Basic science provides a key role in this process by the discovery of new targets and physiologic processes. In drug discovery, in vitro models using tissue/organ baths that define both the efficacy and potency at a defined target, as well as the selectivity of a molecule are crucial in the characterization of such new therapeutic molecules. Such assays lead to the development of novel and selective molecules that can be used to characterize different receptor and enzyme systems in the larger context of in vivo pharmacology.
Isolated tissue and organ preparations have been in use for over one hundred years. These preparations provide researchers with convenient biological models that are independent of the systemic influences of in vivo preparations. Isolated tissue-organ experiments can generally be run in groups of 2, 4, 8 or more sample preparations, thereby enabling a high throughput in most laboratories. These in vitro preparations are also more readily instrumented and can be easily subjected to controlled changes in perfusate, oxygen availability, drug administration etc than is otherwise possible in the intact animal.
In a more precise manner, tissue bath studies allow the ex vivo study of muscle contraction in a system with more than one cell type. Information can be obtained regarding some neural responses (e.g. electrical stimulation and release of neurotransmitters…) as well as contractile and relaxatory processes in the target tissue.
Traditionally, tissue-organ baths are used for in vitro dose response experiments, used extensively to investigate the physiology and pharmacology of tissue preparations (ring/vessel or strip) from various species (chick, toad, rabbit, rat, guinea-pig, etc.). Tissues or organs have been isolated for these studies include muscle (Smooth or Skeletal), arterial rings or strips, uterine tissue or Vas deferens, ileum, colon, atrial or Ventricle and diaphragm. Typically, these experiments are performed in a temperature controlled environment and perfused with an oxygenated physiological solution, which allows the study of evoked tissue responses to pharmacological drug/agents (Dose Response studies), electrical stimulation or both pharmacological and electrical stimulation.The recorded responses or biological activity usually are the contraction/relaxation of muscle in the tissue: Force (isometric), Displacement (isotonic).
These studies are amenable to classical pharmacology such as competition of antagonists (Schild analysis) and can provide a bridge between single cell and in vivo models. The type of transducers/probes (isometric or isotonic) used in organ bath setups will vary depending on the type of tissue and physiological parameters to be investigated.
The advantages of this method include ease in preparation, minimal equipment requirements and the fact that reproducible concentration–effect curves can be obtained using either contractile or relaxant agents.
The increased development and use of transgenic animal models, particularly mice, has extended the scope of isolated tissue and organ preparations by creating models that can express normal or pathological genetic sequences. In turn, isolated preparations can allow molecular biologists to quantify the physiological (phenotypical) effects of altered genetic sequences.