Pentylenetetrazol (Metrazol) shock in normal and adrenalectomized dogs

¹ Biological Laboratory, Princeton University, Princeton, New Jersey

Metrazol-shocked nonadrenalectomized dogs exhibit a drastic though evanescent decline in plasma volume. A similar fall in plasma volume in the adrenalectomized dog persists and culminates in circulatory collapse unless C₁₁ oxysteroids are administered. Loss of circulating fluid volume seems not to be due to shift of water into cells since the modest increase in hematocrit is insufficient to account for the volume change, nor can the volume decline be attributed to loss of vascular fluid into the extracellular compartment; this space decreased along with the plasma volume. The plasma volume loss of Metrazol-shocked dogs without adrenals seems due to intense, unrelieved vasoconstriction initiated by massive stimulation of the central nervous system by the drug, apparently resulting in closure of much of the vascular periphery, sequestration, and trapping of fluid and cells. Glucocorticoids somehow relieve the vasoconstriction and re-establish free blood flow at the periphery of the vascular tree. The fleeting elevation of plasma Na characteristic of Metrazol shock is independent of plasma volume changes and probably neurogenic in origin.