced by adenosine. 5. These results suggest that in the intestinal mesentery, where the blood vessels have negligible tissue parenchyma around them, locally released or synthesized adenosine makes a substantial contribution to the dilatation that is evoked in arteriolar vessels by acute hypoxia and to the active dilatation, or passive distension of the venous vessels. The results also suggest that this contribution is accentuated in chronic hypoxia either by greater release of adenosine or greater vascular sensitivity to it.

The effects of systemic hypoxia on renal function in the anaesthetized rat

1. In rats anaesthetized with Saffan, renal function was monitored from the left kidney from the 5th minute of spontaneous breathing of 12% O2 for two 20 min periods and during air breathing before, between and after the hypoxic periods. Two groups of animals (I and II) were used, each group comprising two subgroups in which the left kidney was innervated or denervated, respectively; in Group II, renal perfusion pressure (RPP) was maintained during the 2nd hypoxic period by occl97uding the distal aorta. 2. In both subgroups of Group I, both hypoxic periods produced hyperventilation, arterial PO2 falling to approximately 50 mmHg. Concomitantly, mean arterial pressure (MABP) fell by similar extents (approximately 23%, from a baseline level of 140 mmHg during the 2nd hypoxic period). In the innervated subgroup, renal vascular conductance (RVC) increased, but glomerular filtration rate (GFR) fell (by 48 and 6%, respectively, during the 2nd hypoxic period), while urine flow, absolute sodium excretion (UNaV) and fractional sodium excretion (FENa) fell (by 52, 63 and 61%, respectively). Baseline urine flow, UNaV and FENa were higher in the denervated subgroup, but hypoxia produced similar percentage changes from baseline in all variables. 3. In Group II, both subgroups showed similar changes during the 1st hypoxic period as the corresponding subgroups of Group I. However, during the 2nd hypoxic period when the fall in MABP was reduced to approximately 7%, the increase in RVC persisted only in the denervated subgroup; there was no significant change in GFR, urine flow, UNaV or FENa in either subgroup. 4. These results indicate that, in the rat, moderate hypoxia produces antidiuresis and antinatriuresis that are not dependent on the renal nerves, but are dependent on the hypoxia-induced fall in MABP. The fall in renal perfusion pressure (RPP) may directly determine renal function, but reflex influences upon the kidney initiated by, for example, arterial baroreceptor unloading, may play a role. The fall in GFR and increase in RVC, which persisted after denervation or when renal perfusion was controlled, implies a local dilatatory influence acting preferentially on the efferent arterioles.

A study on rats of the effects of chronic hypoxia from birth on respiratory and cardiovascular responses evoked by acute hypoxia

1. Comparative studies were performed on eighteen rats 54 days old made chronically hypoxic from birth in an hypoxic chamber at 12% O2 (CHB), and in eight weight-matched control rats (NB, 42 days old); both CHB and NB rats were anaesthetized with Saffan. 2. In NB rats, breathing 12 or 8% O2 for 5 min induced a pattern of response comparable to that described in older rats (10-11 weeks old): an initial increase and secondary fall in minute volume (VE), a fall in arterial pressure (ABP), an increase in muscle vascular conductance, while cerebral blood flow (CBF) increased at the 1st minute in six animals and fell by the 5th minute in all animals. The adenosine receptor antagonist 8-phenyl-theophylline (8-PT, 10 mg kg-1) reduced the secondary fall in VE, the fall in ABP and muscle vasodilatation, indicating they were partly mediated by adenosine. 3. In CHB rats breathing 12% O2, VE was higher (277 +/- 12 vs. 204 +/- 18 ml min-1), arterial partial pressures of O2 (45 +/- 2 vs. 88 +/- 3 mmHg), CO2 (32 +/- 1 vs. 44 +/- 1 mmHg) and ABP (105 +/- 5 vs. 131 +/- 5 mmHg) were lower, while muscle vascular conductance was higher (0.08 +/- 0.01 vs. 0.03 +/- 0.01 ml min-1 mmHg-1) than in NB rats breathing air; these differences were reduced, but not abolished, when CHB rats acutely breathed air for 5 min. 4. In CHB rats, the smaller change from 12 to 8% O2 for 5 min evoked a similar pattern of response to that evoked by 8% O2 in NB rats, except that heart rate (HR) and CBF decreased progressively. However, 8-PT increased baseline VE and reduced ABP in 12% O2 and reduced the secondary decrease in VE and HR evoked by 8% O2, but had no effect on the fall in ABP, or change in muscle vascular conductance. 5. We propose that in CHB rats (i) there is accentuation of the components of the response to acute hypoxia (the fall in ABP, HR and CBF) that form a positive feedback loop which promotes central ventilatory depression and (ii) that adenosine exerts a tonic inhibitory influence on VE and vasodilator influence in muscle and mediates the secondary fall in VE, but not the muscle vasodilation induced by acute hypoxia.

