High-affinity binding sites for human Glu-plasminogen unveiled by limited plasmic degradation of human fibrin

The binding of human 125I-Glu-plasminogen to human plasmin-degraded fibrin was studied. Treatment of preformed and polymerized fibrin with 0.01 IU plasmin/ml resulted in an increased binding of 125I-Glu-plasminogen depending upon the length of time of preincubation of fibrin with plasmin. Binding reached a plateau of 30% of total added radioactivity after 60 min. At this time, less than 10% of fibrin had been digested. Polyacrylamide/urea/acetic acid gel electrophoresis revealed that the radioiodinated plasminogen bound to plasmin-degraded fibrin was of the Glu form. Computerized non-linear regression analysis of the binding experiments revealed that limited plasmic degradation of fibrin progressively generates high-affinity binding sites (Kd approximately equal to 0.3 microM) for Glu-plasminogen. At the time of maximal Glu-plasminogen binding approximately 5 high-affinity binding sites per 100 molecules of fibrin had been generated. The low-affinity type of binding sites were also identified. These observations describe a new mechanism which exquisitely modulates the plasmic breakdown of fibrin by a continuous renewal of high-affinity binding sites for Glu-plasminogen on the surface of the fibrin gel during the fibrinolytic process.

Sensitivity to noradrenaline and electrical stimulation decreases with age in the rat tail artery

We have studied vasoconstrictor responses to noradrenaline and electrical field stimulation in the isolated perfused/superfused tail arteries of rats of 6-7, 16-17 and 30-31 months of age. Maximal vasoconstrictor responses to noradrenaline were the same at all three ages. Sensitivity to noradrenaline and to electrical stimulation were reduced in the 16-17 and 30-31 month old rats. The noradrenaline content of the arteries of the two latter age groups was reduced. We conclude that aging in this resistance vessel is accompanied by a decrease in the arterial noradrenaline content and in the sensitivity of the artery to noradrenaline.

Effect of acute administration of prazosin on blood pressure, heart rate and plasma renin level in the conscious normotensive rat

This study investigated whether the specific alpha-antagonist, prazosin, stimulated basal plasma renin levels and heart rate. Furthermore the beta-adrenergic nervous system was also investigated to ascertain whether it was involved in this effect. Prazosin (0.1 or 1 mg/kg) was injected subcutaneously (s.c.) to conscious normotensive rats, either alone or in combination with the beta-adrenoceptor antagonist, DL-propranolol (1 or 3 mg/kg). Rats bore chronically implanted dorsal aorta cannula for measurement of blood pressure and heart rate and blood sampling for renin determinations. Acute administration of prazosin (1 mg/kg, s.c.) produced a fall in mean arterial pressure accompanied by renin release and tachycardia. A tenfold lower dose of prazosin did not alter blood pressure or heart rate but did stimulate renin release. Acute administration of DL-propranolol, (1 or 3 mg/kg, s.c.) produced falls in blood pressure and heart rate but did not affect plasma renin level. Combinations of prazosin with propranolol gave falls in blood pressure similar to those predicted on the basis of a simple addition of the effects of the two drugs given separately. Prazosin-induced tachycardia and renin release were attenuated by propranolol. It appears that prazosin produces renin release and tachycardia via stimulation of the beta-adrenergic adrenoceptor.

[Reduced sensitivity to noradrenaline and electric stimulation of the caudal artery of the aged rat]

Whilst arterial noradrenaline (NOR) content decreases with age (Waterson, et al. 1974; Neubauer and Christensen, 1978; Embree, et al., 1981), changes in vasoconstriction induced by NOR are equivocal (Tuttle, 1966; Cohen and Berkowitz, 1976; Scott and Reid, 1982; Duckles, et al., 1985). We have investigated changes in responsiveness to NOR in the NOR-rich rat tail artery. Two cm segments of the proximal tail artery from male Ivanos rats of 6/7, 16/17 or 30/31 months were perfused/superfused with Krebs bicarbonate (4 ml/min). Changes in perfusion pressure (mmHg) were determined after (1) electrical stimulation (1 to 30 Hz, 0.3 msec, 15 sec at supramaximal voltage, ES) followed by (2) perfusion with exogenous NOR (1 nM to 10 microM for 2 min at each concentration). Responses to ES were abolished by pretreatment with reserpine (2.5 mg/kg, i.p. at - 18 h) or perfusion with phentolamine (4 microM). They were produced therefore, by liberation of endogenous NOR. Arterial NOR content was determined by HPLC-EC following perchloric acid digestion (0.1 N).

RESULTS

(Table: see text). Asterisks refer to t-test with 6/7 months age group (p less than 0.05, p less than 0.01 and p less than 0.001]. There were no differences in basal perfusion pressure before stimulation or in plateaux responses to maximal concentrations of NOR. In conclusion our results show a decrease in arterial NOR and in sensitivity to both endogenous and exogenous NOR with age.

