Hemodynamic patterns at rest and during aversive classical conditioning in normotensive and borderline hypertensive rats : effects of interacerebroventricular clonidine

Author

John Walter Hubbard

Date of Award

12-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Psychology

Major Professor

James E. lawler

Committee Members

Robert Schaub, Thomas Chen, Neil Greenberg, Joel Lubar

Abstract

Recent studies using the first filial (F₁) offspring of female spontaneously hypertensive rats (SHR) and male Wistar-Kyoto (WKY) normotensive rats have found that this animal develops spontaneous borderline hypertension (systolic BP = 150 mmHg) which can be driven to pathologically hypertensive levels (systolic BP = 185 mmHg) using psychological stress.

The present study sought to characterize and compare the acute hemodynamic and sympathetic-adrenal medullary response patterns of WKY rats with borderline hypertensive rats (BHR), and to determine the role of central α_{-adrenoreceptors in the mediation of these responses using intracerebroventricular infusion of the antihypertensive agent clonidine.}

The studies utilized male BHR and WKY rats 18-28 weeks of age. The animals were implanted with intraventricular (i.v.t.) cannulae and exposed to 5 consecutive days of aversive classical conditioning (200 trials). Arterial catheters and electromagnetic flow probes around the ascending aorta were implanted and hemodynamic measurements were obtained from conscious animals at rest (baseline) and during 20 trials of aversive classical conditioning. The animals received an i.v.t. infusion of 4 μl of normal saline or clonidine (8 μg). Blood samples were taken at the end of each recording period for radioenzymatic assay of plasma catecholamine levels (epinephrine and norepinephrine).

It was found that the hypertension in the BHR was the result of an elevated total peripheral resistance index (TPRI) with a normal cardiac index (CI). The BHR showed a greater pressor response to the psychological stress than did the WKY rats. The pressor response was the result of an increase in TPRI and CI for both strains; however, the increase in resistance was greater for the BHR. In addition, the BHR showed a greater increase in plasma norepinephrine in response to the stress than did the WKY rats.

Intracerebroventricular infusion of clonidine produced a significant reduction in mean arterial BP, which was due to a drop in TPRI, while CI remained unchanged. The clonidine treated animals also had significantly lower plasma epinephrine levels in response to the stress period than did the saline treated subjects.

The role of the sympathetic nervous system in the development of circulatory responses to psychological stress is discussed.

Recommended Citation

Hubbard, John Walter, "Hemodynamic patterns at rest and during aversive classical conditioning in normotensive and borderline hypertensive rats : effects of interacerebroventricular clonidine. " PhD diss., University of Tennessee, 1983.
https://trace.tennessee.edu/utk_graddiss/13080