Daily variability in resting levels of cardiovascular variables in normal subjects and those with homozygous sickle cell disease

Measurements were made of cardiovascular variables and oral temperature in 16 male subjects with homozygous sickle cell disease (SS) and in 17 matched controls (AA) at 10.00 a.m., 1.00 p.m. and 4.00 p.m. All subjects were in a rested state throughout. At 10.00 a.m., mean arterial pressure was lower, while heart rate, total forearm blood flow and cutaneous red cell flux in the forearm were higher in SS than AA. Vascular resistance in total forearm and forearm skin, calculated by dividing arterial pressure by blood flow or red cell flux, were lower in SS but hand cutaneous red cell flux and vascular resistance were not significantly different in SS and AA. In both SS and AA, there were parallel increases over the three sessions, in mean arterial pressure (by approximately 12 and 10%, respectively) forearm vascular resistance (by approximately 17 and 27%) and hand cutaneous vascular resistance and hand cutaneous resistance (by approximately 2240 and 350%) whereas forearm blood flow and hand cutaneous red cell flux fell. By contrast, forearm cutaneous resistance showed no change during the day in SS, but increased progressively in AA (by approximately 75%). These results indicate that, during the day, there is progressive vasoconstriction in forearm muscle and hand skin in SS and AA and also in forearm skin of AA that contributes to a progressive rise in the resting level of mean arterial pressure. We suggest this daily variability should be considered in studies of cardiovascular function: within a given study they should be performed at the same time of day.

G protein expression and second messenger formation in human granulosa cells

The expression of heterotrimeric (alpha beta gamma subunits) GTP-binding regulatory proteins (G proteins) and the activation of G protein-linked receptors in human granulosa cells were investigated. The cells were obtained from stimulated follicles in women undergoing in vitro fertilization and were cultured in serum-supplemented medium. Immunoblotting with specific antibodies showed that granulosa cell membranes express alpha s, alpha i3 alpha i1,2, alpha q,11 and beta subunits. Three antibodies against alpha o failed to detect this protein. The cells responded to hCG and to prostaglandin E2 with a dose-dependent increase in cAMP formation, confirming the functional activation of G alpha s. The alpha 2 adrenoceptor agonist, clonidine, inhibited hCG-stimulated cAMP formation and this effect was blocked with pertussis toxin, thus involving a Gi-type protein, most likely G alpha i2. Oxytocin provoked an increase in formation of inositol phosphates and intracellular calcium concentration, which was partly pertussis toxin resistant, providing evidence of G alpha q,11 activation. However, a significant component of the response to oxytocin could be blocked by pertussis toxin, indicating Gi-mediated phospholipase C activation (by either alpha i or beta gamma subunits). These data demonstrate the presence of G proteins in granulosa cells and suggest a complex regulation of hormonal signalling. The concentration of cAMP in these cells depended on the balance of G alpha s:G alpha i activation, whereas activation of the inositol phospholipid pathway and rises in intracellular calcium involved both Gq,11 and Gi pathways.

Analysis of responses observed in mesenteric microcirculation of the rat during systemic hypoxia