TL-DNA from Agrobacterium rhizogenes plasmid pRi1855 reduces the osmotic pressure in transformed plants grown in vitro

Growth, water content, osmotic pressure and solute content were examined for normal potato (Solanum tuberosum L. cv. Desiree) and a derivative (line D9X8a), which was genetically transformed with TL-DNA from Agrobacterium rhizogenes. Plants were grown (i) in vitro, (ii) in a growth chamber and (iii) in the field. In vitro, the transformed potato plants produced more biomass than the untransformed plants, partly because they had a higher water content. Potassium concentration and osmotic pressure were lower in cell sap extracted from the transformed potato shoots. In some cases the difference was as much as 50%. These differences were less clear, absent or reversed in plants from a growth chamber or from the field. In the field, however, transformed potato senesced early. It is suggested that a cellular basis for these observations may be changes induced by Ri TL-DNA expression products in plant membrane properties.

Orientation-specific cortical responses develop in early infancy

Neurones in the visual cortex of higher mammals differ from those elsewhere in the visual pathway in that the majority respond selectively to particular edge or bar orientations in the stimulus. We have developed a visually evoked potential (VEP) technique which isolates the response of orientation-selective mechanisms from that of cortical or sub-cortical neurones which lack orientation selectivity. We are unable to find such orientation-selective responses in newborn human infants within the sensitivity of our method, but repeated longitudinal testing of individual infants shows that measurable responses emerge around 6 weeks of age. This result is consistent with the idea that human cortical visual function is very immature at birth, but develops rapidly in the first two postnatal months.

Chronic clonidine treatment and its withdrawal: effects on blood pressure and catecholamine synthesizing enzymes in brain-stem nuclei

We have studied the effects of withdrawal from chronic clonidine treatment in the adult male spontaneously hypertensive rat (SHR). SHR received clonidine, 0.1 mg X kg-1 X day-1 i.v. for 10 days. Clonidine was delivered via osmotic minipumps. After 7 days of treatment there was a 16.5 +/- 2.5 mm Hg fall in mean arterial pressure. This was accompanied by a decrease in the dopamine-beta-hydroxylase and phenylethanolamine-N-methyl transferase activities of the A1/C1 region. Withdrawal from clonidine was characterized by tachycardia and an increase in mean arterial pressure and heart rate lability. Phenylethanolamine-N-methyl transferase of the the dopamine-beta-hydroxylase activity remained diminished. The dopamine-beta-hydroxylase activity of the A2/C2 region was also diminished during withdrawal. We suggest that the blood pressure lowering effect of clonidine is accompanied by a decreased capacity to synthesize adrenaline in the A1/C1 region where adrenaline could mediate a pressor effect. Increased blood pressure lability during withdrawal is accompanied by a restoration of synthesis of adrenaline in the A1/C1 region. There is also a decrease in the capacity of synthesis of noradrenaline in the A2/C2 region where adrenaline may mediate a vasodepressor effect.

Oxitropium bromide. Dose-response and time-response study of a new anticholinergic bronchodilator drug

The efficacy and side effects of oxitropium bromide, a new anticholinergic bronchodilator drug, were tested in a double-blind placebo-control study. Twenty-four men, aged 58 to 72 years, with chronic partially reversible obstruction of the airways were used as subjects. Three doses of oxitropium were tested (100 micrograms, 200 micrograms, and 300 micrograms) to determine the optimum dose by metered-dose inhaler. A comparison was also made between oxitropium, fenoterol (400 micrograms), and a combination of oxitropium (200 micrograms) and fenoterol (400 micrograms). Fenoterol produced a greater degree of maximal bronchodilatation than each of the three doses of oxitropium, and its effect was more rapid in onset (30 vs 120 minutes to peak effect); however, the duration of action of oxitropium was greater than that of fenoterol (ie, the forced expiratory volume in one second [FEV1] remained within 5 percent of peak FEV1 for three hours, compared to one hour). Oxitropium in the 100 micrograms dose was inferior to 200 micrograms and 300 micrograms in subjective efficacy scores, peak percent change in FEV1, forced vital capacity, (FVC), mean forced expiratory flow over the middle half of the FVC, and duration of action; there was no difference between 200 micrograms and 300 micrograms. The oxitropium-fenoterol combination had a rapid onset of action, and a greater peak effect was achieved than for oxitropium alone. The main unwanted effect was a mildly unpleasant taste. Anticholinergic effects were not seen in this group of elderly men. Oxitropium bromide therefore is an effective bronchodilator with slow onset but prolonged activity and few side effects when used in patients with moderately severe obstruction of the airways. An appropriate dose appears to be 200 micrograms. Addition of oxitropium to fenoterol appears to offer even greater efficacy.

