Observations on the Responses of Rats with Spontaneous Hypertension and Control Rats to Pressor Drugs and to Hexamethonium

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Abstract
The establishment, by selective breeding, of a colony of rats with a high incidence of spontaneous hypertension has been confirmed by a kymographic technique with femoral artery cannulation. The reaction of rats to several pressor drugs has been altered by selective breeding. In both control and inherited hypertensive rats, the initial level of the blood pressure prior to administration of the drug influences the magnitude of the responses to several pressor drugs but not to norepinephrine. If hypertensives are compared only with other hypertensives and controls with other controls, it is clear that high preinjection pressures have an inhibiting effect on the pressor responses to biologically and synthetically prepared angiotensin, to vasopressin, and possibly lessen also the responses to s-methyl iso-thiourea. When under experimental conditions the blood pressures of rats with inherited hypertension have fallen into the upper range of control rat blood pressures, the responses to epinephrine, vasopressin, s-methyl iso-thiourea and biological angiotensin are greater in the hypertensives than in the controls. The difference in the case of synthetic angiotensin is not statistically significant. In the case of norepinephrine, the responses are equal. Hexamethoniun reduced the blood pressures of inherited hypertensive and control rats to the same level.