Salt and blood pressure: the triangular hypothesis.

If an unselected sample includes individuals whose blood pressure is sensitive to their salt intake and individuals whose blood pressure is not sensitive, then the superposition of these two sub-populations in a scatterplot of individuals' blood pressures against their salt intakes could give a triangular distribution. The non-correlation in the insensitives would obscure the correlation expected in the sensitives. This hypothesis justifies truncation of such data to test for correlation between blood pressure and salt intake among only the individuals in the higher range of blood pressures observed. No criterion of salt sensitivity is needed. The analysis should succeed if salt intake makes a major contribution to hypertension and would be improved if other putative causes were factored out.

Effect of stimulus range on judgements of sweetness intensity in a lime drink.

The effect of the range of levels of the test stimuli on ratings of sweetness intensity is demonstrated for a lime drink. The results are consistent with Poulton's (1979) suggestion that range effects can be predicted from the deviation of the mean response in a session from the mid-point of the response dimension. It is demonstrated that this range bias can be avoided by adding a readily anchored mid-point (ideal) to the response dimension and selecting stimuli so that the mean response is close to this mid-point. This bias-reducing, relative-to-mid-point procedure also produces a stronger linear relationship between ratings and concentration ratios than does the conventional end-point-anchored intensity rating procedure. The similarity of the linear semi-log functions of response relative to extremely sweet and relative to ideally sweet is taken as evidence that the two types of responses are not independent.

Estimation of salt intake by questionnaire.

A questionnaire designed to assess salt intake was tested. This involved principal components analysis of responses from 155 subjects to find the underlying components related to the questions. Validation of the questionnaire used 7-day urinary sodium excretion for 33 subjects, along with table and cooking salt usage over 7-days. This gave comparatively good prediction for total intake (r = 0.66) and table salt use (r = 0.70) but not for cooking salt use (r = 0.17). Test-retest reliability for the estimate of total intake was r = 0.75. This method would therefore offer a useful estimate of total intake, especially where group means are required rather than accurate estimates of individual intakes.

The relationship between salt intake and preferences for different salt levels in soup.

Two experiments are reported with subjects divided according to questionnaire responses into low and high total sodium intake, and low and high table salt use. The stimuli were tomato soup with varying salt concentrations. In Experiment 1 these were rated for salt intensity, pleasantness and intensity relative to ideal. In Experiment 2 the stimuli were presented in restricted concentration ranges or using a method designed to minimise range bias; relative-to-ideal intensity rating was again used. Subjects with a high total intake were found to prefer higher concentrations of salt assessed both with the hedonic and relative-to-ideal intensity ratings, though not with restricted stimulus ranges. Subjects with high table salt use were found to prefer higher concentrations only when assessed using the hedonic ratings. Sensitivity to salt taste was not found to differ between the groups.

Preference and sensitivity to salt taste as determinants of salt-intake.

Total salt-intake was estimated in 33 normal subjects using urinary sodium excretion over 7 days, and table and cooking salt use were measured over the same period. Sensitivity to salt taste was measured for 31 of these subjects using a seven-category rating scale for intensity of saltiness with five concentrations of salt in water, bread and mashed potato. Preferences were assessed using a nine-category hedonic rating scale with the bread and mashed potato to determine the maximally-preferred concentration. No differences were found in the taste measures between subjects divided into high and low intake in terms of total salt-intake or total intake divided by body weight. However, differences were found in sensitivity and preferences between groups divided into high and low table salt use. This may be because the major proportion of total salt-intake arose from salt present in foods and this would not be so open to voluntary control as table salt use.

Effects of stimulus context on preference judgements for salt.

An experiment is reported which confirms earlier findings that the range of stimulus concentration affects the estimate of ideal concentration. The method proposed by Booth et al for reducing range bias has been found to give satisfactory results.

Trimethylamine and egg taint.

1. The sensory qualities of "crabby", "fishy" tainted eggs are closely similar to those of an aqueous solution of trimethylamine (1 x 10(-2) microgram/g). 2. The odour threshold of trimethylamine in water is 5 +/- 1 x 10(-4) microgram/g. 3. The taint occurs in eggs which contain more than 0.8 microgram/g trimethylamine. The reasons why this concentration is higher than that in water are discussed.

Effects of rapeseed meal on laying hens (Gallus domesticus) in relation to fatty liver-haemorrhagic syndrome and egg taint.

Fatty liver-haemorrhagic syndrome (FLHS) occurred in the controls and was modified in hens that received a diet containing 10 per cent rapeseed meal. This diet increased the extent and severity of the hepatic haemorrhage without affecting the reticulin content of the liver but decreased the body weight and liver lipid levels and so weakened the correlation between these parameters and haemorrhage score found in FLHS. Plasma aspartate transaminase and beta-glucuronidase activities tended to increase with the score. The rapeseed meal diet also produced thyroid hypertrophy and since this was greater in the hens that produced tainted eggs and was positively correlated with the trimethylamine (TMA) content of the eggs it was postulated that rapeseed meal goitrogens may be involved as secondary factors in producing the disturbance in TMA metabolism that causes the egg taint. This abnormality was associated with a reduction in the soluble protein content of the liver, which reflected a decrease in TMA oxidase activity, but was not related to hepatic haemorrhage, steatosis or reticulolysis, or to lipid levels and the activities of lysosomal enzymes and transaminases in the plasma.