Effects of inhaled oxitropium and fenoterol, alone and in combination, in chronic airflow obstruction

Twenty-four elderly male patients with moderate-to-severe chronic airway obstruction took part in a double-blind, placebo-controlled, randomized dose-response and response-duration comparison of a new inhaled anticholinergic bronchodilator oxitropium bromide and the inhaled beta-agonist bronchodilator fenoterol hydrobromide. On 6 separate days lung function changes and side effects were monitored for 8 h after either placebo, oxitropium 100, 200 and 300 micrograms, fenoterol 400 micrograms, or oxitropium 200 micrograms plus fenoterol 400 micrograms. Fenoterol alone and in combination with oxitropium produced a rapid peak effect (mean delta FEV1 = 41.6 and 39.5%, respectively at 30 min). Oxitropium alone had a slow onset of action (peak delta FEV1 seen at 120 min: 100 micrograms = 22.7%, 200 micrograms = 29.9%, 300 micrograms = 28.2%). However, mean FEV1 remained within 5% of peak for 60 min after fenoterol, but for 180 min after each dose of oxitropium and after fenoterol plus oxitropium. No differences between oxitropium 200 and 300 micrograms were seen; however, these doses produced more prolonged bronchodilatation than did oxitropium 100 micrograms. The fenoterol-plus-oxitropium combination produced even more prolonged bronchodilatation. The only side effect, seen with each inhaler was a mildly unpleasant taste. No anticholinergic effects were seen. We conclude that oxitropium is an effective bronchodilator with slow onset but prolonged duration of action. In combination with fenoterol it produced both rapid and prolonged bronchodilatation in patients with chronic airflow obstruction.

Discriminative properties of the psychostimulant dl-cathinone in a two lever operant task. Lack of evidence for dopaminergic mediation

In order to analyse further the discriminative stimulus properties of stimulant drugs, rats were trained to discriminate 2.0 mg/kg of dl-cathinone in a two-lever operant task. Dose-related generalization was seen to cathinone itself and to a wide range of stimulant drugs including d-amphetamine, cocaine, methylphenidate, pipradrol and cathine, i.e. (+)norpseudoephedrine. The high degree of specificity of the cathinone cue at the specific training dose studied was shown by the fact that the following nonstimulant drugs failed to generalize at all to cathinone, even in large doses--haloperidol, chlordiazepoxide, fenfluramine and fentanyl. The cathinone cue at 2.0 mg/kg was probably of central origin because phydroxyamphetamine (a polar congener of amphetamine) failed to generalize to cathinone at a dose nearly 50 times the ED50 for amphetamine generalization. Phenylethylamine (PEA; alpha-demethylamphetamine) and deuterated phenylethylamine (alpha, alpha, d2-PEA), a long acting derivative of phenylethylamine which is resistant to metabolism by monoamine oxidase, produced at most partial (60%) generalization to cathinone, even in large doses. alpha-Demethylcathinone failed to generalize at all to cathinone at doses up to 10 times the ED50 for cathinone. Thus, the alpha-methyl groups of both amphetamine and cathinone are important in determining their cue properties. The involvement of dopaminergic systems in the cathinone cue was investigated by examining generalization to apomorphine and antagonism by haloperidol. Apomorphine produced at most 29% generalization to cathinone. Haloperidol, at doses up to 0.3 mg/kg, produced at most 50% antagonism of both the cathinone cue and of the ability of amphetamine to substitute for cathinone. It is suggested that the evidence for dopaminergic mediation of the cue properties of cathinone and of other CNS stimulants is somewhat tenuous, whilst endogenous phenylethylamine may play some part in the mediation of the stimulant cue. Haloperidol, alone and in conjunction with amphetamine or cathinone, produced a remarkable tendency for subjects to emit a greater proportion of their total responses on the inoperative rather than the operative lever than was seen after saline or injections of vehicle. This action of a neuroleptic drug suggests, in accordance with Colpaert, Niemegeers and Janssen (1977), that in drug discrimination antagonism studies involving neuroleptics, and perhaps other drugs, quantal (lever selection) rather than quantitative (percentage of responses on the drug lever) indices may be the procedures of choice.

Development of the discrimination of spatial phase in infancy

The ability to discriminate grating patterns, containing the same spatial frequency components but in different phase relationships, has been studied in infants by comparing looking times following habituation to one pattern. The performance of 1-month-olds was compared with that of 2/3-month-old infants. Both age groups could discriminate a set of components in square-wave-phase (fundamental 0.18 c/deg) from components of the same amplitude combined in random phase. However, these compounds differ in peak-to-trough contrast, which infants of both ages could discriminate even for a constant waveform. When contrast was randomized from presentation to presentation, the older group still demonstrated discrimination, implying that they were sensitive to the pattern differences, but the younger group did not. The younger group also failed to demonstrate discrimination between the two waveforms when they were of fixed, matched, peak-to-trough contrast, indicating that the previous absence of discrimination was not simply due to distraction by the contrast variations. We conclude that 1-month-olds are insensitive to the configuration of these compound grating patterns even when they are capable of detecting their components. This loss of spatial information has some analogies with adult peripheral and amblyopic vision. Like other aspects of vision, it shows striking development between 1 and 3 months of age.

