Download Pilot Study Investigating the Pressor Activity of Vasopressin Infused

Pilot Study Investigating the Pressor Activity of Vasopressin Infused by the
Subcutaneously Implanted SMP 200 Microinfusion Pump in the Telemetered Rat
Christophe Bory C, Philippe Legé, Estelle Chalencon, Jean-Paul Briffaux, Stéphane Milano
WIL Research Europe-Lyon, France
l MATERIAL AND METHODS, continuedl RESULTSl RESULTS, continuedl
INTRODUCTION
Implantable lab animal infusion pumps have become a very convenient and cost
effective method to deliver drugs. When used in combination with telemetry,
implantable infusion pumps allow a more sensitive and powerful means of detecting
drug induced therapeutic and/or adverse effects than when drugs are delivered in
restrained conditions or by tethered infusion. The 2nd generation iPRECIO® SMP-200
(Primetech, Japan) is an implantable, transcutaneously-refillable and programmable
pump for small lab animals, based on a mini-peristalsis flow infusion mechanism.
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OBJECTIVES
The aim of that study was to assess the accuracy of SMP-200 pump in telemetered
rat by using the effects of infused vasopressin on blood pressure as an endpoint.
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MATERIAL AND METHODS
Vasopressin (arginine vasopressin, AVP; antidiuretic hormone, ADH) is a peptide
hormone formed in the hypothalamus, then transported via axons to, and released Figure 1: Key features of the SMP-200 pump and catheter assembly
from, the posterior pituitary into the blood.
SMP-200 pump was used in post-recovery (delayed) infusion mode, whereby
saline is infused first to ensure patency of the catheter and the drug was infused
AVP has two principal sites of action: kidney and blood vessels. The primary function subsequently. After saline infusion at 5 µL/h for one week, the remaining vehicle was
of AVP in the body is to regulate extracellular fluid volume by affecting renal handling withdrawn from the pump reservoir and replaced by AVP dose A, infused for 24h at
of water, although it is also a vasoconstrictor and pressor agent (hence, the name 30 µL/h. The pump was then was programmed for a 24h-stop (no infusion), at the
“vasopressin”). AVP acts on renal collecting ducts via V2 receptors to increase water end of which the reservoir was washed out and refilled with AVP dose B, infused at
permeability (cAMP‑dependent mechanism), which leads to decreased urine 30 µL/h for 24 hours.
formation (hence, the antidiuretic action of “antidiuretic hormone”). This increases
blood volume, cardiac output and arterial pressure.
At the end of the surgical recovery period, the average actual volume of
saline infused was in accordance with the pre‑programmed nominal volume
(840 µL ± 5%).
AVP at 200 ng/h produced a significant increase in blood pressure (+20 mmHg
diastolic) which started at the onset of infusion and was maintained for 24 hours,
as expected. Of note, in 3 out of 6 animals, a higher deviation (± 10%) from the
nominal pre-programmed targeted volume was noted. Despite that discrepancy,
the overall precision of volume delivering was considered as very satisfactory.
A secondary function of AVP is vasoconstriction. AVP binds to V1 receptors on
vascular smooth muscle to cause vasoconstriction through the IP3 signal transduction
pathway and Rho-kinase pathway, which increases arterial pressure; however, the
normal physiological concentrations of AVP are below its vasoactive range. Normal
plasma AVP concentrations are <4 pg ml-1. AVP has a half-life of 10–35 min, being
metabolized by vasopressinases which are found in the liver and kidney. Because
of its vasoactive potency and its short half-life, AVP was considered as an ideal
drug candidate for testing the infusion capabilities of the SMP-200 pump, analyzed
through the effects on blood pressure.
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CONCLUSIONS
The SMP-200 infusion pump is implantable, programmable and refillable and has
the benefit of providing sophisticated infusion protocols in tetherless, free moving
animal. In combination with this gold standard of telemetry, SMP-200 infusion pump
is leading to ever more sensitive and powerful means of detecting drug induced
therapeutic and/or adverse effects.
The precision of SMP-200 was tested in 6 rats telemetered for blood pressure and
infused with two different dose levels of AVP (dose A: 20 ng/h; dose B: 200 ng/h). A
week before pump implantation, rats were instrumented with a TL11M2-C50‑PXT
implant (DSI), placed in the peritoneal cavity and the pressure catheter inserted into
the abdominal aorta.
Then, the infusion catheter of SMP-200 was implanted into the femoral vein and
the pump inserted under the skin of the right flank. The original SMP-200 catheter
was cut 2 cm after the exit port of the pump and replaced by a rat femoral tapered
PU 3 French catheter with rounded tip (SAI, USA). The end of the SMP-200 tube was
connected to the PU catheter via a 22 gauge coupler.
SOT 55 Annual Meeting
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Figure 2: Schematic representation of the infusion protocol
Telemetered blood pressure (systolic, mean and diastolic) signal was acquired
(500 Hz) and analyzed with Notocord hem 4.2 (Notocord Systems, France). Blood
pressure was averaged for 5 min every 30 min. Telemetry data are presented as
means ± SEM, with n = 6.
At the end of the 24h-infusion of AVP at 20 ng/h, the same level of precision was
observed (720 µL ± 5%) but no significant vasopressor effect was detected.
This pilot study demonstrated that, when implanted in vivo, the pump is accurately
delivering the loaded drug. Vasopressin at 200 ng/h produced a significant increase
in blood pressure (+20 mmHg diastolic) in the telemetered rat. The vasoactive effect
started at the onset of the infusion and was sustained during the entire programmed
duration of infusion. Nonetheless, in 3 out of the 6 animals instrumented, a slight
(10%) higher deviation from the nominal preprogrammed targeted volume was
noted.
The precision of these preliminary results was very encouraging, and the reason for
the discrepancy observed during the second vasopressin infusion session is under
investigation with several causes being considered.