Bio-assay for antidiuretic activity in blood of undisturbed rats

¹ Department of Physiology, Harvard School of Public Health, Boston, Massachusetts

In order to study circulating antidiuretic hormone (ADH) levels in rats unaffected by anesthesia or manipulation, a method is presented whereby blood samples may be obtained through an indwelling aortic catheter without disturbing the animal. An intravenous rat bio-assay for ADH is described which is sensitive to absolute doses of 2–3 microunits U.S.P. posterior pituitary standard. To obtain maximum sensitivity and reliability no surgical procedure was performed on the assay rat on the day of assay, as we have found that despite alcohol anesthesia ADH release may still be stimulated in assay animals. With 0.5-ml plasma samples injected into two assay animals simultaneously, ADH activity as low as 4µU/ml plasma could be reliably detected. Antidiuretic activity of plasma from undisturbed rats was generally below 4 µU/ml, but when ether anesthesia was used plasma levels were highly variable though generally markedly increased. In animals dehydrated for 1–3 days plasma levels averaged 14.6 µU/ml. These values are considerably lower than concentrations previously reported for rats, and the difference suggests the importance of minimal disturbance to the donor animal when blood is obtained. The low plasma levels we have observed in dehydrated rats are nevertheless above the level calculated to produce maximum antiduresis.

Submitted on August 19, 1963