Previous studies indicate cardiovascular and endocrinological differences between singleton and twin ovine fetuses (Edwards & McMillen 2002) although no study has examined any differences when these fetuses become adults. Twins are generally of lower birth weight than singleton fetuses and low birth weight has been inversely correlated with metabolic and cardiovascular anomalies that aggregate to form the metabolic syndrome. The present study has examined cardiovascular function, fat deposition and leptin concentration in single and twin sheep at one year of age during the fed and fasted state.

Twelve Mule ewes, half bearing singletons and half bearing twins, were individually housed and fed to requirement from day 1 to term whereupon they lambed naturally. All offspring were ewe-reared as singletons to weaning and grass-fed thereafter. At one year of age they were surgically instrumented under 1-2 % halothane (50:50 O2/N2O) with carotid and jugular cannulae. At least 2 days later cardiovascular recordings and blood samples were taken pre and post feeding. Leptin concentration was measured by RIA. Each animal was then euthanased with a lethal dose of sodium pentobarbitone and all major organs and tissues weighed. Data are Means ± S.E.M. and were analysed by two-way ANOVA (for group i.e. singles vs. twins and treatment i.e. fed vs. fasted) using SPSS 11.1.

There were no differences in basal cardiovascular parameters between singles and twins (e.g. systolic blood pressure; Singletons 102 ± 3; Twins 99 ± 5 mmHg) with the exception of pulse pressure which tended to be higher in singletons (Singletons, 26 ± 1; Twins, 21 ± 1 mmHg; P = 0.009). These values were unchanged during the fed or fasted state. During the fed state, plasma leptin concentrations were similar between groups (Singletons, 2.7 ± 0.6; Twins, 1.9 ± 0.5 ng ml^-1). However, while fasting significantly reduced plasma leptin concentration in singleton lambs (by 62 % to 1.0 ± 0.1 ng ml^-1) it had little effect in twins (by 25 % to 1.5 ± 0.3 ng ml^-1). Twins had significantly more regional fat than singletons (Twins vs. Singletons, perirenal depot, 196 ± 28 vs. 111 ± 22 g; cardiac, 54 ± 5 vs. 32 ± 3 g; subcutaneous, 20 ± 3 vs. 10 ± 2 g). These significant differences were maintained when expressed relative to current weight.

The data confirm the little effect that the constrained late-gestational intrauterine environment that twins experience has upon later basal cardiovascular variables. However, the results of this study do suggest that more subtle effects on metabolism may be indicated in twins as reflected in a greater propensity for fat deposition and insensitivity of leptin concentration to variations in food intake.

This work was supported by the University of Nottingham Fellowship Program and the British Heart Foundation.