Involvement of the renin-angiotensin system in the dipsogenic effect of morphine

This paper examined whether drinking elicited by morphine is dependent upon an intact renin-angiotensin system. Bilateral nephrectomy, carried out one day prior to administration of morphine, completely abolished morphine-induced water intake, pointing to involvement of the kidneys in the dipsogenic effect of morphine. Plasma and renal renin depletion were induced by the clipping of one renal artery followed, one month later, by removal of the clipped kidney. In such renin-depleted rats with subnormal plasma renin levels, morphine and isoprenaline-induced water intakes were linearly related to pre-injection basal plasma renin level. Such a relationship was not found in rats with normal renin levels. These results pointed to the existence of a permissive interaction between morphine and the renin-angiotensin system. Captopril, an inhibitor of the angiotensin converting enzyme, increased morphine-induced water intake. We interpreted this drinking response as being the sum of morphine-induced drinking (following a permissive interaction between morphine and circulating angiotensin I or renin) and captopril-induced drinking (following a captopril-induced increase in circulating renin and angiotensin I levels). The competitive antagonist of angiotensin II, saralasin, had no effect on morphine-induced drinking. This result pointed once again to a permissive interaction between morphine and circulating angiotensin I or renin.

The effects of trimetoquinol on the intact rabbit heart and myocardial adenylate cyclase activity: evidence for spare myocardial beta receptors

We have compared and contrasted the actions of (-)isoproterenol and (+/-) trimetoquinol on rabbit heart preparations. In the presence of either GTP or Gpp[NH]p (guanosine-5'-(beta, gamma imino) triphosphate), trimetoquinol displayed partial agonist activity in stimulating adenylate cyclase activity in a particulate rabbit heart preparation. Trimetoquinol enhanced adenylate cyclase activity 20% or 65% of the maximum obtainable by isoproterenol in the presence of GTP or Gpp[NH]p respectively. In the presence of GTP, concentrations of catecholamines required to enhance cyclase activity 15% of the maximum obtainable with isoproterenol (EC15) were 2.0 X 10(-7) M and 5.5 X 10(-8) M for trimetoquinol and isoproterenol, respectively. In the presence of Gpp[NH]p EC30 values were 2.0 X 10(-7) and 3.5 X 10(-8) M for trimetoquinol and isoproterenol respectively. Trimetoquinol also displayed partial agonist activity for the ability to increase cAMP levels in the isolated perfused rabbit heart. By contrast trimetoquinol was equieffective to isoproterenol at increasing tension development and rate of contraction of the isolated perfused heart. Concentrations of catecholamines required to increase tension and rate of contraction 50% of the maximum obtainable with isoproterenol were 1.5 X 10(-7) M and 1.7 X 10(-8) M for trimetoquinol and isoproterenol, respectively. These data show that only a partial stimulation of adenylate cyclase activity and cAMP levels by trimetoquinol is sufficient to produce maximal changes in mechanical activity of the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of the baroreceptor reflex by general anesthetic agents in the normotensive rat

We have investigated the effects of urethane, a urethane + allobarbital mixture, alpha-chloralose and sodium pentobarbital on baroreceptor reflex function in the normotensive rat. Results were compared to those obtained in the conscious rat. Baroreceptor reflex function was evaluated from the fall in heart rate which accompanied the rise in diastolic arterial pressure following intravenous administration of phenylephrine. All four anesthetic agents attenuated reflex function as shown by a decrease in the bradycardiac response. There was a four to five-fold attenuation with urethane and urethane + allobarbital and a two- to three-fold attenuation with alpha-chloralose and sodium pentobarbital.

Changes in central monoaminergic function during chronic treatment with clonidine in the spontaneously hypertensive rat

Clonidine was administered intravenously via osmotic minipumps at doses of 0.1 and 0.5 mg X kg-1 X 24 h-1. Both doses lowered blood pressure to the same degree by the third day of treatment. Only the higher dose significantly lowered heart rate. There was no tolerance to these cardiovascular effects which were maintained up to the seventh day of clonidine infusion. The only clonidine-induced change in central monoaminergic function was an increase in the adrenaline levels in the hindbrain. No other changes in central monoaminergic function in either cortex or hindbrain were detected at the level of the enzymes (tyrosine hydroxylase) of the neurotransmitters (noradrenaline, dopamine) or of the adrenoceptors [( 3H]clonidine binding). Our results suggest that clonidine lowers blood pressure via inhibition of release of hindbrain adrenaline.

Receptor blockade as a mechanism of deactivation of human neutrophils by pepstatin and formyl-Met-Leu-Phe

