Bridge amplifier

To confirm the functional presence of orally administered β2 agonist clenbuterol along with β1 antagonist atenolol and β3 antagonist SR59230A we measured mean systemic arterial blood pressures and heart rates by attaching an externalized arterial catheter to a physiological pressure transducer that was connected to a PowerLab 8/35 with a bridge amplifier (ADInstruments Inc.). Pressures and heart rates were determined on three separate days and analysed with LabChart software. Pressure transducers were calibrated with a mercury column manometer. Lambs were placed in the sling and physiological pressure transducers were set to the height of the heart. After an acclimation period of at least 10 min, data were recorded for a minimum of eight consecutive minutes under basal conditions. At 29 ± 1 days of age, lambs were challenged with the ADRβ1 agonist dobutamine HCl (12.5 mg ml⁻¹; Hospira, Inc., Lake Forest, IL, USA) to evaluate cardiac responsiveness (Stephens et al. 2011). Data were recorded for 15 min during both basal and dobutamine‐stimulated (10 µg min⁻¹ kg⁻¹) periods.

Conscious BP recording was carried out with a radiotelemetry system, as described previously [21 (link)]. Ten days before making a two-kidney, one-clip (2K1C) model or sham operation, the rats were anesthetized with isoflurane (3%), which was delivered through a nose cone. A telemetry BP probe (model TA11PA-C40, Data Sciences International, St. Paul, MN, USA) was positioned intra-abdominally and secured to the ventral abdominal muscle with the catheter inserted into the lower abdominal aorta. The telemetry signals received by the device were processed and digitized as radiofrequency data, which were recorded and stored in a computer using the Dataquest IV system (Data Sciences International, St. Paul, MN, USA), and the mean values of BP and heart rate (HR) were calculated in a conscious state. Continuous recordings were started 4 days after the probe implantation.
For the microinjection studies, acute BP recording was performed using PE50 catheters under isoflurane (3%) anesthesia. PE50 catheters filled with heparinized saline (100 IU/mL) were placed in the right femoral artery and connected to a BP transducer and a bridge amplifier (AD Instrument, Bella Vista, Australia). The BP and HR data were collected and analyzed with PowerLab software (AD Instrument, Bella Vista, Australia).