Physiological and neuroendocrine correlates of social position in normotensive and hypertensive rat colonies.

The hypothesis to be tested was that socially dominant (D) males in a mixed gender rat colony will have: higher blood pressure (BP) decreased hypothalamic pituitary axis (HPA) activity measured by plasma corticosterone (C) and increased sympathetic activity measured by plasma noradrenaline (NA) as compared to socially subordinate (S) males. BP was measured continuously by implanted aortic telemetry (Data Sciences, MN), plasma noradrenaline measured by HPLC with electrochemical detection and plasma C by RIA. Colonies were established using 8 of each sex of 4 strains: SHR, WKY, and our two Y chromosome congenic strains, SHR/y and SHR/a. Social ranking was determined by physical scarring scores, overall locomotor activity and patrol behaviour. D males had higher BP (active dark cycle) across strains compared to subordinates S: SHR-180 vs 148 mmHg, WKY-145 vs 142 mmHg, SHR/y-185 vs 145 mmHg, SHR/a-180 vs 160 mmHg. Using an acute stressor, BP responsiveness was higher in D than in S SHR and SHR/y males. D males had higher NA levels than S males across strains: (SHR-76% increase, WKY-31% increase, SHR/y-29% increase, SHR/a-40% increase). S males had significantly higher C levels than D males across strains (SHR-29% increase, WKY-123% increase, SHR/y-25% increase, SHR/a-61% increase). The hypertensive Y chromosome (SHR or SHR/y) produced higher SBP during the active dark cycle in D males than in D males with a normotensive Y chromosome (WKY or SHR/a). In conclusion, D males from related hypertensive strains showed elevated sympathetic activity measured by plasma NA and reduced HPA activity measured by plasma C as compared to S males. (Supported by HL-48072-04).