In animal studies, ricin was found to have the highest potency when introduced in which way?

Ricin is a highly toxic protein derived from the seeds of the castor bean plant and is considered a potential biological weapon. Studies conducted with animal models have shown that the method of introduction significantly influences the potency and effectiveness of ricin as a toxin.

When ricin is introduced by injection or inhalation, it bypasses several physiological barriers, allowing for direct absorption into the bloodstream or the respiratory system, leading to rapid systemic effects and a high likelihood of severe toxicity or death. Injection facilitates immediate access to circulation, while inhalation allows the toxin to be delivered directly to the lungs, where it can enter the bloodstream quickly.

This contrasts with ingestion and topical application methods, where the potency is significantly reduced because of the body's natural defenses. For instance, when ingested, ricin is subject to degradation by digestive enzymes and may not effectively reach the bloodstream in a toxic form. Similarly, topical application would require the toxin to penetrate the skin barrier, which is less efficient than direct administration methods like inhalation or injection.

Thus, the introduction of ricin by injection or inhalation reveals its highest potency due to the rapid and direct uptake into the body, leading to greater systemic effects.