1. Direct observations were made of responses to systemic hypoxia (breathing 12 or 6% O2 for 3 min) evoked in terminal arterioles (TA, 14-30 microns internal diameter), precapillary arterioles (PCA, 8-18 microns), collecting venules (CV, 12-30 microns) and small veins (SV, 20-50 microns) of the mesenteric circulation of the anaesthetized rat. Changes in vessel diameter were recorded before and after local blockade of alpha-adrenoreceptors with phentolamine when the mesentery was covered with Saran Wrap, which is impermeable to O2, and then after removal of the Saran Wrap, which would have kept local PO2 relatively high even during systemic hypoxia. 2. The majority of TA showed an initial decrease in diameter of 14 +/- 1% (mean +/- S.E.M.). These responses were reversed to increases in diameter (12 +/- 2%) after phentolamine, but virtually abolished after removal of the Saran Wrap (0.3 +/- 2%). 3. Some PCA showed similar behaviour to the TA; others showed an increase in diameter (11 +/- 1%). The increases in diameter were accentuated after phentolamine (16 +/- 1%), but were reduced after removal of the Saran Wrap (6 +/- 2%). 4. CV and SV showed either a decrease in diameter followed by relaxation towards control levels, or an increase in diameter that waned before hypoxia ceased (6 +/- 1% and 1 +/- 1%, respectively). The responses of CV were not altered by phentolamine (8 +/- 1%), but SV showed larger increases in diameter (5 +/- 1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasminogen activators in ectopic and uterine endometrium

OBJECTIVE

To investigate the expression of the plasminogen activator (PA)-plasmin system components in ectopic endometrium and in uterine endometrium from women with and without endometriosis.

DESIGN

Plasminogen, PAs (urokinase and tissue plasminogen activator), and PA inhibitors (1 and 2) were detected by immunohistochemistry using a alkaline phosphatase staining method.

RESULTS

No differences in staining were found between uterine endometrium of women with endometriosis and women without endometriosis with any of the antibodies used. However, we did find differences between uterine and ectopic endometrium. Although the expression of the components of the PA-plasmin system reflected the cyclic changes in the hormonal levels in uterine endometrium, ectopic endometrium maintained a very high level of plasminogen and urokinase in every sample. We were unable to detect the presence of PA inhibitors in either uterine or ectopic endometrium.

CONCLUSIONS

There is no evidence that uterine endometrium from women with endometriosis is originally more able to implant than that of women without the disease because of an increase in their PA expression. The high levels of urokinase and plasminogen in ectopic endometrium may reflect a more invasive nature of the endometriotic implants in the peritoneal cavity.

Interdependence of respiratory and cardiovascular changes induced by systemic hypoxia in the rat: the roles of adenosine

1. In ten spontaneously breathing, Saffan-anaesthetized rats (group I), respiratory and cardiovascular responses evoked by 10 min periods of hypoxia (arterial partial pressure of O2, Pa,O2, 33 mmHg) were recorded before and after the administration of the adenosine receptor antagonist 8-phenyltheophylline (8-PT, 10 mg kg-1 i.v.). Similar experiments were performed on nine constantly ventilated rats (group II; Pa,O2, 29 mmHg) with arterial partial pressure of CO2 (Pa,CO2) held constant. 2. In group I, hypoxia induced an initial increase and a secondary fall in ventilation (VE) with an accompanying secondary fall in heart rate (HR), arterial pressure (ABP) fell and cerebral vascular conductance (CVC) increased progressively. Cerebral blood flow (CBF) tended to fall with time during hypoxia. 8-PT abolished the secondary falls in VE and HR and reduced the fall in ABP and increase in CVC, while CBF was better maintained. 3. In group II, hypoxia induced a similar cardiovascular response to that in group I, but at the 1st minute of hypoxia, the HR was lower and the increase in CVC was greater. 8-PT did not affect the hypoxia-induced changes in HR, ABP, CVC or CBF. 4. These results indicate specific ways in which the ventilatory and cardiovascular responses induced by hypoxia in the spontaneously breathing rat are interdependent. They also indicate that the influences of 8-PT on the cardiovascular changes induced by hypoxia during spontaneous ventilation are mainly a consequence of its ability to block the centrally mediated contribution of adenosine to the secondary fall in ventilation.

Substitution of arginine 719 for glutamic acid in human plasminogen substantially reduces its affinity for streptokinase

In isolation human plasminogen possesses no enzymatic activity, yet upon formation of an equimolar complex with the bacterial protein streptokinase, it acquires a plasminogen activator function. The region(s) of plasminogen and of streptokinase which mediate complex formation has (have) not been previously published. Here it is reported that a single-residue substitution (Arg719-->Glu) in the serine protease domain of full-length Glu-plasminogen substantially reduces its affinity for streptokinase. The plasminogen variant displays no other significant differences from the wild-type molecule with respect to activation by two-chain urokinase-type plasminogen activator, recognition by monoclonal antibodies, or ability to undergo conformational change. It is concluded that Arg719 in human plasminogen is an important determinant of the streptokinase binding site, although further sites are likely to contribute both to the affinity of plasminogen for streptokinase and to mechanisms by which the active site is formed within the complex.

