Quantification of plasma cortisol levels in ascorbic acid studies using guinea pigs implanted with ACTH pellets.

Area of Science:

• Veterinary Medicine
• Animal Physiology
• Endocrinology

Background:

• Minimizing animal stress during research is crucial for data validity.
• Plasma cortisol is a key indicator of physiological stress in animals.
• Previous methods for blood collection and hormone administration in guinea pigs may cause significant stress.

Purpose of the Study:

• To describe a minimally invasive blood collection technique in guinea pigs.
• To evaluate the impact of ACTH (adrenocorticotropic hormone) pellet implants on plasma cortisol levels.
• To assess the suitability of ACTH pellets for sustained elevation of plasma cortisol.

Main Methods:

• Developed a vacuum-assisted blood collection method from the lateral metatarsal vein in unanesthetized guinea pigs.
• Administered subcutaneously implanted slow-releasing ACTH or placebo pellets.
• Measured plasma cortisol levels to assess stress and hormonal response.

Main Results:

• The described blood collection method caused minimal disruption, as evidenced by stable plasma cortisol levels.
• ACTH pellet implantation led to a 20-fold increase in plasma cortisol within 4 hours.
• Plasma cortisol levels returned to baseline within 24-48 hours, irrespective of ACTH pellet dosage (0.125 mg or 8 mg).

Conclusions:

• The vacuum-assisted blood collection method is suitable for repeated sampling in guinea pigs with minimal stress.
• ACTH pellet implants are not effective for achieving sustained elevation of plasma cortisol levels.
• The study highlights the limitations of slow-releasing ACTH pellets for long-term hormonal studies in this model.