Vasopressin Release Due to Manual Restraint in the Rat: Role of Body Compression and Comparison with Other Stressful Stimuli*

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Abstract
The observation of plasma vasopressin elevations in rats which had been held manually for 1–2 min before decapitation prompted a study of this and other stressful stimuli. Plasma vasopressin concentrations determined by RIA [picograms per ml (±SEM)] were: 1) immediate decapitation after removal from cage, 1.69 ± 0.28; 2) manual restraint for 3 min, 42.4 ± 12.3; 3) light ether anesthesia, 1.97 ± 0.32; 4) forced exercise in the activity wheel (3 min), 2.09 ± 0.28; 5) swimming (3 min), 2.2 ± 0.44; 6) noise by continuous hammering on cages (3 min), 1.64 ± 0.37; 7) electric shock in plastic restrainers, 93 ± 35; 8) restraint in plastic restrainers without electric shock (control for group 7), 1.87 ± 0.43; and 9) body compression by firm squeeze around the trunk (1 min), 283 ± 111 (range, 30–1200 pg/ml). Aside from electric shock, which could well have caused direct excitation of neurohypophysis, no stressful stimulus produced vasopressin elevations except the light squeeze of manual restraint and the firmer squeeze of body compression. We conclude that stress by itself does not stimulate vasopressin secretion in the rat, but that a delay in decapitation during which a struggling animal is manually restrained may be associated with major vasopressin elevation, perhaps due to hypoxia or to hemodynamic changes of as yet undetermined nature.