Differentiation of the peripherally mediated from the centrally mediated influences of adenosine in the rat during systemic hypoxia

In two groups of Saffan-anaesthetized, spontaneously breathing rats we have attempted to identify the peripheral influences of adenosine in mediating the responses evoked by hypoxia by using an adenosine receptor antagonist, 8-sulphophenyltheophylline (8-SPT, 20 mg kg-1 i.v., Group 1) and adenosine deaminase (ADA, 500 units in 0.04 ml infused into the tail artery for 10 min, Group 2); neither of these drugs crosses the blood-brain barrier. Recordings were made of respiration, heart rate, arterial pressure, blood flow and vascular conductance in the femoral artery, with ankle ligated (FBF and FVC, respectively) and in the carotid artery with all branches except the internal carotid ligated (CBF and CVC, respectively, Group 1 only) in order to indicate responses in skeletal muscle and cerebral vasculature. Hypoxia (breathing 8 or 10% O2 for 10 min) evoked an increase followed by a secondary decrease in respiration, tachycardia followed by secondary bradycardia, a fall in arterial pressure, an increase in FVC and CVC and an increase, followed by a decrease, in CBF. Neither 8-SPT nor ADA had any significant effect on the secondary decrease in respiration. The secondary bradycardia was unaffected by 8-SPT, but abolished by ADA. Both drugs reduced the fall in arterial pressure and the increase in FVC; 8-SPT had no significant effect on the increase in CVC, but CBF no longer fell with arterial pressure. We propose that adenosine contributes to the hypoxia-induced fall in arterial pressure by causing vasodilatation in skeletal muscle and possibly by causing bradycardia by a direct action on the heart; other evidence suggests that adenosine contributes to the secondary decrease in respiration by acting on central respiratory neurones. The possibility that the fall in arterial pressure and the secondary falls in CBF, respiration and heart rate, can become interdependent in a positive feedback manner is discussed.

Responses evoked in the forearm vasculature on normal human subjects on repetition of mild, indirect cooling

We have studied responses evoked in the forearm vasculature of normal subjects by mild cooling of the contralateral hand; it was transferred from thermoneutral water at -33 degrees C to water at 16 degrees C for 2 min. Total forearm blood flow was measured by venous occlusion plethysmography, cutaneous red cell flux was monitored with a laser Doppler flowmeter and arterial pressure was recorded by semi-automatic sphygmomanometry. In each of two groups (I and II) of twelve and 15 subjects, mild cooling evoked a rise in mean arterial pressure, but in each group, approximately half (six and eight respectively) showed a decrease in total forearm vascular resistance (FVR) in response to the first cool immersion (dilator group), while the remainder showed an increase in FVR (constrictor group), apart from one of group II who showed no change in FVR. Cutaneous vascular resistance tended to increase in both the dilator and constrictor groups, but this did not reach statistical significance. When cooling was repeated six times in group II, the decrease in FVR (-18% from control) in the dilator group reversed to an increase in FVR (+25%) by the sixth immersion, while the increase in FVR (+55%) in the constrictor group persisted through to the sixth immersion (+23%). We propose that mild cooling evokes a primary reflex vasoconstrictor response in forearm muscles, but that this can be overcome in some subjects by the characteristic muscle vasodilatation of the alerting response which is evoked by novel, or noxious stimuli; the latter is known to habituate on repetition of the stimulus.

A comparative study in subjects with homozygous sickle cell disease and in normal subjects of responses evoked in forearm vasculature by mild, indirect cooling