The pentapeptide pepstatin was shown to be chemotactic for human neutrophils by two techniques: ED50 for chemotaxis was found to be 3 microM by the agarose method and 0.2 microM by the Boyden chamber technique. Pepstatin also induced superoxide radical generation, release of lysosomal enzymes, and a transient increase in intercellular adenosine-3',5'-cyclic monophosphate (cAMP) levels in a dose-dependent manner. Carbobenzoxy-phenylalanyl-methionine (CBZ-PM), which competitively inhibits formyl-methionyl-leucyl-phenylalanine (FMLP) -induced neutrophil functions, also inhibited pepstatin-induced neutrophil function of superoxide generation in a dose-dependent fashion. Likewise, pepstatin inhibited the binding of [3H]FMLP to the cells. Furthermore, preincubation of neutrophils with suboptimal concentrations of FMLP or pepstatin diminished the cellular response toward either factor when tested for their chemotactic activity and for their ability to induce superoxide generation, to release granule enzymes, and to induce a transient increase in intracellular cAMP levels. The concentrations of pepstatin or FMLP tested had no effect on superoxide generation, granule enzyme release, or intracellular levels of cAMP on subsequent challenge with C5a; both of these factors, however, cross-deactivated the chemotactic response of the cells towards C5a. Similar results were observed when cells were preincubated with C5a and subsequently challenged with pepstatin or FMLP. These results suggest that FMLP and pepstatin interact with the same receptor molecules to activate human neutrophil functions. Furthermore, our data indicate that the deactivation of the neutrophil functions of superoxide production and granule enzyme release are receptor specific, but the heterologous deactivation of chemotaxis involves a postreceptor mechanism(s).

Screening for refractive errors in 6-9 month old infants by photorefraction

The method of isotropic photorefraction has been used in a trial of refractive screening of 6-9 month old infants. Data are presented on the calibration of the method against retinoscopic measurements and its reliability. In photorefractive screening of 1096 infants under cyclopentolate cycloplegia 5% were found to be hypermetropic (over +3.5 D), 4.5% myopic, and 1.3% anisometropic (over 1 D). These refractive errors were confirmed on retinoscopic follow-up (with the exception of a few anisometropes). Follow-up of controls shows that one small refractive error was missed in 52 infants. We conclude that photorefraction is a valid and practical screening technique. Longitudinal study of infants with refractive errors will assess the value of early detection, in particular for prediction and prevention of strabismus.

Optics of photorefraction: orthogonal and isotropic methods

Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.

Vision screening and photorefraction - the relation of refractive errors to strabismus and amblyopia

Isotropic photorefraction is a technique well suited for screening infants and young children for refractive errors. The photorefractive measurements have been empirically calibrated against retinoscopic refractions, so errors exceeding selected criteria can be identified in screening and followed up. Such a screening programme is in progress for the population of 6-9 month infants in the City of Cambridge. In 1096 infants screened 5% have been found to have large hypermetropic errors, 1.3% to show a refractive difference between the eyes (anisometropia) and less than 1% to have significant myopia or manifest strabismus. These findings were generally confirmed on retinoscopic examinations. In subsequent follow up of the large hypermetropic errors, most decline with age but a few show little or no change up to age 2 years and some show more change in one eye than the other leading to anisometropia. A trial is underway to examine whether early correction with spectacles can reduce the later incidence of strabismus and amblyopia in hypermetropic infants. Significant astigmatism is found in a large fraction of the infant population; the predominant axis of this astigmatism shows marked and unexplained variations between different locations in England.

Some recent findings on the development of human binocularity: a review

Evidence on the development of binocular function in infancy is reviewed. (1) Visual evoked potentials (VEP) may be recorded from infants in response to dynamic random dot stimuli which alternate between positive and negative binocular correlation. Such responses can only arise in neurones receiving binocular input. (2) Infants' looking behaviour may be shown to depend on the presence of binocular disparity in the stimulus (either random-dot or line stereograms). Results of these techniques agree that binocular function normally develops initially between 2 and 4 months of age. Our own data using VEP show a median age of first binocular response of 13 weeks but with marked individual variations. Binocular development involves the interplay of sensory interaction and oculomotor coordination, but it is unlikely that alignment of the two eyes is the dominant constraint determining the onset of binocular vision. It is possible, but not yet established, that the detection of binocular correlation may precede the ability to discriminate stereoscopic disparities. Infants in the first 3 months of life show an asymmetry of monocular optokinetic nystagmus (MOKN). The response to temporalwards field motion which they lack is driven in cat by a pathway via binocular cortex: thus the development of this response in human infants might depend on development of binocularity. However, the correlation across individual infants between the age of onset of binocularity and the age at which symmetrical MOKN is attained is relatively weak. It is possible that the neuroanatomical basis of MOKN control differs between cat and human.

Adrenalectomy potentiates drinking induced by renal artery constriction

We have tested the hypothesis that the dipsogenic response to an increase in the circulating angiotensin level in the rat is mediated via release of catecholamines from the adrenal medulla. Increases in circulating angiotensin levels were induced by unilateral renal artery constriction in animals which were uninephrectomized and/or adrenalectomized, twenty four hours previously. The dipsogenic response to renal artery constriction was not attenuated by prior adrenalectomy--there was, in fact, a slight potentiation. Adrenalectomy also potentiated the dipsogenic response to injection of hypersomotic saline. We conclude that drinking following renal artery constriction is not mediated by release of catecholamines from the adrenal medulla.

