A radioimmunoassay method for the measurement of plasma insulin is described relying on activated charcoal for the separation of free and bound fractions. The technique illustrates the application of theoretical precepts designed to maximise assay precision in all radioimmunoassay and other saturation assay techniques.
In addition, because particular emphasis has been placed on ensuring that, as far as is possible, all incubation mixtures are similar as possible other than in hormone concentration, non-specific effects appear to have been essentially eliminated. The technique yields a mean normal fasting value of 5.3μU/ml (range 2–14 μU/ml). Its sensitivity is such that 10 μl samples of serum (or plasma) may be assayed.
Dispersed rat adrenal cells prepared from both the capsule and the decapsulated gland were used to investigate the effects on cyclic AMP accumulation of known stimuli of steroidogenesis [ACTH (adrenocorticotrophin), angiotensin II, K(+) ions and 5-hydroxytryptamine]. Since glomerulosa-cell preparations from capsular strippings are normally contaminated with a proportion of fasciculata cells, cells purified by fractionation on a bovine serum albumin gradient were also used. The results showed that: (1) ACTH and angiotensin II stimulated cyclic AMP accumulation in both fractionated and unfractionated zona fasciculata cells; (2) 5-hydroxytryptamine and an increased extracellular K(+) concentration (from 3.6 to 8.4mm) had no effect on cyclic AMP concentrations in fasciculata cell preparations; (3) the addition of ACTH, angiotensin II, 5-hydroxytryptamine or K(+) to the incubation medium resulted in increased cyclic AMP concentrations in unpurified zona glomerulosa cell preparations; (4) fractionation and hence the virtual elimination of fasciculata contamination, did not affect the response to 5-hydroxytryptamine and increased K(+) concentration. However, the responses to ACTH and angiotensin II were markedly lowered but not abolished. These results strongly suggest a link between cyclic AMP production and steroidogenesis in the zone of the adrenal gland that specifically secretes aldosterone. All four agents used stimulated both steroid output and cyclic AMP accumulation. However, at certain doses of 5-hydroxytryptamine, K(+) and angiotensin II the significant increases in corticosterone output were not accompanied by measurable increases in cyclic AMP accumulation.
Objective
To assess the measurement of inactive urinary kallikrein (IUK) to creatinine (Cr) ratio (IUK:Cr) on an untimed urine sample, collected between 16 and 20 weeks of pregnancy, as a predictive test for the development of both proteinuric and nonproteinuric pre‐eclampsia.
Design
A prospective longitudinal study.
Setting
A clinic for antenatal care and a university research department.
Participants
Three hundred and seven normotensive women randomly selected (124 nulliparous and 183 parous) attending the antenatal clinic for their booking visit.
Main outcome measures
1. Nonproteinuric pre‐eclampsia: a rise in diastolic blood pressure of 25 mmHg or more and a crossing of the threshold of 90 mmHg; 2. Proteinuric pre‐eclampsia: same as 1. plus the development of significant proteinuria (> 1+ on urine dipstick).
Results
Thirty‐seven women developed pre‐eclampsia, 12 of whom had proteinuria. Median 1UK:Cr ratio in this group was 78.27, compared with 358.19 in the remainder. Analysis of receiver‐operator characteristics gave an area under the curve of 0803. An IUK:Cr ratio of 170 or less in this study predicted nonproteinuric or proteinuric pre‐eclampsia with a sensitivity of 70% and a specificity of 86%. Ten of the twelve women who had proteinuria had an 1UK:Cr below 170. Median 1UK:Cr for those with proteinuric pre‐eclampsia was 72.91.
Conclusions
Measurement of 1 UK: Cr on a urine sample, collected between 16 and 20 weeks of gestation, represents a simple and practical test for the risk of subsequent pre‐eclampsia, with a sensitivity and specificity comparable to those reported by other investigators using the widely recognised, but less practical, angiotensin I1 sensitivity test.
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