We have studied responses evoked in the forearm vasculature of twelve subjects with homozygous sickle cell disease (SS) and in eight dark-skinned controls of West Indian ancestry (AA) by mild cooling of the contralateral hand in water at 16 degrees C for 2 min; this stimulus was repeated six times at randomized time intervals. Total forearm blood flow was measured by venous occlusion plethysmography, cutaneous red cell flux was monitored by a laser Doppler flowmeter and arterial pressure was recorded by semi-automatic sphygmomanometry. Of the AA subjects, three showed a decrease in total forearm vascular resistance (FVR, of -10%) in response to the first immersion and this reversed to an increase in FVR (+7%) by the sixth immersion. The remaining five showed an increase in FVR (+65%) which persisted until the sixth immersion (26%). By contrast, all SS subjects showed an increase in FVR (+32%) which persisted to the sixth stimulus (+27%). Further, on a scale of discomfort of 0-10, none of the AA subjects rated the cool stimulus higher than 0, whereas SS subjects gave a rating of 7 for the first stimulus which decreased to 5 by the sixth stimulus. Both AA and SS subjects showed an increase in arterial pressure and a tendency towards vasoconstriction in forearm skin. We propose that, as in Caucasian AA subjects, dark-skinned AA subjects showed a primary reflex vasoconstriction in forearm muscle in response to mild, indirect cooling which was overcome in some individuals by muscle vasodilation of the alerting response that is evoked by novel or noxious stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational studies of human plasminogen and plasminogen fragments: evidence for a novel third conformation of plasminogen

The conformations of Glu-plasminogen and defined proteolytic fragments, in the presence and absence of 6-aminohexanoic acid (6-AHA), trans-4-(aminomethyl)cyclohexanecarboxylic acid (t-AMCHA), and benzamidine, were studied using three methods: size-exclusion high-performance liquid chromatography (SE-HPLC), small-angle X-ray scattering (SAXS), and dynamic laser light scattering (DLLS). The well-documented conformational change of Glu-plasminogen with 6-AHA or t-AMCHA was measured as a decrease in molecular elution time by SE-HPLC (8.93 +/- 0.01 to 8.32 +/- 0.01 min) and increases in radius of gyration (30.7 +/- 0.1 to 49.8 +/- 0.3 A) and Stokes radius (40.6 +/- 0.3 to 48.5 +/- 0.3 A) by SAXS and DLLS, respectively. The addition of benzamidine to Glu-plasminogen resulted in a conformation (radius of gyration 41.0 +/- 0.4 A and Stokes radius 46.6 +/- 0.3 A) distinct from that in the presence of 6-AHA. 6-AHA, but not benzamidine, induced significant conformational changes in Lys-plasminogen and kringles 1 + 2 + 3 + 4 + 5. We conclude that Glu-plasminogen adopts three distinct conformations involving two intramolecular interactions: one mediated by regions of the NH2-terminal peptide and kringle 5, competed for by 6-AHA or benzamidine, and the other possibly between kringles 3 and 4, competed for by 6-AHA but not benzamidine.

A link between adenosine, ATP-sensitive K+ channels, potassium and muscle vasodilatation in the rat in systemic hypoxia

1. In anaesthetized rats, systemic hypoxia evoked hyperventilation, tachycardia, a fall in arterial pressure, vasodilatation in skeletal muscle and increases in K+ concentration measured in arterial plasma ([K+]a), venous efflux from muscle ([K+]v) and in right atrial plasma ([K+]at). The ATP-sensitive potassium (K+ATP) channel inhibitor glibenclamide (10 or 20 mg kg-1 i.v.) reduced the muscle vasodilatation and increase in [K+]v, but had no significant effect on the other changes. 2. The adenosine receptor antagonist, 8-phenyltheophylline (8-PT, 10 mg kg-1 i.v.) had similar effects to glibenclamide. 3. Glibenclamide reduced the muscle vasodilatation evoked by the adenosine analogue, 2-chloroadenosine given i.v. (30 micrograms kg-1). 4. Infusion of adenosine (0.3 mg kg-1 min-1 for 5 min) into the hindlimb evoked muscle vasodilatation and an increase in [K+]v, both of which were abolished by 8-PT. 5. We propose that during systemic hypoxia, part of the muscle vasodilatation that can be attributed to adenosine is due to the action of K+, which is released from skeletal muscle fibres through glibenclamide-sensitive K+ channels (possibly K+ATP channels) that are activated by adenosine. This may be a general mechanism for the vasodilator influence of adenosine.

Acute systemic hypoxia and the surface ultrastructure and morphological characteristics of rat leucocytes

We have examined the surface ultrastructure and morphological characteristics of leucocytes obtained from control rats breathing air and rats made acutely hypoxic (breathing 6% O2, for 30 min). Striking ultrastructural and morphological changes occurred in the leucocytes of hypoxic rats. These changes included the appearance of crater-like holes, a reduction in granule size and disruption of the cell membrane. The implications of these findings are discussed.