Reaching for rattles: a preliminary study of contrast sensitivity in 7-10 month old infants

Contrast sensitivity for a 3 cycles deg-1 sinusoidal grating in 7-10 month old infants was tested by presenting gratings and uniform fields on cylinders, with the former providing auditory reinforcement when the infant picked them up. The method shows that a contrast as low as 7.5% can commonly be detected at this age, compared with 1-2% for adults under comparable conditions. However, as the development of hand preferences with the task as an indicator of visual sensitivity, it is concluded that this method is not in its present form suitable for vision testing on a wide scale or in a clinical setting.

Cyclohexamide and renin release following renal artery constriction

Renal artery constriction in the uninephrectomized conscious rat produced "renin release": i.e. an increase in plasma renin level and a decrease in renal cortex renin level, and an increase in mean arterial pressure. A high dose (4 mg.kg-1) of the protein synthesis inhibitor, cyclohexamide, halved the rise in plasma renin level (with no change in renal cortex renin level and a fall in mean arterial pressure). We suggest that the increase in plasma renin level following renal artery constriction depends on (a) release from preformed renin stores and (b) de novo renin synthesis.

The effects of screen size and eccentricity on acuity estimates in infants using preferential looking

The study examined whether screen size (10 degrees vs 19 degrees dia.) and separation (3 degrees vs 10 degrees eccentricity of inner edges) affect the estimates of acuity obtained with 1-3 month infants tested by forced-choice preferential looking. One and 2-month infants (but not 3-month olds) showed higher acuity estimates with the larger screens. Screen separation did not significantly affect acuity estimates for any of the age groups. Possible factors underlying these results are discussed.

Blood pressure overshoot under pentobarbitone anaesthesia following a single dose of clonidine in rats

1. Withdrawal of chronic antihypertensive therapy with clonidine is known to produce a blood pressure overshoot. It has been reported that the same may occur after a single dose of clonidine. 2. A single, intramuscular dose of clonidine (0.05 mg/kg) produced an overshoot in blood pressure, on the day following administration, in normotensive rats anaesthetized with sodium pentobarbitone. 3. No rebound elevation of mean arterial pressure or of heart rate occurred in conscious, normotensive, spontaneously hypertensive or renal hypertensive rats following this dose of clonidine, nor did it occur in rats anaesthetized with ether. 4. It is suggested that the overshoot phenomenon in rats under barbiturate anaesthesia may involve an interaction between an effect of clonidine and the barbiturate.

Interaction between the renin-angiotensin and beta adrenergic nervous systems in drinking and pressor responses after renal artery constriction

Constriction of the remaining renal artery of a uninephrectomized rat produced an increase in plasma renin level, a decrease in renal cortex renin level, an increase in blood pressure and a drinking response. Simultaneous infusion with the angiotensin II antagonist, saralasin, potentiated the rise in plasma renin level and blocked the rise in blood pressure. Drinking was only partially attenuated. Pretreatment with l-propranolol had no effect on the changes in plasma or kidney renin levels, but the increase in blood pressure was potentiated and the drinking response was attenuated. It is concluded that the pressor and drinking responses to renal artery constriction are partially mediated by the beta adrenergic nervous system.

'Preferential looking' for monocular and binocular acuity testing of infants

A method is described for obtaining rapid and reliable estimates of acuity in infants, for both monocular and binocular viewing. The method depends on 'preferential looking', where the infant prefers to look at a striped pattern rather than a blank screen of matched mean luminance. A staircase procedure for testing is followed, with observations being recorded by a 'blind' observer (who does not know on which of the 2 screens the striped pattern is displayed). Monocular acuity estimates have been obtained for a group of infants 3 to 4 months old with normal refractions. Many of these infants show similar acuity values in the 2 eyes, with a few showing reliable differences between the eyes. To check reliability of the method a comparison of 2 independent interleaved staircase estimates of the same eye have been made. In general this check shows highly consistent estimates for a given eye of a given infant. Nearly all infants show slightly higher acuity estimates for binocular viewing than for monocular. The possible reasons for this difference are discussed. The clinical use of such a method is reported for a number of cases. The method has been found to be useful in a variety of clinical conditions where other available tests are not possible on young infants.

Evaluation of a diabetes education programme

An education programme was evaluated for 140 insulin-dependent diabetics and their family members from 1978 to 1980. Dietary, biochemical and other assessments were made before and 6 months after the programme. As a group, the diabetics were initially in good metabolic control and this was maintained, or improved, over the study period. The programme recommended a diet in which complex carbohydrate constituted at least 45% of energy intake and fat was limited to 30%. The diabetics and their family members significantly increased their consumption of complex carbohydrate and decreased fat intake. On this regimen, diabetics did not gain weight and their relatives lost weight. There were also improvements in knowledge of the disorder and in perceptions of susceptibility to complications and barriers to compliance.

