Effects of different handling techniques and handlers on blood pressure measurements in the conscious mouse

Background and Aims: Accurate blood pressure measurement in experimental animals is crucial for hypertension research. There are two main techniques to measure blood pressure in conscious mice: telemetry and tail-cuffplethysmography. Telemetry is the gold-standard technique, which allows continuous measurement in un-restrained animals in the home cage. However, major surgery is involved and the cost of the equipment precludes its use for blood pressure screening of large number of animals. Tail-cuff does not have these limitations, however it involves handling and restraint of the animals, whichcan negatively impact the quality of the data. Female handlers and tube handling as opposed to conventional tail pick-up, were shown to be less stressful for mice (1, 2). We compared the effects of different handling techniques (tube, tail and tail-cup) by male and female handlerson blood pressure during handling and the tail-cuff protocol.

Methods: All experiments were conducted under the guidelines of the United Kingdom Home Office Animals (Scientific Procedures) Act 1986. Male C57/BL6 adult mice (n=6, 25-30g, 20 weeks old) were pre-trained to tail-cuff procedure and were handled by all three compared handling techniques before surgical implantation of radiotelemetry probes (PA-C10, Data Science International) (3). Following recovery, the animals were subjected to simultaneous telemetry and tail-cuff (CODA HT8, Kent Scientific) blood pressure recording sessions (4). Each animal was exposed to each handling technique for 5 days followed by 9 days of rest. Male (n=3) and female (n=4) researchers handled each mouse once. The data is shown as mean ±SEM and analysed using RM-ANOVA or t-test where appropriate.

Results: The baseline readings for systolic blood pressure (SBP) measured by telemetry, when mice were in the home cages, were 119.4±6.2mmHg, which is similar to SBP recordings obtained by tail-cuff: 117.4±10.4mmHg, and comparable to tail-cuff recordings obtained in other studies (5). Handling and restraint resulted in significant blood pressure increases over baseline. Different handling techniques were not significantly different in their effect on SBP, for which the telemetry results were as follows: tail pickup 145±13, tail/cupping 150±13 and tube 148±15mmHg. Elevated blood pressure was not eliminated during acclimatisation in the tube or when tail-cuff recording started, however simultaneous measurements obtained by the tail-cuff were consistently lower: tail 115± 10, tail/cupping 118±12 and tube 118±10mm Hg. There was no significant difference between the handling techniquesat any stage of handling. Different users, also when analysed by gender, had no significantly different effect on blood pressure during handling: 158.2±8.3mmHg vs 163.6±12.4mmHg for female and male handlers respectively.

Conclusions: The different handling techniques or different handlers resulted in similar increases in blood pressure, as measured by telemetry, possibly due to similar levels of stress. The most obvious finding is that there is significant difference between blood pressure recordings obtained simultaneously by telemetry and tail-cuff. The reason for this is currently under investigation.

Supported by an MRC NC3Rs PhD studentship

References:

(1) Hurst, JL, West RJ (2010). Nat Methods 7: 825-826.

(2) Sorge, RE, et al (2014). Nat Methods 11: 629-634

(3) Marshall, NJ, et al (2013) Hypertension 61: 246-252

(4) Feng, M, et al (2008) Am J Hypertens 21: 1288-1291

(5) Smillie SJ, et al (2014) Hypertension 63: 1056-1062