The use of 3H-NIS (tritiated sodium iodide symporter) in rat models is more frequent compared to human studies due to several reasons related to the benefits of animal models, particularly rodents, in biomedical research:

1. Behavioral and Genetic Similarity: Rats are often chosen for studies because their behavior is more aligned with humans compared to other animals, like mice. They also have physiological and genetic traits conducive to modeling human diseases, allowing for more relevant and translational research outcomes source.

2. Control and Manipulation: In animal models, researchers have the flexibility to manipulate environmental and genetic factors to study their effects on development and disease progression. This level of control is not feasible in human studies due to ethical and practical constraints source.

3. Cost and Ethical Considerations: Using animal models is often less expensive and involves fewer ethical complications than conducting similar research on humans. Human studies typically require extensive regulatory oversight and ethical review, making animal models a more practical preliminary step.

4. Scale and Scope of Studies: Rats and other rodents allow for large-scale studies that would be impossible with human participants. The ability to conduct these studies efficiently and at a lower cost makes rodents an ideal choice for initial research stages and exploratory studies.

Images related to the use of rodent models in research further illustrate these advantages:

These aspects underline why 3H-NIS and other experimental methods are predominantly used in rats rather than directly in humans.