Effects of vestibular stimulation in seizure-prone children. An EEG study

Concern that vestibular stimulation may induce seizures in seizure-prone children has been based on hearsay and unconfirmed clinical impressions of practicing therapists. To clarify this issue, we took electroencephalographic recordings of seizure-prone children before, during, and after specific vestibular stimulation. Ten children with seizure histories, 5, to 15 years of age, were exposed to warm and cold caloric vestibular stimuli. Electroencephalographic activity was recorded before, during, and after each vestibular stimulus; recordings were rated and compared prevestibular and postvestibular stimulation. Electronystagmographic recordings were also taken. Results show that vestibular stimulation does not accentuate the abnormal brain wave pattern in seizure-prone children. Six of 10 subjects had a significant reduction in paroxysmal activity (p less than .02). Possible explanations for clinical reports of vestibular induced seizures are given, with suggestions for precautions when applying vestibular stimulation to seizure-prone children.

The role of plasma and renal renin in the rise in blood pressure following unilateral renal artery constriction

Constriction of the artery to the remaining kidney of control rats uninephrectomized 24 h previously induced a sixfold rise in plasma renin level from 11 +/- 1 to 60 +/- 11 ng AI ml-1 h-1, a 43% decrease of renal cortical renin level, and a 21% rise of mean arterial pressure from 119 +/- 2 to 144 +/- 3 mm Hg. Constriction of the artery to a renin-depleted kidney (with a renin level which was 5% of normal) was not followed by any significant increase in plasma renin level or mean blood pressure. Renin-depleted kidneys were produced by removing the clipped kidney from two-kidney one-clip hypertensive rats, 24 h before the experiment. Such a maneuver induces renin depletion but does not completely normalize blood pressure. When a large dose of frusemide (50 mg/kg i.p.) was injected immediately following removal of the clipped kidney, mean arterial pressure (117 +/- 7 mm Hg) returned to control values 24 h later but again constriction of the remaining renal artery failed to induce a rise in plasma renin level or mean arterial pressure. By 7 days after removal of the clipped kidney, plasma renin level and mean arterial pressure were normal and clipping of the remaining kidney (in spite of the fact that kidney renin level was still low) now produced a wave of renin release and an increase in mean arterial pressure. These results suggest that the initial, rapid increase in mean arterial pressure following unilateral renal artery constriction is dependent on an increase in plasma renin level. Our results from animals with kidneys of varying renin levels suggest the existence of a cortical renin content of about 20% of normal below which the kidney is incapable of responding to renal artery constriction with significant renal release. Complete recovery of the renin (and blood pressure) response to clipping occurred when the renin content had reached about 75% of normal.

Renin release by renin-depleted rats following hypotensive haemorrhage and anesthetics

1. Renin-depletion, described as a decrease in renal cortex and plasma renin levels, was produced by clipping one renal artery of a rat and leaving the contralateral kidney in place (two kidney one clip hypertension), One month later the clipped kidney was removed and after 24 h recovery such rats were found to be renin depleted: renal cortex and plasma renin levels were 8 and 63% of normal respectively. 2. Such renin depleted rats were incapable of releasing renin (as judged by increase in plasma renin level) in response to severely hypotensive haemorrhage and had very blunted renin release responses to pentobarbital and urethane anesthesia (59 and 17% of normal respectively). 3. Our results confirm the hypothesis that a low renal renin status is associated with low basal and stimulated renin release. We suggest that the renin depleted rat may be a useful model for the study of the role of the renin angiotensin system in phenomena such as blood pressure compensation following hypotensive haemorrhage and drinking induced by beta-adrenoreceptor agonists.

Does the Catford drum give an accurate assessment of acuity?

Adult emmetropes and myopes were tested with the Catford drum and the results compared with subjective (Landolt C) acuity. For he emmetropes the Catford drum was found to overestimate visual acuity by a factor of approximately 4. For myopes, and emmetropes viewing through plus lenses, the discrepancies were much larger. Since the Catford drum not only overestimates acuity but will do so by a factor which varies for different visual disorders, caution is needed in clinical interpretation of results obtained with it.

Contrast sensitivity function of preschool children

A procedure specifically adapted for children of preschool age has been used to measure contrast sensitivity in emmetropic children aged 3 to 5 years. Mothers of the children acted as adult observers using the same procedure. The results show that the contrast sensitivity function of adults and children is very similar, sensitivity for the children being slightly lower than that for adults at all spatial frequencies. The sensory and cognitive factors involved in these differences are discussed.

Cortical binocularity in infants

The primate visual cortex, including that of man, receives separate input from each eye and these interact in binocular cortical neurones. This organization is known to be vulnerable to disruption in early life. To understand the development of human visual cortex, and to detect and assess disorders of binocular function at the earliest possible age, a robust method is needed for detecting binocular interactions in the infant's visual system. We have done this by recording cortical visual evoked responses (VERs) to the onset and offset of binocular correlation in a large-screen dynamic random dot display. We report here that, in general, the human infant has a functional binocular visual cortex by 3 months of age, with some individuals showing cortical binocularity at an earlier age.

Influence of streptozotocin-induced diabetes on blood pressure and on renin formation and release

I.v. injection of 40 mg/kg or 65 mg/kg streptozotocin reliably induced diabetes in female Sprague-Dawley rats, but failed to induced hypertension within the following 42 days. In most animals injected with the higher dose and in some animals injected with the lower dose the tail blood flow was permanently impaired so that no blood pressure signals could be obtained by tail plethysmography. This phenomenon occurred also when the drug was injected into the jugular vein and thus was not due to a local effect of streptozotocin. 15 days after 65 mg/kg streptozotocin, the mean arterial pressure of the rats was similar to that of controls, when measured inthe awake state (carotid cannula) or under ether anaesthesia. 42 days after streptozotocin, under pentobarbital anaesthesia, the blood pressure was again normal in the animals given 40 mg/kg of the drug and depressed in the animals given 65 mg/kg of the drug 42 days previously. The increase of blood pressure induced by 1 microgram/kg (-)-noradrenaline i.v. was similar in the latter group of animals and in controls. The renal cortical renin concentration was much lower than in controls 42 days after either dose of streptozotocin, while the plasma renin activity was normal (40 mg/kg) or increased 65 mg/kg). The low renal renin content may have been due to the diabetic state, rather than to the drug itself. Adrenal medullary dopamine-beta-hydroxylase activity was increased 42 days after the higher dose of streptozotocin.

The renal effects of clonidine in unanesthetized rats

Clonidine s.c. (0.01-0.3 mg/kg), in unanesthetized rats, caused an initial rise (+20 mm Hg), followed by a continuous fall of BP and a dose-dependent natriuresis and diuresis for up to 2 h. Glomerular filtration rate (GFR) (CIn) increased during the first 20 min, while effective renal plasma flow (ERPF) (CPAH) remained normal. Subsequently, between 20 and 60 min after injection, ERPF (CPAH) decreased considerably while GFR had reverted to its normal value. In saline-infused rats clonidine diuresis was accompanied by an "inappropriate" positive free water clearance. Pentobarbital anesthesia suppressed the initial BP peak and the diuresis. Phenoxybenzamine (1 mg/kg i.v.) was antinatriuretic in saline diuresis; the effect of phenoxybenzamine + clonidine on diuresis and salt excretion represented the sum of the effects of both drugs, but phenoxybenzamine enhanced the clonidine-induced increase of GFR. Neither haloperidol (1 mg/kg i.v.) nor bulbocapnine (3 mg/kg i.v.) interfered with the renal effects of clonidine. Clonidine s.c. caused hyperglycemia and glucosuria which did not account for the natriuresis. Clonidine thus appears to increase the GFR and "filtration fraction" (FF) by a phenoxybenzamine-insensitive rise of glomerular ultrafiltration, to depress ERPF by alpha-adrenergic afferent vasoconstriction, to induce natriuresis by a tubular action not blocked by phenoxybenzamine and to exert an antivasopressin effect, either by depressing pituitary vasopressin secretion or the renal response to vasopressin.

Effect of chronic clonidine treatment and its abrupt cessation on mean blood pressure of rats with a normal or an elevated blood pressure

1. Clonidine (6 mg of base/l of water) was given as drinking fluid to normotensive rats or rats with established or early hypertension. 2. Spontaneous hypertensive rats (6 months old: average dose of clonidine, 0.6 mg 24 h-1 kg-1) showed a sustained fall in blood pressure over 3 weeks. 3. The same clonidine solution given for 6 weeks to two-kidney Goldblatt rats with early-stage hypertension (average dose of clonidine: 1 mg 24 h-1 kg-1) or spontaneously hypertensive rats (clonidine dose: 1 mg) induced a fall in mean blood pressure, but no change in normotensive rats. 4. Replacement of clonidine by water induced hypertension and lability which led to death in hypertensive but not in normotensive rats.

The role of circulating renin in drinking in response to isoprenaline

1. In nephrectomized rats, S.C. (0.12 mg. kg body wt.(-1)) or intracerebroventricular (I.C.V.: 0.03 mg. kg(-1)), isoprenaline failed to elicit drinking. However, when preceded (5-20 min) by a non-dipsogenic dose of I.V. pig renin, S.C. isoprenaline induced a marked, and I.C.V. isoprenaline a smaller drinking response. 2 hr after I.V. renin, S.C. isoprenaline no longer caused drinking.2. Pig renin did not enhance drinking in response to 0.12 mg. kg(-1) isoprenaline S.C. in intact or sham-operated rats.3. Isoprenaline (0.12 mg. kg body wt.(-1), S.C.) caused a larger fall of blood pressure in unanaesthetized nephrectomized than in intact unanaesthetized rats, but it was not the resulting hypotension that interfered with the nephrectomized rats' ability to drink, since intact rats with similar falls in blood pressure drank avidly in response to large doses of isoprenaline.4. Since the rate of inactivation of pig renin in nephrectomized rats was not modified by isoprenaline, drinking in nephrectomized animals in response to renin+isoprenaline was not attributable to increased plasma renin levels.5. Since isoprenaline induces drinking in the presence of circulating renin, but in the absence of renin release from kidneys, renin plays a permissive role in isoprenaline-induced drinking. Angiotensin and isoprenaline may interact at the level of intracranial receptors.